over voltage

Contents

1 Introduction 1

2 Damage due to lightning and surges 5

2.1 Damage statistics 52.2 Examples 10

2.2.1 Damage in hazardous areas 102.2.2 Damage to industrial plants 152.2.3 Damage to power supply systems 242.2.4 Damage to a house 272.2.5 Damage to aircraft and airports 362.2.6 Damage to wind power stations 382.2.7 Catastrophic damage 39

3 Origin and effect of surges 43

3.1 Atmospheric overvoltages 453.1.1 Direct and close-up strikes 45

3.1.1.1 Voltage drop at the impulse earthing resistance 483.1.1.2 Induced voltages in metal loops 49

3.1.2 Remote strikes 563.1.3 Coupling of surge currents on signal lines 57

3.1.3.1 Ohmic coupling 583.1.3.2 Inductive coupling 583.1.3.3 Capacitive coupling 59

3.1.4 Magnitude of atmospheric overvoltages 603.2 Switching overvoltages 61

4 Protective measures, standards 67

4.1 Lightning protection 694.1.1 Risk analysis, protection levels 744.1.2 External and internal lightning protection, DIN VDE

0185 Part 1, DIN V ENV 61024-1 (VDE V 0185 Part100) 78

4.1.3 Concept of lightning protection zones, DIN VDE0185-103 (VDE 0185 Part 103) 79

4.1.3.1 LEMP-protection planning 834.1.3.1.1 Definition of lightning protection levels 834.1.3.1.2 Definition of lightning protection zones 834.1.3.1.3 Room shielding measures 844.1.3.1.4 Equipotential bonding networks 904.1.3.1.5 Equipotential bonding measures for supply

lines and electric lines at the boundaries ofthe lightning protection zones 92

4.1.3.1.6 Cable routing and shielding 944.1.3.2 Realization of LEMP protection 974.1.3.3 Installation and supervision of LEMP

protection 994.1.3.4 Acceptance inspection of LEMP protection 1004.1.3.5 Periodic inspection 1014.1.3.6 Costs 101

4.2 Surge protection for electrical systems of buildings, IEC60364, DIN VDE 0100 103

4.2.1 IEC 60364-4-443/DIN VDE 0100 Part 443 1044.2.2 IEC 60664-1/DIN VDE 0110 Part 1 1054.2.3 IEC 60364-5-534/DIN VDE 0100 Part 534 109

4.3 Surge protection for telecommunications systems, DINVDE 0800, DIN VDE 0845 110

4.4 Electromagnetic compatibility including protectionagainst electromagnetic impulses and lightning,VG 95 372 112

4.5 Standards for components and protective devices 1124.5.1 Connection components, E DIN EN 50164-1

(VDE 0185 Part 201) 1134.5.2 Arresters for lightning currents and surges 113

4.5.2.1 Arresters for power engineering, IEC61643-1/E DIN VDE 0675 Part 6 113

4.5.2.1.1 Important data for arrester selection 1194.5.2.1.2 Coordination of the arresters according to

requirements and locations 1204.5.2.1.3 N-PE arrester, E DIN VDE 0675 Part

6/A2 1214.5.2.2 Arresters for information technology,

IEC SC 37A/E DIN VDE 0845 Part 2 1224.5.2.2.1 Important data for arrester selection 1244.5.2.2.2 Arrester coordination according to

requirements and locations 1254.5.2.3 Arrester coordination 125

vi Contents

5 Components and protective devices: construction, effect andapplication 127

5.1 Air terminations 1275.2 Building and room shields 1295.3 Shields for lines between screened buildings 1385.4 Shields for cables in buildings 1415.5 Optoelectronic connections 143

5.5.1 Optical fibre transmission system 1445.5.2 Optocoupler 145

5.6 Equipotential bonding 1455.7 Isolating spark gaps 1505.8 Arresters 153

5.8.1 Arresters for power engineering 1555.8.1.1 Surge arresters for low-voltage overhead lines,

class A 1555.8.1.2 Lightning current arresters for lightning

protection equipotential bonding, class B 1575.8.1.3 Surge arresters for protection of permanent

installation, class C 1675.8.1.4 Surge arresters for application at socket outlets,

class D 1745.8.1.5 Surge arresters for application at equipment

inputs 1755.8.1.6 Application of lightning current arresters and

surge arresters 1755.8.1.6.1 Graded application of arresters, energetic

coordination between surge arresters andequipment to protect 178

5.8.1.6.2 Application of arresters in different systemconfigurations 182

5.8.1.6.3 Selection of arrester backup fuses 1965.8.2 Arresters for information technology 206

5.8.2.1 Arresters for measuring and control systems 2095.8.2.1.1 Blitzductor®CT: Construction and mode of

functioning 2105.8.2.1.2 Blitzductor®CT: Selection criteria 2235.8.2.1.3 Blitzductor®CT: Examples of application 2285.8.2.1.4 Arresters for intrinsically safe measuring

and control circuits and their application 2385.8.2.1.5 Arresters for cathodic protection systems 2465.8.2.1.6 Arresters in Euro-card format 2485.8.2.1.7 Arresters in LSA-Plus technology 248

5.8.2.2 Combined protective devices for power supplyinputs and information technology inputs 253

Contents vii

5.8.2.3 Protective devices for data networks/systems 2555.8.2.3.1 Protective devices for application-neutral

cabling 2555.8.2.3.2 Protective devices for token ring-cabling 2625.8.2.3.3 Protective devices for Ethernet twisted pair-

cabling 2655.8.2.3.4 Protective devices for Ethernet coax-cabling 2675.8.2.3.5 Protective devices for standard cabling 2715.8.2.3.6 Protective devices for data telecontrol

transmission by ISDN base terminal 2775.8.2.3.7 Protective devices for data telecontrol

transmission by ISDN primary multiplexterminal 284

5.8.2.3.8 Protective devices for data telecontroltransmission by analogous a/b-wireterminal 286

6 Application in practice: Some examples 293

6.1 Industrial plants 2956.1.1 Fabrication hall 2956.1.2 Store and dispatch building 2966.1.3 Factory central heating 3026.1.4 Central computer 3076.1.5 European installation bus (EIB) 3096.1.6 Other bus systems 3136.1.7 Fire and burglar alarm system 3136.1.8 Video control system 3166.1.9 Radio paging system 3186.1.10 Electronic vehicle weighbridge 320

6.2 Peak-load power station 3236.3 Mobile radio systems 3286.4 Television transmitter 3346.5 Mobile telecommunication facility 3396.6 Airport control tower 343

7 Prospects 351

Index 353

viii Contents

Chapter 1

Introduction

Business, industry and public institutions depend on electronic dataengineering. Electronic data processing (EDP) systems, measuring andcontrol systems, instrumentation and control as well as secondary tech-nology are all part of a modern industrial plant. Data recording devicesat the production facilities are connected to office terminals and com-puters by information networks ranging between buildings—togethermaking CIM (computer integrated manufacturing). Open networks,where different types of computers and different operating systemscommunicate, are often the basis for CIM. This rapidly expandingbusiness process is now approaching the CIE (computer integratedenterprise) or CIB (computer integrated business); in other words, thecomplete integration of all ranges of administration into a multi-EDPsystem. The future lies in the computer-integrated factory or incomputer-integrated business and administration.

Everywhere, computers in local banks are connected to the computingcentre of the main bank. This ‘networked’ world, with its growing flowof information, is, however, severely hindered by interference or damageto the essential transmission systems in the telephone and data networks,as well as at terminals (Figure 1 a). Dependence on electronic dataprocessing can quickly lead to catastrophe if the system fails.

An American study in 1987 highlighted the seriousness of the situ-ation. According to this, banks will only be able to manage without EDPfor 2 days, sales-oriented enterprises will be able to manage for 3.3 days,manufacturers for 4.9 days, and insurance companies for 5.6 days. Aninvestigation by IBM Germany disclosed that enterprises withoutfunctioning EDP would be on the verge of ruin after about 4.8 days. Inmany business sectors within the European Market this risk will certainlycontinue to increase in the future.

Computer safety experts point out that nine out of ten enterprises willclose if the computer fails for two weeks. The most frequent reason for

the failure of such electronic systems is transient electromagnetic interfer-ences that disturb the flow of data and destroy electronic equipment.

Risk can be controlled by electromagnetic compatibility (EMC) meas-ures. This specifies conditions under which any kinds of electric equipmentdo not disturb each other and also where electromagnetic phenomena,for example, lightning discharges, will not disturb their function.

The European Community has declared EMC as a protection goal byissuing the ‘Richtlinie des Rats vom 3. Mai 1989 zur Angleichung derRechtsvorschriften der Mitgliedstaaten über die ElektromagnetischeVerträglichkeit’ (Council Directive of 3 May 1989 to Harmonise Laws ofthe Member Nations concerning Electromagnetic Compatibility). Allapparatus, facilities and systems that include electric or electroniccomponents must demonstrate sufficient ‘withstand’ levels against elec-tromagnetic disturbances to guarantee proper operation of equipment.

The instructions of the Council especially mention the following facil-ities: industrial equipment, telecommunication networks and equipment,mobile radio sets, information technology equipment, private sound andTV-radio-receivers, commercial mobile radio and radio-telephones, med-ical and scientific apparatus and equipment, household appliances andelectronic household equipment, radio sets for navigation, electronic edu-cation gear, transmitters for radio and television, and luminaires andfluorescent lamps. These instructions were transferred into German lawon 9 November 1992 as the ‘Gesetz über die Electromagnetische Verträg-lichkeit von Geräten (EMVG)’ (Law on the Electromagnetic Compatibilityof Devices (EMCD)) and was fully valid as from 1 January 1996. A change tothe EMVG was made on 30 August 1995. Violation of the EMC law, andthus of the EMC general instructions, is deemed a summary offence.

Among the threats from the electromagnetic environment, lightningdischarge (Figure 1 b) is the most important and therefore this deter-

Figure 1 a Partial lightning currents propagate on lines and mains

2 Overvoltage protection of low voltage systems

mines to a great extent the protective measures that must be undertakenin the framework of EMC. Therefore, modern lightning protection doesnot only mean protection of buildings but especially the protection ofthose devices covered by Section 2, item 4 of EMVG, meaning that alightning protection system also must be erected, even if it is not neces-sary for the building, for the equipment it contains, in the sense ofSection 2, item 4 of EMVG.

This book presents proven lightning and surge protection measures,taking into account the latest standards and engineering. The com-ponents and devices that are used to achieve these protective measuresare explained in terms of their function and application by means ofpractical examples.

Sources

SACHSE, CH.: ‘Computersicherheit – Tanz auf dem Vulkan’ (Management-Wissen, 1987) No. 6, pp. 68–72PIGLER, F.: ‘EMV und Blitzschutz leittechnischer Anlagen’ (Siemens AG,Berlin u. München, 1990)SCHWAB, A. J.: ‘Elektromagnetische Verträglichkeit’ (Springer Verlag, Berlin,Heidelberg, New York, 1990)BEIERL, O.: ‘Elektromagnetische Verträglichkeit beim Blitzeinschlag in einGebäude’ (Fortschrittsberichte VDI, 1991) Reihe 21, Nr. 93 (VDI-VerlagGmbH, Düsseldorf)KOHLING, A.: ‘EG-Rahmenrichtlinie und Europäische Normen zur EMV’,etz Elektrotech. Z., 1991, 12, (9), pp. 438–441

Figure 1 b Lightning discharge – a special electromagnetic source of interference

Introduction 3

GONSCHOREK, K.-H. and SINGER, H.: ‘Elektromagnetische Verträg-lichkeit’ (B. G. Teubner, Stuttgart–Leipzig, 1992)HABIGER, E.: ‘Elektromagnetische Verträglichkeit. Grundzüge ihrerSicherstellung in der Geräte- und Anlagentechnik’ (Hüthig BuchverlagGmbH, Heidelberg, 1992)HABIGER, E.: ‘Handbuch Elektromagnetische Verträglichkeit’ (VerlagTechnik GmbH, Berlin–München, 1992)MEYER, H. (Ed.): ‘Elektromagnetische Verträglichkeit von Automatisie-rungssystemen’ (VDE-Verlag, GmbH, Berlin/Offenbach, 1992)DIN VDE 0870 Teil 1: ‘Elektromagnetische Beeinflussung (EMB)’ Begriffe.(VDE-Verlag, GmbH, Berlin/Offenbach, July 1984)Richtlinien des Rats vom 3 May 1989 zur Angleichung der Rechtsvorschriftender Mitgliedstaaten über die Elektromagnetische Verträglichkeit (89/336/EWG). Brüssel: Amtsblatt der Gemeinschaft L 139/19 (23 May 1989)Gesetz über die Elektromagnetische Verträglichkeit von Geräten (EMVG),9 Nov. 1992. Bundesgesetzblatt Teil 1, Nr. 52 (12 Nov. 1992)Erstes Gesetz zur Änderung des EMVG vom 30 August 1995 (1. EMVG ÄndG).Bundesgesetzblatt Teil 1. Nr. 47 (8 Sept. 1995).‘Guidelines on the Application of Council Directive 89/336/EEC of 3 May 1989on the Approximation of the Laws of the Member States Relating to Electro-magnetic Compatibility’ (Directive 89/336/EEC Amended by Directives 91/263/EEC, 92/31/EEC, 93/68/EEC, 93/97/EEC)SCHNITZLER, J.: ‘Rechtliche Aspekte für Planer, Errichter und Prüfer vonBlitzschutzanlagen’. 2. VDE/ABB-Fachtagung (6–7 Nov. 1997) Neu-Ulm:Neue Blitzschutznormen in der Praxis


Chapter 2

Damage due to lightning and surges

Damage to electronic installations is increasing due to the followingfactors: (i) the increasing use of electronic equipment and systems,(ii) the lower signal levels, which means higher sensitivity, and (iii) theincreasing use of networks that cover large areas. Although the con-comitant destruction of electronic components is not often spectacular,interruptions to operations in most cases are rather long. Thus, the con-sequential damage is often considerably higher than the damage to thehardware (Figure 2 a).

2.1 Damage statistics

One important electronic insurance company in Germany reported thatthe costs of compensation for surge damage due to electromagnetic

Figure 2 a Computer board damaged by lightning surges

disturbances on electronic systems and equipment, such as communica-tion systems, computers, measuring devices and medical appliances,have quadrupled within a period of ten years (Figure 2.1 a). In 1984 8.5%of all damage adjustments were caused by surges. In 1993 34.6%, in 199435.5%, in 1995 33% out of 11000 cases of damage and in 1996 26.6%and in 1997 31.68% out of 8722 cases of damage were caused by surges(Figure 2.1 b).

Figure 2.1 a Development of the percentage of damage due to surges comparedwith the total damage sum

(Source: Württembergische Feuerversicherung AG, Stuttgart)

Figure 2.1 b Electronics sector: damage in 1997 (analysis of more than 9600cases of damage)


In the former Federal Republic of Germany (FRG) in 1990, damagecosts to electronic equipment and systems caused by surges may haveexceeded one billion DM. Surge damage analysis has shown that light-ning discharges are the dominant disturbances, followed by those due toswitching operations in power technical systems. There are also dangerscaused by electrostatic discharge.

A statistic concerning lightning damage published for many yearsby the Upper Austrian fire prevention authority (Table 2.1 a) shows(additionally to the damage due to direct lightning strikes), indirectdamage caused by electromagnetic lightning disturbances. Such indirect

Table 2.1 a Damage statistics of the Fire Prevention Authority, Upper Austria

Damage due to lightning and surges 7

damage costs are far higher than those due to direct lightning. Forexample, in 1993 there were 23646 indirect damage incidents amountingto 86.2 million ÖS (Austrian schillings), compared to 64 direct damageincidents for which 27.4 million ÖS had to be compensated.

There is now worldwide agreement that the danger radius around apoint struck by lightning is about 2km (Figure 2.1 c, a). Within this domainelectronic systems are affected by conducted and radiated disturbancesthat may cause destruction (Figure 2.1 c, b). In the case of an electro-

Figure 2.1 c (a) Lightning discharge hazard 2km around the strike point

Figure 2.1 c (b) Electronic systems are interfered with or damaged by conductedand radiated interference


magnetic disturbance by lightning, the hardware damage is only asmall part of the total impact. Consequential damage, such as factorystandstill due to the breakdown of computer systems or pollution due tothe failure of measuring and control systems in chemical plants, causesthe greatest proportion of the total loss, to say nothing of the possibleliabilities.

Insurers only compensate for hardware damage, and today they usu-ally pay for the damage only if it is a first event. Thereafter, they willdemand installation of protective measures according to the level ofstandardization and engineering technology, otherwise they will cancelthe insurance contract (Figure 2.1 d). It is a usual condition for the

Figure 2.1 d Text of a letter from the Liability Insurance Association of theGerman Industry concerning ‘surge damage’


conclusion of new contracts that proof of existing relevant protectivemeasures be supplied.

2.2 Examples

Some examples of damage due to lightning discharge, switchingoperations or electrostatic discharge now follow.

2.2.1 Damage in hazardous areas

The disastrous consequences of lightning strikes in hazardous areas willbe illustrated by the following five examples.

In 1965 a 1500m3 solid-roof petrol tank in the DEA-Scholven refineryin Karlsruhe was struck by lightning. The tank exploded and burnt outcompletely (Figure 2.2.1 a). Figure 2.2.1 b shows the measuring equip-ment inside the tank. The ohmic resistance of a nickel spiral with floatserves for measuring the temperature in the tank. As lightning struck thetank there was a flashover from the tank to the wires of the measuringcable which had the potential of the ‘remote’ earth. The explosive mixturewas struck and the tank burnt out.

A similar remarkable case happened ten years later in the Nether-lands. A 5000m3 kerosene tank exploded due to a lightning strike (Figure2.2.1 c). The inner tank temperature was controlled by a thermoelementconnected to the control room by a 200m long measuring cable whichalso had, as in the above-mentioned case, the ‘remote’ earth potential. As

Figure 2.2.1 a Burned out tank due to a lightning strike, Karlsruhe, 1965(Source: DEA-Scholven, Karlsruhe)


one of the surrounding willow trees was struck by lightning, there was adischarge from the roots of the tree to the earthing system of the tank.The potential of the tank system increased in accordance with itsimpulse earthing resistance. As a consequence, there was a sparkover tothe measuring line and due to this open sparkover, the kerosene-air–mixture caught fire. An amateur photographer shot pictures of thislightning strike and the following explosion (Figure 2.2.1 d).

A lightning strike with severe consequences also happened in a chem-ical plant in Herne in August 1984 where an alcohol tank burnt out(Figure 2.2.1 e). Here, TÜV experts managed to find out the reason for

Figure 2.2.1 b Measuring equipment to determine the temperature inside the tank

Figure 2.2.1 c Lightning strike to a kerosene tank, Netherlands, 1975


Figure 2.2.1 d (a)

Figure 2.2.1 d (b)

Figure 2.2.1 d (a, b) 250m highexplosion cloud after the lightningstrike to a kerosene tank

(Source: Brood, T.G.P.)

Figure 2.2.1 e Burning alcohol tankdue to a lightning strike, Herne,1984

(Source: Kartenberg, H. J.)


the damage. Once again it was a measuring cable entering the tank withthe potential of the ‘remote’ earth that led to the burn out.

In October 1995 lightning struck the Indonesian oil refinery Pertaminain Cilacap on the south coast of Java. The tank exploded and the burningoil set fire to six neighbouring tanks (Figures 2.2.1 f and g). Again thereason was incomplete equipotential bonding. Thousands of Cilacapinhabitants and 400 Pertamina employees had to be evacuated for theirsafety. There was a standstill for about 18 months for this refinery whichsupplied 34% of Indonesia’s inland need. This meant that oil, petrol,kerosene and diesel, worth about DM600000, had to be imported dailyfor the supply of Java. Only in Spring 1997 was the company able torestart its own production.

In June 1996 a lightning strike in New Jersey, USA, set fire to petroltanks containing 300000 gallons of petrol. About 200 people had to beevacuated (Figure 2.1 h).

The reasons for these cases of damage are indicated as shown in Figure2.2.1 i. Lightning hits an almost closed Faraday cage which has a hole. Aline coming from a distant building and which is earthed there enters thishole. Between the lightning-struck Faraday cage and this ‘remote’ eartha voltage drop develops that is caused by the lightning current at theimpulse earth resistance (e.g. in Figure 2.2.1 i, 100kV). Conventionalmeasuring line insulations, however, can only withstand impulse voltagesof some 100V; higher values will cause punctures with arcing.

Sources

v. THADEN, H.-W.: ‘Tankbrand durch Blitzeinschlag’ (Erdöl u. Kohle-Erdgas-Petro-chemie, 1966), pp. 422–424BROOD, T. G. P.: ‘Bericht über infolge Blitzeinschlag verursachte Brände inzwei geschützten Tanks für die Lagerung von brennbaren Flüssigkeiten’. 13.Intern. Blitzschutzkonf., Venedig (1976), Referat R-4.5WESTDEUTSCHE ALLGEMEINE ZEITUNG: ‘Herner Tank-Unglück –Blitzschlag trotz einer Schutzanlage’ (4 Dec. 1984)THE JAKARTA POST: ‘Cilacap fire won’t affect domestic fuel oil supplies’ (26Oct. 1995)THE NEW YORK TIMES: ‘Lightning starts fuel tank fire in New Jersey’(12 June 1996)SIRAITI, K. T., PAKPAHAN, P., ANGGORO, B., SOEWONO, S, ISKANTO, E.,GARNIWA, I., and RAHARDJO, A., ‘An analysis of origin of internal sparksin kerosene tank due to lightning strikes’. Lightning and Mountains ’97, June1997, Chamonix Mont Blanc/FranceZORO, R., SUDIRHAM, S., and SASONGKO, D. (ITB Bandung, Indonesia):‘Kerosene tank explosions due to lightning strikes in an Indonesian refineryplant’. Lightning and Mountains ’97, June 1997, Chamonix Mont Blanc/France


Figure 2.2.1 f, g Oil refinery Pertamina, Cilacap/Java, 1995. Seven tanks burnedout due to a lightning strike


2.2.2 Damage to industrial plants

Repeated and extensive surge damage was caused to Europe’s largestcomputer-controlled lorry factory, Daimler–Benz AG, at Wörth, nearKarlsruhe. Often the production came to a standstill and, correspond-ingly, extended production losses resulted from both direct and remotelightning strikes. The factory halls are on a site with a length of 1.5kmand a width of 1km. In two shifts, 10000 workers produce 400 lorries pershift. The material stock computers are connected with those in produc-tion control by a DC data transmission system; this digital symmetrictransmission system works at ±350mV. At the beginning of the 1980s,surges repeatedly damaged the linked equipment, each time bringing withit a complete production standstill.

Figure 2.2.1 h Lightning strike sets petrol tank on fire, New Jersey, USA, 1996


In a textile mill in the former GDR the fire alarm system was activatedby the ionization detector following a lightning strike on the roof of ahigh-bay warehouse. This activated the automatic sprinkler system. Con-sequential water damage was about 1 million DM. The warehouse wasonly equipped with an ‘external lightning protection system’.

A lightning strike to the roof was also the reason for a productionstandstill in the cutting department of a ready-made clothes manu-facturer in Dresden, in 1989. Here the central computer and machinecontrol were disturbed by the 80m long data cable. The so-called‘external lightning protection system’ could not prevent this damage;‘internal lightning protection’ measures were absent.

Systems with cables and lines crossing several buildings are especiallyendangered. In the Leuna works, in 1989, thunderstorms caused a failureof electronic control and supervision equipment causing a standstill inproduction. Distributed sensors in the process system were connectedwith the control room by cables the shields of which were bonded withthe equipotential bonding bar of the control room. Complete lightningprotection equipotential bonding, however, had been neglected and onlya few special cables were connected with protective diodes. The damageloss exceeded 1 million DM.

A lightning occurrence in 1983 will now be described due to itsparticular characteristics. The conclusions that are drawn are valideven today. The case entails the administration tower of Klöckner–Humboldt–Deutz in Cologne (Figures 2.2.2 a and b). This was struck bylightning that was diverted to earth by the ‘external lightning protec-tion system’. Because of the absence of an ‘internal lightning protection

Figure 2.2.1 i Lightning strike to the Faraday cage causes flashover to the line atthe ‘Faraday hole’


system’, about 100 terminals (Figure 2.2.2 c) and numerous computerprocessors (Figure 2.2.2 d) in the computer centre (about 120m away)were disturbed by this strike (Figure 2.2.2 e). Hardware damage aloneamounted to 2 million DM; the consequential loss due to the non-availability of the computer systems was about 4 million DM. Duringthis particular thunderstorm other neighbouring industrial plants hadsurge damage to their computers, telephone and telex systems. Thereasons for these types of damage can be explained by considering Figure2.2.2 f. If lightning strikes building �1 , a partial lightning current willflow into building �2 only because of the resistive coupling (Section3.1.3 (a)) and thus cause damage there. Microelectronic components andcircuits can also be destroyed by electrostatic discharge (Figures 2.2.2 g).

False tripping of common ‘residual current circuit breakers’ (RCCB)due to electromagnetic interference at lightning discharge in close sur-roundings can occur. Reports such as: ‘Numerous animals killed becauseof an indirect lightning strike. In an intensive animal breeding farm14000 chickens suffocated as the ventilators failed because of falsetripping of a residual current circuit breaker, after an indirect lightningstrike’ are not unusual. It must be explained that in intensive chickenbreeding farms about 15000 chickens are reared within six weeks ona surface area of about 1000m2 (Figure 2.2.2 h). During this period,the birds are fed automatically. But, besides food and water, the continu-ity of air supply (Figure 2.2.2 i) is of obvious vital importance. If, forexample, the ventilation system is shut down by false tripping of the

Figure 2.2.2 a Lightning strike into the administration building of Messrs KHD,Cologne, 1983


Figure 2.2.2 b Administration building behind the computing centre (MessrsKHD)

Figure 2.2.2 c Computer terminals in the administration building (MessrsKHD)


Figure 2.2.2 d Computing centre (Messrs KHD)

Figure 2.2.2 e Computer PCB damaged by lightning surge


Figure 2.2.2 f At a lightning strike to building �1 : Surge damage in buildings

�1 and �2

Figure 2.2.2 g (a, b) MOS module damaged by electrostatic discharge.(Source: 3M Deutschland GmbH, Neuss)

Figure 2.2.2 g (a)

Figure 2.2.2 g (b)


Figure 2.2.2 h Automatic feeding

Figure 2.2.2 i Ventilator in an intensive animal breeding building


corresponding residual current circuit breaker, the chickens will suffocatewithin 20 minutes.

In 1987 a defect was to occur in the 20kV cable network of the townNeumarkt while several switching operations were made. This gave riseto switching surges in the 220/380V system, leading to flashover withdamaging arcs in the reactive-current compensation system of the localabattoir (Figures 2.2.2 j).

There were several instances of damage of up to 70000DM each in acombined building services and access control system with about 300interconnected individual components. In the parts of the buildingaffected, the automatic access control only functioned after several daysof repair. In each of these cases the reason was a surge ‘incoupling’ intoexternal components, like code card scanners, due to lightning. Allexternal components of the control system are connected to a centralcomputer by station computers and bus connections. The printed boardsof the station computers and bus couplers were thus damaged by theincoupling of the surges (Figures 2.2.2 k, a and b).

A loss of about 100000DM occurred as surges damaged the printedboards of a printing press (Figure 2.2.2 l, a), (Figure 2.2.2 l, b). Forthis production phase this was the only machine available (maximumcapacity machine). A longer standstill of production, due to some dif-ficulties in obtaining spare parts for this machine, caused problems indelivery and a great loss of income. The reason for the defective machine

Figure 2.2.2 j (a, b) Reactive current compensation system in a slaughter housedamaged due to switching surges, Neumarkt, 1987

Figure 2.2.2 j (a)

Figure 2.2.2 j (b)


was a cable fault in the 20kV power supply system, causing surges in thelow-voltage system.

Sources

HASSE, P., and PRADE, G.: ‘Das Auslöseverhalten von FI-Schutzschalternbei Gewittern. de/der elektromeister + deutsches elektrohandwerk’, 4(1980), pp. 203–207

Figure 2.2.2 k (a) and (b) Surge damage in a building services control system

Figure 2.2.2 k (a) Figure 2.2.2 k (b)Damaged interface card Damaged bus coupler

Figure 2.2.2 l (a) Surge damage at a printing press


GUGENBAUER, A.: Blitze–Feuerzauber der Natur. die österreichischefeuerwehr (1983) H. 7HASSE, P.: ‘Überspannungsschutz von Niederspannungsanlagen – Einsatzelektronischer Geräte auch bei direkten Blitzeinschlägen. 3. aktualisierteAuflage’ (Verlag TÜV Rheinland, Köln, 1993)DAUSEND, A.: ‘Überspannungsschutz als Teil des betrieblichen Risk-Managements’ Teil II: Schadenfälle aus der Praxis. In: HASSE, P. (Ed.): 5.Forum für Versicherer ‘Blitz- und Überspannungsschutz – Massnahmen derEMV’ (Dehn + Söhne, Neumarkt, 1994)

2.2.3 Damage to power supply systems

The public is alarmed sometimes by reports of lightning strikes to powersupply systems or even nuclear power stations. In 1983 lightning struckthe 110/20kV transformer substation of the town Neumarkt (Figures2.2.3 a and b). There was considerable damage to the switching stationand a failure of the 220V direct voltage control. The 20kV surge arresterswere already damaged by the initial partial lightning strikes (Figure 2.2.3c) and, thus, the subsequent lightning strikes could no longer be dis-charged. Sparkover arcs occurred in one switchbay (Figure 2.2.3 d) whichran along the bus bar and damaged other switchbays. Further short-circuit arcs were generated on the 20kV overhead lines. Heavy conductorrope vibrations made the ropes glow and tear. To add further to theproblems, the supplying 110kV transformer exploded during this thun-derstorm (Figure 2.2.3 e) with the consequence that the whole town ofNeumarkt (about 30000 inhabitants) lost power for about six hours.

Figure 2.2.2.l (b) Damaged module of the printing press control


Figure 2.2.3 a Transformer substation 110/20kV, OBAG, Neumarkt

Figure 2.2.3 b Site plan of the transformer substation 110/20kV, OBAG,Neumarkt


Figure 2.2.3 c Surge arresters destroyed by lightning strike

Figure 2.2.3 d Damage in 20kV switching bays due to lightning surge


Sources

DER SPIEGEL: ‘Blitz im Atommeiler’ (1983) No. 36, p. 15NEUMARKTER TAGBLATT: ‘Kurzschluss in Kernkraftwerk’ (22 May 1985)

2.2.4 Damage to a house

Lightning strikes into unearthed aerials of houses (without lightning pro-tection systems), such as the family house in Figure 2.2.4 a, occur fre-quently. Figures 2.2.4 b to h show the damage caused by lightning current

Figure 2.2.3 e Exploded 110kV transformer due to lightning strike, Neumarkt, 1983


on its path of sparkovers and punctures through the electrical wiring ofthe house. The lightning current flows over the aerial standpipe (Figure2.2.4 b), feeding partial lightning currents into the power system, aerialline, telephone line and water pipe. So, usually, all connected electricalappliances and the telephone system will be damaged. In the case men-tioned, the fuel oil pipe was also damaged, and oil leaked into the cellar.In a circle of radius more than 1km, telephone systems failed due to thislightning strike; the traffic-light systems of the town were also disturbedand RC circuit breakers were tripped within a radius of about 3km.

Figure 2.2.4 a Site plan of a house damaged by lightning, Neumarkt, 1986

Figure 2.2.4 b Damage near the antenna-pole in the loft, Neumarkt, 1986


In 1994, during a thunderstorm burst, the radio aerial of a central taxistation in Neumarkt was struck by lightning (Figure 2.2.4 i). The wholeradio system was destroyed (Figure 2.2.4 j). The electrical cables andsocket outlets were torn out of the walls and the entire electrical equip-ment (TV and household appliances) was damaged so heavily that itcould no longer be used.

Figure 2.2.4 d Antenna line damaged by lightning strike

(a) Neumarkt 1986 (b) Similar case

Figure 2.2.4 c Punctures to concealed cables due to lightning strike

(a) Neumarkt 1986 (b) Similar case


Figure 2.2.4 e Distribution cabinets damaged by lightning strike

(b) Similar case (c) Similar case

(a) Neumarkt 1986


Figure 2.2.4 f Boiler damaged by lightningstrike, Neumarkt, 1986

Figure 2.2.4 h Puncture from thepower line to the metal oil pipe due tolightning strike, Neumarkt, 1986

Figure 2.2.4 i (a, b) Lightning strike to the Lutter taxi central office, Neumarkt,1994

Figure 2.2.4 g Telephonesystem damaged by lightningstrike, Neumarkt, 1986

Figure 2.2.4 i (a)

Figure 2.2.4 i (b)


A pressure wave smashed windows and window frames. Tiles were tornoff the wall and there were cracks in the ceilings and the walls. Socketoutlets were torn out of the wall (Figure 2.2.4 k). Partial lightning cur-rents were conducted along the telephone system and the power supplysystem, thus causing other damage in the neighbourhood (Figure 2.2.4 l).

In the vicinity and wider surroundings this lightning strike causedconsiderably more damage than listed here. In the office of the DistrictPresident, the district hospital, the inferior court, the municipal worksand the abattoir, as well as in industrial and commercial enterprises, thecomputer systems and telephones were damaged. In the district hospital,a church, an elementary school and a museum, the safety and fire alarmsystems were damaged (Table 2.2.4 a). In Figure 2.2.4 m, circles aredrawn, at a separation of 1km, around the lightning striking point(marked by an arrow). The locations of the damage are marked bybullets. Damage occurred, even at a distance of 3km from the point ofstrike, for example, in the traffic-light system at the southern perimeterroad of the town. The Neumarkter Nachrichten duly reported on thedamage caused to telephone and cable television connections in 40households and numerous individual TV sets.

Repeatedly, there are extended disturbances in telecommunicationsectors due to solitary lightning strikes. The Hamburger Abendblatt of12 July 1995 reported on a thunderstorm two days previously when25000 Telecom customers in the suburbs of Hamburg were concernedby failures of cable TV. Some 50 microchip amplifiers had to be repairedin Pinneberg, Wedel, Quickborn and Norderstedt. Underground cablesdamaged by lightning currents reveal high interference energies.

Figure 2.2.4 j Damaged radio system Figure 2.2.4 k Damagedelectrical lines


The reason for the above examples of damage is that electrical light-ning interferences are conducted through power and data lines from thepoint of strike over distances of several kilometres directly to the inputsof electronic systems and equipment (Figures 2.1 c and 2.2.4 n). Tele-phone systems, for example, are used in data processing and alarmsystems, making them susceptible.

Sources

NEUMARKTER NACHRICHTEN: ‘Blitzschlag zerfetzte Leitungen und hobden Dachstuhl’ (2–3 Aug.1986)NEUMARKTER NACHRICHTEN: ‘Unheil mit einzigem Blitzschlag’ (3 May1994)HAMBURGER ABENDBLATT: ‘Kabelfernsehen: Vom Blitz getroffen’ No. 160(12 July 1995)

Figure 2.2.4 l Lightning damage (at Telekom systems) in the surroundings ofthe point of strike


Table 2.2.4 a Consequences of a lightning strike to the Lutter Taxi CompanyNeumarkt, 1994


Table 2.2.4 a continued –

Figure 2.2.4 m Lightning damage in a radius of 3km around the point of strike


2.2.5 Damage to aircraft and airports

The following report from the Kölnischen Rundschau of 12 November,1987, for example, describes the damage due to a lightning strike to anairliner:

“Immediately after take-off, the Boeing 747 flying to Newark (New Jersey)entered a thunderstorm zone. Within a few minutes, four lightning dischargesstruck the plane with 225 passengers and 18 crew members on board. Autopilot,weather radar and the radio connection to the tower were knocked out. Also themanual control of the elevator was damaged so strongly that the pilot andcopilot had to use their whole strength to keep the Jumbo flying. A BritishAirways jet flying in the same space followed the distress call of the struckBoeing and piloted it on the correct glide path to the emergency landing. Aftertouchdown, Captain Richards – a former Phantom fighter pilot and Vietnamveteran – stated that the braking thrust reversal of the four engines had alsofailed. Only the landing gear brakes still worked. The plane was brought to astandstill a few metres before the end of the runway. Later, in the Continentalrepair hangar, more than a hundred instances of fire damage to the shelland wings of the Jumbo were counted. Parts of the tail fin were missing. Chiefpilot Fred Abbott told: ‘I never saw a plane that was damaged so heavily bylightning.’ ”

There are reports from the Public Information section of the GermanFederal Ministry of Defence in January 1986 of an electrostatic accidentinvolving a rocket:

“The fire accident with a Pershing II motor stage happened on 11 January 1985on the Waldheide near Heilbronn. During this accident, three members of theUS Army were killed, nine were injured. The accident investigation was finishedby the American investigation committee in December 1985. It confirms the

Figure 2.2.4 n Dangerous surges in neighbouring buildings


Figure 2.2.5 a Newspaper reports concerning lightning strikes to planes, thecontrol tower of the Frankfort/Main airport, the Changi airport(Singapore) and the Düsseldorf airport


statement of the first accident report of 15 April 1985, that a discharge of staticelectricity was the reason for the accident . . .” [The results are then elaborated]From the evidence supplied, the report of 15 April 1985 concludes that a dis-charge of static electricity caused a spark discharge in the propelling charge ofthe motor stage, which was the cause for the fire accident.

On 14 November 1964 the space ship Apollo 12 and then the Saturn Vrocket were struck by lightning 36 seconds after lift-off from Cape Canav-eral. The space ship was about 2000m above ground when a lightningstrike between the rocket and the launching platform on the ground wasnoticed. The crew registered disturbances of the energy supply, a numberof other electrical disturbances and the response of some safety switches.

On 26 March 1987, a 78 million dollar Atlas Centaur rocket went outof control 51 seconds after its launch from Cape Canaveral and had to bedestroyed over the Atlantic together with its freight, an 83 million dollarPentagon satellite. The reason for the loss of control was a lightningstrike to the nose of the rocket. A piece of fibreglass from the wreckrevealed a carbonized hole, having a diameter of about 5 cm, which wasvery similar to the holes registered after lightning strikes to airplanes.Owing to the strike, the main computer gave false commands to thedriving engines so that the rocket’s trajectory failed and it had to bedestroyed.

A lightning strike tripped the ignition mechanisms of three smallresearch rockets on 10 June 1987 which were ready for launch at theNASA base on Wallops island, offshore Virginia. On board the rocketswere measuring devices for thunderstorm research. The rockets had acommon earthing system. According to eyewitness reports, they liftedoff ‘simultaneously’ as lightning struck. After a short flight, they fell intothe Atlantic without causing any damage.

Newpaper reports about lightning strikes to passenger planes and con-trol towers at airports (Figure 2.2.5 a) show that the hazard can extendbeyond the immediate system that is damaged.

Sources

DOLOMITEN: ‘Blitzeinschläge in Flugzeuge’ No. 230 (2–3 Oct. 1993)SONNTAG AKTUELL, STUTTGART: ‘Ein Blitz zerschlug die Radarnase desAirbus – Passagiere wohlauf’ (3 Oct. 1993)BLITZSCHLAG IN CHANGI AIRPORT/SINGAPUR (summer 1995)

2.2.6 Damage to wind power stations

The lightning protection of wind power stations is of current and futureimportance in Britain, Germany and other European countries. Light-ning damage, especially to rotor blades (Figure 2.2.6 a), greatly exceeds


what is expected, both in frequency and height. Cases are known whereinsurance companies see no possibility of further insurance after a singlelightning strike, that is, until the operator or the producer provides anadequate lightning protection system (Figure 2.2.6 b).

2.2.7 Catastrophic damage

At the 21st International Conference on Lightning Protection (ICLP),S. Lundquist described an especially intense lightning storm in Skane,Southern Sweden, on 1 July 1988. The fire brigade in the town of Lundrecorded 1400 alarms. There was a breakdown of the telephone exchangeand the mobile police radio was damaged. As an example of manysimilar life-endangering cases, the situation in the municipal hospital wasdescribed. As the 130kV system failed due to the lightning strike, thehospital was deprived of power for 80 minutes. The lights went out,elevators stopped and the appliances in the intensive care unit could notwork. The emergency power generator refused to start because the con-trol computer was damaged; because of the failure of the telephone andthe central fire alarm, the technical staff could not be called. When theyhad managed to start the emergency power generator by hand after halfan hour, it failed shortly afterwards due to overheating as the ventilatorwas supplied by the unfused system. There was serious damage also tothe low-voltage mains distribution, the control room and the computerterminals. This episode was particularly horrendous.

The consequences of lightning strikes into tall or extended buildingsbecome apparent from events reported from all over the world. Light-ning strikes into large-scale buildings, such as office buildings anddepartment stores, cause current failures resulting in: stoppage of fullelevators, breakdown of the lighting, tripping of sprinkler systems,flooding of rooms by protective gas, blocking of electronically secured

Figure 2.2.6 a Lightning damage to the rotor blade of a wind power generator


doors and garage doors, failure of air-conditioning systems as well asbreakdown of the telephone network (Figure 2.2.7 a) and the controlsystems. Failures of this kind can lead to life-endangering situations and,not least, panic.

What characterizes disturbances and failures due to a lightning strikein a building is that safety-relevant systems may be involved at the sametime, as well as the infrastructure over a wide area that may also be dis-turbed. During a thunderstorm with spatial and temporal distributionof lightning, vast damage to vital infrastructure is possible. Catastrophicevents, as described by some examples, should not be tolerated. There-fore, precautions must be taken to avoid personal danger. Safety must be

Figure 2.2.6 b Report from the Stuttgarter Zeitung, 25 March 1995


guaranteed for the power and information technology systems that areabsolutely necessary for vital infrastructure in special situations. Theseinclude: airports, public transport, traffic guide and signal systems,hospitals, power stations, above all nuclear power stations and switchingplants, high-power transmitters, signal and alarm systems for civil pro-tection, meeting places, schools, kindergardens and mass sports facilities,office and computing centres, buildings with extended safety systems,systems for large-scale supervision of pollutants (including radioactivity)in the air, water and ground, control and alarm systems for defencepurposes, telephone exchanges and satellite and relay stations.

Sources

LUNDQUIST St.: ‘Effects on the society of an intense lightning storm’,Tagungsband 21. Internationale Blitzschutzkonferenz (ICLP), Berlin (22–25Sept. 1992)THÜRINGER ALLGEMEINE: ‘Ein Blitz legte Telefone “tot” ’ (29 June 1994)HASSE, P., and WIESINGER, J.: ‘Can you avoid disasters caused by light-ning?’ DEHN Publication No. SD 261E, reprint from etz, 1993, 2, pp. 154–156

Figure 2.2.7 a Lightning strike causes collapse of the telephone network(Source: Thüringer Allgemeine, 29 June 1994)


Chapter 3

Origin and effect of surges

Electromagnetic compatibility (EMC) engineering usually proceeds froman interference model consisting of a source of interference (trans-mitter), a coupling mechanism (path) and a potentially susceptibleequipment (receiver) (Figure 3 a).

Electrical systems with electronic devices as potentially susceptibleequipment are endangered by conducted interferences and interferingradiation (Figure 3 b) from the following six sources of interference:

(i) Direct and close-up lightning discharges

Lightning electromagnetic impulse (LEMP): predominantly conductedinterference such as lightning currents and partial lightning currents,potential increase of the struck system as well as interfering radiation.

(ii) Power technical switching operations

Switching electromagnetic impulse (SEMP): predominantly conductedinterference as well as magnetic interfering radiation.

(iii) Power technical system perturbation

Predominantly conducted interference with voltage distortions.

(iv) Electrostatic discharges

(ESD): predominantly conducted interference by spark discharge.

(v) Low and high frequency transmitters

Resulting in continuous interfering radiation.

Figure 3 a Interference model

(vi) Nuclear explosions

Nuclear electromagnetic impulse (NEMP): with a resulting impulse-shapedinterfering radiation.

The coupling between the source of interference and potentially suscep-tible equipment can be realized by either conduction and/or radiation(electric field, magnetic field or electromagnetic field). The coupling pathcan be described in the equivalent circuit diagram by combinationsof resistances and/or capacitances and/or inductances.

Potentially susceptible equipment includes telecommunications engin-eering systems (i.e. electrical systems with electronic equipment and facili-ties). In lightning protection engineering, structural facilities, such asmeeting places and areas with fire and explosion hazards, are consideredto contain potentially susceptible equipment in the sense of EMC. Suchpotentially susceptible equipment is found in (i) commercial areas (e.g.,industry, trade, commerce, agriculture, banks and insurance buildings),(ii) public areas (e.g., hospitals, meeting places, air traffic control facili-ties, museums, churches and sports facilities), and (iii) private areas.

In the following Sections, lightning discharges and switching opera-tions as sources of interference are described according to their priority.

Sources

DIN EN 61000 series. ‘Electromagnetic compatibility (EMC)’.

Figure 3 b Electronic system endangered by radiation and conductedinterference


3.1 Atmospheric overvoltages

Lightning, as a source of interference, affects buildings and indoor elec-trical equipment and systems.

Surges of atmospheric origin (Figure 3.1 a) are basically due to either adirect-/close-up strike or a remote strike. In the case of a direct strike(Figure 3.1 a, case �1 ), lightning strikes the protected building; but inthe case of a close-up strike, lightning strikes an extended system or a line(e.g., a pipeline, data or power transmission line) leading directly into theprotected system. However, in the case of a remote strike (Figure 3.1 a,case �2 ), for example, the overhead line is struck. ‘Reflected surges’(travelling waves) are produced in transmission lines by cloud-to-cloudlightning, and overvoltages are induced by lightning in the surroundingarea.

3.1.1 Direct and close-up strikes

Lightning current in a lightning channel and in the lines of the lightningprotection system (a) causes a voltage drop at the impulse earth resist-ance of the earthing system (�1a in Figure 3.1 a) and (b) induces surgevoltages and currents in loops formed by installation lines inside thestructure (�1b in Figure 3.1 a). Owing to the voltage drop at the impulseearth resistance, partial lightning currents also will be discharged by thesupply lines that have been connected as a measure of lightning pro-tection equipotential bonding.

A lightning strike in the surrounding area causes induced surge vol-tages and thus surge currents in installation loops especially due to itsmagnetic interfering radiation. If lightning strikes a feeding overhead

Figure 3.1 a Reasons for surges at lightning discharges

Origin and effect of surges 45

line, there will be conducted surge voltages and currents on the incomingpower line. Lightning between thunderstorm cells in clouds generatesconducted surge voltages and currents on power lines and on other wide-ranging line systems due to interfering electromagnetic radiation.

The parameters of lightning current components (first partial light-ning surge current, subsequent lightning surge current and lightning longduration current) are specified in the following standards: VG 95371 inaccordance with IEC 61024-1, DIN V ENV 61024-1 (VDE 0185 Part100), IEC 61312-1 and DIN VDE 0185 Part 103 (Figure 3.1.1 a). Herethree protection levels are specified in accordance with IEC, or twodegrees of danger in accordance with VG (Table 3.1.1 a).

If an exact analysis is not possible or justified because of the expense,the partial lightning currents on supply lines coming from a struckbuilding can be estimated in accordance with IEC 61312-1 and DIN

Figure 3.1.1 a Lightning current components (protection level I acc. to IEC61024-1/ENV 61024-1 or degree of danger ‘high’ acc. to VG96901

Table 3.1.1 a Lightning current parameters


VDE 0185 Part 103. As shown in Figure 3.1.1 b, it is assumed that 50%of the lightning current flows into the earthing system of the structureand 50% is distributed equally to the outgoing remote-earthed supplysystems (e.g., piping, power and communication lines). To make thingsless complicated one assumes that the partial lightning currents in everysupply system will be distributed equally to the different conductors(e.g., L1, L2, L3, and PEN of a power technical cable or four wires of adata line).

In DIN V ENV 61024-1 (VDE V 0185 Part 100) annex C there is amethod to estimate the lightning partial currents discharged by theincoming lines (for the case when lightning strikes the protected system).Hence, the lightning current will be distributed to the earthing system,the external conductive parts and the incoming lines (which are con-nected directly or by arresters) now as follows:

The share It of lightning current on every external conductive part andevery line depends on their number, their equivalent earth resistance andthe equivalent earth resistance of the earthing system:

It =Z × I

nt × Z + Zt

where Z is the equivalent earth resistance of the earthing system, Zt isthe earth resistance of the external conductive parts or lines, nt is thetotal number of the external conductive parts or lines and I is the light-ning current according to the protection level.

If electrical or information technology (IT) lines are not shielded orlaid in metal conduits, every conductor carries a partial current accord-ing to It/n′ where n′ is the total number of conductors in these lines (Table3.1.1 b).

Figure 3.1.1 b Estimation of the partial lightning currents on supply systems(acc. to IEC 61312-1; VDE 0185 Part 103)


Sources

VG 95 371-2: ‘Elektromagnetische Verträglichkeit (EMV) einschliesslichSchutz gegen den elektromagnetischen Impuls (EMP) und Blitz’; AllgemeineGrundlagen; Begriffe (Beuth Verlag, GmbH, Berlin), March 1994IEC 61024-1: ‘Protection of structures against lightning. Part 1: General prin-ciples’. International Electrotechnical Commission, Geneva CH-1211, March1990DIN V ENV 61024-1 (VDE V 0185 Teil 100): ‘Blitzschutz baulicher Anlagen.Teil 1: Allgemeine Grundsätze’ (VDE Verlag, GmbH, Berlin/Offenbach), Aug.1996IEC 61312-1: 1995-02: ‘Protection against lightning electromagneticimpulse. Part 1: General principles’. Central de la Commission Electrotech-nique Internationale. Geneva CH-1211, Feb.1995DIN VDE 0185 Teil 103: ‘Schutz gegen elektromagnetischen Blitzimpuls.Teil 1: Allgemeine Grundsätze’. (IEC 1312-1: 1995, modifiziert,) (VDE Verlag,GmbH, Berlin/Offenbach) Sept. 1997

3.1.1.1 Voltage drop at the impulse earthing resistance

The maximum voltage drop ûE arising at the impulse earthing resistanceRst of the affected building is calculated in terms of the maximum value îof lightning current (Figure 3.1.1.1 a):

ûE = îRst

This voltage drop ûE, however, is not dangerous for the protected system,if the lightning protection equipotential bonding has been installedeffectively. National as well as international lightning protection stand-ards presently call for a comprehensive lightning protection equipoten-

Table 3.1.1 b Equivalent earthing resistances Z and Z1 depending on the earthresistivity


tial bonding, where all lines (incoming or outgoing) are connected dir-ectly or by spark gaps or surge protective devices to the earthing system.In the event of a lightning strike, the potential of the whole system willrise by ûE , but, within the system, there will be no dangerous differences.

3.1.1.2 Induced voltages in metal loops

The maximum rate of lightning current rise, Δi/Δt, effective during theperiod Δt, determines the peak values of electromagnetically inducedvoltages in all open or closed installation loops which are in the vicinityof conductors carrying lightning current.

The magnetically induced square-wave voltage, U, in a metal loopduring a period of Δt is given by (Figure 3.1.1.2 a):

U = M �Δ i

Δt�where U is in V, M is the mutual inductance of the loop in H and Δi/Δtthe current rate of rise in A/s.

For the sizing of lightning protection systems, the maximum values ofthe average front current rate of rise I/T1, effective during the front timeT1 , of Table 3.1.1 a can be used.

To estimate what maximum induced square-wave voltages, U, have tobe taken into account in installation loops (e.g., in a building) it isassumed that the loops are in the vicinity of infinitely extended, lightningcurrent-carrying down conductors.

For the square-wave voltage of a square loop formed by an infinitelywide lightning current-conducting line and an installation line (e.g., theprotective conductor of the electrical installation, which is connected to

Figure 3.1.1.1 a Potential increase compared with the distant earth by the peakvalue of the lightning current


the down conductor of the lightning protection system at the equipoten-tial bonding bar), the following is applicable:

U = M1 �Δi

Δt�where U is in kV, M1 is the mutual inductance of the loop in μH and Δi/Δt the current change in the lightning current conducting line in kA/μs.M1 depends on the side length a of the loop and the cross section q ofthe lightning current conducting line. This can be taken from Figure3.1.1.2 b. According to the requirements, Δi/Δt = I/T1 can be taken fromTable 3.1.1 a (Figure 3.1.1.2 c).

For a square loop, formed by an installation line which is insulatedfrom an infinitely wide lightning current conducting line, the following isapplicable for the square-wave voltage:

U = M2 �Δi

Δt�where U is in kV, M2 is the mutual inductance of the loop in μH and Δi/Δt the current change in the lightning current conducting line in kA/μs.M2 depends on the side length of the loop a and the distance s betweenthe loop and the lightning current conducting line. This can be takenfrom Figure 3.1.1.2 d. Δi/Δt = I/T1 is taken from Table 3.1.1 a, accordingto the requirements (Figure 3.1.1.2 e).

Apart from the induced effects in wide loops, which are due to installa-tion configurations, the induced effects in very small elongated loopsformed by parallel wires of unshielded, layer-wise stranded, cables in thesurroundings of lightning current conducting lines are also of interest.Induced voltages arising between the wires are called ‘transverse volt-

Figure 3.1.1.2 a Induced square-wave voltages in loops by the rate of rise Δi/Δtof the lightning current


ages’. They can be harmful especially to electronic equipment. For asmall elongated loop formed by the wires of an installation line and runin parallel to an infinitely wide lightning current conducting line, thefollowing is applicable for the square-wave voltage:

U = M′3 l �Δi

Δt�where U is in V, M′3 is the wire length-related mutual inductance of theloop in nH/m, l is the length of the installation line in m and Δi/Δt thecurrent change in the lightning current conducting line in kA/μs. M′3depends on the distance of the wires b, and on the distance s between theinstallation line and the lightning current conducting line. This can be

Figure 3.1.1.2 b Mutual inductance M1 to calculate the square-wave voltages insquare loops, formed by lightning current-carrying conductorand installation line

Figure 3.1.1.2 c Example


taken from Figure 3.1.1 2 f. Δi/Δt = I/T1 is to be taken from Table 3.1.1 a,according to the requirements (Figure 3.1.1.2 g).

For a small elongated loop, formed by the wires of an installation lineand run in a distance vertically to an infinitely wide lightning currentconducting line, the square-wave voltage is given by:

U = M′4 b �Δi

Δt�where U is in V, M′4 is the wire-distance-related mutual inductance ofthe loop in nH/mm, b is the wire distance in mm and Δi/Δt the currentchange in the lightning current conducting line in kA/μs. M′4 depends onthe line length l and the distance s between the installation line and thelightning current conducting line. This can be taken from Figure 3.1.1. 2h. Δi/Δt = I/T1 is to be taken from Table 3.1.1 a, according to therequirements (Figure 3.1.1.2 i).

In contrast to the high voltage values in the case of wide loops, thereare only induced voltages up to about 100V in small, elongated loops.But, keep in mind that these are transverse voltages on informationtechnology lines, which are operated by nominal voltages in the range1–10V and which are connected to surge-sensitive electronic equipment.In the case of lines with twisted wires and especially in the case ofelectromagnetically shielded lines, the induced square-wave voltages willbe very much reduced compared to the values calculated according tothe above equations and the transverse voltage values are usually notdangerous.

Figure 3.1.1.2 d Mutual inductance M2 to calculate the square-wave voltages insquare loops, formed by installation line (an equipotentialbonding line, between the loop and the lightning current-carrying conductor, does not have any influence on M2).


Figure 3.1.1.2 e Example

Figure 3.1.1.2 f Mutual inductance M′3 to calculate the square-wave voltages intwo-wire lines (an equipotential bonding line, between the loopand the lightning current-carrying conductor, does not have anyinfluence on M′3).

Figure 3.1.1.2 g Example


If a metal loop is short-circuited or its insulating distance punctureddue to the induced square-wave voltage U, an induced current ii flows inthe loop for which the following equation is applicable:

dii

dt+

1

πii =

M

L �di

dt� with τ =L

R

where t is the time in s, τ is the time constant of the loop in s, R is theohmic resistance of the loop in Ω, L is the self-inductance of the loop in

Figure 3.1.1.2 h Mutual inductance M′4 to calculate the square-wave voltages intwo-wire lines (an equipotential bonding line, between the loopand the lightning current-carrying conductor, does not have anyinfluence on M′4).

Figure 3.1.1.2 i Example


H, M is the mutual inductance of the loop in H and i the lightningcurrent in the lightning current conducting line in A.

Formulas and examples to calculate the self-inductance L are indi-cated in the ‘Handbuch für Blitzschutz und Erdung’.

In the vicinity of the lightning channel or the lightning currentconducting lines, rapidly changing magnetic fields will arise due to theextreme rate of increase of the lightning current. Surges of up to100000V are generated by these fields within the building in wide ‘induc-tion loops’ formed by the effects of installation lines, such as power andinformation technology lines, water and gas pipings.

Figure 3.1.1.2 j, for example, shows a computer connected to the powerand the data system. The data cable is duly connected to the equipoten-tial bonding bar after entering the building; then the cable goes throughthe data socket outlet into the computer. The power cable is also con-nected to the equipotential bonding bar by lightning current arrestersand supplies the computer through the power socket outlet. As the powerand the data cable are independently installed lines, they can form aninduction loop including a surface of 100m2. The open ends of this loopare in the computer; here the surge, magnetically induced into the loop,becomes effective. Not only in the case of direct lightning strikes, but alsoin the case of strikes in closer proximity, surges of such intensity can beinduced into the loop, causing punctures in the equipment or sometimeseven fire.

The computer must be protected from these lightning surges ‘on thescene’, meaning at the equipment itself or directly at its power and datasocket outlets (Section 5.8.2.3).

Figure 3.1.1.2 j Electronic equipment endangered by induced lightningovervoltages


Sources

HASSE, P., and WIESINGER, J.: ‘Handbuch für Blitzschutz und Erdung’(Pflaum Verlag München; VDE Verlag, Berlin; 4th edn, 1993)

3.1.2 Remote strikes

In the case of remote strikes, travelling surges either propagate along thelines (�2a and �2b in Figure 3.1 a), or lightning strikes (�2c in Figure 3.1 a)in the vicinity of the protected systems, thereby generating electro-magnetic fields which affect the system.

In particular, damage due to surges of atmospheric origin in the1990s has shown that electronic installations, up to a distance of about2km from the lightning point of strike, are susceptible to induced orconducted surges and surge currents (Section 2.1). This wide area ofdanger is due to the increasing sensitivity of high-technology equipmentto cables extending beyond the building and the growth in the use ofsensitive networks.

The maximum permissible length of data transmission lines connect-ing equipment has increased dramatically with advances in technol-ogy. For example, the interface V.24/V.28 (which was introduced duringthe advent of electronic data processing techniques) specifies the elec-trical characteristics of line drivers permitting a direct bonding up toabout 15m cable length. Today, however, there are line drivers and inter-faces available on the market which allow a direct bonding over twistedtwin-core cables up to a length of about 1000m!

When lightning partial currents flow in cables they generate longi-tudinal and transverse voltages (Figure 3.1.2 a).The longitudinal voltage

Figure 3.1.2 a Surges in a cable


ul generated between the wire and the metal cable shield creates stresson the insulation of the connected device between its input terminals andthe earthed enclosure. The transverse voltage uq is established betweenthe wires and this exerts pressure on the input circuit of the connecteddevice. If the lightning partial current î2 is known, the longitudinalvoltage ûl can be calculated from the cable coupling resistance Rk (Table3.1.2 a).

3.1.3 Coupling of surge currents on signal lines

The following examples will demonstrate how surge currents can becoupled ohmically, inductively and capacitively onto the signal lines ofextended systems. Consider the arrangement with device 1 in building 1and device 2 in building 2. The devices are interconnected by a signal line.Furthermore, we will assume that both devices are connected to the

Table 3.1.2 a Coupling resistances at lightning currents


respective equipotential bonding bar (PAS) in the buildings by means ofprotective conductors PE.

3.1.3.1 Ohmic coupling

In Figure 3.1.3.1 a lightning strikes building 1, causing a potential differ-ence of some 100kV at the ohmic earth resistance RA1 . A voltage of thismagnitude is sufficient to sparkover the insulation distance in devices 1and 2 so that an ohmically cross-coupled surge current can flow fromPAS 1, through device 1, along the signal line, through device 2, PAS 2and RA2. The value of this surge current (it can have a peak value ofseveral kA) depends on the relative values of the ohmic resistances RA1

and RA2.

3.1.3.2 Inductive coupling

As already shown, voltages are induced in metal loops by the inductivefields of the lightning channel or the lightning current conducting lines.

Figure 3.1.3.2 a shows the two wire signal line between devices 1 and 2,forming an induction loop. A transverse voltage of several kV will beinduced in this loop if lightning strikes building 1, giving rise to an in-coupled current of up to several kA. These voltages and currents stressthe components at the inputs or outputs of the equipment.

Figure 3.1.3.2 b shows another possible example of inductive coupling.The induction loop is formed by the signal line and the earth. If lightningstrikes building 1, a high voltage (some 10kV) will be induced in this loopleading to a sparkover of insulation distances in devices 1 and 2 and to anincoupled current of several kA.

Figure 3.1.3.1 a Ohmic coupling


3.1.3.3 Capacitive coupling

If lightning strikes the ground or a lightning conductor, the lightningchannel or lightning conductor will be raised to a high voltage (some100kV) compared to the surroundings because of the potential differ-ence at the earth electrode resistance RA.

The signal line between device 1 and device 2 in Figure 3.1.3.3 ais capacitively coupled with such a lightning channel or lightning

Figure 3.1.3.2 a Inductive coupling: Induction loop between the wires of thesignal line

Figure 3.1.3.2 b Inductive coupling: Induction loop between signal line andearth


conductor. The coupling capacities are charged and cause an ‘injected’current (some 10A) which flows to the ground over the insulation dis-tances in devices 1 and 2.

3.1.4 Magnitude of atmospheric overvoltages

Remote strikes initially cause surges of some 10kV. The generated cur-rents are relatively low in value. Direct strikes, however, give rise tolightning currents of far greater and more severe magnitude: currents of200kA (protection level I) and voltage peaks of several 100kV can occur.

Low-voltage installations can usually only withstand impulse break-down voltages of several kV and therefore are susceptible to damage, oreven destruction, by the tens of kV produced by remote strikes or 100kVproduced by direct strikes (Table 3.1.4 a). The withstand voltage of someelectronic devices can be as low as 10V. Hence, the values of voltagesoccurring due to atmospheric discharges can be 100 to 10000 timeshigher than the voltages that can be carried non-destructively by low-voltage systems containing electronic equipment.

Therefore, these high values of overvoltages must be reduced to valueswhich are clearly below the permitted impulse breakdown/sparkovervoltages by means of protective measures or surge protective devices. Toguarantee protection, even in the event of direct lightning strikes, thesurge protective devices employed must also be able to discharge highpartial lightning currents non-destructively.

Figure 3.1.3.3 a Capacitive coupling


Sources

HASSE, P., and WIESINGER, J.: ‘Handbuch für Blitzschutz und Erdung’(Pflaum Verlag, München; VDE Verlag, Berlin; 4th edn, 1993)HASSE, P.: ‘Überspannungsschutz von Niederspannungsanlagen – Einsatzelektronischer Geräte auch bei direkten Blitzeinschlägen’, (Verlag TÜVRheinland, Köln, 3 aktualisierte Auflage 1993)HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept’ (PflaumVerlag, München; VDE Verlag, Berlin-Offenbach, 1994)

3.2 Switching overvoltages

Switching overvoltages in power plants can also affect low-voltage sys-tems and secondary engineering systems, especially due to capacitivecoupling. In certain cases, these values can exceed 15kV. Examples of thecause of these switching overvoltages are as follows:

(a) Disconnection of an open-circuit power line (or capacitors) (Figure3.2 a). When the switch opens, the instantaneous value of the supplyvoltage on the line results in a high potential difference between thesystem and the disconnected line. The potential difference, which isestablished in only a few milliseconds, can cause a flashback betweenthe switch contacts that are yet to close. The line voltage thenbalances at a level equal to the instantaneous value of the supply

Table 3.1.4 a Impulse flashover voltages/impulse breakdown voltages(1.2/50 μs) in electrical systems and equipment up to 1000V


voltage and the arc between the switch contacts is quenched. Thisprocess can occur several times. The switching overvoltage generatedby the equalization of the appropriate instantaneous value of thesupply voltage has the characteristic of a damped oscillation with afrequency of several 100kHz. The initial amplitude of these switch-ing surges always corresponds to the potential difference between theswitch contacts at the moment of the flashback and this amplitudecan be a multiple of the nominal supply voltage.

(b) Disconnection of an open-circuit transformer. If an open-circuittransformer is disconnected from the network, its self-capacitance isloaded by the energy of the magnetic field. The inductive–capacitvecircuit now oscillates until all of the energy in the ohmic resistanceof the circuit is converted into heat. The resulting switching over-voltages can reach amplitudes of several times the value of the nom-inal supply voltage.

(c) Earth fault in the floating (earth-free) network. If an earth faultoccurs at the outer conductor of a floating network, then the poten-tial of the complete conductor system will be altered by the value ofthe voltage of the affected conductor with respect to earth. If theearth fault arc interrupts, the effect is similar to that of an open-circuit conductor or capacitor being disconnected: switching over-voltages will develop with damped oscillations.

In addition to switching overvoltages from power plants of this nature,which capacitively influence low-voltage systems, rapid variations in cur-rent can also generate surges in low-voltage systems by inductive coup-ling. Such sudden current variations can be due to either the connectionor disconnection of a heavy load, or a short circuit, an earth fault ordouble earth fault.

Switching overvoltages can also be generated within the low-voltagesystems themselves due to the following:

• the disconnection of inductances connected in parallel with the sourceof voltage, such as transformers, inductors or coils of contactors and

Figure 3.2 a Switching surges on disconnection of a capacitance


relays. (In this case, switching overvoltages are generated in a similarway to that described above for the disconnection of an open-circuitpower transformer.)

• the disconnection of inductances in the series arm of the current cir-cuit such as conductor loops, series inductors, or the inductances ofthe actual conductors. (These inductances try to maintain the flow ofcurrent, even if the circuit is interrupted. The magnitude of the switch-ing overvoltages that arise depends on the value of the current at thetime of disconnection.)

• intentional disconnection of circuits by means of switches, or un-intentional disconnection brought about by the tripping of fuses orcircuit breakers, or by line discontinuity before the natural currentzero-axis crossing. (Rapid changes in current resulting from occur-rences such as these give rise to switching surges, normally withdamped oscillations, which are a multiple of the nominal voltage ofthe system.)

• by phase control circuits, commutation effects in brush collectorsystems, and by sudden unloading of machines and transformers.

Extensive measurements taken in different low-voltage networks haveshown that the most remarkable surges have been caused by interferingradiation of arcs generated in switchgear.

Electromagnetic interference by switching in power technical systemsis usually more frequent than lightning interferences.

For conducted, broadband interference a difference is made in theEMC standards between high and low energy impulses or pulses depend-ing on the type of switching operation. It is possible that switching inter-ference is generated outside a building and enters through the power linesor it can be generated internally. This is either defined analogously to thelightning interference as combined surge voltage and surge current inter-ference or as impressed surge voltages.

In part the broadband, high energy, conducted interference of switch-ing processes is equated to the conducted lightning interference inside thebuilding (with a duly carried out lightning protection equipotentialbonding). So interference for different types of environment with corre-spondingly adjusted peak values is defined in the VG standards (Tables3.2 a and 3.2 b).

An impressed surge voltage due to disconnection processes or overcur-rent protective components is defined in DIN VDE 0160. The surgevoltage 0.1/1.3ms (0.1ms rate of rise, about 0.15ms front time) with apeak value uN/max will be superimposed on the peak value uN/max of thealternating current voltage.

Broadband, low energy switching voltage interference, (i.e. bursts)are shown in DIN VDE 0847 Part 4-4. These impressed voltage impulses5/50ns (5ns rate of rise, about 7.4ns front time) with peak values


depending on the severity of testing are supplied as pulse packages intopower and communication lines through coupling capacities.

Apart from conducted interference, considerable interfering radia-tion can also be due to the switching processes themselves (e.g.arcs generated by the withdrawing of disconnectors) inducing more con-ducted interferences.

Sources

FGH MANNHEIM: ‘Transiente Überspannungen’, Fachberichte der FGHMannheim, etz-a Elektrotech. Z., 1976, 97(1), pp. 2–27MENGE, H.-D.: ‘Ergebnisse von Messungen transienter Überspannungen inFreiluft-Schaltanlagen’, etz-a Elektrotech. Z., 1976, 97(1), pp. 15–17

Table 3.2 a Lightning interference ‘1.2/50μs’

Table 3.2 b Lightning interference ‘10/700 μs’


LANG, U., and LINDNER, H.: ‘Überspannungen in Hochspannungsschaltan-lagen – Schutz von Sekundäreinrichtungen’, Elektrizitätswirtschaft, 1986, 22,pp. 680–683SCHWAB, A. J.: ‘Elektromagnetische Verträglichkeit’ (Springer Verlag, Berlin,Heidelberg, New York, 1990)HASSE, P.: ‘Überspannungsschutz von Niederspannungsanlagen – Einsatzelektronischer Geräte auch bei direkten Blitzeinschlägen’, 3. aktualisierteAuflage (Verlag TÜV Rheinland, Köln, 1993)HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept’ (PflaumVerlag, München; VDE Verlag, Berlin-Offenbach, 1994)VDEW: ‘Hinweise für die Messung von transienten Überspannungenin Sekundärleitungen innerhalb von Freiluft-Schaltanlagen’ VereinigungDeutscher Elektrizitätswerke – VDEW e. V., Ausgabe Oct. 1975DIN EN 61000-4-5 (VDE 0847 Teil 4-5): 1996-09: ‘Elektromagnetische Ver-träglichkeit (EMV)’. Teil 4: Prüf- und Messverfahren. Hauptabschnitt 5:Prüfung der Störfestigkeit gegen Stossspannungen (IEC 1000-4-5: 1995);Deutsche Fassung EN 61000-4-5: (VDE Verlag, GmbH, Berlin/Offenbach,1995)DIN EN 61000-4-4 (VDE 0847 Teil 4-4): 1996-03: ‘Elektromagnetische Ver-träglichkeit (EMV)’. Teil 4: Prüf- und Messverfahren. Hauptabschnitt 4:Prüfung der Störfestigkeit gegen schnelle transiente elektrischeStörgrössen/Burst; EMV-Grundnorm (VDE Verlag, GmbH, Berlin/Offenbach,March 1996)DIN VDE 0160: 1988-05: ‘Ausrüstung von Starkstromanlagen mit elektro-nischen Betriebsmitteln’ (VDE Verlag, GmbH, Berlin/Offenbach, May 1988)DIN-VDE-Taschenbuch 515: ‘Elektromagnetische Verträglichkeit 1. DIN-VDE-Normen’ (VDE Verlag, GmbH, Berlin/Offenbach, 1991)VG 96 903 Teil 76/08.89: ‘Schutz gegen Nuklear-ElektromagnetischenImpuls (NEMP) und Blitzschlag’. Prüfverfahren, Prüfeinrichtungen undGrenzwerte. Verfahren LF 76: Prüfung mit Direkteinspeisung eines Span-nungsimpulses 1,2/50�s und eines Stromimpulses 8/20�s (Beuth-Verlag,GmbH, Berlin, Aug. 1989)


Chapter 4

Protective measures, standards

For a considerable time increasingly refined methods have been usedworldwide to measure lightning currents at high towers, HV overheadlines and in lightning trigger stations. Field measuring stations alsoregister the radiated electromagnetic interference fields of lightningdischarges. From the results of research, lightning as a source of inter-ference is understood and defined with regard to the present protectionproblems. It is also possible to simulate lightning currents with theirextreme values in the laboratory; this is a prerequisite for testing protectiveinstallations, components and devices. Also lightning interference fieldscan be simulated for the testing of information technology equipment.

Because of such wide ranging basic research and the development ofprotection concepts, such as the concept of lightning protection zones asorganizing principle of an EMC, as well as suitable protective measuresand devices against field generated and conducted interference due tolightning discharges, we now have the necessary conditions for protectingsystems in such a way that the final risk of failure can be kept extremelylow. Thus, it can be guaranteed that the essential infrastructure canbe maintained and catastrophes avoided in cases of extraordinaryatmospheric threats.

The necessity of standardizing complex EMC-oriented lightning pro-tection measures, containing also so-called surge protection measures,has been realized. The International Electrotechnical Commission (IEC)as well as the European (Cenelec) and national standards committees(DINVDE, VG) produce standards on the following:

• Electromagnetic interference of lightning discharge and its statisticaldistribution as a basis for the assignment of interferences to protectionlevels

• Methods to estimate the risk of determining the protection levels

• Measures to discharge the lightning current

• Measures for screening electromagnetic lightning fields

• Measures to discharge conducted lightning interference

• Requirements and tests for protective components

• Protective concepts within the scope of an EMC-oriented manage-ment plan

When designing a protection system, it is first necessary to decidewhether to protect the device or installation solely against destruction oragainst interference as well. The effects of interference are normallycovered by ‘classical’ considerations of the electromagnetic compatibility(EMC) of a device; and the possible destruction of devices is the mostimportant consideration in surge protection analysis.

In contrast to normal electromagnetic interference, lightning dischargesand nuclear explosions are relatively rare and of very short duration.Hence, system design is usually limited to avoiding the destruction ofdevices by surges. Short-term signal fluctuations can be accepted. This,for example, is the procedure in standard low-voltage systems in wideranges of industrial measurement and control installations and in tele-communication and electronic data processing systems. In certain specialcases, however, such as the control systems of nuclear power stations,alarm systems and military installations, there must be no error signalseven in the case of a lightning discharge or nuclear explosion. Someinstallations require a combination of lightning protection, switchingsurge protection, electrostatic discharge protection and protectionagainst nuclear electromagnetic pulses.

The protective measures described in the following paragraphs, such asexternal and internal lightning protection, shielding, and surge limita-tion, are methods which partly overlap and also complement oneanother. If possible, they should be considered at the initial stages ofconstruction of structural systems and electrical consumer installations,but sometimes they can be realized subsequently.

On passing of the law on the electromagnetic compatibility of devices(‘Guidelines on the application of Council Directive 89/336/EEC of 3May 1989 on the approximation of the laws of the Member States rela-ting to electromagnetic compatibility’), the ‘equipment’ must have a suf-ficient immunity also against lightning interference. The word ‘equip-ment’ does not only mean all electric and electronic devices but alsoinstallations and systems which contain electric or electronic modules. Tosecure, for example, the protection of complex power and informationsystems of a building in the case of a direct or close-up lightning strike,extensive analysis by a lightning protection expert is necessary. With anEMC analysis, convenient planning for a building and reliable cooper-ation of all electronic building functions at normal operation can besecured. With priority system planning, the EMC measures of lightningprotection are realized so that safe, interference-free operation is pos-sible; likewise for the case of direct lightning interference.


Sources

HASSE, P.: ‘Überspannungsschutz von Niederspannungsanlagen – Einsatzelektronischer Geräte auch bei direkten Blitzeinschlägen’ (Verlag TÜVRheinland, Köln, 3. aktualisierte Auflage, 1993)HASSE, P.: ‘Blitz-/Überspannungsschutz – Stand der Normung’, 5. Forum fürVersicherer (Dehn und Söhne, Nürnberg, Oct.1994)HASSE, P., and WIESINGER, J.: ‘Lightning protection for fulfilling the principlesof EMC ’, DEHN publication No. SD 321E, reprint from etz, 7, 1995, pp.12–13HASSE, P.: ‘Blitzschutz für Gebäude und Elektrische Anlagen – 1’, VDE/ABB-Blitzschutztagung, 1996, 11, pp. 960–964; 1996, 12, pp. 1107–1112

4.1 Lightning protection

According to national and international lightning protection engineeringand standards, a lightning protection system for buildings requires theprotection of the whole system against the effects of lightning. Thisconsists of external lightning protection and internal lightning protec-tion. External lightning protection involves the air termination systems,the down conductors and the earthing system. Internal lightning protec-tion involves all additional measures preventing magnetic and electricimplications of lightning current in the volume to be protected. Above allelse, there is lightning protection equipotential bonding which reducesthe potential differences caused by lightning current.

According to the international lightning protection standard, the ‘pro-tected volume’ is the structural system that is to be protected by a light-ning protection system. The primary task of lightning protection is tointercept lightning by an air termination system, to discharge the light-ning current through a down conductor system to the earthing systemwhere it will be dissipated into the ground. Furthermore, the ohmically,capacitively and inductively ‘incoupled’ interference must be reduced toharmless values in the protected volume.

In Germany, DIN VDE 0185 Parts 1 and 2 have been enacted since1982 for the erection, planning, extension and alteration of lightningprotection systems. This VDE guide, however, does not include details ofwhether a lightning protection system has to be provided for a buildingor not. Building regulations of the German Federal Countries, nationaland regional regulations and specifications, instructions and directionsof the insurance companies and the danger characteristics for lightningprotection systems in the immovables of the German Federal ArmedForces can be used as decision makers.

If a lightning protection system for a structural system or building isnot made a prerequisiste by the building regulations of an individualcountry, it is entirely up to the building supervisory board, the owner orthe operator to decide upon its necessity. Should there be a decision for

Protective measures, standards 69

the installation of a lightning protection system, it must be carried out inaccordance with the corresponding standards or relevant regulations. Asan accepted rule of engineering, however, a standard or regulation onlystipulates the minimum requirements at the time of coming into force.Developments in the field of engineering and related latest scientific find-ings may be registered from time to time into a new standard or regula-tion. Thus, the presently valid DIN VDE 0185 Part 1 and 2 only reflectsthe state of engineering of about twenty years ago. In the interim yearsthere have been important changes in building services managementsystems and electronic data processing. Thus, a building lightning protec-tion system planned and installed according to the state of engineeringtwenty years ago will no longer be sufficient. Damage statistics of theinsurance companies clearly confirm this fact (Figures 2.1 a and 2.1 b).However, the latest results of lightning research and engineering arereflected in the internationally agreed lightning protection standards.Technical Committee 81 (TC81) of the IEC has international com-petence, Technical Committee 81X (TC81X) of the Cenelec has European(regional) competence and Committee K251 of the German Electro-technical Commission (DKE) has national competence in lightning pro-tection standardization. Table 4.1 a shows the current state as well as thefuture tasks of the IEC standardizing work in this field. Through Cenelec,IEC standards are transferred into European Standards (ES) (sometimesmodified): for example, IEC 61024-1 in ENV 61024-1. But Cenelec alsoworks out its own standards: for example, EN 50164-1 to 4 (Table 4.1 b).

Figure 4.1 a illustrates the mechanism for the development of an IECstandard through Cenelec to the DKE using the example of IEC 61024-1:

Figure 4.1 a Lightning protection standards: International (IEC), regional(CLC), national (DKE)


Tabl

e4.1

aS

tandard

s w

ithin

IE

C T

C 8

1

• IEC 61024-1: 1990-03 ‘Protection of structures against lightning.Part 1: General principles’ has been valid worldwide since March1990.

• The European draft standard ENV 61024-1: 1995-01 ‘Protection ofstructures against lightning. Part 1: General principles’ has been inforce since January 1995.

• This draft standard (translated into the national languages) will betested in the European countries (for about three years); in Ger-many, for example, as DIN V ENV 61024-1 (VDE V 0185 Part100) ‘Gebäudeblitzschutz. Teil 1: Allgemeine Grundsätze’ (withnational annex). (‘Lightning protection of buildings. Part 1: Generalprinciples’)

• After final consideration at Cenelec, there will then be the bindingstandard EN 61024-1 for all European countries.

• In Germany this standard will be published as DIN EN 61024-1(VDE 0185 Part 100).

In August 1996 the German draft standard DIN V ENV 61024-1(VDE V 0185 Part 100) was published (Figure 4.1 b). During the tran-sitional period until the final standard, either this draft standard or thestandard DIN VDE 0185-1 (VDE 0185 Part 1): 1982-11 ‘Blitzschutzan-lage, Allgemeines für das Errichten’ can be applied.

ENV 61024-1 is based on the latest technical state. Its applicationguarantees safe protection of the structure. Therefore, application ofENV 61024-1, including the national annex, is recommended in order toobtain a more effective protection, on the one hand, and to gatherexperience in the application of the later exclusively valid EuropeanStandard, on the other hand.

Table 4.1 b Cenelec-standards ‘Lightning Protection’


Lightning protection measures for special systems DIN VDE 0185-2(VDE 0185 Part 2): 1982-11 will be treated in a later standard. Until thenthe standard DIN VDE 0185-2 (VDE 0185 Part 2): 1982-11 is valid.These special systems can be carried out according to ENV 61024-1;additional requirements in DIN VDE 0185-2 (VDE 0185 Part 2): 1982-11 must be taken into account.

A lightning protection system planned and installed according tothe draft standard ENV 61024-1 will rather prevent damage at thestructure. Persons are protected inside the structure, and they will not beendangered by damage to the structure (e.g., fire).

The protection of extended electrical power and information engineer-ing installations in and at the structure cannot be guaranteed by the verymeasures of lightning protection equipotential bonding according toENV 61024-1. In particular the protection of information technologyequipment (communications technology, instrumentation and control,computer networks etc.) requires special protective measures on the basisof IEC 61312-1: 1995-02 ‘Protection against lightning electromagneticimpulse. Part 1: General principles’ because of the low admissiblevoltages.

The standard DIN VDE 0185-103 (VDE 0185 Part 103), with theregulations of IEC 61312-1, has been valid since September 1997 (Figure4.1 c).

To estimate the damage risk due to a lightning strike, standard IEC61662: 1995-04 ‘Assessment of the risk of damage due to lightning’with Amendment 1: 1996-05 ‘Assessment of the risk of damage dueto lightning’, Annex C ‘Structures containing electronic systems’ isapplicable.

Figure 4.1 b Use of the European Draft Standard (ENV) in Germany


Sources

DIN VDE 0185: ‘Blitzschutzanlage. Teil 1: Allgemeines für das Errichten. Teil2: Errichten besonderer Anlagen’ (VDE Verlag, GmbH, Berlin/Offenbach,Nov. 1982)IEC 61024-1: ‘Protection of structures against lightning. Part 1: Generalprinciples’. International Electrotechnical Commission, Genève, March 1980DIN V ENV 61024-1(VDE V 0185 Teil 100): ‘Blitzschutz baulicher Anlagen.Teil 1: Allgemeine Grundsätze’ (VDE Verlag, GmbH, Berlin/Offenbach, Aug.1996)E DIN EN 50164-1(VDE 0185 Teil 201): ‘Blitzschutzbauteile. Teil 1:Anforderungen für Verbindungsbauteile’. Deutsche Fassung prEN 50164-1:(VDE Verlag, GmbH, Berlin/Offenbach, May 1997)IEC 61312-1: ‘Protection against lightning electromagnetic impulse. Part 1:General principles’. Centre de la Commission Electrotechnique Internation-ale Genève, Feb. 1995DIN VDE 0185-103 (VDE 0185 Teil 103): ‘Schutz gegen elektromag-netischen Blitzimpuls. Teil 1: Allgemeine Grundsätze’, (IEC 1312-1: 1995,modifiziert) (VDE Verlag, GmbH, Berlin/Offenbach, Sept. 1997)IEC 61662: ‘Assessment of the risk of damage due to lightning’. BureauCentral de la Commission Electrotechnique Internationale, Genève, April1995

Amendment 1: ‘Assessment of the risk of damage due to lightning, Annex C:Structures containing electronic systems’. Bureau Central de la CommissionElectrotechnique Internationale, Genève, May 1996

4.1.1 Risk analysis, protection levels

Basically new in these lightning protection standards are methods for theassessment of the risk of damage due to lightning and the subdivision ofthe protective measures into protection levels.

Figure 4.1 c New German Lightning Protection Standards


The assessment of the risk of damage due to a lightning strike into astructure helps the lightning protection planner to decide whether or nota lightning protection system is to be recommended and to choosesuitable protective measures. The purpose of choosing a sufficient pro-tection level is to reduce the risk of damage due to direct lightning strikesto below an acceptable value. The selection of a sufficient protectionlevel for the lightning protection system can be based on the expectednumber of direct strikes (Nd) and on the accepted number of strikes (Nc)that will cause damage.

The flow diagram for the selection of the lightning protection sys-tems, is shown in DIN V ENV 61024-1 (VDE V 0185 Part 100) in Figure4.1.1a.

Figure 4.1.1 a Flow diagram for the selection of a lightning protection system


Proceeding from a lightning density Ng (lightning strikes per km2 andyear), which is applicable for the region where the building stands, theaverage annual number Nd of lightning strikes to be expected forthe building/surface Ae can be determined by means of the equivalentsurface Ae (in km2). That is

Nd = Ng Ae

The equivalent surface Ae will be determined according to Figure 4.1.1 b.The equivalent surface Ae takes into account that lightning strikes inthe direct vicinity of a structure have the same consequence as directstrikes.

According to the national annex NB of this standard the following isspecified:

Nc = A B C

where Nc is the accepted strike frequency, A is the building constructioncomponent (type of construction, material), B is the component dealingwith the use and contents of the building, and C is the component con-sidering consequential damage.

To determine these components, the following are taken into account:

• Component A (building construction): construction of the walls, roofconstruction, roof covering, and roof superstructures.

• Component B (building utilization and contents): utilization bypeople, nature of building contents, value of building contents, andmeasures and installations for damage reduction.

Figure 4.1.1 b Determination of the equivalent collection area Ae for anindividual building


• Component C (consequential damage): danger to the environmentdue to the building contents, failure of important public services sup-plied by the building installations, and other consequential damage.

The value of the accepted strike frequency Nc must be compared withthe actual number of annual strikes Nd. The comparison allows a deci-sion—whether a lightning protection system is necessary or not, and, inthe affirmative, what version has to be chosen:

If Nd < Nc , a lightning protection system is not necessary.If Nd > Nc, a lightning protection system with efficiency

E ≥ 1 −Nc

Nd

in accordance with the protection level of Table 4.1.1 a should be installed.After calculation of E, the protection level must be derived from thefollowing:

E > 0.98 protection level I with additional protective measures0.95 < E ≤ 0.98 protection level I0.90 < E ≤ 0.95 protection level II0.80 < E ≤ 0.90 protection level III

0 < E ≤ 0.80 protection level IVE < 0 lightning protection not necessary.

Additional protective measures, for example, include those to reducethe contact and step voltages, those to avoid the spreading of fire, andthose to reduce voltages in sensitive installations induced by lightning.

By the protection level the following is stipulated:

• efficacy of the lightning protection system (Table 4.1.1a)

• radius of the rolling sphere, protective angle, mesh size (Table 4.1.1 b)

• lightning characteristics (Table 4.1.1 c)

Table 4.1.1 a Relation between protection level and efficiency


• factor ki to determine the safety distance between the lightning pro-tection system and metal installations/electrical and informationtechnology equipment

• clearances between the down conductors

• minimum lengths of the earth electrodes

• inspection intervals.

4.1.2 External and internal lightning protection, DIN VDE 0185Part 1, DIN V ENV 61024-1 (VDE V 0185 Part 100)

DIN V ENV 61024-1 (VDE V 0185 Part 100) as well as DIN VDE 0185Part 1 essentially deal with (Figure 4.1.2 a): air termination system, downconductor system, earthing system, lightning protection equipotentialbonding, and safety clearances (at proximity points).

Table 4.1.1 b Assignment of angle of protection, rolling sphere radius and meshsize to the protection levels

Table 4.1.1 c Assignment of the lightning current parameters to the protectionlevels


The lightning protection system consists of both external and internallightning protection. External lightning protection consists of the airtermination system, the down conductor system and the earthing system.Internal lightning protection includes all additional measures to avoidelectromagnetic interference due to lightning current in the protectedvolume.

Lightning protection equipotential bonding is that part of the internallightning protection which reduces the potential differences caused by light-ning current. Lightning protection equipotential bonding is realized bybonding the conductors of the external lightning protection system with themetal frame of the structure, with the metal installations, with the externalconductive parts, and with the power and information technology equipmentin the volume to protect.

Bonding measures include: equipotential bonding lines, if the con-tinuous electric conductivity is not achieved by the natural connections;and arresters, if direct connections with the equipotential bonding linesare not allowed (Figure 4.1.2 b).

Lightning protection equipotential bonding must be carried out inaccordance with DIN V ENV 61024-1.

4.1.3 Concept of lightning protection zones, DIN VDE 0185-103(VDE 0185 Part 103)

Since September 1997 the international standard IEC 61312-1 ‘Pro-tection against lightning electromagnetic impulse – Part 1: Generalprinciples’ is also valid in Germany as DIN VDE 0185-103 (VDE 0185

Figure 4.1.2 a External and Internal Lightning Protection according to IEC61024-1/ENV 61024-1


Part 103): 1997-09 ‘Schutz gegen elektromagnetischen Blitzimpuls. Teil1: Allgemeine Grundsätze’.

This standard became necessary because of the increasing use of manykinds of electronic systems including computers, telecommunicationfacilities, control systems etc. (called information systems in this stand-ard). Such systems are used in many fields of commerce and industry,including the control of production facilities with high capital value, widedimensions and great complexity, where failures due to lightning strikesare very undesirable for cost and safety reasons. A risk analysis whichfocuses on the LEMP hazard to electronic equipment is indicated in IEC61662, Amendment 1 ‘Assessment of the risk of damage due to light-ning’, Annex C ‘Structures containing electronic systems’.

With regard to general principles of protection against lightning strikesDIN V ENV 61024-1 (VDE V 0185 Part 100) is applicable; however, itdoes not treat the protection of electric and electronic systems. Thestandard DIN VDE 0185-103 (VDE 0185 Part 103) is concerned withthe lightning electromagnetic impulse and its interfering fields and there-fore is a basis for the protective system.

The general principles for protection against the electromagneticlightning pulse (or LEMP: lightning electromagnetic impulse) aredescribed in DIN VDE 0185-103 (VDE 0185 Part 103). Here it is shownhow a structure can be subdivided into several lightning protection zones(in DIN VDE 0185-103 (VDE 0185 Part 103) called LPZ: lightningprotection zone) according to the concept of lightning protection zones,and how the equipotential bonding has to be carried out at the zoneinterfaces (Figure 4.1.3 a).

The protected volume (or ‘volume to protect’) will be subdivided intolightning protection zones. The different protection zones are formed by

Figure 4.1.2 b Lightning protection equipotential bonding for incoming services


building screens, shielded rooms and devices using existing metalstructures. The individual protection zones are characterized by obviouschanges of the fieldborne and conducted lightning interference at theirboundaries. When a metal supply system passes a zone boundary andthus the electromagnetic screen of a zone, this supplying system must betreated at the interface. For passive conductors (pipes, cable sheaths) thisis done by conductive connections to the zone screen; for electrical linesby the use of arresters that discharge the interfering energy.

Figure 4.1.3 a Example for the subdivision of a building into several lightningprotection zones (LPZ) and sufficient equipotential bonding


In the standard DIN VDE 0185-103 (VDE 0185 Part 103):

• the execution of the protective measures on the basis of the conceptof lightning protection zones is shown from concept planning to itsacceptance

• primary lightning interferences are specified

• generator circuits are indicated for the simulation of lightning currents

• the timing functions of the lightning current components are shownfor calculation analyses

• measures of lightning protection equipotential bonding are treated

• electromagnetic building and room screening is described

• the application of arresters is determined.

The LEMP-protection management for new buildings, as well as forfar-reaching alterations in the execution or use of structures, is describedin this standard (Table 4.1.3 a). In the following sections the tasks thatmust be fulfilled by the different management steps are described andpractical examples are given.

Sources

HASSE, P., and WIESINGER, J.: ‘EMV-Blitz-Schutzzonen-Konzept’ (PflaumVerlag, München; VDE Verlag, Berlin/Offenbach, 1994)HASSE, P.: ‘Blitzschutz-Management – Planung und Organisation’.Tagungsband 1. VDE/ABB–Blitzschutztagung ‘Blitzschutz für Gebäude undElektrische Anlagen’. (Kassel, 29 Feb.–1 March,1996)

Table 4.1.3 a LEMP-protection management for new buildings and forcomprehensive alterations in development or utilization of existingbuildings


HASSE, P.: Neu: DIN VDE 0185 Teil 103: ‘Schutz gegen elektromagnetischenBlitzimpuls’. Teil 1: Allgemeine Grundsätze – Anwendung in der Praxis – (I).de (der elektromeister + deutsches elektrohandwerk), 1997, 14, pp. 1352–1356, 17, pp. 1552–1558, 18, pp. 1691–1693IEC 61662, Amendment 1: ‘Assessment of the risk of damage due to light-ning, Annex C: Structures containing electronic systems’. Bureau Central dela Commission Electrotechnique Internationale, Genève, May 1996

4.1.3.1 LEMP-protection planning

The LEMP-protection planning for the system to protect must be carriedout by a lightning protection expert (who has well-founded knowledge ofEMC) in close coordination with the owner, the architect, the installer ofthe information system, the planners, and other relevant institutions and,if necessary, with the subcontractors. The planning should begin withdefinition of the lightning protection levels.

4.1.3.1.1 Definition of lightning protection levels By analysing the risk inaccordance with DIN V ENV 61024-1 (VDE V 0185 Part 100), annex F, oraccording to DIN IEC 61662 (VDE 0185 Part 101), where the structure’ssite, the building construction, its use, content, and possible subsequentdamage are considered, the adequate protection level for the structure toprotect can be determined as described in Section 4.1.1.

4.1.3.1.2 Definition of lightning protection zones As shown in Figure4.1.3 a, the volume to protect will be divided into protection zones. Thedifferent protection zones will be created by the screening of the build-ing, the rooms, and the equipment by using the existing metal com-ponents such as metal facades, reinforcements and metallic enclosures.Numbering of the protection zones is according to their damping of theelectromagnetic lightning fields. The undamped environs will be definedas lightning protection zone 0 which will be subdivided into thefollowing:

• lightning protection zone 0A, where direct lightning strikes occur

• lightning protection zone 0B, where direct strikes are prevented by theair-termination system (in accordance with the effectivity of the light-ning protection level).

The definition of lightning protection zones and the determination oftheir boundaries in the case of complex systems usually will be developedstep-by-step, while the lightning protection expert regularly consults themain involved and responsible parties concerning construction andoperation, in order to reach an optimally balanced overall concept byusing all structural (technical and economical) realities.

At this point, it should be emphasized that on defining the protec-tion levels and on determination of the lightning protection zones the


essential basic data for the total costs of the lightning protection systemto be planned and installed are fixed. So it is, for example, quite usual toattribute different protection levels to the individual buildings of anextended industrial plant (as shown in Figure 4.1.3.1.2 a) by means ofa risk analysis.

Depending on the actual requirements, the air terminations, downconductors and earthing systems can be executed as ‘isolated’, ‘partlyisolated’, or ‘building integrated’, as shown in Figure 4.1.3.1.2 b. Figures4.1.3.1.2 c to e show the execution in practice.

Best positioning of the air terminations is made possible by means ofthe rolling sphere method: either in a drawing (Figure 4.1.3.1.2 f a) orusing a scale model (Figure 4.1.3.1.2 f b). Only those parts of the buildingthat are touched by the rolling sphere (Figure 4.1.3.1.2 f c), need airterminations.

In the following planning step, room shielding measures will bespecified.

4.1.3.1.3 Room shielding measures Of special importance for the plan-ning of building and room shields for the lightning protection zones arethe existing metal components of the building (e.g., metal roofs andfacades, steel reinforcements in concrete, expanded metals in walls, metallattices, metal supporting structures, metal piping) forming an effectiveelectromagnetic shield, if there is an intermeshed connection. Already bythis stage of planning it must be specified (and agreed upon by the con-struction companies) that:

• all steel reinforcements in ceilings, walls, and floors must be inter-connected and bonded with the earthing system (at least every 5m)(Figures 4.1.3.1.3 a)

Figure 4.1.3.1.2 a Lightning protection zones (LPZ) with protection levels (PL)


Figure 4.1.3.1.2 b (a) Lightning protection zones in case of an ‘isolated’lightning protection system

Figure 4.1.3.1.2 b (b) Lightning protection zones in case of a ‘partly isolated’lightning protection system

Figure 4.1.3.1.2 b (c) Lightning protection zones in case of a ‘building-integrated’ lightning protection system


Figure 4.1.3.1.2 c Example of an ‘isolated’ lightning protection system

Figure 4.1.3.1.2 d Example of a‘partly isolated’ lightning protectionsystem

Figure 4.1.3.1.2 e Example of a‘building-integrated’ lightning protectionsystem


Figure 4.1.3.1.2 f (a–c) Positioning of an air-termination system by means ofthe rolling sphere method

Figure 4.1.3.1.2 f (a) Planning by drawing

Figure 4.1.3.1.2 f (b) Using a model Figure 4.1.3.1.2 f (c) Surfacesmarked are touched by the rollingsphere


Figure 4.1.3.1.3 a (a)

Figure 4.1.3.1.3 a (b)

Figure 4.1.3.1.3 a (c)


Figure 4.1.3.1.3 a (d)

Figure 4.1.3.1.3 a Effective electromagnetic shielding by: (a, b) Steel mats onthe roof; (c, d) Bonding of reinforcements in floors, walls andceilings; (e, f ) Application of fixed earthing terminals forbridging of expansion joints or bonding of reinforcements ofprefabricated concrete parts

Figure 4.1.3.1.3 a (e) Figure 4.1.3.1.3 a (f)


• metal facades will be turned into shields by connecting them with theearthing system (every 5m or less) (Figure 4.1.3.1.3 a g)

• lost sheet metal forms in floors, ceilings, and walls must be intercon-nected and bonded with the earthing system (at least every 5m)

• steel constructions must be connected to the earthing system

• steel reinforcements of the foundations must be connected to theearthing system (at least every 5m) (Figure 4.1.3.1.3. a h).

4.1.3.1.4 Equipotential bonding networks Provision must be made, evenat the planning phase, that all metal installations entering a lightningprotection zone must be connected. This connection must be either dir-ectly, or over disconnection spark gaps, or over arresters, to the lightningprotection equipotential bonding bar.

Such installations include:

• earth electrodes (telecommunication earth electrodes, earth electrodesin accordance with DIN VDE 0141 (directly or over disconnectionspark gaps), auxiliary earth electrodes, measuring earth electrodes (overdisconnection spark gaps), and earth-contact shielding conductors).

• electric lines (metal sheaths and armour of cables as well as shields oflines, communications cables (telecommunication and data cables),aerial cables, and power cables (under consideration of DIN VDE0100 Parts 410 and 540)).

Figure 4.1.3.1.3 a (g)


• non-electric lines (water pipes, heating pipes, gas pipes, ventilation andair-conditioning ducts, fire extinguishing pipes, and piping of cathodi-cally protected systems or such with stray current protection measures(over disconnection spark gaps)).

Figure 4.1.3.1.3 a (g–h) Bonding of the continuous interconnected metalfaçade with the earthing system; (h) Internal surface earthelectrode realized by floor slab reinforcement, which isbonded by hot-galvanized steel strips (in raster 5 m x 5 m)

Figure 4.1.3.1.3 a (h)

Figure 4.1.3.1.4 a Lightning protection equipotential bonding bar


In the case of extended technical communication systems, the equi-potential bonding bar for the lightning protection must be planned insuch a way (approximately at ground level inside the building) that it cantake over the function of the ‘earth bus’. Then it usually will be laid asan ‘earth ring bus’ inside the building (Figure 4.1.3.1.4 a). It is requiredthat this ring-equipotential bonding bar be connected to have a lowimpedance with the earthing system and the zone screen.

In the case of protection measures using the concept of lightningprotection zones, the planner is free to decide between a mesh-like orstar-type configuration of the equipotential bonding system. Usually amesh-like functional equipotential bonding system (Figure 4.1.3.1.4 b)will be planned. The devices in a protection zone shall be interconnectedby lines (as many as possible and as short as possible), with the metalparts of the protection zone and the protection zone screen. Also herethe planner will employ the already existing metal components of abuilding, such as the reinforcement in the floor, the walls and the ceiling,the metal grates in double bottoms and (non-electric) metal installations,such as ventilation pipes and cable racks. Typically, a meshing of at leastone metre mesh size will be desired. Figure 4.1.3.1.4 c shows the bond-ing of two meshed protection zones, whereby the shields are integratedinto the equipotential bonding system. Figure 4.1.3.1.4 d illustrates thatrather complex zone structures may be planned. Protection zones nestedwithin each other and local protection zones of different equipotentialbonding concepts are interconnected here.

4.1.3.1.5 Equipotential bonding measures for supply lines and electriclines at the boundaries of the lightning protection zones As soon as thelightning protection zones for the system to protect have been deter-mined in agreement with all parties concerned, the interfaces for allmetal supply systems including the electric lines must then be clearlydefined. Wherever a supply system penetrates a zone boundary and,thus, the electromagnetic screen of a zone, this supply system must betreated. For supply systems and lines that do not conduct voltages andcurrents, this is realized by an electrically conductive connection; livelines will be equipped with arresters that discharge the interfering ener-gies in the case of lightning-induced overvoltages from the lines to theearthed zone screen.

Figure 4.1.3.1.5 a, for example, shows the interfaces of supply systemswhich come from lightning protection zone 0A into lightning protectionzone 1 on ground level, and overhead lines coming from lightning protec-tion zone 0A or 0B into lightning protection zone 1. It is the same withall supply systems inside the protected volume: if they lead from onelightning protection zone into another, they must also be treated at theinterfaces.

In the case of a lightning strike, the lightning current will not only be


Figure 4.1.3.1.4 b Meshed functional equipotential bonding system in a lightningprotection zone

Figure 4.1.3.1.4 c Bonding of lightning protection zones with the correspondinglymeshed functional equipotential bonding

Figure 4.1.3.1.4 d Bonding of lightning protection zones with meshed and star-shaped functional equipotential bonding at a complex zonestructure


discharged over the earthing system, but a rather considerable part alsoover the supply systems entering the lightning protection zone 1 fromoutside ground. At their points of entry, these systems are bonded with thescreen of lightning protection zone 1. If the planner does not make anydetailed calculations, it may be assumed, in accordance with DIN VDE0185-103 (VDE 0185 Part 103), that 50% of the whole lightning current(with its parameters in Table 4.1.1 c defined according to the protectionlevel) must be discharged over the outgoing supply systems. It may befurther assumed that the lightning current will be distributed equally to allmetal and also electric line systems (Figure 4.1.3.1.5 b). When a line systemconsists of several component conductors, for example (e.g., outer con-ductor and protective conductor, a power technical line or several cores ofan information technology line) it may be assumed that again the light-ning partial current will be distributed equally to the different conductors/cores of a line system. In the worst case, shields are counted as componentconductors. For a closed outer cable shield and copper braid shield, aconsiderably higher share can flow over the shield than over the innerconductors. Here the current distribution (particularly that depending onthe coupling resistance) must be determined individually.

It is also possible, in a close-up lightning strike as shown in Figure4.1.3.1.5 c, that a considerably higher lightning current can be led to theinterface at lightning protection zone 1 by one single supply systemthan would have been the case, according to the above estimation, for adirect strike. This must also be taken into account when the determin-ations for planning of the equipotential bonding measures are made.

4.1.3.1.6 Cable routing and shielding Two local, spatially separated light-ning protection zones can be turned into one lightning protection zone

Figure 4.1.3.1.5 a Interfaces at lightning protection zone boundaries


by means of a bonding line screen (a metal cable conduit, a shieldedcable route or outer cable shields) (Figure 4.1.3.1.6 a). Easy handlingcalculation principles for the planner are given in the ‘Handbuch fürBlitzschutz und Erdung’ (Handbook for Lightning Protection and Earth-ing). Figures 4.1.3.1.6 b (a and b) show cable ducts, the reinforcement of

Figure 4.1.3.1.5 b Partial lightning current on external supplying systems in caseof a direct strike into the lightning protection system

Figure 4.1.3.1.5 c Partial lightning current on external supplying systems in caseof a close-up strike


Figure 4.1.3.1.6 a Line shield bonded with building-shields

Figure 4.1.3.1.6 b (a) Basic structure

Figure 4.1.3.1.6 b Cable duct with continuously interconnected reinforcement

Figure 4.1.3.1.6 b (b) Practical realization


which is bonded to a screen. The welded duct reinforcement, with a meshsize of typically 15cm and a rod diameter of typically 6mm, which iscontinuously connected in the longitudinal direction by means of clamps,can be connected directly to the building foundation reinforcement.

Within lightning protection zones 1 and higher, electromagnetic-ally shielded cables shall be used for information technology purposes. Atleast both ends of the shields must be bonded. Then, the shields will alsobe effective within the scope of the meshed functional equipotentialbonding as equipotential bonding lines. Alternatives to shielded cablescan be either metal, closed, and continuous cable stages, or metal pipes,or shielded cable conduits.

Figure 4.1.3.1.6 c shows how, by parallel routing of power and infor-mation technology lines, the surface of the induction line loop can bereduced. As an additional measure the lines can be laid in line shields(e.g., conduits). The ends of the conduits must be bonded with the cor-responding terminal. However, it is also possible to turn the enclosure ofthe devices into local lightning protection zones which are either con-nected with unshielded lines, and must then be protected at the zoneinterfaces, or with shielded lines forming a common protection zone forlines and devices.

Sources

HASSE, P., and WIESINGER, J.: ‘Handbuch für Blitzschutz und Erdung’(Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach; fourth edn, 1993)

4.1.3.2 Realization of LEMP protection

This step of the LEMP-protection management process, coming after theLEMP-protection planning, includes the following:

• preparation of survey diagrams and descriptions

• working out of tender specifications

• making of detailed drawings and flow diagrams for the installation.

These works can be carried out by an electrotechnical engineering office.Here, for example, it will be specified how the connection of the incom-ing metal piping to the reinforcement, at the interface of lightningprotection zones 0A and 1, has to be carried out to conduct lightningcurrent and be EMC-compliant. Or, it will be indicated how metal stages,cabinets, enclosures and cable racks are to be included into the meshedfunctional equipotential bonding in rooms containing information tech-nology systems and equipment (Figure 4.1.3.2 a). Cable lists (and types),number of wires, handling of the shield, electrical and mechanical inter-face configurations, operating voltages, transmission frequencies, backupfuses etc., have to be indicated. Also, the test values of the arresters used


for the bonding of lines at the interfaces of the lightning protection zonesmust be stipulated (Table 4.1.3.2 a).

The arresters provided within a scheme using the concept of lightningprotection zones are connected in series in the respective cable run.Therefore, the output levels of the arresters must be stipulated in such away that the coordination with the downstream arrester or device orsystem (characterized by its basic strength) is guaranteed, and that theprospective system short-circuit currents can be controlled.

Figure 4.1.3.1.6 c Measures of shielding and optimal cable routing


Basically, the planner is free to determine how best to use and coordin-ate the arresters and devices or systems, as long as it is guaranteed thatinterference will be reduced to levels below the basic strength of thedevices or systems to protect in the respective lightning protection zones.

4.1.3.3 Installation and supervision of LEMP protection

Essentials of this step of LEMP-protection management are:

• quality assurance at the installation

• documentation

• revision of detailed drawings.

Figure 4.1.3.2 a Meshed functional equipotential bonding at a cabinet entry

Table 4.1.3.2 a Typical test values of arresters installed at the line interfaces oflightning protection zones


It is here that system builders, lightning protection experts, engineeringofficers, and the supervising authority cooperate or liaise.

If, for example, structural steel mats are bonded by means of hot-galvanized steel strips, steel wires and clamps (Figure 4.1.3.3 a), control iseasily possible by inspection and photodocumentation.

In the case of lightning current arresters for power technical systems(installed at the interface of lightning protection zone 0A and 1, Figure4.1.3.3 b), care must be taken to carry out professional installation (e.g.,for expulsion arresters a sufficient separation must be maintained betweenneighbouring live bare parts). In the case of lightning current arrestersfor information technology lines, special attention must be paid to theseparate installation of the lines coming from lightning protection zone0A and those leading into lightning protection zone 1 (Figure 4.1.3.3 c).

In larger systems it is useful to install protection cabinets (Figure4.1.3.3 d) as a central interface between two lightning protection zones.

4.1.3.4 Acceptance inspection of the LEMP protection

An independent lightning protection expert or a supervising authoritywill carry out the control and documentation of the system state at theacceptance inspection stage of the LEMP protection.

Figure 4.1.3.3 a Floorreinforcement with support-reinforcement bonded bywires/strips and clamps

Figure 4.1.3.3 b Lightning current arrestersfor the power technical line at the transitionfrom lightning protection zone OA into lightningprotection zone 1


4.1.3.5 Periodic inspection

To safeguard the reliability performance of the protection system it isnecessary that lightning protection experts or supervising authoritiesmake periodic inspections. The standard draft DIN VDE 0185 Part 110:1997-01 ‘Blitzschutzsystem. Leitfaden zur Prüfung von Blitzschutzsys-temen’ (‘Lightning protection system. Guide for testing lightning protec-tion systems’) describes the kind of tests, test turns, test measures andthe documentation involved.

Sources

DIN V VDE V 0185-110 (VDE V 0185 Teil 110):1997-01: ‘Blitzschutzsysteme.Leitfaden zur Prüfung von Blitzschutzsystemen’ (VDE Verlag, GmbH, Berlin/Offenbach, Jan. 1992)

4.1.3.6 Costs

The requirement that information technology electronic systems mustnot be damaged by electromagnetic interference due to direct or close-uplightning strikes has led to a new quality and dimension of lightning

Figure 4.1.3.3 c Lightningcurrent arresters for theinformation technology line(lightning protection zoneOA → lightning protectionzone 1)

Figure 4.1.3.3 d Protective cabinet withconnected cable shields and arresters


protection engineering. The correspondingly developed concept,embodied in DIN VDE 0185-103 (VDE 0185 Part 103), lightning protec-tion zones (Figure 4.1.3.6 a) has turned out to be a very efficient man-agement method in complex and manifold problems; it has also beenproven as a universal organizing principle: for example, computingcentres, administration buildings, control and instrumentation technicalsystems, power plants including solar and wind power plants, telephonecentral offices, radar systems and main transmitters.

Also the costs of EMC-compliant lightning protection can be calcu-lated from the many existing projects. In the case of newly-built large-scale projects, about 0.5% max. to 1% of the gross building cost must beallocated to achieve an effectiveness of protection of about 99%. In sub-sequent installation and retrofitting, the costs will increase by a factor of10 and the effectiveness of protection reduces to 95–90%.

Sources

HASSE, P., and WIESINGER, J.: ‘Requirements and tests for EMC-orientedlightning protection zones’, etz, DEHN publication, reprint from 1990, No. 21,pp. 1108–1115HASSE, P., and WIESINGER, J.: ‘Handbuch für Blitzschutz und Erdung’(Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach; 4. Auflage, 1993)HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept’ (PflaumVerlag, München; VDE Verlag, Berlin/Offenbach, 1994)HASSE, P., WIESINGER, J., ZAHLMANN, P., and ZISCHANK, W.: ‘A future-

Figure 4.1.3.6 a Concept of lightning protection zones


oriented principle for the coodination of arresters in low-voltage systems’,DEHN publication, reprint from etz, 1995, No. 1, pp. 20–23HASSE, P.: ‘Blitzschutz-Management – Planung und Organisation. 1st VDE/ABB-Blitzschutztagung “Blitzschutz für Gebäude und Elektrische Anlagen” ’(29 Feb.–1 March 1996, Kassel)WETTINGFELD, J.: ‘Was ist neu in ENV 61024-1/01.95 (DIN VDE 0185 Teil100)? 1st VDE/ABB-Blitzschutztagung “Blitzschutz für Gebäude und Elek-trische Anlagen” ’, (29 Feb.–3 March 1996, Kassel)STEINBIGLER, H.: ‘Verfahren und Komponenten des Gebäudeblitzschut-zes. 1st VDE/ABB-Blitzschutztagung “Blitzschutz für Gebäude und Elek-trische Anlagen” ’ (29 Feb.–1 March 1996, Kassel)WIESINGER, J.: ‘Was ist neu in IEC 1312-1/02.95 (DIN VDE 0185 Teil 103)?1st VDE/ABB-Blitzschutztagung “Blitzschutz für Gebäude und ElektrischeAnlagen” ’ (29 Feb.–1 March 1996, Kassel)KERN A.: ‘Blitz-Schutzzonen mit Schirmungen und Schnittstellen. 1st VDE/ABB-Blitzschutztagung “Blitzschutz für Gebäude und Elektrische Anlagen” ’(29 Feb.–1 March 1996, Kassel)PUSCH, H., and RAAB, V.: Gebäudeblitzschutz – Neue Europanorm. TAB,1996, 12, pp. 69–73HASSE, P.: ‘Blitzschutz für Gebäude und Elektrische Anlagen – 1’, VDE/ABB-Blitzschutztagung, 1996, 11, pp. 960–964; 1996, 12, pp. 1107–1112MÜLLER, K.-P.: ‘Neue Blitzschutznormung’, Elektropraktiker, 1996, 6DIN VDE 0185: ‘Blitzschutzanlage – Teil 1: Allgemeines für das Errichten –Teil 2: Errichten besonderer Anlagen’ (VDE Verlag, GmbH, Berlin/Offenbach, Nov. 1982)IEC 61024-1: ‘Protection of structures against lightning. Part 1: Generalprinciples’. International Electrotechnical Commission, Genève, March 1990IEC 61312-1: ‘Protection against lightning electromagnetic impulse. Part 1:General principles’. Central de la Commission Electrotechnique Internation-ale, Genève, Feb. 1995IEC 61662: ‘Assessment of the risk of damage due to lightning’. BureauCentral de la Commission Electrotechnique Internationale, Genève, April1995DIN V ENV 61024-1(VDE V 0185 Teil 100): 1996-08: ‘Blitzschutz baulicherAnlagen. Teil 1: Allgemeine Grundsätze (IEC 61024-1: 1990, modifiziert)’(VDE Verlag GmbH, Berlin/Offenbach, Aug. 1996)DIN VDE 0185-103 (VDE 0185 Teil 103): 1997–09: ‘Schutz gegen elektro-magnetischen Blitzimpuls (LEMP). Teil 1: Allgemeine Grundsätze. Identischmit IEC 81(Sec)44’ (VDE Verlag, GmbH, Berlin/Offenbach, Sept. 1997)

4.2 Surge protection for electrical systems of buildings, IEC60364, DIN VDE 0100

A detailed treatment of the surge protection of buildings is given inIEC/TC 64. Corresponding international standards in IEC 60364 areprovided in chapter 44 of the publication. Part 440 is the relevant chapterin the national standard series DIN VDE 0100.


Chapter 44 of the above document is divided as follows:

Chapter 44 Protection in case of surgesSection 441 GeneralSection 442 Protection of low-voltage systems in case of earth

faults in systems with higher voltageSection 443 Protection against surges due to atmospheric influencesSection 444 Protection against electromagnetic interference in

systems of buildings.

Also relevant from IEC 60364 (chapter 53) is the following section:

Section 534 Selection and installation of surge protection facilities.

4.2.1 IEC 60364-4-443/DIN VDE 0100 Part 443

The current document IEC 60364-4-443: 1995-04 ‘Publication 364: Elec-trical installations of buildings; Part 4: Protection for safety; Chapter 44:Protection against overvoltage; Section 443: Protection against overvolt-ages of atmospheric origin’/ DIN VDE 0100 Teil 443 ‘Errichten vonStarkstromanlagen mit Nennspannungen bis 1000V SchutzmassnahmenSchutz gegen Überspannung infolge atmosphärischer Einflüsse’ containsthe following statement:

“These standard requirements are provided for describing measureswhich limit transient overvoltages, in order to reduce the risk of faults inthe system and the connected equipment, to an acceptable dimension.This procedure is in agreement with the principles of the insulationcoordination in the Publication IEC 664 ‘Insulation coordination in low-voltage systems and equipment’.

“Overvoltage categories are intended for distinguishing differentdegrees of availability of the equipment. Availability of equipment isdifferentiated according to the demands concerning continuity of oper-ation and acceptable risk of faults, damage and failures. In connectionwith the preferred surge resistance level of the equipment, they allow asuitable insulation coordination of the whole system to be achieved,which reduces the risk of faults/failures to an acceptable level/limit andare a basis for a surge protection (regulation).

“A higher reference number of the overvoltage category indicates ahigher specific surge resistance of the equipment, and means at the sametime a wider choice of surge regulation/protection methods.”

In the above standard, environmental conditions AQ 1 to AQ 3 aredefined upon which the application of surge arresters depends. Classifi-cations with regard to the effect of lightning are:

• AQ 3: direct effect of lightning (cross reference to IEC 61024-1)

• AQ 2: indirect effect of lightning, danger from the supply system

• AQ 1: negligible effect of lightning.


Sources

IEC 60364-4-443: ‘Electrical installation of buildings – Part 4: Protection forsafety (chapter 44): Protection against overvoltages (Section 443): Protec-tion against overvoltages of atmospheric origin or due to switching’. BureauCentral de la Commission Electrotechnique Internationale, Genève, April1987E DIN VDE 0100 Teil 443: 1987-04: ‘Errichten von Starkstromanlagen mitNennspannungen bis 1000 V. Schutzmassnahmen; Schutz gegen Über-spannungen infolge atmosphärischer Einflüsse. (Identisch mit IEC64(CO)168’ (VDE Verlag, GmbH, Berlin/Offenbach, April 1987)

4.2.2 IEC 60664-1/DIN VDE 0110 Part 1

IEC 60664-1 ‘Insulation coordination for equipment within low-voltagesystems. Part 1: Principles, requirements and tests’ became valid in 1992.In Germany DIN VDE 0110-1 (VDE 0110 Part 1) is valid: 1997-04‘Isolationskoordination für elektrische Betriebsmittel in Niederspan-nungsanlagen. Teil 1: Grundsätze, Anforderungen und Prüfungen (IEC60664-1: 1992, modified).’ In this standard the insulation coordinationfor equipment in low-voltage systems is specified. It is valid for equip-ment having a rated alternating voltage up to 1000V, with nominalfrequencies up to 30kHz, or a rated direct voltage up to 1500V.

Therein are defined the following:

(a) Insulation coordination: Reciprocal classification of the insulationcharacteristics of electrical equipment, under consideration of theexpected microenvironmental conditions and other importantstresses.

(b) Surge withstand voltage: Maximum value of the surge voltage ofconventional shape and polarity which does not lead to puncture orsparkover of the insulation under specified conditions.

(c) Rated surge voltage: Value of a surge withstand voltage, indicated bythe producer for an equipment or a part of it, indicating the specifiedwithstand capability of the respective insulation with regard toperiodic peak voltages.

(d) Overvoltage category: A numerical value that specifies a surge with-stand voltage. Note: Overvoltage categories termed I, II, III, and IVare used.

(e) State of limited overvoltage: State within an electric system where theexpected transient overvoltages remain limited to a specified height.

In this standard the principles of the ‘insulation coordination’ arespecified as follows: Insulation coordination comprises the selection ofthe electrical insulation characteristics of a piece of equipment, regard-ing its application and its surroundings. Insulation coordination can only


be achieved if the rating of the equipment is based on the stress to whichit will be exposed during its probable lifetime.

With respect to ‘transient overvoltages’ it points out that insulationcoordination regarding transient overvoltages is based on a state oflimited overvoltages. There are two kinds of limitation:

• In-system limitation. The state within an electrical system where,due to the characteristics of the system, it can be assumed thatthe expected transient overvoltages remain limited to a specifiedheight.

• Protective limitation. The state within an electrical system where, dueto the use of special overvoltage limiting means, it can be assumedthat the expected transient overvoltages will be limited to a specifiedheight.

Note 1: Overvoltages in large and complex systems, such as low-voltagesystems that are exposed to multiple and changing influences, can only bejudged on a statistical basis. This applies especially for overvoltages ofatmospheric origin, as well as if the limitation is achieved due to anin-system limitation, or to a protective limitation.Note 2: An examination concerning the probability as to whether anin-system limitation exists or whether a protective limitation will benecessary, is recommended. This examination requires knowledge ofthe electrical system data, of the keraunic level, the height of thetransient overvoltage etc. (This examination procedure is applied inIEC 60364-4-443 for power systems in buildings which are connected tolow-voltage systems.)Note 3: The special overvoltage limiting means may contain com-ponents for storage or discharging of energy and are able to safelydischarge the energy of the overvoltages expected at the place ofinstallation.

To apply the principle of insulation coordination, two different kindsof transient overvoltages must be considered:

• Transient overvoltages originating from the system to which theequipment is bonded by its terminals.

• Transient overvoltages originating from the equipment.

This basic safety standard explains to ‘technical committees’ (i.e., thosewho are responsible for the standardization of different equipment) howthe insulation coordination can be achieved. For the purpose of sizingequipment in accordance with the insulation coordination, such tech-nical committees must specify an overvoltage category according to theprobable use of the equipment, under consideration of the systemparameters for the connection of which it is provided.

The overvoltage categories are a means of maintaining the operation of


devices in accordance with the necessary requirements, and differentiat-ing between the degrees of availability with regard to a possible risk offailure. In connection with special values of the ‘surge withstand voltage’for devices, the categories enable a suitable insulation coordination in thewhole installation; they are the basis for the limitation of overvoltages sothat the risk of failure can be reduced to an acceptable value. A highernumerical value of the overvoltage category indicates a higher ‘surgewithstand capability’ of the device and offers a wider choice of methodsof surge limitation.

The principle of the overvoltage categories is applied for equipmentthat is directly supplied by the low voltage system. Application of over-voltage categories is based on the surge protection requirements con-tained in IEC 60364-4-443. (Note: Atmospheric overvoltages mostly arenot weakened in the course of the installation.) Examinations haveshown that a probability oriented concept is suitable as described in thefollowing:

Determination of an overvoltage category for directly supplied systemequipment must be realized on the basis of the following generaldescription:

• Overvoltage category I equipment is intended for connection to thefixed electrical installation of a building. Outside the device measureshave been taken, either in the fixed installation or between the fixedinstallation and the device, in order to reduce the transient overvolt-ages to the respective value.

• Overvoltage category II equipment is intended for connection tothe fixed installation of a building. (E.g., devices include householdappliances, portable tools and items of similar loading.)

• Overvoltage category III equipment is part of the fixed installation,and other devices, where a higher degree of availability is expected.(E.g., devices include distribution boards, circuit-breakers, distribu-tions (IEV 826-06-01, including cables, bus bars, distribution cabinets,switches, socket outlets) in the fixed installation and devices for indus-trial use, as well as other devices, such as stationary motors withpermanent connection to the fixed installation.)

• Overvoltage category IV equipment is intended for use at or nearthe feed into the electrical installation of buildings, and that fromthe main distribution into the direction of the system. (E.g., devicesinclude electricity meters, overcurrent circuit-breakers and ripple-control units.)

The rated surge voltage of the equipment is given in Table 4.2.2 aaccording to the determined overvoltage category and the rated voltageof the equipment. (Note that equipment with a special rated surge volt-age, having more than one rated voltage, may be suitable for differentovervoltage categories.)


For equipment that can generate overvoltages at the terminals of theequipment (e.g., switchgear) the rated surge voltage means that theequipment must not generate overvoltages exceeding this value; that is, ifit is operated in accordance with the respective standard and the instruc-tions of the producer. (Note that there is always a residual risk thatovervoltages may be generated that exceed the value of the rated surgevoltage, depending on the conditions of the circuit.)

Equipment operating under the conditions of a higher overvoltagecategory is allowed provided that a suitable surge limitation is enforced.Suitable surge damping can be attained by using:

• a surge protective installation

• a transformer with separated windings

• a distribution system with a multitude of branches (which are able todischarge the energy of surges)

• a capacitance which is able to charge up to the energy of surges

• a resistance or similar damping elements which are able to dischargethe energy of surges.

It should be taken into account that every surge protective installationwithin the system or the equipment might have to discharge more energythan a surge protective installation at the connection point of the system,if the latter has a higher operating voltage.

Table 4.2.2 a Rated impulse voltage for equipment (energized directly from thelow-voltage mains)


4.2.3 IEC 60364-5-534 / DIN VDE 0100 Part 534

During the preparation of this book (starting in January 1997) bothstandard drafts:

• E DIN IEC 64/867/CDV (VDE 0100 Part 534):1996-10 ‘Electricalinstallations of buildings – Selection and Erection of electrical equip-ment – Switchgear and controlgear – Devices for protection againstovervoltages (IEC 64/867/CDV: 1996)’

• E DIN VDE 0100-534/A1 (VDE 0100 Part 534/A 1):1996-10 ‘Elec-trical installations of buildings – Selection and Erection of electricalequipment – Switchgear and controlgear – Devices for protectionagainst overvoltages – Amendment A1 (proposal for a Europeanstandard)’

were available. The aforementioned IEC standard draft has now beenrefused by the German DKE subcommittee UK 221.3 ‘ProtectionMeasures’ on the grounds that its aim no longer meets the currenttechnical state and is, therefore, of no assistance in the erection ofsurge-protective installations.

The main reason for this refusal is the fact that the surge protectionmust not only consider switching operations and remote lightning strikes(IEC 61024/61312-1), but also it must consider close-up or direct light-ning interference (IEC 61024/61312-1). Thus, it is necessary to cater forin a single standard not only the selection and installation of arresters forlightning protection, but also surge protection.

Today, the accepted state of engineering is such that a complexlightning/surge protection system requires more than one type of arrester.

Taking this requirement into account, three arrester types (classes I, IIand III) with different protection capacities are standardized in the rele-vant product standard DIN IEC SC 37A/44/CDV (VDE 0675 Part 6A1).A multistage protective concept, realized by means of these differenttypes of arresters, includes not only surge protection but also protectionagainst direct lightning strikes.

A second standard draft, prepared by the German UK 221.3, isproposed for the development of the above-mentioned IEC paper. Thesuggested main section 534 of ‘Einrichtungen zum Schutz beiÜberspannungen’ treats, on the one hand, the selection and the installa-tion of protective equipment for the surge protection due to indirectatmospheric discharges and switching operations according to IEC60364-4-443 (according to DIN VDE 0100-443 (VDE 0100 Part 443) )and, on the other hand, the selection and the installation of protectiveequipment due to lightning currents and surges in connection with directlightning strikes and lightning strikes in the vicinity of buildings accord-ing to IEC 61024-1 and IEC 61312-1.

Thus, the regulations for the selection and the installation of the


protective equipment and their compatibility with the protective meas-ures against electric shock applied in the system are presented in oneprinciple section of the erection standard for low voltage systems. Thesestandard drafts, however, are not under discussion and so they will not beconsidered further. Nevertheless, the description of the different applica-tion possibilities of arresters in the power technical system (given inchapter 5.8.1.6.2) refers to this German draft.

Sources

HASSE, P., and WIESINGER, J.: ‘Handbuch für Blitzschutz und Erdung’(Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach; Fourth edn, 1993)E DIN IEC 64(Sec)675 ( VDE 0100 Teil 443/A3): ‘Errichten von Starkstroman-lagen mit Nennspannungen bis 1000V – Schutzmassnahmen. Schutz beiÜberspannungen infolge atmosphärischer Einflüsse und von Schaltvorgän-gen’, Oct. 1993IEC 60364-4-443: ‘Electrical installation of buildings – Part 4: Protection forsafety (chapter 44): Protection against overvoltages (Section 443): Protec-tion against overvoltages of atmospheric origin or due to switching’, April1995E DIN IEC 64/867/CDV (VDE 0100 Teil 534): ‘Elektrische Anlagen vonGebäuden – Auswahl und Errichtung elektrischer Betriebsmittel – Schalt-geräte und Steuergeräte – Überspannungs-Schutzeinrichtungen. (VDEVerlag, GmbH, Berlin/Offenbach, Oct 1996E DIN VDE 0100-534/A1 (VDE 0100 Teil 534/A 1): Elektrische Anlagen vonGebäuden – Auswahl und Errichtung von Betriebsmitteln – Schaltgeräte undSteuergeräte – Überspannungs-Schutzeinrichtungen – Änderung A1 (Vor-schlag für eine Europäische Norm). (VDE Verlag, GmbH, Berlin/Offenbach,Oct. 1996)DIN VDE 0110-1 (VDE 0110 Teil 1): Isolationskoordination für elektrischeBetriebsmittel in Niederspannungsanlagen. Teil 1: Grundsätze, Anforderun-gen und Prüfungen (IEC 664–1: 1992, modifiziert) (VDE Verlag, GmbH,Berlin/Offenbach, April 1997)

4.3 Surge protection for telecommunications systems, DIN VDE0800, DIN VDE 0845

DIN VDE 0800 Part 1: 1989-05 ‘Fernmeldetechnik – AllgemeineBegriffe, Anforderungen und Prüfungen für die Sicherheit der Anlagenund Geräte’ (‘Telecommunications – General concepts, requirementsand tests for the safety of facilities and apparatus’). The scope of appli-cation of this VDE regulation refers to the safety of the facilities andapparatus of telecommunication engineering (in the following: telecom-munication systems and telecommunication devices) with regard to theprevention from danger to life or health (of people and animals) and


things. This standard is also applicable for the safety of information ordata processing systems for which no other standards are valid.

DIN VDE 0800 Part 2: 1985-07 ‘Erdung und Potentialausgleich in derFernmeldetechnik’. (‘Telecommunications; earthing and equipotentialbonding’.) The following is quoted regarding the treatment of ‘lineshields’ (i.e., a shield out of conductive material which accompanies thelines in a certain geometric form) and the integration of steel construc-tions or reinforcements:

• In the version as an electromagnetic screen (according to DIN IEC60050 Part 151: 1983-12, section 151-01-16) the line shield can con-tribute to equipotential bonding, as both of its ends are connected to areference potential.

Integration of steel constructions and reinforcements into the earth-ing system. If there are particularly high demands on the earthingsystem of a building regarding the function, in order to avoid poten-tial differences between different points of the building and therebycause equalizing currents, measures should be taken to include thesteel construction and the reinforcement into the earthing system.For this purpose the reinforcement shall be connected with the earthbus bar, if the components of the reinforcement are continuouslyconnected.

• Equalizing currents in the reinforcement, in parallel with equipotentialbonding conductors between points of different potential, can lead tointerference in the telecommunication system if, because of excessiveimpedance, an inadmissible coupling with telecommunication circuitsoccurs, or contact resistances are submitted to fluctuations. Thecontinuous connection of the reinforcement, for example, can berealized by welding or careful lashing. If, owing to the statics, weldingis not possible, additional steel structures should be put in place, whichmust be welded to each other and lashed to the reinforcement. Thecontinuous connection of the building reinforcement is (even in thecase of buildings made out of prefabricated parts) only possibleduring the erection of the building. Equipotential bonding by steelconstructions and reinforcement must therefore already be takeninto consideration at the planning stage of the foundations and thebuilding construction.

DIN VDE 0845 Part 1: 1987-10 ‘Schutz von Fernmeldeanlagen gegenBlitzeinwirkungen, statische Aufladungen und Überspannungen ausStarkstromanlagen – Massnahmen gegen Überspannungen’.

The scope of application is quoted as follows:

• This standard is valid for measures against dangerous or interferingsurges in telecommunication systems. These surges are caused by elec-tromagnetic interference or by lightning effects or static charges.


Thereby also the devices and transmission lines belonging to the tele-communication system are taken into consideration.

For external lightning protection (the interception and down-conduction of lightning currents) DIN VDE 0185 Part 1 is applicable,and for aerial systems DIN VDE 0855 Parts 1 and 2.

Sources

HASSE, P., and WIESINGER, J.: ‘Handbuch für Blitzschutz und Erdung’(Pflaum Verlag, München; VDE Verlag, Berlin/Offenbach; Fourth edn, 1993)DIN VDE 0800 Teil 1: ‘Fernmeldetechnik. Allgemeine Begriffe, Anforderun-gen und Prüfungen für die Sicherheit der Anlagen und Geräte’ (VDE Verlag,GmbH, Berlin/Offenbach, May 1989)DIN VDE 0800 Teil 2: ‘Fernmeldetechnik. Erdung und Potentialausgleich’(VDE Verlag, GmbH, Berlin/Offenbach, July 1985)DIN VDE 0845 Teil 1: ‘Schutz von Fernmeldeanlagen gegen Blitzeinwirkun-gen, statische Aufladungen und Überspannungen aus Starkstromanlagen.Massnahmen gegen Überspannungen’ (VDE Verlag, GmbH, Berlin/Offenbach, Oct. 1987)

4.4 Electromagnetic compatibility including protection againstelectromagnetic impulses and lightning, VG 95 372

The standard VG 95 372: 1996–03 gives a survey of the VG standards forelectromagnetic compatibility (EMC) including protection against elec-tromagnetic impulses (EMP) and lightning. A tabulated list for EMC isgiven in Figure 4.4 a.

Source

VG 95 372: ‘Elektromagnetische Verträglichkeit (EMV) einschliesslich Schutzgegen den Elektromagnetischen Impuls (EMP) und Blitz – Übersicht’. (BeuthVerlag, GmbH, Berlin, March 1996)

4.5 Standards for components and protective devices

International (IEC) as well as regional (Cenelec) standardizing workon components for lightning protection systems and surge protectivedevices has now progressed. National (DIN VDE) standards and draftswith testing authorization are also available. These standards shall beconsidered in the following only as far as it is necessary for the under-standing of the mode of function and the possibilities of using thesecomponents and protective gear.


4.5.1 Connection components, E DIN EN 50164-1 (VDE 0185 Part 201)

For lightning protection components (terminals, connectors) the stand-ard draft E DIN EN 50164-1 (VDE 0185 Part 201) ‘Lightning protectioncomponents. Part 1: Requirements for connection components’ has beenavailable since May 1997. This specifies the requirements and tests forlightning current conductive connection components. This standard willeventually replace the national DIN-regulation DIN 48 810/8.86.

The standard draft E DIN EN 50164-1 is currently under revision bythe European Standardizing Committee (Cenelec). In addition toconditioning/ageing considerations (simulation of corrosion stress aris-ing in practice) the standard also includes a test by lightning currents(10/350 μs), which is as follows:

Corresponding to their classification indicated by the producer, theconnection components are classified as H and L and tested accordingly:

H (high loading) test current 100kA (10/350 μs)L (normal loading) test current 50kA (10/350 μs)

Criteria for the passing of the lightning current tests are, for example, asufficiently low contact resistance, no perceptible damage, deformationor loose parts as well as requirements for the release torque of the screwedconnection parts.

4.5.2 Arresters for lightning currents and surges

A difference is made between lightning current arresters (tested bysurge currents of wave shape 10/350 μs) and surge arresters (tested by surgecurrents of wave shape 8/20μs).

4.5.2.1 Arresters for power engineering, IEC 61643-1/E DINVDE 0675 Part 6

The German standard draft E DIN VDE 0675 Part 6 ‘Surge arresters foruse in AC supply systems with nominal voltages ranging from 100 V to1000V’ has been available since 1989.

In March 1996 E DIN VDE 0675-6 A1 (VDE 0675 Part 6/A1)‘Amendment A1 to the draft DIN VDE 0675-6 (VDE 0675 Part 6)’ withtesting authorization was published and in October 1996 E DIN VDE0675-6/A2 (VDE 0675 Part 6/A2) ‘Amendment A2 to the draft DINVDE 0675-6 (VDE 0675 Part 6)’. Also in October 1996 DIN IEC 37A/44/CDV (VDE 0675 Part 601) ‘Surge protective devices for low-voltagedistribution systems. Part 1: Performance requirements and testingmethods (IEC 37A/44/CDV: 1996)’ was introduced. This later IEC stand-ard was valid in February 1998 as IEC 61643-1 ‘Surge protective devicesconnected to low-voltage distribution systems, Part 1: Performance


requirements and testing methods’. The activities of the IEC SC 37Acommittee which is competent for the international standardization ofarresters are shown in Figure 4.5.2.1 a.

The yellow printed E DIN VDE 0675 Part 6/A1 is based on the draftDIN VDE 0675 Part 6/1989-11. The categories and classifications of thearrester types have been mostly retained. These arresters are subdividedinto four requirement classes:


• Class A. Arresters which are installed in low voltage overhead linesand at places where they cannot be touched. Testing is made withsurge currents of wave shape 8/20μs (Figure 4.5.2.1 b).

• Class B. Arresters installed for the purpose of lightning protectionequipotential bonding and controlling direct lightning strikes. Thesearresters are tested by a simulated lightning test current Iimp of waveshape 10/350μs (Figure 4.5.2.1 b).

• Class C. Arresters installed for the purpose of surge protection in thefixed installation, for example, in the distribution area. These arrestersare tested by the nominal discharge surge current isn of wave shape8/20 μs (Figure 4.5.2.1 b).

• Class D. Arresters installed for the purpose of surge protection in thefixed or mobile installation, especially in the socket outlet area orbefore terminals. For testing this arrester group, a hybrid generator

Figure 4.4 a Survey of the VG-standards for EMC including protection againstEMP and lightning


(with an apparent interior resistance 2 Ω) generating an open-circuitsurge voltage 1.2/50 μs and a short-circuit surge current 8/20 μs is used.The open-circuit voltage Uoc of the hybrid generator, used for testing,is indicated as a parameter for these arresters.

The tests/amendments in Part A1 concern above all the electricalrequirements and test procedures, which will be briefly explained in thefollowing as far as it is relevant for the user:

Figure 4.5.2.1 a Standardization in IEC SC 37A ‘Low-voltage surge protectivedevices’

Figure 4.5.2.1 b Comparison of test currents for surge protective devices (SPDs)


(a) Lightning test current (Iimp) for class B arrestersThe lightning test current Iimp (10/350 μs) replaces the former lightningtest current of wave shape 8/80 μs (Figure 4.5.2.1 b).

Iimp is determined by the following parameters: peak value (Ipeak),charge (Q), specific energy (W/R), and wave shape (10/350 μs).

For the wave shape the value 10 indicates a front rise time of10μs and 350 μs the time to the half-value in a wave tail of 350μs ofthe lightning wave. The lightning test current Iimp of the wave shape10/350μs conforms most closely with the first surge current ofnatural lightning discharges and is used worldwide for lightningsimulation.

(b) Determination of the measured limiting voltage: Protection level Up

The testing procedure to determine the measured limiting voltageis subdivided according to the type and class of the arrester. Themeasured limiting voltage is the highest value from differentlycarried out tests. The protection level, which has been determinedwith reference to the insulation coordination, must not be exceededby the measured limiting voltage.

(c) Conditioning and operating duty test, discharge capacityHere the performance of the arresters regarding their dischargeand follow-current quenching capacity is tested (see Figure 4.5.2.1c). Now that the interior structure of the arrester is known, asource of voltage corresponding to its follow current is chosen(Table 4.5.2.1 a) and conditioned in accordance with its require-ment class:

A, B and C ⇒ 15 surge currents 8/20μs with isn

D ⇒ 15 combined surges 1.2/50μs /8/20μs with Uoc/2Ω

On testing the operating duty, the arrester will be submitted to fivesurge currents, according to its class, in steps up to the maximumvalue, whereby its thermal stability will be controlled:

• A, C surge currents up to Imax (maximum discharge surge cur-rent 8/20μs)

• B surge currents up to Iimp (lightning test current 10/350 μs)

• D combined surge up to Uoc/2Ω

(d) Disconnecting device for arresters and thermal stability of arrestersOn testing the disconnecting device and the thermal stability ofarresters, a difference is generated, whether a spark gap coveredarrester or an arrester based on a varistor is concerned. The differ-ence is generated to obtain a practice-like simulation of possiblecauses of fault:

• Arresters based on varistors. It is assumed that, over the courseof years, the leakage current will increase due to repeated surge


current loadings. This leads to a heating or increased powerloss in the arrester. This ‘thermal drift’ is simulated in the dis-connection test. The disconnecting device must separate thearrester from the system before the enclosure becomes too hotwhich might present a fire hazard.

• Arresters with spark gaps or spark gaps in series. Here the assumedfault is that there are too frequent and too high discharge currentsor too many follow-current quenching processes.The electrodesof the integrated spark gaps are welding and a short circuit isgenerated. On testing, this fault will be simulated by short-circuiting spark gaps with a copper conductor. The maximum

Figure 4.5.2.1 c Flow diagram ‘operating duty test’


backup fuse certified by the producer must disconnect the arresterfrom the system before there is noticeable damage at the arresteror fire hazard due to the arrester.

Sources

IEC 61643-1: ‘Surge protective devices connected to low-voltage powerdistribution systems, Part 1: Performance requirements and testingmethods’. Bureau Central de la Commission Electrotechnique Internation-ale, Genève, Feb. 1998

4.5.2.1.1 Important data for arrester selection

• Rated voltage Uc. The value Uc indicates the maximum operating volt-age the arrester is rated for and at which the certified performance dataare met.

• Protection level Up. This parameter characterizes the ability of anarrester to limit interference to a non-dangerous voltage value Up. Therequired protection level of the arrester depends on the place of instal-lation (overvoltage category) and/or on the electric strength of thedevice to be protected.

Table 4.5.2.1 a Power frequency source of voltage for arrester conditioning:uc: continuous operating voltage of an arrester/rated voltage;IF: follow-current of the arrester; Ip uninfluenced short-circuitcurrent


• Discharge capability. This parameter is of decisive importance if thearrester must be selected according to the arising hazards (direct light-ning strike, remote strike, induced surges).

This value characterizes the real performance of the arrester and indi-cates the lightning test currents/surge currents/combined surges that cansafely be discharged without disturbing its function considerably. Thisindication is also reflected in the arrester classification:

Lightning test currents, Iimp ⇒ Class BSurge currents, isn or Imax ⇒ Class A, CCombined surge, Uoc ⇒ Class D

• Breaking capacity/follow-current quenching capability IF. This item isimportant for spark-gap based arresters. It indicates the limit at whichthe system follow-current will be quenched automatically by thearrester.

• Disconnecting device/back-up fuse. These data are always of import-ance. This is particularly so if the arrester is overloaded or wronglyconceived, or aged due to a large number of discharges. Arrestersdesigned according to E DIN VDE 0675-6/A1 are proving able to turninto a safe fault state in the case of an overload/defect on testing of thedisconnecting device and thermal stability.

4.5.2.1.2 Coordination of the arresters according to requirements andlocations. Figure 4.5.2.1.2 a and Table 4.5.2.1.2 a show the coordinationof the arresters:

Figure 4.5.2.1.2 a Application possibilities of arresters in the IEC-overvoltagecategories


• Class B arresters (lightning current arresters). The location of thelightning current arresters is the area of the house supply where highlightning partial currents may arise.

• Class C arresters. The typical location of these surge arresters is in thesubdistribution. This is where the residual voltages of the lightningcurrent arresters and surge currents (8/20μs) in the kA range must besafely controlled.

• Class D arresters. These arresters are located either between the dis-tributor and the terminal or at socket outlets.

With regard to the requirement for class D, rather than proceeding froman impressed surge current, the concern is for the voltage liable to causedanger Uoc; this will be limited to a low value. Typical values of danger-ous voltages (arising at the terminal inputs, socket outlets) are in therange 2.5–4kV.

4.5.2.1.3 N–PE arrester E DIN VDE 0675 Part 6/A2. In E DIN VDE0675-6/A2 (VDE 0675 Part 6/A2): 1996–10 ‘Surge arresters. Part 6:Application in AC supply systems with nominal voltages ranging from100 to 1000V. Amendment A2 for the draft DIN VDE 0675-6 (VDE0675 Part 6)’ N–PE arresters are standardized. These will be installedbetween the neutral conductor (N) and the protective conductor (PE).

What is the task of such N–PE arresters? For reasons of personalprotection, class B and C arresters are usually installed (in energy flowdirection) before a fault current circuit-breaker (also see chapter5.8.6.1.2). To safeguard the disconnection of a faulty arrester by theback-up fuse in the TT-system, a ‘3 + 1-circuit’ is used. The three outer

Table 4.5.2.1.2 a Selection help and assignment of arresters


conductors L1, L2 and L3 are connected to arresters and then with theneutral conductor N. Between the neutral conductor N and the pro-tective conductor PE, the N–PE arrester is installed. In the case of adefective (short-circuited) arrester (at the outer conductor), a short-circuit current is generated between the concerned outer conductor Land the neutral conductor N which can be disconnected by the backupsystem fuse in the time provided. If the arresters were installed betweenL and PE, the current flowing in a TT-system over the defective arresterbetween L and PE would not be sufficient to trip the system fuse (fur-ther details in chapter 5.8.1.6.2.2). N–PE arresters must be able to con-duct the sum of the interference currents of L1, L2 and L3 , towards N.For N–PE arresters the requirements listed in Table 4.5.2.1.3 a arevalid.

4.5.2.2 Arresters for information technology, IEC SC 37A / E DINVDE 0845 Part 2

Since October 1993, the German standard draft DIN VDE 0845 Part 2‘Schutz von Einrichtungen der Informationsverarbeitungs- und Telekom-munikations-technik gegen Blitzentladung, Entladung statischer Elek-trizität und Überspannungen aus Starkstromanlagen’. (‘Protection ofData Processing and Telecommunication Equipment Against LightningDischarge, Electrostatic Discharge and Surges from Power Plants’) hasbeen available.

In this standard draft a difference is made between the following surgeprotective devices:

Table 4.5.2.1.3 a N–PE arrester. Voltages and currents in accordance with EDIN VDE 0675 Part 6/A2


• gaps, including: (i) surge arresters, gas-filled (or gas discharge tube);(ii) creeping discharge arresters/air spark gaps; (iii) disconnectingspark gaps; and (iv) quenching spark gaps

• semiconductor protective elements and varistors

• surge limiters

• protecting and isolating transformers, including reduction trans-formers.

As this list shows, the standard draft DIN VDE 0845 Part 2 coverscomponents as well as surge protectors (surge limiters).

In the international standardization (IEC), components and pro-tectors are treated in separate standard drafts (Figure 4.5.2.1 a):

• The specifications of the components (Components for low-voltagesurge protection devices) are just being worked out by committeeSC 37 B. At present there are four drafts:

Draft IEC 61647-1: Specifications for gas discharge tubes (GDT)Draft IEC 61647-2: Specifications for avalanche breakdown diodes(ABD)Draft IEC 61647-3: Specifications for metal oxide varistors (MOV)Draft IEC 61647-4: Specifications for thyristor surge suppressors(TSS).

• The specifications for surge protection devices are currently beingworked out by the committee SC 37 A / WG4. This is entitled:

IEC 61644-1: Surge protection devices connected to telecommuni-cation and signalling networks.

There are plans to work out a second part, describing the selection andthe application of surge protectors.

As the standardizing work is developed by committee SC 37 A, therequirements concerning tests of arresters for information technologyand arresters for power technology will be ensured and coordinated withregard to their classes of requirement and the conditions of application.

The yellow printed E DIN VDE 0845 Part 2 specifies requirementsand tests made for surge protection devices to be used in installations ofdata processing and telecommunication technology.

The user-relevant electrical requirements and tests for surge limitersare briefly explained later.

For surge limiters, the standard draft identifies a difference betweentype 1 and type 2: namely, that type 1 surge limiters are provided for useagainst transient overvoltages (for example, caused by lightning), andthat type 2 surge limiters are provided for locations where additional ACinterference lasting up to 0.5 s must be taken into account.


Source

Entwurf DIN VDE 0845 Teil 2: ‘Schutz von Einrichtungen der Informations-verarbeitungs und Telekommunikationstechnik gegen Blitzeinwirkungen,Entladung statischer Elektrizität und Überspannungen aus Starkstroman-lagen. Anforderungen und Prüfungen von Überspannungsschutzeinrich-tungen’. (VDE Verlag, GmbH, Berlin/Offenbach, Oct. 1993)

4.5.2.2.1 Important data for arrester selection

• Nominal voltage UN. The nominal voltage of an arrester serves for typecharacterization and is usually identical to the nominal voltage of thesystem where the arrester will be used.

• Rated voltage Uc. The value Uc indicates the maximum operating volt-age for which the arrester is rated, and where its specified performancedata are met. This value is a support for the user in selecting anarrester for the maximum operating data of a system or equipment.

• Nominal current IN. The nominal current is the maximum admissibleoperating current that may be carried over a current path of an arrester.

• Operating frequency range. In the operating frequency range thearrester shows an insertion loss of 3dB or less. As the arresters usuallyhave a low pass characteristic, the operating frequency range isdescribed by the cut-off frequency fG.

For use in digital transmission systems a special data transmissionspeed vs is required instead of an operating frequency range. The possibledata transmission speed for an arrester is associated with the trans-mission procedure used in the system. This procedure determines thenecessary cut-off frequency in a system with a low pass characteristic. Intelecommunication engineering Vs = 2fG, or practically, for example,vs = 1.25 × fG.

• Current carrying capacity/discharge capability. Here the same criteriaare valid as for arresters for power engineering (see section 4.5.2.1a).

The standard draft E DIN VDE 0845 Part 2 does not state anyrequirements for lightning current arresters (lightning test currents Iimp).In the present state of engineering there are also arresters for informa-tion technology equipment which are lightning current conductive (seechapter 5.8.2).

• Protection level Up. In the standard draft E DIN VDE 0845 Part 2 thisvalue is also called the ‘maximum residual voltage’. This parametercharacterizes the maximum voltage that can arise at the terminals ofthe arrester for the specified loadings. When selecting an arrester itmust be borne in mind that this value is below the destruction limit ofthe subsequent device.

Further selection criteria are described in chapter 5.8.2.


Source

Entwurf DIN VDE 0845 Teil 2: ‘Schutz von Einrichtungen der Informations-verarbeitungs und Telekommunikationstechnik gegen Blitzeinwirkungen,Entladung statischer Elektrizität und Überspannungen aus Starkstroman-lagen. Anforderungen und Prüfungen von Überspannungsschutzeinrich-tungen’ (VDE Verlag, GmbH, Berlin/Offenbach, Oct. 1993)

4.5.2.2.2 Arrester coordination according to requirements and locationsA detailed coordination of the arresters for information technologyequipment according to the requirements and locations is not givenin the standard draft E DIN VDE 0845 Part 2. Only a subdivisioninto loading classes according to their current carrying capacity hasbeen made. A practicable coordination of the arresters into classes ofrequirements and locations is described in chapter 5.8.2.

Source

Entwurf DIN VDE 0845 Teil 2: 1993-10: ‘Schutz von Einrichtungen der Infor-mationsverarbeitungs und Telekommunikationstechnik gegen Blitzein-wirkungen, Entladung statischer Elektrizität und Überspannungen ausStarkstromanlagen. Anforderungen und Prüfungen von Überspan-nungsschutzeinrichtungen’ (VDE Verlag, GmbH, Berlin/Offenbach)

4.5.2.3 Arrester coordination

Now that classes of requirements and locations of the lightning currentand surge arresters are known, the user or the project organizer mustensure the coordination of the arresters with regard to the devices to beprotected. This is the only way to achieve optimally harmonized protec-tion for systems and devices. In chapter 5.8.1.6.1, consideration is givento the graded use of arresters; the principle of energetic coordination willalso be explained.

Sources

HASSE, P., and ZÄUNER, E.: ‘Ableiter für Blitzströme und Überspannungen’,Neue VDE-Bestimmung, Auswahlhilfe für den Praktiker. de, 1996, H. 15 and16, pp. 1397–1400HASSE, P.: ‘Überspannungsschutz von Niederspannungsanlagen – Einsatzelektronischer Geräte auch bei direkten Blitzeinschlägen’ (Verlag TÜV Rhein-land, Köln, 3. aktualisierte Auflage, 1993)E DIN VDE 0675 Teil 6: ‘Überspannungsableiter zur Verwendung in Wech-selstromnetzen mit Nennspannungen zwischen 100V und 1000V’ (VDEVerlag, GmbH, Berlin/Offenbach, Nov. 1993)


E DIN EN 50164-1 (VDE 0185 Teil 201): ‘Blitzschutzbauteile. Teil 1:Anforderungen für Verbindungsbauteile. Deutsche Fassung prEN 50164-1’(VDE Verlag, GmbH, Berlin/Offenbach, May 1997)E DIN VDE 0675-6/A1 (VDE 0675 Teil 6/A1): ‘Überspannungsableiter zurVerwendung in Wechselspannungsnetzen mit Nennspannungen zwischen100V und 1000V. Änderung A1 zum Entwurf DIN VDE 0675–6 (VDE 0675 Teil6)’ (VDE Verlag, GmbH, Berlin/Offenbach, March 1996)E DIN VDE 0675-6/A2 (VDE 0675 Teil 6/A2): ‘Überspannungsableiter. Teil 6:Verwendung in Wechselspannungsnetzen mit Nennspannungen zwischen100V und 1000V. Änderung A2 zum Entwurf DIN VDE 0675-6 (VDE 0675 Teil6)’ (VDE Verlag, GmbH, Berlin/Offenbach, Oct.1996)E DIN IEC 37A/44/CDV (VDE 0675 Teil 601): ‘Überspannungsschutzgerätefür den Einsatz in Niederspannungs-Verteilungsnetzen. Teil 1: Anforderun-gen an ihr Betriebsverhalten und Prüfmethoden (IEC 37A/44/CDV: 1996)’(VDE Verlag, GmbH, Berlin/Offenbach, Oct. 1996)E DIN VDE 0845 Teil 2 (VDE 0845 Teil 2) ‘Schutz von Einrichtungen derInformationsverarbeitungs und Telekommunikationstechnik gegen Blitzein-wirkungen, Entladung statischer Elektrizität und Überspannungen ausStarkstromanlagen. Anforderungen und Prüfungen von Überspannungs-schutzeinrichtungen’ (VDE Verlag, GmbH, Berlin/Offenbach, Oct. 1993)


Chapter 5

Components and protective devices: construction,effect and application

In this chapter components and protective devices used for surge controland/or the realization of the EMC-oriented lightning protection zoneconcept will be introduced with particular regard to construction, modeof functioning and fields of application. These include:

• Air terminations for the erection of air-termination systems; in particu-lar, the protection of electrical installations on flat roofs against directlightning strikes and thus assessing the lightning protection zone 0B.

• Materials and components serving for the erection of building androom shields for lightning protection zone 1 and higher.

• Materials and components by means of which it is possible to realizethe shielding of power and telecommunication lines connecting neigh-bouring buildings.

• Shields for lines within lightning protection zone 1 and higher.

• Optoelectronic bondings.

• Components for equipotential bonding systems.

• Protective devices to discharge lightning currents and to limit over-voltages. Power and telecommunication lines, for example, are pro-tected at the interfaces of the lightning protection zones by lightningcurrent arresters, installed at the interface of lightning protectionzones 0A and 1. Protective gear is also to be installed, for example,directly at the inputs of systems and devices, if they have their own(local) protection zones.

5.1 Air terminations

Air terminations are fixed points for likely lightning strikes used to avoiduncontrolled strikes and to prevent the volume to be protected from

direct strikes. Air terminations comprise air-termination rods and air-termination wires. The latter may be laid as a meshed network. Thelocation of air terminations is usually defined by the ‘rolling sphere’method (Figures 4.1.3.1.2 f a, b and c). This means that a certain radiusof rolling sphere will be assigned to every protection level in accordancewith DIN ENV 61024-1 (Table 4.1.1.b).

Finally, air terminations form a system of protection for structures onthe roof (such as ventilators and air-conditioning systems). On flat roofs‘partly isolated’ lightning protection systems are usually installed asdescribed in chapter 4.1.3. This air-termination system is spatially separ-ated from lightning protection zone 1, so that there is a lightning protec-tion zone 0B between the air-termination system and lightning protectionzone 1 (Figures 4.1.3.1.2 b and d). For smaller roof structures this pro-tection can be achieved by individual or a combination of several airtermination rods. For larger roof structures protection by means of airtermination rods is not often possible as the rods would be too high andthus there is danger of leaning. As an alternative an isolated air termin-ation is the best solution. The distance between air terminations and struc-tures on the roof must at least comform to the calculated safety distance.

Air-termination networks must form a protective volume including allstructures on the roof.

Figures 5.1 a and b show examples of roof superstructures in light-ning protection zone 0B.

Figure 5.1 a Roof-ventilation cowl protected by an air-termination rod


Sources

HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept (PflaumVerlag, München; VDE Verlag, Berlin/Offenbach, 1994)DEHN u. SÖHNE Druckschrift: DS 626/0598 ‘Isolierte Blitz-Fangeinrichtun-gen’ (Dehne + SÖHNE, Neumarkt), May 1998

5.2 Building and room shields

Extended metal components (e.g., metal roofs and facades, steelreinforcements in concrete, expanded metals in walls, lattices, metalsupporting constructions, piping) which form an effective electro-magnetic shield (see chapter 4.1.3, Figure 4.1.3.1.3 a) by their meshedinterconnection (according to DIN VDE 0800 Part 2, DIN VDE 0185Parts 1 and 103, DIN VDE 0845 Part 1) are especially important forshielding magnetic fields and for the creation of lightning protectionzones.

Figure 5.2 a shows how, in principle, a steel reinforcement and themetal window and door frames can form an electromagnetic cage (holescreen). In practice, however, it is not possible to weld or clamp everynodal point for large structures. The achievable shield attenuation orshielding factors of steel reinforcements are shown in Figure 5.2 b for theespecially interesting frequency range of lightning interference from

Figure 5.1 b Structures of air-conditioning systems protected by a mesh network

Components and protective devices: construction, effect and application 129

100Hz to 1MHz. The damping indicated in this Figure is applicable forthe case when a plain magnetic field influences the shield out of steelreinforcement. For estimation of the magnetic field strength at any pointinside a lightning current-carrying cage structure, an approximation

Figure 5.2 a Room shield by means of steel reinforcement

Figure 5.2 b Shielding effect of the reinforcement steel


formula is indicated in the draft of IEC 61312-2. The magnetic fieldstrength depends mainly on the mesh size of the shield and on the dis-tance from the shield (Figure 5.2 c).

Figure 5.2 d shows how structural steel mats (e.g., concrete steel matsQ 377) in concrete are interconnected for shielding purposes by means ofsuitable clamps (Figures 5.2 e). Often, hot-galvanized steel conductors(round 10mm dia. or flat 30mm × 3.5mm) are used for bonding thereinforcements (Figures 5.2 f and g). Thus, control (shortly before fillingin the concrete) is easier.

For bridging expansion joints or bonding the reinforcement of pre-fabricated concrete parts, fixed earthing terminals, shown in Figures 5.2 hand i, are provided. To such fixed earthing terminals or projectingbonding conductors (Figure 5.2 j) the ‘earth bus ’ or ‘earth ring bus’ (ringequipotential bonding bars) are connected (Figure 5.2 k). Metal facades(Figures 5.2 l and m) are also used for shielding purposes; the facade steelsheets, being interconnected, are to be bonded to the metal subconstruc-tion and to the reinforcement (Figure 5.2 n).

Some of the above-mentioned shielding measures can also be appliedto the establishment of room shields (lightning protection zone 2 andhigher). In particular this concerns the use of steel reinforcements (infloors, walls and ceilings), expanded metal (in walls and ceilings) andlattices.

Smaller shields for lightning protection zones 2 and higher, or shields

Figure 5.2 c Magnetic field strength as function of the wall distance and the meshsize of a grid structure


Figure 5.2 d (a)

Figure 5.2 d (a, b) Building shield out of interconnected structural steel matsand reinforcing rods

Figure 5.2 d (b)


Figure 5.2 e (a–d) Bonding of (overlapping) structural steel mats andreinforcing rods

Figure 5.2 e (a) Figure 5.2 e (b)

Figure 5.2 e (c) Figure 5.2 e (d)

Figure 5.2 f Floor reinforcement bonded with support reinforcement by wiresand clamps


Figure 5.2 g (a–d) Clamps for the connection of bonding wires with thereinforcement

Figure 5.2 g (c) Figure 5.2 g (d)

Figure 5.2 g (a) Figure 5.2 g (b)

Figure 5.2 h (a and b) Fixed earthing terminal with connection to thereinforcement

Figure 5.2 h (b)

Figure 5.2 h (a)


Figure 5.2 i Fixed earthing terminals for bridging the expansion joints

Figure 5.2 j Brought out bonding wire of the reinforcing mats for connectionto a ring equipotential bonding bar

Figure 5.2 k ‘Earth bus’ (according to DIN VDE 0800 Part 2)


Figure 5.2 l Metal façade of an office building

Figure 5.2 m Metal subconstruction for metal façade (Source: H. Neuhaus)

Figure 5.2 n Down conductor system with connection to the air-terminationsystem and to the earthing system with effective electromagneticshielding


of local lightning protection zones, are usually formed by the enclosures(sheet steel cabinets, sheet steel covered racks, sheet steel enclosures) oftelecommunication systems and devices (Figures 5.2 o and p).

Sources

HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept (PflaumVerlag, München; VDE Verlag, Berlin/Offenbach, 1994)

Figure 5.2 o Structure of an electronic cabinet

Figure 5.2 p Connection of the baseframes for the electronic cabinets to thereinforcement of the building


MÜLLER, K.P.: ‘Wirksamkeit von Gitterschirmen, z.B. Baustahlgewebemat-ten, zur Dämpfung des elektromagnetischen Feldes’. VDE-Fachbericht 52:Neue Blitzschutznormen in der Praxis (VDE Verlag Gmbh, Berlin/Offenbach,1997)

5.3 Shields for lines between screened buildings

In chapter 4.1.3.1.6 (Figure 4.1.3.1.6 a) it was shown how two spatiallyseparated lightning protection zones can be changed into a single light-ning protection zone by means of a line shield. The shields used will beintroduced here as follows:

• Shielding of cables in metal conduits or closed trays which are con-nected on both sides at the building input (Figures 5.3 a and b).

• Use of buried cables with conductive shield which will be connected atthe building input (Figures 5.3 c and d). For protection against directlightning strikes it may be useful to incorporate superimposed earthropes.

Figure 5.3 a Shielding of cables in metal conduits or closed trays


Figure 5.3 b Steel conduits and metal pull boxes form a closed line screen

Figure 5.3 c Shielding of underground cable routes by conductive screens andsurface laid copper-ropes

Figure 5.3 d Cable with external ‘lightning protection’ screen, core pair screenand pairing


• Erection of cage-shaped reinforced cable ducts, if a multitude of con-ventional cables (e.g., between two buildings) is laid (Figures 5.3 eand f). This cable duct reinforcement must be bonded to the buildingreinforcement.

Expansion joints in continuously reinforced cable ducts must bebridged analogously to the building expansion joints. Similarly, duct

Figure 5.3 e Screening of underground cable routes by cages

Figure 5.3 f (a, b) Practical execution of a cable duct with continuouslyinterconnected reinforcement steel

Figure 5.3 f (a)

Figure 5.3 f (b)


connectors underneath or between adjacent buildings must be bridged.Also, with regard to cable ducts, it must be ensured that the maximumadmissible voltage loadings on the cables laid or on the connectedequipment will not be exceeded. Even so, depending on the assumedpartial lightning current on the cable duct and on the cross section of thecable duct and, thus, on the number of longitudinal reinforcement rods,there may still arise voltage gradients from some 10V to over 100Vper metre length of the cable duct.

Sources

HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept (PflaumVerlag, München; VDE Verlag, Berlin/Offenbach, 1994)KERN, A.: ‘Blitz-Störschutz als Massnahme der EMV am Beispiel einerausgedehnten Industrieanlage. 2. Forum für Sachverständige (Dehn u.Söhne, Nürnberg, Nov. 1995)

5.4 Shields for cables in buildings

Cables shall be run near the equipotential bonding lines. These are partsof the steel construction, reinforced walls, cable supporting structures,cable trays or other electrically conductive parts which are connected tothe equipotential bonding system at least at both ends. In principle,shielded cables should be used (Figure 5.4 a). This applies for electronicor data cables as well as for higher voltage levels. Pair-twisted signal

Figure 5.4 a Connection of cable screens to a local equipotential bonding bar


cables are to be preferred. For related lines of one signalling circuit atwisted pair each is to be used, so that the incoupled transverse voltageon cable runs must be neglected. The limitation of the incoupled seriesvoltage determines the protection measures.

To lessen surges by overcoupling, power and signalling cables must beconsequently separated, if possible by using cable supporting structureswhich are included in the equipotential bonding (Figures 5.4 b and c).Different separations are needed depending on the cable parallel runninglength. Thus:

Figure 5.4 c Line screen out of continuous metal cable racks and metal coveringswith pipe bends removed (Source: H. Neuhaus)

Figure 5.4 b Cable support constructions


for l < 5m distance at randomfor 5m < l < 20m distance > 10 cmfor l > 20 m distance > 20 cm.

Also in existing systems it may become necessary to shield the cableroutes (subsequently). For this purpose a retrofit set is shown in Figures5.4 d (a and b), consisting of shielded sleevings (yard goods) providedwith a closing system in the longitudinal direction. Tests for this set havedemonstrated a shield damping of about 50dB.

Sources

HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept’ (PflaumVerlag, München; VDE Verlag, Berlin/Offenbach, 1994)KERN, A.: ‘Blitz-Störschutz als Massnahme der EMV am Beispiel einerausgedehnten Industrieanlage’ 2. Forum für Sachverständige. (Dehnu. Söhne, Nürnberg, Nov. 1995)BROCKE, R., FRENTZEL, R., and ZAHLMANN, P.: ‘Schirmung von Kabel-trassen gegen Blitzeinkopplungen.’ etz 1996, No. 20

5.5 Optoelectronic connections

In systems of great transmission bandwidth and extra sensitive electroniccomponents, apart from the specific use of surge protection devices, cir-cuit parts or component conductor systems will be opened by the inser-tion of optoelectronic coupling gaps (Figure 5.5 a). Before detailing theapplication possibilities and limitations of optoelectronic componentsfrom the viewpoint of surge protection, these components and deviceswill be introduced separately as follows.

Figure 5.4 d EMC-retrofit assembly for cable screening: (a) Components ofscreening tube (yard goods) bonding set and terminal clamps(b) Two samples bonded

Figure 5.4 d (a) Figure 5.4 d (b)


5.5.1 Optical fibre transmission system

An optoelectronic connection consists of a transmitter, optical fibre andreceiver. The transmitter converts an electrical signal into an optical sig-nal which is then transmitted to a receiver by an optical fibre. The opticalsignal is then converted back to an electrical signal in the receiver. Light-emitting diodes (LEDs) or laser diodes are used in the transmitters. Theoptical fibre conductors are usually made of glass fibre although plasticfibres are sometimes used. Individual fibres have diameters rangingbetween 100 and 150 μm. A single complete conductor can comprisebetween 10 and 100 fibres. Photodiodes, phototransistors, photothyris-tors or other photoelectronic devices are used in the receivers. Figure5.5.1 a shows the principle of an optoelectronic system for data transmis-sion over long distances.

Optical fibre transmission systems have the following advantages overtraditional conductor systems: there is no crosstalk between two lines;they have high transmission capacities in a system of low mass; and theyare very space-efficient in the installation.

If the optical fibre is of pure glass, there are further advantages withregard to surge protection: namely, optimal electrical insulation betweentransmitter and receiver, and insensitivity to incouplings. However, itmust be taken into account that optical fibre cables often have a metalsheath for damage protection which can be heated by lightning to such adegree that the cable will be damaged.

The components introduced so far are used for the construction ofoptical fibre systems for data transmission over long distances. If, how-ever, a potential separation of elements of an electronic system isrequired, then optocouplers are used.

Figure 5.5 a Subdivision into component conductor systems


5.5.2 Optocoupler

The optocoupler is a combination of radiation emitting (input) and radi-ation sensitive (output) components. Light transmission between thesetwo components takes place across a thin layer of optical medium whichsimultaneously isolates the input from the output (Figure 5.5.2 a). Opto-couplers are available having a voltage withstand of some 100V to 10kVbetween input and output. However, this voltage only indicates the insu-lation strength between input and output. Semiconductor componentswith known surge sensitivity are connected between the terminals of theoptocoupler; this means that special attention must be paid to a sufficientlimitation of differential-mode overvoltages when using them in trans-mission systems. Furthermore, these semiconductor components, namelythe diode and the phototransistor, can be thermally destroyed by low,long-duration overvoltages and this may reduce the voltage strength ofthe insulation gap between input and output.

Optocouplers are used as optoelectronic coupling elements for signaltransmission in cases where galvanic separation is required in sensitivesystem elements (Figure 5.5.2 b). Their function is thus comparable withthat of transmitters being primarily used for blocking low common-modevoltages. They cannot, however, be used for protection against voltageshigher than their transmitter/receiver surge withstand capability.

Most optoelectronic systems are supplied with mains current. There is,therefore, another galvanic coupling through the mains supply whichalso is susceptible to the danger of entering overvoltages. Surge protectiondevices should thus be incorporated.

Source

TRAPP, N.: ‘Die Optimierung des Inneren Blitzschutzes durch den Einsatzoptoelektronischer Baugruppen’. 16. Internationale Blitschutzkonferenz,Szeged, 1981, Beitrag R-5.04

5.6 Equipotential bonding

Lightning protection equipotential bonding of a ‘volume to protect’includes all incoming metal installations as explained in Section

Figure 5.5.1 a Fibre-optic transmission system: basic circuit diagram(Source: Siemens)


4.1.3.1.4. Figure 5.6 a shows an equipotential bonding bar which is usedfor the main equipotential bonding according to DIN VDE 0100 Parts410 and 540, as well as for lightning protection equipotential bondingaccording to DIN VDE 0185.

In the case of extended telecommunication systems, a duly shapedlightning protection equipotential bonding bar (installed at ground levelinside the building) also functions as an ‘earth bus’ and is usuallyinstalled as an ‘earth ring bus’ inside the building (DIN VDE 0800 Part2). The ‘earth ring bus’, a ring equipotential bonding bar, is a copper barhaving a minimum cross section of 50mm2 for surface mounting at a

Figure 5.5.2 a Optocoupler: Function diagram

Figure 5.5.2 b Connection of input and output lines to a data processing systemby optocoupler


distance of some centimetres from the wall. At distances of about 5m itshould be bonded to the foundation earth electrode (DIN VDE 0800Part 2) (Figures 4.1.3.1.4 a and 5.2 j). This bonding can also be realizedover the reinforcement. An equipotential bonding bar such as that inFigure 5.6 a can be sufficient for small local systems.

If the discharge system consists of plain metal components whichconstitute an effective electromagnetic shield (Figure 5.6 b), the equi-potential bonding bars can be directly bonded with the shield. A low-impedance coupling of the external conductors and their shields isrequired for lightning protection equipotential bonding at the interfacebetween lightning protection zones 0 and 1. Equipotential bondingis, therefore, often carried out using a bonding plate with multipleradial or even coaxial connections of the conduits or line shields (Figure5.6 c).

Equipotential bonding is not only for the protection of electronicsystems but it must also fulfil special functions. A low-impedance equi-potential bonding system, that is, an entity formed of interconnectedequipotential bonding lines including the metal parts of the electric sys-tems (such as enclosures, racks, cable trays etc. Figures 5.6 b, 5.2 o, 5.4 b)and the building (e.g., reinforcement in floors, walls and ceilings, support-ing structures between floors) is possible using a meshed, plane orspace-covering formation. Such a meshed overall building equipotentialbonding system is the best way to reduce overvoltages in telecom-munication systems and is the basis for the coordinated use of arresters(surge protection devices, filters etc.).

Different types of functional equipotential bonding systems as neededfor telecommunication facilities and systems, are described in section

Figure 5.6 a Equipotential bonding bar (acc. to DIN VDE 0618) with snap-onterminals for conductor cross sections 25 to 95mm2


4.1.3.1.4. Metal supports, cabinets, enclosures, cable racks etc. in roomswith telecommunication facilities and systems must be included in themeshed functional equipotential bonding, as Figures 5.6 b, 5.2 o, 5.4 band 5.6 d show.

Another possibility for achieving functional equipotential bondingis to create an equipotential bonding network by means of the metalsupporting structures between floors. It is useful to install a local ringequipotential bonding bar, as shown in Figure 5.2. j, which then isconnected to the ‘earth ring bus’ several times (also over the steelreinforcement or the protection zone screen) (Figure 5.6 e).

Figure 5.6 b Connection of air terminations, equipotential bonding, earthing andinstallation to the reinforcement (Source: Frentzel, R., TÜV SouthGermany)

Figure 5.6 c Connection of piping entries to the reinforcement (Source: Frentzel,R., TÜV South Germany)


Above all else, functional equipotential bonding shall include:

• metal enclosures and racks of the telecommunication systems

• conductors of electrical systems which do not carry operational volt-ages and/or currents.

In the latter case, these include: (i) the protective conductors (PE) ofthe power system, (ii) the earth electrode conductors of the telecommuni-cation system, (iii) the outer shields of the telecommunication cables, andif necessary, the chassis terminals of the electronic devices and systems.

Sources

HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept (PflaumVerlag, München; VDE Verlag, Berlin/Offenbach, 1994)DIN VDE 0800 Teil 2: ‘Fernmeldetechnik. Erdung und Potentialausgleich’(VDE Verlag, GmbH, Berlin/Offenbach, July 1985)

Figure 5.6 d Wall bushing of cable racks in meshed functional equipotentialbonding

Figure 5.6 e Equipotential bonding bar for communication technology room


5.7 Isolating spark gaps

Enclosed spark gaps which can carry test currents of 10/350 μs (Section4.5.2 b) without being destroyed are known as isolating spark gaps.Up to their sparkover voltage, these spark gaps provide the electricalseparation of two metal installations. Once the nominal spark-overpoint is reached, they create an electrical bonding path for the light-ning current. This coupling is reset after the decay of the lightningcurrent. Isolating spark gaps (Figure 5.7 a) are used at clearancesbetween the lightning protection system and other earthed systemparts in order to avoid uncontrolled arcing or puncturing at thesepoints. They are used to incorporate metal installations, for example,into the lightning protection equipotential bonding system in caseswhere these installations cannot be interconnected due to corrosioneffects (Figure 5.7 b).

High specifications must be fulfilled for explosion-protected isolatingspark gaps (Figure 5. 7 c). These are used to avoid open sparking in theevent of a lightning strike in hazardous areas, for example, for bridgingthe insulation flanges in pipelines. The lightning impulse sparkovervoltage 1.2/50 of such spark gaps should be not higher than 50% of the50 Hz sparkover AC voltage (effective value) of the insulating flange tobe protected.

The impulse sparkover voltage of a spark gap depends on the rate ofrise of the generated overvoltage wave. The steeper the wave, the shorterthe time during which failure can occur. This voltage–time relationship isclearly shown by the impulse characteristic.

Figure 5.7 d shows the impulse characteristic of the explosion-protected spark gap in Figure 5.7 e. It is extremely flat: hence, the sparkgap limits rapidly rising overvoltage impulses to almost constant valuesof about 2kV.

‘Sparkover voltage’ is not the only relevant factor in the design of aparallel-connected isolating spark gap. After the tripping of the isolatingspark gap, a voltage with peak value û = L(di/dt)max is generated at theinsulating part. L is the loop inductance and di/dt the rate of rise ofcurrent (Figure 5.7 e).

From an equation supplied in the ‘Handbuch für Blitzschutz undErdung’, the maximum value of inductance may be calculated for asquare loop of length 300mm, and a rope cross section of 25mm2 Cu (r =2.8mm). This is L = 0.16μH.

After a direct strike the lightning current flows to both sides of apipeline and a maximum rate-of-rise of current of (di/dt)max = 40kA/μscan be assumed. For an impulse wave of 4/10μs, this corresponds to apeak value of 120kA.

From the above data, the peak value of the voltage û = 6.4kV fora loop length of 300mm, and isolating spark gap elements with an


effective sparkover voltage of more than 5kV (i.e., peak value û = 5kV √2≈7kV) can be connected in parallel without any further testing.

Maximum requirements are for isolating spark gaps. At the instant ofthe lightning strike, the gaps should be capable of carrying the lightningcurrent through a protective insulation and afterwards retain the fullinsulating strength (cf. Sections 6.4 and 6.5). High-current spark gapsof this nature, type HSFS (Figure 5.7 f ), must therefore be capable of

Figure 5.7 c Explosion-protected isolating spark gap

Figure 5.7 a Isolatingspark gap

Figure 5.7 b Isolating spark gap for isolating metalsystems of different potentials


conducting especially high lightning currents without being destroyedand, during normal operation, they must offer the same high reliabilityas normal insulation components.

This spark gap type HSFS has been proven in military applicationsand is in compliance with the requirements and tests of VDE specifica-tions and DIN VDE 0800 Part 9. Figure 5.7 g shows such a high-

Figure 5.7 d Impulse voltage–time curve of the explosion-protected isolatingspark gap (Figure 5.7 c)

Figure 5.7 e Voltage drop û caused by (di/dt)max


efficiency spark gap under test conditions with a laboratory simulatedlightning current. The unit blows the arc through special openingsduring discharge of the surge currents. This type of spark gap is housedin an enclosure which is equipped with baffle plates (Sections 6.4and 6.5).

Sources

HASSE, P.: ‘Überspannungsschutz von Niederspannungsanlagen – Einsatzelektronischer Geräte auch bei direkten Blitzeinschlägen. (Verlag TÜVRheinland, Köln, 3. aktualisierte Auflage, 1993)HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept (PflaumVerlag, München; VDE Verlag, Berlin/Offenbach, 1994)DIN VDE 0800 Teil 9: ‘Fernmeldetechnik. KU-Werte sicherheitsbezogenerBauelemente und Isolierungen’ (VDE Verlag, GmbH, Berlin/Offenbach, May1989)

5.8 Arresters

According to their ranges of application, surge protective devices (SPDs)for power engineering and for information technology can be subdividedinto two kinds: namely, lightning current arresters and surge arresters (cf.Section 4.5.2.1 and 4.5.2.2).

SPDs are internationally standardized in IEC 61643-1:1998-02 ‘Surgeprotective devices connected to low-voltage power distribution systems.Part 1: Performance requirements and testing methods’. In this standardthe SPDs are distinguished according to test classes (I, II, III). It is

Figure 5.7 f High-current spark gap,type HSFS

Figure 5.7 g High-current spark gap,type HSFS tested by laboratorysimulated lightning current


somewhat difficult for the user to understand this classification because itis primarily meant for the producer of the SPDs.

A rather user-convenient SPD standardization is included in theGerman DIN VDE 0675 Part 6/6A1 and 6A2 (Table 5.8 a). Asthe requirements and tests of the German standard are more severe thanthe international standards, the German standard is taken as a basis forarrester classification.

Lightning current arresters must be able to discharge (high energy)lightning currents or considerable parts of them non-destructively. Theyare dimensioned and tested in accordance with IEC 61643-1/E DINVDE 0675 Part 6 and Part 6/A1 (Figure 5.8 a). Surge arresters only servelimiting overvoltages at relatively low-energy surge currents.

Figure 5.8 a �1 Test current impulse (10/350 μs) for lightning currentarresters; �2 Test current impulse (8/20 μs) for surgearresters according to E DIN VDE 0675 Part 6/A1

Table 5.8 a

E DIN VDE 0675 Part 6/A1 IEC 37A/447/CDV

Arresters class B, for lightning protectionequipotential bonding purposes according to DINVDE 0185 Part 1

Arrester: ‘Class I’

Arresters class C, for surge protection purposes inthe permanent installation, especially for use insurge withstand category (surge category) III

Arrester: ‘Class II’

Arresters class D, for surge protection purposes inthe mobile/permanent installation, especially foruse in surge withstand category (surge category) II

Arrester: ‘Class III’


5.8.1 Arresters for power engineering

As explained in chapter 4.5.2, arresters for systems and equipment inpower engineering are subdivided into requirement classes A, B, C andD according to IEC 61643-1/E DIN VDE 0675 Part 6 and Part 6 A1(Figure 5.8.1 a and Tables 5.8.1 a and b).

Class A arresters are used in low-voltage overhead lines. Class B, Cand D arresters are used in permanent building installations. The highestrequirements for discharge capability are for class B arresters. Theseare lightning current arresters used in the scope of lightning- and surge-protection at the interface of lightning protection zones 0A/1. Sucharresters must be able to carry lightning partial currents with wave shape10/350μs non-destructively for several strikes. The task of these lightningcurrent arresters is to prevent destructive lightning partial currents frompenetrating the electrical system of a building. According to the latest‘Technical Supply Conditions’ of German power supply companies,lightning current arresters may also be installed before the meter.

Surge arresters are installed (at the boundary of lightning protectionzones 1/2) for protection against surges arising between the active con-ductors L1, L2, L3 and N as against the protective conductor PE. These areclass C surge arresters with a discharge capacity of some 10kA (8/20 μs).

The final link in lightning and surge protection for power engineeringsystems is the terminal protection (boundary of lightning protectionzones 2/3). The main task of the class D arresters used is to protectagainst surges arising between L and N. These are mainly switchingovervoltages.

5.8.1.1 Surge arresters for low-voltage overhead lines, class A

Surge arresters for use in low-voltage overhead lines (Figure 5.8.1.1 a) areusually constructed as a series connection of spark gap and voltage-dependent resistor (Figure 5.8.1.1 b) designed for a nominal dischargesurge current of 8/20μs with 5 kA peak value (Table 5.8.1.1 a). Such aloading occurs in cases of remote lightning striking into the power sup-ply system. In the case of a direct lightning strike the spark gap weldsand the non-linear resistor fuses. A disconnector separates the defectivearrester from the system (e.g., indicated by a detached indicator sleeve).

Figure 5.8.1.1 c indicates the voltage UM arising between overhead lineand ‘earth’ on discharging a 5kA (8/20) surge current. UM is composed of:

• the protection level UP (about 2kV)

• the voltage drop at the earth conductor inductance (at a 5kA 8/20surge current, (di/dt)max is about 1 kA/μs, therefore the voltage droppeak value is about 10kV)

• the voltage drop at the impulse earth resistance RE (peak value about50kV).


The total of these (time-related) potential gradients results in thecurve UM = f (t) in Figure 5.8.1.1 c, b, with a peak value UM ofabout 55kV. Hence, these arresters, when used in low-voltage over-head lines, cannot effectively protect the connected consumer installa-tions (Figure 5.8.1.1 c, a) in discharging the nominal discharge surgecurrent. Primarily, they protect the low voltage overhead line systemsthemselves.

Figure 5.8.1 a Application of arresters in a power technical network

Table 5.8.1 a Requirement classes of arresters for power technical systems inaccordance with E DIN VDE 00675 Part 6 and E DIN VDE 0675Part 6/A1


5.8.1.2 Lightning current arresters for lightning protection equipotentialbonding, class B

Lightning current arresters have to meet the requirements in Table5.8.1.2 a. There may be a (computer based) calculation of the requiredlightning current-carrying capability according to the respective installa-tion factors.

According to IEC 61312-1:1995-02: ‘Protection against lightningelectromagnetic impulse. Part 1: General principles’ the distributionshown in Figure 5.8.1.2 a may be assumed concerning the distribution of

Table 5.8.1 b Assignment of the arrester gear

Figure 5.8.1.1 a Arrester hookedinto the overhead line (Source:Siemens)

Figure 5.8.1.1 b Structure of the arresterin Figure 5.8.1.1 a: (1) fusible point, (2)fusible strip, (3) indicating sleeve, (4) non-linear resistor disc (silicon carbide), (5)spark gap (Source: Siemens)


the lightning and lightning partial currents at a lightning strike into theair-termination system. The lightning current arrester loading can beestimated as follows. A lightning current of 200kA (10/350 μs) is themaximum loading for protection level I (according to Table 5.8.1.2 b).According to Figure 5.8.1.2 a this lightning current is distributed asfollows: (a) 50% (100kA, 10/350 μs) is discharged through the earthingsystem, and (b) 50% (100kA, 10/350 μs) is discharged by the connectedsupply systems (power system, information technical system, metal pip-ing etc.). If, in the worst case, there is only the power system, it will beloaded by 50% of lightning current. Considering the worst case of onlytwo conductors (L and PEN), there will be a loading of 50kA (10/350μs)each per conductor. For this worst case scenario the loading of a one-pole lightning current arrester will have the following parameters: a peakvalue 50kA (10/350 μs), a charge of 25As and a specific energy of0.625MJ/Ω.

Lightning current arresters for such high demands are mostly air-gliding spark gap structures which are able to extinguish the flowingmains follow-current automatically after having been activated (Figure5.8.1.2 b). Such leakage current-free gliding spark gaps are often a con-struction of rotationally symmetric electrodes with a spacing insulatinglayer which has an arc-exhausting effect. Their ‘breakwater function’ is amajor advantage of such spark gap arresters. Wave shape 10/350 μs light-ning currents are shortened to surge currents of wave shape < 8/20μswhich are compatible for downstream installed surge arresters.

Figure 5.8.1.2 c shows four such practice-proven lightning currentarresters. The DEHNport® lightning current arrester (Figure 5.8.1.2 d) isequipped with a capacitively-controlled tandem gliding spark gap. Itconsists of three rotationally symmetric electrodes with spacers made outof different insulating materials. Thus, a high discharge capacity of75kA (10/350 μs) at a low protection level of 3.5kV (1.2/50 μs) isachieved. This arrester exhausts hot gases when discharging lightningcurrents. Therefore other bare, live metal parts must be kept in minimumdistances as shown in Figure 5.8.1.2 e.

Table 5.8.1.1 a Arresters – class A


Usual types of lightning current arrester based on spark gaps are ableto extinguish mains follow-currents of up to 4kAeff (50Hz) automatically.The spark gap in the lightning current arrester must establish a ‘countervoltage’ (arc voltage) in the range of the supplying system voltage inorder to obtain a better follow-current extinguishing capability. There-fore, a completely new function principle had to be developed for therequired follow-current-limiting spark gap. This is based on optimizedarc cooling by radial and axial blowing. The necessary cooling gas is

Figure 5.8.1.1 c Protective effect of arresters installed at overhead lines(a) Spatial arrangement (b) Voltages at discharging a5 kA(8/20μs) impulse current

Figure 5.8.1.1 c (a)

Figure 5.8.1.1 c (b)


Table 5.8.1.2 a Arresters – class B

Table 5.8.1.2 b Lightning current parameters acc. to IEC 61024-1 resp. IEC61312-1 (ENV 61024-1)

Figure 5.8.1.2 a Assumed distribution of the lightning current


generated under the influence of the arc by the surrounding plasticmaterial. Owing to the forced blowing, the arc voltage will be increased.

Figure 5.8.1.2 f shows the principle of a radially and axially blown arc(RADAX-flow technology). The cooling gas released under the influenceof arc streams radially (from all sides) towards the arc and ‘compresses’it. Owing to the reduced cross section of the arc pillar, the arc resistancewill rise and the arc voltage increase. The gas heated by the influence ofthe arc is finally exhausted by an axial gas streaming through an expul-sion nozzle. For RADAX-flow spark gap technology, the follow-current(let-through current) actually flowing through the arrester will be limitedto a very low value, independent of the possible mains short-circuitcurrent (section 5.8.1.6.3).

The use of RADAX-flow technology in series bays of usual dimensions(Figure 5.8.1.2 g) has led to a completely new generation of lightningcurrent arresters combining a high surge current discharge capabilitywith the breaking performance of a circuit breaker: The problem offalse tripping of fuses due to mains follow-currents is solved. Because ofthese excellent operating characteristics, lightning current arresters inRADAX-flow technology are especially suitable for installation in thesealed part of a consumer system (mains distribution system).

DEHNbloc® and DEHNbloc® NH contain a pressure-controlledencapsulated gliding spark gap (Figure 5.8.1.2 h, a). The encapsulation ofthe spark gaps prevents the ‘blowing’ of these lightning current arresters.Thus, the spacing problem (safety distances) is solved (Figure 5.8.1.2 h,d). The discharge capacity of these encapsulated gliding spark gaps isabout 25kA (10/350μs) and the protection level is lower than 4kV (1,2/50μs). Owing to the pressure-controlled arc quenching, the mains follow-current will be safely controlled. The leakage-current-free encapsulatedgliding spark gap is embedded into a special insulating material with arc-quenching characteristic. The pressure arising at the activation of thespark gaps enforces the quenching effect of the insulating material.

Figure 5.8.1.2 b Behaviour of a lightning current arrester based on a spark gap


Figure 5.8.1.2 c Lightning current arrester (from left to right):(a) DEHNport ®, (b) DEHNport ® Maxi, (c) DEHNbloc ®,(three-pole design), (d) DEHNbloc ® NH

Figure 5.8.1.2 c (c) Figure 5.8.1.2 c (d)

Figure 5.8.1.2 c (a) Figure 5.8.1.2 c (b)


Figure 5.8.1.2 d (a)DEHNport® with tandemgliding spark gap

Figure 5.8.1.2 d (b)Sectional model tandemgliding spark gap

Figure 5.8.1.2 d (c)Function principle

Figure 5.8.1.2 e Lightning current arrester type DEHNport ®, installed at theinput of a power supply line from lightning protection zone 0 intolightning protection zone 1


Figure 5.8.1.2 f Basic circuit diagram for an arc blown out radially and axially inRADAX-flow technology

Figure 5.8.1.2 g Lightning current arrester DEHNport with RADAX-flowtechnology in the mains connection box for application in thearea before the meter


The DEHNbloc® (Figure 5.8.1.2 h, b) is a compact, three-pole arresterunit (with a space-saving width of only four modules). It is especiallysuitable for the common TN-C system. Also the multifunction terminalsfor the clamping of both terminal wires and comb-type bars are easy touse (comparable to the DEHNport®). The DEHNbloc® NH (Figure5.8.1.2 h, c) is the first lightning current arrester for mounting on

Figure 5.8.1.2 h (c)DEHNbloc® NH

Figure 5.8.1.2.h (b) DEHNbloc ®

Figure 5.8.1.2.h (d) Installation without minimumdistances

Figure 5.8.1.2 h (a)Encapsulated gliding spark gap


NH-fuse bases size 00 (also in fuse-disconnector blocks). Installation bya usual fuse handle is possible without operational interruption. This isespecially attractive for application in industrial plants.

Because of the gliding spark gap technology the ‘breakwater function’is guaranteed and thus an energetic coordination (as explained inchapter 4.5.4) with surge arresters based on varistor technology, likeDEHNguard®, is possible.

DEHNport®, DEHNport® Maxi, DEHNbloc® NH and DEHNbloc®

can be installed upstream of the meter because of the leakage current-freeoperation and the high insulation resistance.

Another special lightning current arrester (according to E DIN VDE0675 Part 6/A2) based on air spark gaps is the N-PE lightning currentarrester DEHNgap B (Figure 5.8.1.2 i). What is the task of an N-PElightning current arrester?

Lightning current arresters should be installed as close as possible tothe building input. In the TT-system this means an installation upstreamof the residual-current device. In the case of an earth fault in this range,the upstream fuse must disconnect. But this is not guaranteed underunfavourable earthing conditions.

On using the N–PE lightning current arrester DEHNgap B in a ‘3 +1-circuit’, where the three phases (L1, L2, L3) are connected to glidingspark gaps (e.g., the DEHNport) and a spark gap is installed betweenneutral conductor N and protective conductor PE (chapter 5.8.1.6), thereis a short-circuit current between the phases and neutral conductor inthe case of an arrester fault which the upstream fuse can now breakin the time provided.

The N–PE lightning current arrester type DEHNgap B can safelyconduct the residual current of the incoupled lightning between theearthing system and the neutral conductor up to 100kA (10/350 μs) at asparkover voltage < 4kV (1.2/50μs).

The compact enclosure design with a space of two modules and themultifunction terminals for clamping both the terminal wires and comb-type bars makes the N–PE lightning current arrester DEHNgap B veryeasy to use.

Also a quench gap (Figure 5.8.1.2 j) is suitable for the inclusion ofpower lines into the lightning protection equipotential bonding at theinterface of lightning protection zones 0 and 1. It is also able toextinguish mains follow-currents automatically. This lightning currentarrester has been proven in practice for years and is included in thestandards DIN VDE 0804 Part 2 and DIN VDE 0845 Part 1. Quenchgaps are, for example, used in the lightning current arrester arrange-ment described in chapter 6.5 (Figures 6.5 b and 6.5 c) to protecttransportable telecommunication facilities and for the connection ofthe mains supply of TV transmitters (chapter 6.4, Figures 6.4 e and6.4 f, b).


5.8.1.3 Surge arresters for protection of permanent installation, class C

According to DIN VDE 0675 Part 6, class C surge arresters are used inthe permanent building installation.

At lightning protection zone interfaces 0B/1 and higher, the phases (L1,L2, L3) of the mains are equipped with surge arresters. In TT and TN–Ssystems, where the N conductor is run separately from the PE conductor,the N conductor also has an arrester.

Valve-type arresters are constructed according to DIN VDE 0675Parts 1 and 6 or IEC 99.1 and consist of a spark gap and voltage-dependent resistor connected in series; their nominal discharge surgecurrent is 5kA (8/20 μs); the voltage arising at the consumer installationis about 1.5kV.

Figures 5.8.1.3 a and b show valve-type arresters containing one air-spark-gap and one silicon carbide resistor. Voltage and current charac-teristics for voltage limitation are shown in Figure 5.8.1.3 c. Valve-typearresters are characterized by their quenching voltage Ul (continuousoperating voltage Uc according to DIN VDE 0675 Part 6), at which anarrester (in an operating duty test) is still able to extinguish the mainsfollow-current automatically. Figure 5.8.1.3 d shows the voltage andcurrent during such an operating duty test according to DIN VDE 0675Part 1 at a valve-type arrester for Ul = 280V, whereas Figure 5.8.1.3 eshows the protection characteristic of this arrester.

If the valve-type arrester shown in Figure 5.8.1.3 a is overloaded, theintegrated disconnector separates the defective arrester from the mains.Downstream consumer installations will stay alive. However, such defect-ive arresters must be replaced as they no longer protect against surges.

Figure 5.8.1.2 i DEHNgap B Figure 5.8.1.2 j Quench gap


Valve-type arresters have indicators to show the defective and discon-nected state (Figure 5.8.1.3 f).

Figure 5.8.1.3 g shows an arrester for NH fuse bases size 00 (connectedto L and PE). Figure 5.8.1.3 h shows a practical example. Replacement ofan arrester in a live state is easy by means of an NH fuse handle. Ifholders with a microswitch (Figure 5.8.1.3 i) are used, the projecting pin of

Figure 5.8.1.3 b Nonlinear resistor type gapped surge arrester (acc. to Figure5.8.1.3 a), installed in a low-voltage distribution system

Figure 5.8.1.3 a Nonlinear resistor type gapped surge arrester


Figure 5.8.1.3 c Performance of a nonlinear resistor type gapped surge arrester(series connection of spark gap and silicon carbide varistor)

Figure 5.8.1.3 d Performance of a nonlinear resistor type gapped surge arrester(acc. to Figure 5.8.1.3 a) during the operating duty test

Figure 5.8.1.3 e Protective characteristic of a nonlinear resistor type gappedsurge arrester (acc. to Figure 8.1.3 a)


the disconnected arrester will press this switch and a remote indication ofthe necessary arrester replacement becomes possible.

Recent surge arrester models have zinc oxide varistors (Figure 5.8.1.3 j)where almost no mains follow-current arises; these can be used without aseries connected spark gap. Figure 5.8.1.3 k shows such a surge arrester ina modular design with a thermally controlled zinc oxide varistor forspace-saving installation in distribution systems (Figure 5.8.1.3 l).

The basic overvoltage limiting behaviour is shown in Figure 5.8.1.3 m;

Figure 5.8.1.3 h Surge arrester (acc. to Figure 5.8.1.3 g), installed in adistribution system

Figure 5.8.1.3 f Nonlinear resistor typegapped surge arrester with disconnectorand indicator (acc. to Figure 8.1.3 a).Arrester on the right is defective,disconnector has operated (pushed upbutton)

Figure 5.8.1.3 g Surge arrester inNH type of construction


Figure 5.8.1.3 k Surge arrester in modular design, type DEHNguard®

Figure 5.8.1.3 i Remoteindication of the operation of thearrester disconnector (acc. toFigure 5.8.1.3 g) by microswitch

Figure 5.8.1.3 j Metal oxide varistor

Figure 5.8.1.3 k Surge arrester in modular design, type DEHNguard ®


the limiting voltage is exclusively determined by the residual voltage atthe discharge of the impulse current. A live surge arrester on a metaloxide basis (without spark gaps) carries the current corresponding toits U/I characteristic (Figure 5.8.1.3 n). Such arresters are always ‘inoperation’, whereas an arrester based on a spark gap needs ‘activation’by an overvoltage.

Usual surge arresters based on ZnO have a discharge capability of

Figure 5.8.1.3 l Surge arrester DEHNguard® installed at the input of a powersupply line from lightning protection zone 1 to lightningprotection zone 2

Figure 5.8.1.3 m Performance of a surge arrester based on metal oxide (acc. toFigure 5.8.1.3 k)


15kA (8/20 μs). The protection element must be able to conduct thisdischarge current safely and without changing the characteristic atleast 20 times. This is sufficient to prevent overloading in the case of a‘creep under’ of a backup lightning current arrester and correctly dimen-sioned decoupling impedance (chapter 5.8.1.5). If for example, owing tounfavourable conditions, there is a missing backup lightning currentarrester (in spark gap technology), this discharge capacity is exceededand thus the varistor overloaded, then it will be automatically discon-nected from the mains. This prevents a defective arrester from disturbingthe operation. Remote control is possible by a local indicator and apotential-free changeover contact.

DEHNguard® T (Figure 5.8.1.3 o) consists of two parts: a base and anattachable varistor module which can be replaced in case of overloading.For insulation measurements of the system, quick removal is advanta-geous. To avoid errors, the base and varistor module are provided withcode pins according to their nominal voltage.

Figure 5.8.3.1 p shows a surge arrester with degree of protection IP ×4W. This is particularly suitable for industrial applications (to be pluggedinto NH fuse holders, size 00) and has (like the arrester shown in Figure5.8.1.3 g) an integrated backup fuse which does not need any furtherbackup fuse on the mains (section 5.8.1.5).

The 3 + 1 circuit (chapter 5.8.1.5) allows the application of surgearresters upstream of the residual current device. The three phase con-ductors (L1, L2, L3) are connected to varistors towards the neutral con-ductor N, and the surge arrester DEHNgap C (Figure 5.8.1.3 q), basedon a spark gap having a sparkover voltage of about 1.5kV (1.2/50), is

Figure 5.8.1.3 n U/I characteristic of a varistor


installed between neutral conductor N and protective conductor PE.Thus, the upstream fuse can meet the disconnection requirements in thecase of a fault.

The space-saving one modular design of the surge arresters DEHN-guard® and DEHNgap C and the multifunction terminals for wires andusual comb-type bars make them especially easy to install.

5.8.1.4 Surge arresters for application at socket outlets, class D

Surge arresters for mobile application at socket outlets (overvoltage cat-egory II) are assigned to requirement class D according to E DIN VDE0675 Part 6. Such pluggable protectors (Figure 5.8.1.4 a) are oftenequipped with additional filters (Figure 5.8.1.4 b). The SF protector has avisual function indicator (green lamp) and a visual fault indicator (redlamp). When overloading it is disconnected automatically from themains without power interruption. The plug-in surge protection adaptershown in Figure 5.8.1.4 c is a combination of surge arrester and interfer-ence suppressor filter.

Further types of surge arresters used in this range are shown in Figures5.8.1.4 d to f: According to design and testing, these are class D pro-tectors. The surge protection socket outlet (Figure 5.8.1.4 d) has a super-visory device and a disconnection device with a green lamp as visualfunction indication and a red lamp as fault indication (indication of thedisconnected mains). The surge arrester NM-DK 280 (Figure 5.8.1.4 e) issuitable for application in cable ducts and flush-mounted boxes. Becauseof its feed-through terminals it can be easily inserted into circuits. It isadaptable to all types of switches as it can be covered by the central discaccording to DIN 43 696.

The protector shown in Figure 5.8.1.4 f is for power supply protectionof industrial electronics equipment (e.g., programmable controllers,SPC) against surges and high-frequency disturbance voltages.

Figure 5.8.1.3 q Surgearrester DEHNguard® C

Figure 5.8.1.3 p Surgearrester VNH 280

Figure 5.8.1.3 o Surgearrester DEHNguard® T


5.8.1.5 Surge arresters for application at equipment inputs

Equipment with a power technical input (which may form its own light-ning protection zone) can be directly protected at this input by surgearresters as mini-modules (Figure 5.8.1.5 a) and (Figure 5.8.1.5 b). Theyprotect electronic equipment of overvoltage category I. These arrestersare designed and tested according to E DIN VDE 0675 Part 6 asclass D.

5.8.1.6 Application of lightning current arresters and surge arresters

Planning and execution of surge protection measures in the scopeof an EMC-compliant protection strategy must lead to a coordinated

Figure 5.8.1.4 a Pluggable surge arresterprotects mains input of a computer

Figure 5.8.1.4 b SF-protector(surge arrester with filter) forprotection against transientsurges and frequent interferencevoltages

Figure 5.8.1.4 c SFL-protector: Multiple socket outlet with surge arrester andfilter


protection system. A consequence of the often missing system consider-ation today is the uncoordinated installation of arresters at differentpoints of the system which impair or even neutralize each other or havean inadmissible retroactive effect on the whole system. One of the first

Figure 5.8.1.4 d Socket outlet(with earthing contact) withovervoltage protection

Figure 5.8.1.4 e Surge protective deviceNM-DK 280 for cable ducts

Figure 5.8.1.4 f SPS-protector: Surge protector with interference suppressorfilter


essentials for the planning and execution of surge protection for a com-plex system is an organizing principle which subdivides the protectedsystem into areas of graded demands. The EMC-oriented concept oflightning protection zones is such a principle. The concept of lightningprotection zones allows the determination of the corresponding stressparameters for the individual arresters. The list of requirements for thearresters used can be basically subdivided into requirements for the indi-vidual arresters and requirements which are due to the system characterof the total protection. The most important parameter for an individualarrester is its surge current-carrying capability.

The demanded parameter value is due to the conditions of applicationof the arrester in the concept of lightning protection zones. For a light-ning current arrester (at the boundary of LPZ 0A/1) these values are dueto the primary lightning threat parameters (IEC 61312-1) and the realconditions of installation. For the design of the individual arresters thequestion of how many partial systems and conductors the total lightningcurrent is distributed over must also be clarified (IEC 61312-1).

Within lightning protection zone 1 there still remains the conductedresidual parameters of the lightning current arrester as well as the over-voltages induced by the electromagnetic field of lightning and internalsources of interference (e.g., switching operations) as stress parametersfor downstream protective equipment.

The requirements for surge arresters that are installed at the boundaryof lightning protection zone LPZ 1/2 must include this stressing. Thereare additional requirements for the different arresters as individual elem-ents because of the system character of the whole protection system. Itis necessary that the protection levels of the different arresters in the

Figure 5.8.1.5 aSurge protective mainsmodule VC 280/2

Figure 5.8.1.5 b Surge arrester (acc. to Figure5.8.1.5 a) connected to power pack


protection system be in accordance with the rules of insulation coordin-ation of IEC 60664-1 (Figure 5.8.1.6 a). Coordination of the arrestersbetween each other ensures that the individual protection devices areloaded as effectively as possible and maximum safety of the system isachieved.

In addition to these specific requirements of surge protection there aredemands for harmonization of surge protection–system protection,requiring coordination between the arresters’ parameters and the valuesof the conventional system protection devices (fuses, circuit breakersetc.).

The special regulations which both the planner and installer (electri-cian) of the protective system must take into account are handled in thefollowing notes.

5.8.1.6.1 Graded application of arresters, energy coordination betweensurge arresters and equipment to protect. The requirements for cascadedarresters in a protection system depend on the concept of protectionzones. The planner is in charge of selecting the different coordinatedarresters which must reduce step-by-step the incoming (lightning partialcurrents) or internally generated (switching surges) hazard to the with-stand capability of the terminal units to be protected.

To adapt a surge protection device (SPD, arrester) to the peripheralinterface of a piece of equipment the interference immunity factor of theequipment and the maximum let-through parameters (output param-eters) of the SPD must be known. This must be coordinated with theenergy loadability of the equipment input. In addition to the arrester

Figure 5.8.1.6 a Example for the application of lightning current arresters andsurge arresters


protection level the maximum values of the integral parameters of out-put voltage and output current are also of importance for energycoordination.

Coordination, in this case, means to dimension a protective circuitupstream of an equipment interface in such a way that only at an immi-nent overloading of the device’s internal protective circuit will theupstream protective grade (SPD) become effective. The ‘operatingbehaviour’ of the upstream protective grade (SPD) and the loadability ofthe equipment’s protective circuit must overlap one another (i.e., form acommon ‘interface’). Only thus is it possible to obtain a good balancebetween the costs for the protective circuit and the benefits which areachieved.

The ‘conditions of adaptation’ described, however, are not only validfor the surge protective device and terminal unit but also for the use ofarresters in a graded concept of protection zones (Figures 5.8.1.6.1 a).

For a lightning current stressing arrangement according to 5.8.1.6 aand 5.8.1.6.1 a, the class C surge arrester in the subdistribution boardwill operate first due to its low protection level. According to its nominaldischarge data this arrester has a protection level < 1.5kV. This voltage isinsufficient to operate the upstream class B lightning current arrester (asthe operating value of this spark gap is between 3 and 3.5kV). In ordernot to overload the class C surge arrester in the subdistribution board,there must be an additional series voltage drop on the line between thesurge arrester and the lightning current arrester which, in sum with the

Figure 5.8.1.6.1 a (a) Protective gear for power technical systems at theinterfaces of lightning protection zones (LPZ)


protection level of the class C surge arrester in the subdistribution,reaches the operating value of the spark gap in the class B lightningcurrent arrester. In the 230/400V mains this series voltage drop can beobtained by using the cable impedance, or by using a concentratedinductance (decoupling choke).

The cable inductance depends on the routing of the protective con-ductor PE. If the protective conductor is in one cable with L1, L2, L3 andN (as for cable type NYM-J), a cable length of at least 15m is the neces-sary decoupling length between the class B lightning current arrester andthe class C surge arrester (Figure 5.8.1.6.1 b). If the protective conductoris separate from L1, L2, L3 and N (as for cable type NYM-O), and thedistance between the protective conductor and cable is 1m (as in Figure5.8.1.6.1 c) the necessary minimum decoupling length is 5m. If thesecable lengths cannot be realized, the class B and class C arresters can becoordinated by decoupling chokes (Figure 5.8.1.6.1 d). With suchdecoupling chokes there is the possibility of installing the arresters in oneplace (Figure 5.8.1.6.1 e), and insecurities due to installation (such as theactual line length) can be avoided. Responsibility for this arrangementthus passes over from the installer to the producer of the protectivedevices who indicates the necessary induction value for the coordinationof his arresters.

For dimensioning the decoupling choke it is possible to choose theinductance value as low as possible by using all securities granted by theprotective devices, or to increase the safety of the graded protective cir-cuit by a higher minimum inductance value. Increasing the inductancevalue by several microhenry (μH) does not mean any restriction onnormal operation. On the contrary, because of too strictly dimensioned

Figure 5.8.1.6.1 (b) Currents through surge arresters and lightning currentarresters at lightning strikes


Figure 5.8.1.6.1 b Necessary decoupling line length for arresters of requirementclasses B and C when protective conductor PE is in the cable

Figure 5.8.1.6.1 c Necessary decoupling line length for arresters of requirementclasses B and C when laying the protective conductorseparately

Figure 5.8.1.6.1 d Decoupling inductance DEHNbridge (15μH) for the energycoordination of lightning current arresters (DEHNbloc®,DEHNport®, DEHNport® Maxi, DEHNbloc® NH) andsurge arresters (DEHNguard®) at lightning impulse current10/350 μs


decoupling inductances, the surge arresters might be overloaded, espe-cially at the coordination between lightning current and surge arresters,and its service life being drastically reduced would mean a failure ofsurge protection. For the usual lightning current and surge arresters,decoupling chokes with an inductance > 10 μH are sufficiently dimen-sioned and a long service life for the protective combination isguaranteed.

The arrester set shown in Figure 5.8.1.6.1 f, lightning current arrester,decoupling choke and surge arrester, is offered as a complete lightningcurrent tested mains connection unit (Figure 5.8.1.6.1 g).

Because of the different tasks of class C and D surge arresters,coordination between both of these arresters is also necessary. Safecoordination is guaranteed if there is at least 5m of cable type NYM-Jbetween the class C and D arresters (Figure 5.8.1.6.1 h).

5.8.1.6.2 Application of arresters in different system configurations. Pro-tective measures to avoid dangerous electric shock are necessary in everyelectrical system. Normally live parts must be insulated, covered,sheathed or arranged to exclude contact and electric shock. This measureis called ‘protection against direct contact’. Of course, there may not beany hazard (by electric shock), but if a fault occurs (e.g., damaged insula-tion) there is the likelihood of accidental energization of the metallicenclosure (body of an electrical equipment). Protection against suchdangers is called ‘protection in case of indirect contact’.

Figure 5.8.1.6.1 e Decoupling inductance DEHNbridge coordinates lightningcurrent arresters and surge arresters


Figure 5.8.1.6.1 f Mounting assembly of the protective combinationDEHNport® – DEHNbridge – DEHNguard® in the TN–Csystem

Figure 5.8.1.6.1 g Mains connection box, type Netz-AK, tested by lightningimpulse current

Figure 5.8.1.6.1 h Necessary decoupling line length for class C and D arresters


Usually, the maximum permissible permanent contact voltage UL

is 50V AC and 120V DC. Higher contact voltages must be discon-nected automatically at least after 5 s (in special cases within 0.2 s).Higher contact voltages which may arise from a fault must be dis-connected automatically within 0.2 s in circuits of 35A nominal currentwith socket outlets and in circuits containing class I portable equip-ment which is normally kept in hand during operation. In all othercircuits higher contact voltages must be disconnected automaticallywithin 5 s.

Protective measures for indirect contact with protective conductors aredescribed in IEC 60364-4-41. If triggered by fault these measures causeautomatic disconnection or indication. Installing measures for ‘protec-tion in case of indirect contact’ will entail a contract dealing with systemtype and protective equipment.

According to IEC 60364-4-41 a complete low-voltage distributionsystem from the current source to the final equipment is mainly charac-terized by:

• earthing conditions of the current source (e.g., low-voltage side of thedistribution transformer)

• earthing conditions of the exposed conductive parts in electricalconsumer systems.

There are three basic types of distribution: (i) the TN-system, (ii) theTT-system and (iii) the IT-system. These letters have the followingmeanings:

• The first letter describes the earthing conditions of the feeding currentsource:‘T’ direct earthing of one point of the current source (usually the

neutral of the transformer winding)‘I’ insulation of all active parts from earth or bonding of one point

of the current source to earth via an impedance.

• The second letter describes the earthing conditions of the exposedconductive parts of the electrical system:‘T’ exposed conductive parts are directly earthed, regardless of a

possible earthing of one point of the current supply‘N’ exposed conductive parts are directly bonded with the operational

earth electrode (earthing of the current source).

• Further letters describe the running of the neutral conductor andprotective conductor:‘S’ neutral conductor and protective conductor are separated‘C’ neutral conductor and protective conductor are combined (in one

conductor).


Thus, three variants are possible for the TN-system: (i) TN–S, (ii) TN–Cand (iii) TN–C–S.

The following protective equipment can be installed in the differentsystems:

• overcurrent protective device

• residual current device

• insulation monitoring device

• fault voltage-operated protective device.

As already mentioned, coordination between system type and protect-ive equipment is necessary, as follows:

(a) TN-system with:


• residual current device.

(b) TT-system with:




(c) IT-system with:



• insulation monitoring device


Protective equipment that can be installed as protection for the case ofindirect contact in the different systems is as follows:



• insulation minitoring device


Measures of personnel protection are of top priority in the installationof power systems. All other protective measures, such as lightning andsurge protection (of electrical systems and installations) must be sub-ordinate to the protective measures taken for the case of indirect contactwith a protective conductor (considering the system type and the pro-tective equipment) and must not be annulled by the use of protectivegear (for lightning and surge protection). Also arrester faults must betaken into account (even though they would seem to be unlikely). This isespecially important as lightning current and surge arresters are alwaysinstalled towards the protective conductor which, however, in the case ofarresters in connection with residual current circuit breakers, can lead toconflict situations.


Figure 5.8.1.6.2 a shows an arrangement of arresters downstream ofthe residual current circuit breaker (seen in direction of power flow)intended to realize the ‘protection in case of indirect contact’. For suchan arrangement it may occur that the surge current, which will bedischarged towards the protective conductor (PE) at overvoltage limita-tion, is interpreted as a residual current by the upstream residual currentcircuit breaker. Thus, the residual current circuit breaker will try to inter-rupt the circuit concerned. The product standard IEC 61008-1, applic-able for residual current devices, requires that residual current circuitbreakers must be surge-proof, but only to an impulse amplitude of 250A(8/20μs) or as a selective type of residual current circuit breaker (markedby |S |) up to an impulse amplitude of 3kA (8/20 μs). Arrestersof classes B and C, provided for application in the permanent installa-tion, however, have a much higher nominal impulse current dischargecapacity. Especially in class B arresters (lightning current arresters), theresidual current circuit breaker should be of such a quality (i) that itcould safely carry surge currents conducted by the lightning currentarrester and (ii) that there is no mistripping at such surge currentstressing.

A mistripping of the residual current circuit breaker is undesirable inview of the supplying safety of the consumer system and shall, therefore,be avoided. A remedy for this problem is an arrester installation (indirection of power flow) upstream of the residual current circuit breakeras shown in Figure 5.8.1.6.2 b. The discharged surge currents now nolonger flow through the residual current circuit breaker and cannot beinterpreted as residual current. Mistripping of the residual currentcircuit breaker is thus avoided.

A further argument for the installation of arresters upstream of the

Figure 5.8.1.6.2 a Installation of arresters downstream of the residual-currentdevice (RCD)


residual current circuit breaker can be obtained from a close considera-tion of Figure 5.8.1.6.2 c. All parts of the electrical installation, includingthe arrester, are subject to overloading. Overloaded arresters will eitherbe disconnected from the mains by the thermal disconnector accordingto E DIN VDE 0675 Part 6 (e.g., due to ageing reasons) or they areshort-circuited by a sudden high energy input. This short-circuitedarrester is a critical detail if installed downstream of the residual currentcircuit breaker. Because of its location between N and PE, it provides abonding link between neutral (N) and protective conductor (PE) down-stream of the residual current circuit breaker. Thus, if the equipment isfaulty, as shown in Figure 5.8.1.6.2 c, the current arising over exposedconductive parts of the equipment will not be clearly identified asresidual current and might, perhaps, not lead to the required disconnec-tion of the residual current circuit breaker. This double fault which, onthe one hand, provides a short-circuited arrester between N and PEalthough, on the other hand, defective equipment is rather rare, shouldalso be taken into consideration when considering the safety of thepersonnel.

If there is such a faulty arrester between N and PE in a constella-tion according to Figure 5.8.1.6.2 d, the residual current arising can beclearly identified at a defective piece of equipment downstream ofthe residual current circuit breaker, leading to a safe disconnection of theresidual current circuit breaker.

Therefore, arresters of classes B and C must be installed (in the direc-tion of power flow) upstream of the residual current circuit breaker. Tosafeguard the ‘protection at indirect contact’ in connection with theuse of arresters, especially those of classes B and C, only overcurrentprotective devices are accepted as disconnection elements.

A description now follows of the application of lightning current and

Figure 5.8.1.6.2 b Installation of arresters upstream of RCD


surge arresters in different system configurations: (i) TN, (ii) TT and (iii)IT systems. Such wiring proposals have been introduced in the Germanstandard draft E DIN VDE 0100–534/A1. The reader should note thatthe solutions presented show the application of lightning currentarresters in the area of the service entrance box (i.e., in the area in frontof the meter). Therefore, the competent power supplying companyshould be approached for permission to install lightning current arrestersbefore the meter.

5.8.1.6.2.1 TN system. For the TN-system overcurrent and residualcurrent protective devices are permitted for ‘protection in case of indirectcontact’. Lightning current and surge arresters (classes B and C) mayonly be installed behind overcurrent protective devices for ‘protection in

Figure 5.8.1.6.2 c Faulty arrester and faulty equipment downstream of RCD

Figure 5.8.1.6.2 d Faulty arrester upstream of RCD and faulty equipmentdownstream of RCD


case of indirect contact’ to safeguard measures of personnel protectionalso in case of an arrester fault.

Arresters used in connection with fuses must be considered as over-current protective equipment. Depending on the strength of the nextbackup supply fuse and on the capacity of the arrester backup fuse,an additional separate backup fuse in the arrester branch must beprovided.

Rated voltages valid for the use of class B, C and D arresters in the TNsystem are as follows:

Uc ≥ 1.1 × UN

For a 230/400V system, this becomes

URc ≥ 1.1 × 230V = 253V

Figure 5.8.1.6.2.1 a shows lightning current and surge arresters in theTN–C–S system. This shows that class D surge arresters are installeddownstream of the residual current circuit breaker. These class D surgearresters for terminal protection usually provide transverse surge protec-tion (surges between L and N). At a surge limitation between L and Nthere is no surge current discharge to PE, thus the residual current circuitbreaker cannot interpret a residual current. Class D surge arresters areconceived for a nominal discharge capability of 1.5kA (8/20 μs). Onusing a surge current proof residual current circuit breaker, these surgecurrents cannot trip or damage the residual current circuit breaker.Figures 5.8.1.6.2.1 b to e show the arresters introduced in chapters 5.8.2to 5.8.4 within the concept of lightning protection zones and thenecessary lightning and surge protection measures for a TN–C–S system.

Lightning current and surge arresters in the TN–S system are shownin Figures 5.8.1.6.2.1 f to j .

Figure 5.8.1.6.2.1 a Application of arresters in the TN–C–S system


Figure 5.8.1.6.2.1 b Lightning protection equipotential bonding in the TN–Csystem: Mounting diagram DEHNport®

Figure 5.8.1.6.2.1 c Lightning protection equipotential bonding in the TN–Csystem: Mounting diagram DEHNbloc® (three pole)

Figure 5.8.1.6.2.1 d Overvoltage protection in the TN–C system: Mountingdiagram DEHNguard® / DEHNguard® T


Figure 5.8.1.6.2.1 e Overvoltage protection of the terminal equipment in the TN–C–S system: Mounting diagram surge protective deviceNM–DK 280 (alternative protective gear: NSM–, SF or Sprotector)

Figure 5.8.1.6.2.1 f Application of arresters in the TN–S system

Figure 5.8.1.6.2.1 g Lightning protection equipotential bonding in the TN–Ssystem: Mounting diagram DEHNport®


Figure 5.8.1.6.2.1 h Lightning protection equipotential bonding in the TN–Ssystem: Mounting diagram DEHNbloc® (three pole) /DEHNbloc® (one pole)

Figure 5.8.1.6.2.1 i Overvoltage protection in the TN–S system: Mountingdiagram DEHNguard® / DEHNguard® T

Figure 5.8.1.6.2.1 j Overvoltage protection of terminal equipment in the TN–Ssystem: Mounting diagram surge protective device NSM-protector (alternative protective gear: NM–DK 280, S orSF protector)


5.8.1.6.2.2 TT-system. In the TT-system overcurrent protective devices,residual current devices and in special cases also fault voltage-operatedprotective devices are permitted for ‘protection in case of indirectcontact’. Also here, the lightning current and surge arresters are installeddownstream of the overcurrent protective devices (Section 5.8.1.6.2).

By installing class B and C arresters in the TT-system the conditionsfor the use of overcurrent protective devices in ‘protection in case ofindirect contact’ must be fulfilled. Should there be a fault (i.e., in the caseof a defective arrester), currents must flow which would cause an auto-matic disconnection of the overcurrent protective devices within 5 s. Inother words, short-circuit currents must flow. An arrester arrangement inthe TT system, as in Figure 5.8.1.6.2.1 a and 5.8.1.6.2.1 f, show that forthe TN system there would be no short-circuit currents in the case of afault, but only earth-fault currents. Earth-fault currents, however, cannottrip an upstream overcurrent protective device in the required timeperiod. Class B and C arresters in the TT system are therefore installedin L towards N. This ensures that in case of a defective arrester a short-circuit current can be generated in the TT-system which will trip the nextbackup overcurrent protective device.

As, however, lightning currents basically arise towards earth (PE), anN–PE arrester must form the bond between N and PE. The N–PE light-ning current arrester must meet especially high demands as it must beable to carry the lightning partial currents of L1, L2, L3 and N non-destructively.

The following rated voltages, Uc, are relevant to the application ofarresters in the TT-system:

arresters between L and N

Uc ≥ 1.1 × UN

arresters between N and PE

Uc ≥ 1.1 × UN × 0.5

that is, at least ≥ 250V AC. Thus, for a 230/400V TT system:

with arresters between L and N

Uc ≥ 1.1 × 230V = 253V

with arresters between N and PE

Uc ≥ 1.1 × UN × 0.5 = 126.5V

that is, at least UC ≥ 250V.

The lightning current-carrying capacity of class B arresters is rated inaccordance with lightning protection levels I, II, III/IV of IEC 61024-1.Concerning the lightning current carrying capacity of the arrestersbetween N and PE the following data for lightning protection level mustbe achieved as a minimum:


I Iimp ≥ 100kA (10/350 μs)II Iimp ≥ 75kA (10/350μs)III/IV Iimp ≥ 50kA (10/350μs).

Class C arresters are also installed between L and N as well as between Nand PE. A discharge capacity of iN > 20kA (8/20 μs) is required for thearrester between N and PE in connection with class C arresters.

Figure 5.8.1.6.2.2 a shows lightning current and surge arresters in theTT system. As in the TN system, class D surge arresters are installedafter the residual current circuit breaker. The surge current discharged bythese surge arresters usually is so low that it will not be interpreted asresidual current by the residual current circuit breaker. Nevertheless, asurge current proof residual current circuit breaker should be provided.Figures 5.8.1.6.2.2 b to e show installations of this kind.

Figure 5.8.1.6.2.2 a Application of arresters in the TT system

Figure 5.8.1.6.2.2 b Lightning protection equipotential bonding in the TTsystem: Mounting diagram DEHNport® / DEHNgap B


Figure 5.8.1.6.2.2 c Lightning protection equipotential bonding in the TTsystem: Mounting diagram DEHNbloc® / DEHNgap B

Figure 5.8.1.6.2.2 d Overvoltage protection in the TT system: Mounting diagramDEHNguard®/DEHNgap C, DEHNguard® T/DEHNgap C

Figure 5.8.1.6.2.2 e Overvoltage protection of terminal equipment in the TTsystem: Mounting diagram surge protective adapter S/SFprotector (alternative protective gear: NSM protector,NM–DK 280)


5.8.1.6.2.3 IT-system. Overcurrent protective devices, residual currentdevices, insulation monitoring devices, as well as fault voltage-operatedprotective devices in special cases, are permitted for the IT-system as‘protection in case of indirect contact’. Whereas, in the TN- or TT-systemthe ‘protection in case of indirect contact’ at first fault is guaranteed bythe corresponding disconnection conditions of the overcurrent protect-ive devices or residual current devices, there is only an indication of faultin the IT-system. A contact voltage that is too high cannot occur becausean earth reference is made in the IT-system at first fault. With regard toits operating state, the IT-system then changes over into a TN- or TT-system. An IT-system can, therefore, safely continue after the firstfault, so that processes or productions (e.g., in the chemical industry)already begun can still be finished. At the first fault the protectiveconductor PE takes the potential of the defective phase, which is notdangerous because through the protective conductor all exposed conduct-ive parts and touchable metal parts have this potential, so there are nodangerous potential differences to be bridged.

Nevertheless, it must be considered that in case of the first fault, theIT-system potential of the non-faulty conductors to earth correspondsto the potential between the phases. Thus, in a 230/400V IT-system thereis a potential of 400V at the non-faulty arresters in the case of a defectivearrester. This possible operating state must be taken into account onselecting the arresters with regard to their rated voltage. For the useof arresters of class B, C and D in the IT-system the following ratedvoltages are applicable:

Uc ≥ 1.1 × UN × √ 3

thus, for a 230/440 V–IT-system,

Uc ≥ 1.1 × 230V × √ 3Uc > 440V

For a second fault in the IT-system a protective device must then betripped. With respect to the use of arresters in the IT-system in connec-tion with a protective device for the ‘protection in case of indirect con-tact’ the statements of section 5.8.1.6.2 are applicable. Thus, in theIT-system too, the installation of class B and class C arresters upstreamof the residual current circuit breaker is advisable. Figure 5.8.6.2.3 ashows lightning current and surge arresters in the IT-system.

Different arresters in the IT-system are shown in Figures 5.8.1.6.2.3 band c.

5.8.1.6.3 Selection of arrester backup fuses. Arrester data sheetsusually indicate the maximum permissible backup fuse for the arrester.This indication is required by the product standards IEC 61343-1/DINVDE 0675 part 6.


The primary task of this arrester backup fuse is to safeguard the short-circuit capability. Standardized testing of the arrester’s short-circuitcapability will prevent dangerous sparking of the arrester in the case ofan internal short circuit (which may be due to a surge current thatexceeds the nominal discharge capacity of the arrester) and the generated50Hz short-circuit current. Special types of arrester have integrated this

Figure 5.8.1.6.2.3 a Application of arresters in the IT system

Figure 5.8.1.6.2.3 b Lightning protection equipotential bonding in the IT system:Mounting diagram DEHNport®

Figure 5.8.1.6.2.3 c Surge protection in the distribution cabinet in the IT system:Mounting diagram DEHNguard® / DEHNguard® T


backup fuse in their enclosure. Most arresters on the market, however,are not equipped with such a backup fuse. Therefore, the next upstreamsystem fuse can be taken as the backup fuse for the arrester if its nominalvalue does not exceed that of the maximum permissible fuse (Figure5.8.1.6.3 a). If, however, the nominal value of the system fuses F1–F3exceeds the nominal value of the maximum backup fuses for the arrest-ers, separate backup fuses having the nominal value of the maximumpermissible backup fuse must be installed before the arrester (Figure5.8.1.6.3 b).

In addition to securing short-circuit capability there is still anotherfunction of an arrester backup fuse which is especially important forclass B arresters (lightning current arresters). These are mostly designedas spark gap arresters in view of the high electrical and mechanical stresson discharging a lightning current. This guarantees a high nominal dis-charge capability of the arrester. Spark gap arresters generate a 50Hz

Figure 5.8.1.6.3 a Use of system fuses as arrester backup fuses

Figure 5.8.1.6.3 b Application of separate arrester backup fuses


mains follow-current which must be safely quenched after the decay ofthe lightning interference. This mains follow-current can be as high as theprospective short-circuit current at the place of installation of the light-ning current arrester. Spark gap arresters are usually able to quenchmains follow-currents having a prospective short-circuit current value ofabout 4kAeff (50Hz). If the prospective short-circuit current exceeds thearrester mains follow-current quenching capability, the backup fuse mustdisconnect the mains follow-current.

Most service entrances have a prospective short-circuit current below3kAeff (50Hz) so that there are few practical cases where the backupfuse must disconnect a mains follow-current higher than 4kA.

In particular, arresters based on spark gaps (i.e. lightning currentarresters), due to the operation of which a mains follow-current can begenerated, load their upstream fuses (arrester backup fuses) with mainsshort-circuit currents. To keep this loading of parts of the power systemas low as possible, the spark gaps must be designed in such a way that notevery discharge process generates a mains follow-current. Spark gapsmeeting these requirements are constructed as multiple gliding sparkgaps (as used in the lightning current arresters DEHNport©, DEHN-bloc©, DEHNbloc© NH). On the operation of this type of spark gap, twopartial arcs will be generated which oppose the emergence of a mainsfollow-current already from the beginning of the arc by the total voltagedrop of both arcs.

In Figure 5.8.1.6.3 c a lightning current arrester with tandem glidingspark gap is compared with a usual simple spark gap with respect to thefrequency of a generated mains follow-current. This diagram reveals that

Figure 5.8.1.6.3 c Comparison of the follow-current frequency (in %) oflightning current arresters with spark gaps


mains follow-currents are less frequent with a multiple gliding sparkgap and that the stressing of the arrester backup fuse and the upstreampower system by mains short-circuit currents is considerably reduced.

With respect to the use of lightning current arresters in power systemsand fuses it must be taken into account that they are first loaded bylightning surge currents followed by the mains short-circuit currents. Incontrast to mains follow-currents, lightning surge currents in the powersystem cannot be avoided as these are impressed currents. The perform-ance of NH fuses at lightning surge current loading has been closelyexamined. Figure 5.8.1.6.3 d shows the fuse characteristics. Dependingon the nominal current of the fuse and the surge current in the test, thereare three different characteristics of NH fuses: (i) no melting, (ii) meltingand (iii) explosion.

(i) No melting. The energy input by the lightning surge current is too low forthe fuse strip to be melted. An installation of the arresters (according toFigure 5.8.1.6.3 a) guarantees the continued supply to the downstreamconsumer as is the case at a configuration according to Figure 5.8.1.6.3 b.

(ii) Melting. The energy of the lightning surge current is high enough to meltthe fuse strip of the NH fuse and thus to interrupt the current paththrough the fuse. Figure 5.8.1.6.3 e shows the oscillogram of a fuse meltingby lightning surge currents. Typical for the fuse performance is that theimpressed lightning surge current keeps on flowing without being influ-enced by the behaviour of the fuse. After the melting integral of the fusehas been exceeded by the lightning surge current, an arc will be generatedin the fuse which will be realized by the potential over the fuse.

For the arrester configuration according to Figure 5.8.1.6.3 a, the

Figure 5.8.1.6.3 d Performance of NH fuses during the impulse current loading10/350μs


downstream consumer system then will be disconnected. Thus, the solu-tion variant according to Figure 5.8.1.6.3 b comes to the fore. Sometimes itis suggested to choose fuses of size F4–F6 selectively to the fuses F1–F3.Practically this means that the relation of the nominal currents of the fusesF1–F3 to F4–F6 is 1.6: 1. This selective characteristic of fuses is onlyrelevant with regard to the mains follow-currents (50Hz) but not withregard to lightning surge currents.

To emphasize this statement consider the following example. Under theaspect of selectivity let the nominal current of the fuses F1–F3 be 160Aand the nominal current of the fuses F4–F6 be 100A. This configurationis loaded by a lightning surge current of 25kA (10/350 μs) for each path.At such a loading F1–F3 as well as F4–F6 will be tripped according toFigure 5.8.1.6.3 d. Such a configuration is not selective under lightningsurge current loading! Thus, the downstream consumer system would bedisconnected.

More severely still, the voltage drop of the melting fuses F4–F6 2kV(according to 5.8.1.6.3 e) occurs in the arrester branch, that is to say inparallel with the protected consumer-system. This voltage drop is a drivingvoltage for downstream arresters and might cause their overloading. Toavoid this effect, arrester fuses F4–F6 must be as strong as possible which,in practice, means that F4–F6 only must be used, if F1–F3 are strongerthan the indicated maximum permissible arrester backup fuse. The nom-inal current of F4–F6 then shall be as high as the maximum permissiblearrester backup fuse.

(iii) Explosion. The energy of the lightning surge current is so high that the fusestrip of the NH fuse evaporates in an explosion. As a result, the enclosureof the NH fuse may split (Figure 5.8.1.6.3 f). Beside these mechanical

Figure 5.8.1.6.3 e Current and voltage at a melting 25A NH fuse during alightning impulse current loading (10/350μs)


effects there are also the electrical aspects described under ‘melting’ (note(ii) above).

Different problems require solutions for the arrester backup fuses intheir fields of application. Consider the following:

(i) Protection against indirect contact in case of defective arresters. This is thetask of the backup fuses of all arresters of classes B, C and D (for arrestersin class D, additional residual current circuit breakers can be used). Forthis purpose the fuses must be designed in such a way that the defectivearresters will be safely disconnected from the low-voltage system in therequired time.

(ii) Securing short-circuit withstand capability of the arresters. To guarantee theshort-circuit withstand capability indicated by the producer the permittedmaximum backup fuse must, under no circumstances, be exceeded.

(iii) Disconnection of too high mains follow-currents. Particularly in the case oflightning current arresters based on spark gaps, mains follow-currentsmay arise. On application of the permitted maximum backup fuse, themaximum follow-current quenching capacity of the arrester is also

Figure 5.8.1.6.3 f NH fuse burst due to lightning impulse current loading


reached. If there is a weaker backup fuse, mains follow-currents will bedisconnected which might be safely quenched by the arrester itself. There-fore, the backup fuse of a lightning current arrester must be as strong aspossible and separate backup fuses in the arrester branch should beavoided if the system conditions allow it.

If the system fuses F1–F3 (Figure 5.8.1.6.3 b) are weaker than themaximum permitted arrester backup fuse and additionally F1–F6 arerequired (allowing the disconnection of the arrester branch for mainten-ance) then for F4–F6 NH-disconnecting blades should be used.

To conclude the subject of ‘arrester backup fuses’ consider yet againthe follow-current extinguishing capability of the lightning currentarrester DEHNport® Maxi introduced in section 5.8.1.2.

Figure 5.8.1.6.3 g shows the typical breaking oscillogram (uninfluencedshort-circuit surge current 37kAeff’, cos φ = 0.23) of the arrester DEHN®

Maxi in RADAX-flow technology. The spark gap arc voltage shown inthe left part of the Figure is in its amplitude almost equal to the systemvoltage. The typical ‘dipping’ of the system voltage of conventional sparkgaps will not occur. This excludes interference in electronic devices whichare sensitive to voltage dips or voltage supply deviations. In the right partof the oscillogram the effective limitation of the mains follow-current isreadable. It represents the uninfluenced (i.e., the theoretically possible) aswell as the following short-circuit current through the arrester. Obviouslyit is only a very low share of the theoretically possible current that loadsthe arrester and thus the whole low voltage system. A further effect ofthe high arc resistance is the reduction of the duration of current flow.

The oscillogram shows that, even in case of an impulse short-circuitcurrent of 37kAeff, the pre-arcing current through the examined arresterin RADAX-flow technology is only about 1.7kA. If this value is trans-ferred to a diagram, as is usual for the selectivity considerations of over-current protective devices (fuses, circuit breakers), one obtains Figure5.8.1.6.3 h. This shows the let-through current integral (∫ I 2t) of aRADAX-flow arrester at different short-circuit currents. For better clas-sification the melting integrals of NH fuses of different nominal currents

Figure 5.8.1.6.3 g Interruption of a short-circuit current by RADAX-flowtechnology (DEHNport® Maxi)


are indicated. Arresters in RADAX-flow technology can, as Figure5.8.1.6.3 h shows, effectively limit short-circuit currents of 50kAeff.

The integral of the let-through current remains lower than the meltingintegral of a 40A NH fuse, meaning that this fuse will not trip. The let-through current limitation secures the selectivity between the overcurrentprotective devices in the low-voltage consumer system and the lightningcurrent arresters.

On using an arrester of class B (lightning current arrester) inRADAX-flow technology in the main current supply system the trippingof the backup fuse at the service entrance or meter board by mainsfollow currents is avoided. Operation of the lightning current arresterremains practically unnoticed by the user.

Sources

IEC 61643–1: ‘Surge protective devices connected to low-voltage powerdistribution systems – Part 1: Performance requirements and testingmethods’. International Electrotechnical Commission, 3 rue de Varembe,Geneva, Feb. 1998E DIN VDE 0675 Teil 6: ‘Überspannungsableiter zur Verwendung in Wech-selstromnetzen mit Nennspannungen zwischen 100V und 1000V’. (VDEVerlag, GmbH, Berlin/Offenbach) Nov.1989E DIN VDE 0675-6/A1 (VDE 0675 Teil 6/A1): ‘Überspannungsableiter zurVerwendung in Wechselstromnetzen mit Nennspannungen zwischen 100Vund1000 V’. Änderung A1 zum Entwurf

Figure 5.8.1.6.3 h Selectivity limit current DEHNport® Maxi at differentbackup fuses


DIN VDE 0675-6 (VDE 0675 Teil 6) (VDE Verlag, GmbH, Berlin/Offenbach)March 1996E DIN VDE 0675-6/A2 (VDE 0675 Teil 6/A2): ‘Überspannungsableiter. Teil 6:Verwendung in Wechselstromnetzen mit Nennspannungen zwischen 100Vund 1000V’. Änderung A2 zum EntwurfDIN VDE 0675-6 (VDE 0675 Teil 6) (VDE Verlag, GmbH, Berlin/Offenbach)Oct. 1996IEC 61312-1: ‘Protection against lightning electromagnetic impulse – Part 1:General principles’. International Electrotechnical Commission, Geneva,Feb. 1995IEC 60664-1: ‘Insulation coordination for equipment within low-voltage sys-tems – Part 1: Principles, requirements and tests. International Electro-technical Commission, Geneva, Oct. 1992IEC 60364-4-41: ‘Electrical installations of buildings – Part 4: Protection forsafety’. Chapter 41: ‘Protection against electric shock’. International Electro-technical Commission, Geneva, Oct. 1992IEC 61008-1: ‘Residual current operated circuit-breakers without integralovercurrent protection for household and similar uses (RCCBs). – Part 1:General principles’. International Electrotechnical Commission, Geneva,Dec. 1996IEC 61024-1: ‘Protection of structures against lightning – Part 1: Generalprinciples’. International Electrotechnical Commission, Geneva, March 1990E DIN VDE 0100-534/A1 (VDE 0100 Teil 534/A1): ‘Elektrische Anlagen vonGebäuden. Auswahl und Errichtung von Betriebsmitteln. Schaltgeräte undSteuergeräte, Überspannungs-Schutzeinrichtungen – Änderung A1 (Vor-schlag für eine Europäische Norm)’. (VDE Verlag, GmbH, Berlin/Offenbach)Oct. 1996DEHN u. SÖHNE: ‘Installation of SPD for power supply systems and equip-ment’. DS 655/E/397. (Dehn + Söhne, Neumaret) March 1997DEHN u. SÖHNE: ‘Energy coordination – The selective surge protection’. DS641/E/597. (Dehn + Söhne, Neumaret) May 1997HASSE, P., and WIESINGER, J.: ‘Handbuch für Blitzschutz und Erdung’ (VDEVerlag, Berlin; Pflaum Verlag, München, Fourth edn, 1993)HASSE, P., and WIESINGER, J.: ‘EMV – Blitz-Schutzzonen-Konzept’ (VDEVerlag, Berlin; Pflaum Verlag, München, 1993)RAAB, V.: ‘Blitz und Überspannungsschutz-Massnahmen in NS-Anlagen’,Elektropraktiker, Berlin, Teil 1, 1996, 50, (11), pp. 944–951; Teil 2, 1996, 50,(12), pp. 1043–1046.HASSE, P., and EHRLER, J.: ‘Konzeptionelles Vorgehen beim Blitz und Über-spannungsschutz komplexer Anlagen’, Elektrotechnik, 1996, (2), pp. 53–58;1996, (3), pp. 69–73; 1996, (6), pp. 49–54.POSPIECH, J., NOACK, F., BROCKE, R., HASSE, P., and ZAHLMANN, P.:‘Blitzstrom–Ableiter mit Selbstblas-Funkenstrecken – Ein neues Wirkprinzipfür den Blitzschutz in Niederspannungsnetzen’, Elektrie, Berlin, 1997, 51,pp. 9–10.RAAB, V., and ZAHLMANN, P.: ‘Folgestrombegrenzender Blitzstrom-Ableiterfür Hauptstromversorgungssysteme’, Elektropraktiker, Berlin, 1997, 51, p. 12.HASSE, P., ZAHLMANN, P., POSPIECH, J., and NOACK, F.: ‘Generationswech-sel bei Blitzstrom–Ableiter für Niederspannungsanlagen’, etz, 1998, No. 7–8


5.8.2 Arresters for information technology

According to IEC 61644-1/DIN VDE 0845 the generic term ‘surge pro-tective devices (SPDs)’ in the field of information technology does notonly mean modules but also includes protective circuits which limit theovervoltages in systems and equipment to permissible values.

Protective circuits gradually reduce surges by the series connection ofovervoltage limiting modules and decoupling elements (Figure 5.8.2 a).Overvoltage limiting elements with decreasing limiting voltage anddecreasing energy loadability are connected in series. Decoupling elem-ents can be resistors, inductors, capacitors or filters. There are two typesof arrester depending on the requirements and loading at their place ofinstallation in accordance with the concept of lightning protection zones.These are, namely, (i) lightning current arresters (which are tested by animpulse current wave 10/350 μs) and (ii) surge arresters (which are testedby an impulse current wave 8/20 μs).

Highest demands, with regard to their discharge capability, are madeon lightning current arresters. Within the scope of the lightning andsurge protection system they are installed at the interface of the lightningprotection zone 0A/1. They prevent disturbing lightning partial currentsfrom penetrating into the information technology network.

To guarantee interference-free and surge-proof operation of informa-tion technology equipment a disturbance arising in the informationsystem must be limited to a level which is below the interference ordestruction limit of the equipment. The interference and destruction

Figure 5.8.2 a Graded protection (stepped protection in accordance with DINVDE 0845)


limits of the equipment, however, are largely unknown and not indicated.A starting point is offered by the indicated surge immunity againstimpulse shaped surges which has been tested in EMC surge immunitytests according to IEC 61000-4-5/EN 61000-4-5.

To avoid disturbances or even the destruction of information tech-nology equipment, surge arresters must limit the disturbing influences tovalues below the surge immunity of the equipment to protect. In contrastto the selection of protective devices in power systems which haveuniform conditions in the 230/400V system regarding voltage andfrequency, there are different kinds of signals to be transmitted ininformation technology systems in terms of the following:

• voltage (e.g., 0–10V)

• current (e.g., 0–20mA, 4–20mA)

• signal supply (symmetrical, unsymmetrical)

• frequency (DC, LF, HF)

• type of signal (analogue, digital).

Each of these electrical parameters of the signal to be transmitted cancontain the information which shall be actually transmitted. Signalsmust therefore not be influenced by the installation of lightning currentand surge arresters in information technology systems.

As for power engineering, there are different types of arresters for theindividual places of application in the information technology, such as (i)in a permanent installation (Figure 5.8.2 b), (ii) at socket outlets (Figure5.8.2 c) and (iii) at equipment inputs (Figure 5.8.2 d).

Figure 5.8.2 e shows the installation of lightning current and surgearresters at computing centre interfaces in accordance with the conceptof lightning protection zones. To reduce the influence of the electro-magnetic field, building or room shielding measures have been realized atthe interfaces of lightning protection zones 0 and 1 as well as at lightningprotection zones 1 and 2, as has already been detailed in Section 5.2. Thepower system is included into the lightning protection equipotentialbonding by lightning current arresters at the interface of lightning pro-tection zones 0 and 1. The local equipotential bonding at the transitionof the lines from lightning protection zones 1 to 2 is achieved by surgearresters. The surge protection of the information technology system isstructured analogously.

Arresters used in the information technology side of a system pro-tected as described will be introduced by way of examples in the followingSections. To facilitate understanding the protective devices are classifiedaccording to whether they are mainly used in measuring and controlsystems (chapter 5.8.2.1) or mainly in data networks/systems (chapter5.8.2.3). Combined protective devices for power and information tech-nology equipment inputs (chapter 5.8.2.2) are also introduced.


Figure 5.8.2 b Blitzductor®s CT for protecting the measuring and controltechnology of a petrochemical system (installed in a protectivecabinet)

Figure 5.8.2 c Data socket outlets with surge arresters

Figure 5.8.2 d Pluggable surge arresters for use at terminal equipment


Sources

IEC 61644-1 Ed.1: ‘Surge protective devices connected to telecommunica-tions and signalling networks – Part 1: Performance requirements and test-ing methods’. International Electrotechnical Commission, Geneva, Oct. 1998DIN VDE 0845 Teil 1: ‘Schutz von Fernmeldeanlagen gegen Blitzeinwirkun-gen, statische Aufladungen und Überspannungen aus Starkstromanlagen.Massnahmen gegen Überspannungen’ (VDE Verlag, GmbH, Berlin/Offenbach) Oct. 1987E DIN VDE 0845 Teil 2: ‘Schutz von Einrichtungen der Informationsverarbei-tungs und Telekommunikationstechnik gegen Blitzeinwirkungen, Entladungstatischer Elektrizität und Überspannungen aus Starkstromanlagen.Anforderungen und Prüfungen von Überspannungs-schutzeinrichtungen’(VDE Verlag, GmbH, Berlin/Offenbach) Oct. 1993IEC 61000-4-5: ‘Electromagnetic compatibility (EMC) – Part 4: Testing andmeasurement techniques (Section 5): Surge immunity test’. InternationalElectrotechnical Commission, Geneva 1995HASSE, P., and WIESINGER, J.: ‘EMV-Blitz-Schutzzonen-Konzept München(Pflaum Verlag, Berlin/Offenbach: VDE Verlag, Berlin/Offenbach)DEHN u. SÖHNE: ‘Selection and installation of surge protective devices.Type Blitzductor® CT for protection of control and instrumentation systemsacc. to IEC 61312-1. DS 656/E/897’, Aug. 1997

5.8.2.1 Arresters for measuring and control systems

Blitzductor®s as protective devices for measuring and control systemshave had a proven record for decades. The energy coordinated arresterfamily Blitzductor® CT will serve as an example to describe the construc-tion, effects and application of this type of arrester.

Figure 5.8.2 e Lightning partial current proof interface connection for acomputer centre with asymmetrical interface (V24/RS 232 C)


5.8.2.1.1 Blitzductor® CT: Construction and mode of functioning. TheBlitzductor® CT is designed in two parts (Figure 5.8.2.1.1 a): Protectionmodules are fitted on a universal base (which can be used almostindependently from the operating parameters of the circuit to beprotected like a modular terminal block). The Blitzductor® CT, as a four-pole structure (Figure 5.8.2.1.1 b), has two input and two outputterminals to connect one double wire (type D) or two single wires (typeE). Since it has a width of only 12mm (2/3 module) and a height of58mm a space-saving installation is possible.

A choice of more than 40 protective modules is available to provide foroptimal discharge capability, protection and performance of the surgeprotective device for the interface to be protected. These can be pluggedinto the universal base (Figure 5.8.2.1.1.c, a). By means of a contact

Figure 5.8.2.1.1 a Blitzductor® CT with different protective modules

Figure 5.8.2.1.1 b Blitzductor® CT, type MD, for application in earth-free signallines (e.g., telephone lines)


mechanism in the base, the protective module can be exchanged duringits live state without interruption of the signal transmission. With thesebase elements a universal pre-wiring of the system becomes possiblewithout even knowing the later operating parameters.

If, later, the operating parameters are known then adequate protectivemodules are employed. This changes the modular terminal blocks intoan adjusted protective device. This is particularly advantageous whenplanning in accordance with the concept of lightning protection zones.Use of the Blitzductor® CT bases, which will be already inserted at thepre-installation stage, means that space can be reserved for completesurge protection. The protective devices are safely earthed via the DINrail (according to EN 50 0229) and the snap-on base support.

To realize the complex protection philosophy there are also screenterminals at the base (for contacting the screens of cables). Direct orindirect earthing of the cable screen is possible by the insertion of a gasdischarge arrester into the base bay (Figure 5.8.2.1.1 c, b). Thus earthingand equipotential bonding systems can be realized which are adjustedaccording to the system to protect.

There are three ‘performance categories’ of the Blitzductor® CT. Theseprotective types of module include: (i) the lightning current arrester, (ii)the surge arrester and (iii) the combined arrester. Thus

(i) Protective module type B (Figure 5.8.2.1.1 d) is designed as a ‘lightningcurrent arrester’ for impulse currents Iimp: 2.5kA (per wire) wave shape10/350μs.

(ii) Protective module type M is dimensioned as a ‘surge arrester’ for nominaldischarge currents isn: 10kA (per wire) wave shape 8/20μs (Figure 5.8.2.1.1 e).

Figure 5.8.2.1.1 c (a) Blitzductor® CT: left: plug-in protective module; right:base


Figure 5.8.2.1.1 c (b) Blitzductor® CT: left: contacts: base/protective module;right: circuit

Figure 5.8.2.1.1 d Blitzductor® CT, protective module type B: top: basic circuitdiagram; bottom: rated discharge current IIMP = 2.5kA(10/350μs) per wire

Figure 5.8.2.1.1 e Rated discharge current isn = 10kA (8/20μs) for protectivemodules, type M


• Protective module ME (Figure 5.8.2.1.1 f) protects earthed signalwires (a typical application is for example the Pt 100 four-phasemeasurement).

• Protective module MD (Figure 5.8.2.1.1 g) is provided for non-earthedwire pairs (as for symmetric signal wires which are connected via isolat-ing transformers).

• Protective module ME/C (Figure 5.8.2.1.1 h) protects optocoupler inputsor inputs with intrinsic protective circuit (clamping diodes) and thereforehas decoupling resistors at the output.

• Protective module MD/HF is designed for the protection of HF-transmission links and is equipped with a diode-matrix (Figure5.8.2.1.1 i).

Figure 5.8.2.1.1 j Basic circuit diagram, module MD/Ex

Figure 5.8.2.1.1 h Basic circuitdiagram, module ME/C

Figure 5.8.2.1.1 f Basic circuitdiagram, module ME

Figure 5.8.2.1.1 i Basic circuitdiagram, module MD/HF

Figure 5.8.2.1.1 g Basic circuitdiagram, module MD


• Protective module MD/Ex (Figure 5.8.2.1.1 j) (having a 500V ACwithstand capability to earth) is provided for instrinsically safe meas-uring circuits.

(iii) Protective module B is designed as a ‘combined arrester’ for impulse cur-rents Iimp: 2.5kA (10/350 μs) per wire, however, with a protection level like asurge arrester protective module M (Figure 5.8.2.1.1 k).

Basically, there are two types of Blitzductor® CT: E types (for con-necting two single wires and for limiting surges between every wire andearth) and D types (for connecting a double wire and for limitingsurges between the two wires). The voltage limiting characteristic ofboth types is shown in Figure 5.8.2.1.1 l. Other characteristics toconsider include:

(i) Nominal voltage. The nominal voltage indication on the Blitzductor®s CTis the upper value of the signal voltage range which can be transmittedover the protective device under nominal conditions without any limitingeffects of the protective device. The nominal voltage is indicated as a DC

Figure 5.8.2.1.1 k Blitzductor® CT, protective module type B . . . . Top: basiccircuit diagram; bottom: rated discharge current IIMP = 2.5kA(10/350μs) per wire, however, protective level like surgearrester (M)


value. On AC voltage transmission the AC peak value must not exceed thespecified nominal voltage. Figure 5.8.2.1.1 m shows nominal voltages fordifferent types of Blitzductor® CT.

(ii) Protection level. The protection level of the Blitzductor® CT characterizesits performance in limiting the output voltage. The specified protectionlevel value is higher than the maximum value of the limiting voltages in thetests, the measured limiting voltage being the maximum voltage measuredat the terminals of the surge protective device during the loading withsurge currents and/or surge voltages (with specified impulse waveshape andamplitude). The standardized procedure is as follows.

• Limiting voltage at a 1 kV/μs steepness of the applied test impulse

This test (Figure 5.8.2.1.1 n) determines the operating characteristic ofgas discharge arresters. These protective elements have a ‘switch charac-teristic’: The mode of function of a gas discharge arrester can bedescribed as a switch, the resistance of which can ‘jump’ automaticallyfrom > 10GΩ (in the inactive state) to values < 0.1Ω (active state) if acertain voltage is exceeded, so that the overvoltage is almost short-circuited (Figure 5.8.2.1.1 o). The activating voltage of the gas dischargearrester depends on the rate of rise (du/dt) of the incoming impulse.Hence, the higher the rate of time the higher the activating voltage ofthe gas discharger arrester. To compare the operating values of differentgas discharge arresters a rate of rise of 1kV/μs will be applied at theelectrodes of the gas discharge arrester and the activating value will bedetermined.

• Limiting voltage at nominal discharge current

This test (Figure 5.8.2.1.1 p) is for determining the limiting characteristic(Figure 5.8.2.1.1 q) of protective elements with constant limitingcharacteristic.

Figure 5.8.2.1.1 l Surge limitation of the Blitzductor® CT types . . . E and . . . D


Figure 5.8.2.1.1 m Nominal voltage data for different Blitzductor® CT types

Figure 5.8.2.1.1 n Test assembly for the determination of the limiting voltage ata voltage rate of rise du/dt = 1 kv/μs

Figure 5.8.2.1.1 o Sparkover characteristic of a gas-filled surge arrester, at du/dt = 1 kv/μs


(iii) Nominal current

The nominal current IN of the Blitzductor® CT characterizes the maximumpermissible operating current of the measuring and control circuit to pro-tect (Figure 5.8.2.1.1 r ). IN is determined by the current carrying capacityand the power loss of the impedances used for the decoupling between gasdischarge arresters and fine protective elements and by the follow-currentextinguishing capability of the gas discharge arresters. It is indicated as aDC value. Table 5.8.2.1.1 a indicates the nominal currents of differenttypes of Blitzductor® CT.

(iv) Cut-off frequency

The cut-off frequency describes the behaviour of the Blitzductor® CT inrelation to frequency (Figure 5.8.2.1.1 s). The cut-off frequency is the fre-quency which causes (under defined test conditions) an attenuation loss aE

of 3dB (compare E DIN VDE 0845 Part 2: 1993-10). This frequencyusually refers to a 50 Ω system.

Figure 5.8.2.1.1 p Test assembly for the determination of the limiting voltage atnominal discharge current isn

Figure 5.8.2.1.1 q Limiting voltage at nominal discharge current


(v) Energy coordination, coordination characteristics

The regulations for energy coordination specified in section 5.8.1.6.1 arealso valid for information technology systems. Owing to the low operatingcurrents of these systems, however, a coordination of arresters by ohmicresistor elements is also possible here. The Blitzductor® CT has integrateddecoupling elements so that external decoupling measures can be avoided:These protective devices can be directly installed side by side.

Whereas, in the case of a low-voltage consumer system, one can gener-ally proceed from a surge immunity of the system which has been speci-fied in the scope of the insulation coordination, proceeding along similarlines would be a failure for information technology interfaces. Only bylegal demands for an adequate immunity of the interfaces of informationtechnology equipment due to the EC-general regulations for EMC andthe standardization of reproducible testing methods is it possible todescribe the important parameters needed for the surge protection of

Figure 5.8.2.1.1 r Nominal current of Blitzductor® CT

Table 5.8.2.1.1 a Nominal currents of the Blitzductor® CT-types

Figure 5.8.2.1.1 s Typical frequency response of a Blitzductor® CT


input circuits. To decide whether the equipment to protect can withstandthe residual let-through impulse of an upstream arrester, a comparisonof the arrester let-through parameters and the impulse parameters of thespecified equipment interface immunity is necessary. This point is shownin Figure 5.8.2.1.1 t.

The standard series IEC 61000-4 . . . /EN 61000-4 . . . has been statedfor testing a piece of equipment with regard to its immunity againstvarious electrical transients. Testing with high-energy transient surges asthey arise for the case of switching overvoltages or induced lightningovervoltages is described in IEC 61000-4-5/EN 61000-4-5.

As the description of the interference immunity test reveals, there areparallels to the voltage proof test of insulations. However, on analysingboth testing procedures as well as their final background and the testtechniques used it is observed that the only common parameter of thetests is the voltage impulse wave of 1.2/50μs of the unloaded generator.Although the ‘voltage proof test’ examines the insulation of the testobject, thus interpreting by this means ‘sparkover’ or ‘puncturing’ ofthe insulation as a failure, the specimen might otherwise ‘react’ in the‘interference immunity test’. Such a reaction, for example, can be thelimitation of the test impulse by means of protective elements (diodes,varistors, gas discharge arresters). In contrast to the voltage proof test,this reaction or response of the protective elements is not considered as afailure. Functional endurance, during the test, is the most important, sothat depending on the test specimen, a temporary degradation of theperformance is permissible. In addition to the differences in testingapproach and evaluation of both tests there is another considerabledifference in the current–time loadings at the ‘response’ of the testspecimen. Whereas the current flow, in the case of insulation sparkoveror puncture in the test circuit, is usually almost negligible at voltageproof tests, there will be an energetic loading caused by the impulsecurrent at the response of the device protection during the interferenceimmunity test.

The kind of testing used for the equipment to protect is important forthe dimensioning of surge protective devices for information technology:

Figure 5.8.2.1.1 t Basic mode of functioning of the Blitzductor® CT


• At a given voltage surge withstand capability the output level of thearrester only must be below the voltage surge withstand capability ofthe terminal equipment in order to guarantee a sufficient protection.

• If, however, the dimensioning of the arrester depends on the giveninterference immunity of the terminal equipment, both of the follow-ing conditions must be met: (i) the protection level of the arrester mustbe lower than the voltage surge withstand capability of the terminalequipment; and (ii) the maximum output energy of the arrester mustbe lower than the maximum permissible input energy of the terminalequipment (Figure 5.8.2.1.1 u).

To decide whether the equipment to protect withstands the residuallet-through impulse of a Blitzductor® CT, a comparison of theBlitzductor®-let-through values with the impulse parameters of the inter-ference immunity test specified for the equipment interface (acc. to IEC61000-4-5/EN 61000-4-5) (Figure 5.8.2.1.1 n) must be carried out.

By introducing ‘coordination characteristics’ (KK) (Figure 5.8.2.1.1 v)a Blitzductor® CT can easily be coordinated with the equipment to beprotected:

• Coordination characteristics provide information about the dischargecapability of the Blitzductor® CT (input characteristic) and about itsprotective effect related to a 2 Ω hybrid impulse (output characteristic).

• By determining the permissible input loading of the equipment inter-face, based on its basic interference immunity conforming to stand-ards, the coordination characteristic (input characteristic) of eachinterface can be ascertained and is comparable to the output charac-teristic of the coordination characteristic of the Blitzductor® CT.

Figure 5.8.2.1.1 u Verification of safe coordination by comparison of theadmissible energy loading of a device interface tested inaccordance with standard IEC 61000-4-5 with the ‘cut-offenergy’ of the protector Blitzductor® CT


Analogously to such an ‘adjustment’ of the Blitzductor® CT to theequipment interface the ‘coordination’ of cascaded Blitzductor®s CT canbe achieved. In addition to the operating parameters (such as operatingvoltage, nominal current, transmission frequency etc.) it only need beconsidered that the ‘input’ of a Blitzductor® CT or terminal equipmentmust fit with the ‘output’ of an upstream Blitzductor® CT.

The necessary ‘input’ of the first Blitzductor® CT (of this mutually andequipment coordinated ‘protective chain’) is determined by the threat-parameters of the whole system. Figure 5.8.2.1.1 w shows such a co-ordination with the protector family Blitzductor® CT under applicationof the coordination characteristics (KK). Blitzductor® CT types, withtheir coordination characteristics (KK), are listed in Table 5.8.2.1.1 b.

A protective cascade, as designed by the producer under the aspects ofsufficient safety such as the protector Blitzductor® CT family, is able toguarantee in a modern concept of lightning protection the trouble-freerunning of the system over a long period of time. Thus, the integralresponsibility of the arrester producer is becoming a new factor in thecooperation of protector producer and protector applier at a time whenthe producer liability is of special importance.

Sources

EHRLER, J., and HASSE, P.: ‘Energetisch koordinierte Überspan-nungsschutzgeräte erfüllen die Anforderungen moderner Informationstech-nik’, Elektrotechnik, 1996, (12), pp. 73–76DEHN + SÖHNE: ‘Blitzductor® CT. Energy coordination in communication/signalling systems’. DS 643/E/197DEHN + SÖHNE: ‘Selection and Installation of surge protective devices.Type Blitzductor® CT for protection of control and instrumentation systemsacc. to IEC 61312-1’. DS 656/E/Aug. 1997

Figure 5.8.2.1.1 v Coordination characteristics (KK) of the Blitzductor® CTfamily


HASSE, P., and ZAHLMANN, P.: ‘Koordinierter Einsatz von Blitzstrom undÜberspannungs-Ableitern im Blitzschutz – Umsetzung von DIN VDE 0185Teil 103, E DIN VDE 0675 Teil 6, Teil 6/A1, Teil 6/A2 und E DIN VDE 0100 Teil534 A1 in die Praxis. 2 (VDE/ABB Fachtagung, Neu Ulm, Nov. 1997)IEC 61000-4-5: ‘Electromagnetic compatibility (EMC) – Part 4: Testing andmeasurement techniques – (Section 5): Surge immunity test. InternationalElectrotechnical Commission, Geneva 1995

Figure 5.8.2.1.1 w Example for the energy coodinated application of theBlitzductor® CT by means of their coordinationcharacteristics (KK)

Table 5.8.2.1.1 b Blitzductor® CT types and their coordination characteristics


5.8.2.1.2 Blitzductor® CT: Selection criteria. Ten of the most importantselection criteria (SC) for arresters in measurement and control systemsare presented here through the example of the Blitzductor® CT protectorfamily. Their application will be described.

SC A: What discharge capability is necessary? Types B . . . or M . . . ?

The selection of the discharge capability of the Blitzductor® CT dependsupon which protection requirements shall be fulfilled by this arrester. Adistinction has to be made as to whether the measurement and controlsystem (or the telecommunication system) is only endangered by surges(which are effective as impulse currents being simulated by a 8/20 μswave) or whether by partial lightning currents (simulated by 10/350μsimpulse currents):

• Lightning protection, MCR-cable leading beyond the building. In thiscase (Figure 5.8.2.1.2 a) the terminal equipment to be protected is in abuilding with lightning protection. The measuring, controlling andregulating (MCR) or telecommunication cable (which connects theterminal equipment with a sensor) is a line leading beyond the buildingto a sensor in the field. As the building has lightning protection, theapplication of a lightning current arrester is necessary. Here the Blitz-ductor® CT types B or B . . . are suitable.

• No lightning protection, but MCR-cable leading beyond the building.Here the building with the terminal equipment to be protected has nolightning protection (Figure 5.8.2.1.2 b). Direct lightning strikes arenot expected. Lightning current proof arresters type B or type B . . .are only necessary if the MCR-cable can be charged by lightning

Figure 5.8.2.1.2 a Lightning protection, measuring and control cable crossingbuildings


strikes into neighbouring buildings (close-up strikes). If not, onlyBlitzductor® CT types M . . . are used.

• Lightning protection but no MCR-cable leading beyond the building. Inthis case (Figure 5.8.2.1.2 c) the MCR/telecommunication cabling doesnot have any lines leading beyond the building. Although the buildinghas lightning protection no lightning partial current can be coupledinto the considered part of the telecommunication system (the MCR-system is in lightning protection zone 1). So, in this case surge arresterswhich are characterized as type M . . . in the Blitzductor® CT family areused.

• No lightning protection, no MCR-cable leading beyond the building. Thebuilding has no lightning protection and there is no MCR/telecommunication cable leading beyond the building (Figure 5.8.2.1.2d). To protect the MCR devices only surge arresters are necessary.Protective modules type M . . . are used.

SC B: Longitudinal or transverse surge protection. Types . . . E or . . . D?

Longitudinal surges always arise between signal wires and earth, whereastransverse surges are generated between two signal wires. The interfer-ences in the signal circuits are mostly longitudinal surges. This means,for the selection of protective devices, that usually fine protective devicesare used between signal wires and earth, that is, the Blitzductor® CT,type . . . E.

For certain inputs to equipment, such as isolating transformers, a fineprotection between wire and earth is not necessary. Gas dischargearresters can protect against longitudinal surges. However, having a dif-ferent impulse sparkover characteristic, gas discharge arresters can also

Figure 5.8.2.1.2 b No lightning protection, but measuring and control cablecrossing buildings


cause transverse surges. That is why, in such a case, fine protection asoffered by the Blitzductor® type . . . D is necessary between the signalwires.

SC C: Which cases require Blitzductor® CT with output decouplingTypes . . . E/C?

Sometimes it is necessary to protect equipment inputs against longi-tudinal and transverse surges. The inputs of such electronic MCRequipment are usually already provided with protective circuits or haveoptocoupler inputs to separate the potential of the signal circuit from the

Figure 5.8.2.1.2 c Lightning protection, but no measuring and control cablecrossing buildings

Figure 5.8.2.1.2 d No lightning protection, no measuring and control cablecrossing buildings


internal circuit of the MCR equipment. This requires additional meas-ures for decoupling the Blitzductor® CT from the input circuit of theequipment to be protected. Decoupling is guaranteed by additionaldecoupling elements between fine protective elements and output ter-minals of the Blitzductor® CT, type . . . E/C.

SC D: Which cases require Blitzductor®s CT with higher cut-offfrequencies? Types . . . D/HF?

Like every transmission system the protective circuit of the Blitzductor®

CT also has a sort of low-pass characteristic. An indication of the cut-off frequency (Section 5.8.2.1.1) shows from what frequency the ampli-tude of the signal to be transmitted will be attenuated by more than 3dB.To keep the reaction of the Blitzductor® CT on the transmission systemwithin the permissible limits, the cut-off frequency must be higher thanthe signal frequency of the signal circuit. The indication of the cut-offfrequency is applicable for sinusoidal parameters. In the field of datatransmission, however, there are mostly no sinusoidal signal forms.Therefore, it must be taken into account that the maximum data rate ofthe Blitzductor® CT is higher than the transmission rate of the signalcircuit. On transmitting pulse shaped signals where the rising and thefalling pulse edge is evaluated it must be considered that this edgechanges within a certain period from ‘low’ (L) to ‘high’ (H) or from H toL. This time interval is important for the recognition of an edge and forthe passing of a ‘prohibited area’. Thus, this signal needs a frequencybandwidth which is considerably wider than that necessary for thefundamental wave of this oscillation. The cut-off frequency of the pro-tective device must therefore be levelled correspondingly high. A rule ofthumb is that the cut-off frequency must not be lower than the fivefoldfundamental wave frequency. Here the types BD/HF or MD/HF arenecessary.

SC E: What about the nominal current IN of the Blitzductor® CT?

Owing to the electrical characteristics of the components used in the pro-tective circuit of the Blitzductor® CT the signal current which can betransmitted over this protective device is limited. This means for theapplication that the nominal current IN of the Blitzductor® CT must behigher than (or equal to) the operating current of the MCR system.

SC F: What about the nominal voltage UN of the Blitzductor® CT?

The nominal voltage UN of the Blitzductor® CT must be higher than themaximum arising operating voltage of the MCR circuit so that the pro-tective device will not show any limiting effect under normal conditions.The maximum operating voltage to be expected in a signal circuit usually


can be compared with the nominal voltage of the transmission system(under consideration of tolerances). In the case of signal circuit currentloops (e.g., 0–20mA) the open circuit voltage of the system can be ratedas the maximum possible operating voltage.

SC G: To what do the voltage indications refer: wire/wire or wire/earth?

Signal supply in MCR circuits can be symmetrical or asymmetrical. Onthe one hand, the operating voltage of the system can be indicated aswire/wire voltage and, on the other hand, as wire/earth voltage. Thismust be considered on selecting the protective device Blitzductor® CT.For different circuits of the Blitzductor® CT fine protective elementsdifferent nominal voltages are indicated. The different relativities of thenominal voltages of the Blitzductor® CT modules have been explained inSection 5.8.2.1.1.

SC H: For what are the series impedance data of the Blitzductor® CT?

For the coordination of the protective elements decoupling impedancesare installed into the Blitzductor® CT. Being directly in the signal circuitthey can influence it. Especially in current loops (0 . . . 20mA, 4 . . .20mA) the installation of Blitzductor® CT can cause the maximumpermissible ohmic resistance of the signal circuit to be exceeded, a factthat must be clarified before installation.

SC I: What about the application of the Blitzductor® CT-coordinationcharacteristics (KK)?

For equipment used in different electromagnetic environmental condi-tions, IEC 61000-4-5/EN 61000-4-5 specifies different test severity levelsregarding the immunity against impulse shaped interferences. The testseverity runs from level 1 to 4, severity level 1 claiming the lowest immun-ity (to the equipment to be protected) and level 4 the highest. Asdescribed in section 5.8.2.1.1 this means that the ‘let-through energy’related to the Blitzductor® CT protection level must be lower than theimmunity level of the equipment to be protected. By means of the Blitz-ductor® CT coordination characteristics (KK) a coordinated applicationof the Blitzductor® CT for the protection of programmable controllersis possible. If, for example, a programmable controller has been testedaccording to test severity level 1, the coordinated Blitzductor® CT onlymust have a maximum ‘let-through energy’ which corresponds to thisinterference level, thus it must have output characteristic 1.

In practice, this means that severity level 4 tested programmable con-trollers can work interference-free if the Blitzductor® CT output has aprotection level corresponding to test severity degree 1, 2, 3 or 4. Thus, itis very easy for the user to select suitable protective devices.


SC J: Single or multistage protection. Types B and M . . . or only type B . . . ?

Depending on the infrastructure of the building and the protectionrequirements of the concept of lightning protection zones it may benecessary that lightning and surge arresters are either installed spatiallyseparated or in one position in the system (Figure 5.8.2.1.2 e).

In the first case, the application of the Blitzductor® CT with protectivemodule type B as a lightning current arrester as well as Blitzductor® CTprotective module type M . . . as a surge arrester is necessary. In thesecond case lightning and surge protective measures shall be carried outin one position in the system; here the combined arrester Blitzductor®

CT, type B . . . is applied.

Sources

DEHN + SÖHNE: ‘Selection and installation of surge protective devices.Type Blitzductor® CT for protection of control and instrumentation systemsacc. to IEC 61312-1’. DS 656/E August 1997IEC 61000-4-5:1995: ‘Electromagnetic compatibility (EMC) – Part 4: Testingand measurement techniques (Section 5): Surge immunity test’. InternationalElectrotechnical Commission, Geneva 1995

5.8.2.1.3 Blitzductor® CT: Examples of application. The following threeexamples of application show the selection of protective devices of theBlitzductor® CT family by means of the above described selection cri-teria (SC) A to J. The result of every single step of the selection is enteredinto a selection table under the column ‘single result’. The column ‘con-

Figure 5.8.2.1.2 e Single and multistep protection


secutive result’ then shows the influence of the particular single result onthe consecutive selection result. At the end of every selection table thefinal result ‘The applicable Blitzductor® CT’ can be read.

Source

DEHN + SÖHNE: ‘Selection and installation of surge protective devices.Type Blitzductor® CT for protection of control and instrumentation systemsacc. to IEC 61312-1. DS 656/E/897

5.8.2.1.3.1 Lightning/surge protection for electronic vehicle weighbridges.Electronic vehicle weighbridges (for road and railway vehicles) are sus-ceptible to incoupled surges due to the large distance between measuringsensor and the evaluation unit (especially at outdoor weighing machines).The damaging of components and the failure of the whole weighingsystem is a considerable impairment to a commercial enterprise. Someexamples concerning how to select lightning surge protective devices fora weighing machine are now described.

The electrical measurement of the non-electric parameters of force ormass is made indirectly by measuring electrical resistance. Strain gaugesare used as ohmic transducer elements. These consist of resistance foilswhich are coated on the carrier mostly in ‘meanders’. The extension orcompression of a strain gauge along the printed conductor causes achange in length and cross section of the printed conductors and thus achange in their ohmic resistance. Strain gauges are coated onto a deform-ing carrier in such a way that two strain gauges are in extension and twostrain gauges are in compression. These gauges are coupled in a bridge sothat strain gauges stressed in equal directions are located in diametricallyopposing branches (Figure 5.8.2.1.3.1 a). This bridge will be suppliedwith a DC voltage.

Figure 5.8.2.1.3.1 a Basic diagram: Electronic weighbridge system


The resistance changes due to the extension are very small andregarding the limits concerning the thermal stressing of the straingauges, the bridge diagonal voltage is only some millivolts within thenominal range of the bridge supply voltage of up to 12V. To compen-sate for the influence of temperature and voltage drop on long connect-ing cables two compensating leads are run from the measuring sensor tothe evaluation unit. This procedure is called the six-conductortechnique.

Table 5.8.2.1.3.1 a indicates the single results which are due to the

Table 5.8.2.1.3.1 a Lighting/surge protection for electronic vehicle weighbridges:Selection procedure (SC: selection criterion)


individual selection criteria SC (A to J) and the consecutive selectionresults as well as the final result: Blitzductor® CT, type BE 12 (for circuit,see Figure 5.8.2.1.3.1 b; for technical data, see Table 5.8.2.1.3.1 b). Figure5.8.2.1.3.1 c shows the protection of an electronic weighing machine(with four measuring sensors) using Blitzductor® CT type BE 12.

To standardize the equipment of the weighing system with protectivedevices, all measuring leads have been equipped with the same Blitzduc-tor® CT types. It is proven practice to assign one protector each to thewire pairs for supply, compensation and measuring. On subsequentinstallation of protective devices into the measuring circuits, the weigh-ing system must be re-calibrated.

The Blitzductor® CT may only be installed into the measuring circuitsof weighing systems to be calibrated if the protective devices have beenconfirmed by an authorized testing institute of the EC (e.g., the FederalInstitute of Technical Engineering) together with the weighing machine.

Lightning and surge protection of the 230V supply of the weighingsystem is also necessary (for reasons of clarity this is not shown in theFigure 5.8.2.1.3.1 c).

Source

DEHN + SÖHNE: ‘Selection and installation of surge protective devices. TypeBlitzductor® CT for protection of control and instrumentation systems acc. toIEC 61312–1’. DS 656/E Aug. 1997

5.8.2.1.3.2 Lightning/surge protection for field-bus systems. Because ofthe automation process individual sections of production are inter-connected by field-bus systems. Automation systems can be establishedwith field-buses where decentral control systems are also included(Figure 5.8.2.1.3.2 a). Such systems are especially endangered by in-coupled surges due to their spatial extension. If such field-bus system

Figure 5.8.2.1.3.1 b Blitzductor® CT, type BE 12: Basic circuit diagram


components are damaged there is relatively little hardware loss but agreat deal of production loss due to the subsequent production stand-still. The field-bus is a serial bus system having technical and functionalcharacteristics for the networking of automation units at the lower andmedium performance level. Well-known bus systems for automationtechnology include: Profibus®, Interbus-S, DIN Messbus, D-Net,Suconet, Bit-Bus, SINEC L1, PLS-Net, SINEC L2 DP and CANbus.

Table 5.8.2.1.3.1 b Blitzductor® CT-type BE 12: Technical data


In most cases it is a serial interface (type RS 485) which is connectedto a combined transmitting and receiving line (party-line). The transmis-sion process of the RS 485 interface makes a difference evaluation ofthe wire signal voltages. Owing to the twisting of the wires the bus lineis insensitive to inductive incouplings between its wires (transversesurges). Thus, the surge threat for the RS 485 interface is in the transientpotential increase of the signal wires to earth (longitudinal surges).

Table 5.8.2.1.3.2 a again shows the step-by-step procedure to deter-mine the suitable protective devices. This is a two-stage protective system

Figure 5.8.2.1.3.1 c Suppressor circuit for electronic weighbridge system withfour measuring sensors

Figure 5.8.2.1.3.2 a Basic diagram: Field-bus system


out of the lightning current arrester Blitzductor® CT, type B 110 andsurge arrester Blitzductor® CT, type MD/HF 5 (for circuits, see Figure5.8.2.1.3.2 b; for technical data, see Table 5.8.2.1.3.2 b).

Figure 5.8.2.1.3.2 c shows the protection of an actuator, distributedinputs and outputs, sensors and programmable controllers connectingfield-bus systems with the selected Blitzductors.

Lightning and surge protection of the 230V supply is also necessary(but not shown in Figure 5.8.2.1.3.2 c for reasons of clarity).

Table 5.8.2.1.3.2 a Lightning/surge protection for field-bus system: Selectionprocedure (SC: selection criterion)


Figure 5.8.2.1.3.2 b (a) Figure 5.8.2.1.3.2 b (b) Blitzductor®

CT, type MD/HF 5

Table 5.8.2.1.3.2 b Blitzductor® CT-types B 110 and MD/HF 5: Technical data


Source

DEHN u. SÖHNE: ‘Selection and installation of surge protective devices.Type Blitzductor® CT for protection of control and instrumentation systemsacc. to IEC 61312-1. DS 656/E Aug. 1997

5.8.2.1.3.3 Surge protection for electrical temperature measuringequipment. Electrical temperature measuring of media in technologicalprocesses is performed in all industrial fields. The areas of applicationcan be very different: from food processing to chemical processes to theair-conditioning of buildings. Generally, there is a large distance betweenthe location of the measuring sensor and the measured-data indicatoror processing equipment. Into these long bonding lines surges can beincoupled which are not necessarily caused by atmospheric discharges.

The following description contains a suggestion of how to protect aPT 100 standard resistance thermometer against surges. The buildingwhere the measuring equipment is installed has no lightning protection.The temperature is determined by measuring the electrical resistance.The resistance thermometer (PT 100) has a resistance value of 100 Ω at0 °C. Depending on the temperature, this value changes by 0.4 Ω/K. Todetermine the temperature, a constant measuring current is impressedcausing a voltage drop at the resistance thermometer which is pro-portional to the temperature. This measuring current is limited to 1mAin order to avoid self-heating of the resistance thermometer. Thus, at thePT 100 there will be a voltage drop of 100mV at 0 °C, which will betransmitted to the place of indication or evaluation (Figure 5.8.2.1.3.3 a).

Figure 5.8.2.1.3.2 c Suppressor circuit for field-bus system


An example of the different possible connection systems for a PT 100measuring sensor is shown by the four-conductor connection in Figure5.8.2.1.3.3 a. So, the influence of the conductor resistance and itstemperature-sensitive fluctuations on the measuring result are excluded.The PT 100 sensor is supplied by an impressed current. Changes in theconductor resistance will be automatically compensated for by theadjustment of the supply voltage. There is a high-resistance pick-upat the sensor by the measuring transducer of the changing measuringvoltage Um depending on the temperature of the measuring resistance.

Table 5.8.2.1.3.3 a shows how to proceed step-by-step with the selec-tion of suitable protective devices. For the Blitzductor® CT, type ME5, surge arresters are necessary (for circuit, see Figure 5.8.2.1.3.3 b; fortechnical data, see Table 5.8.2.1.3.3 b).

Figure 5.8.2.1.3.3 c shows the protection of electrical temperaturemeasuring equipment. To standardize the equipment of the temperaturemeasuring system with surge protective devices, supply and measuringlines are protected by the same Blitzductor® CT-types. It is proven prac-tice to assign one protector each to the wire pairs for supply and formeasurement.

Surge protection of the 230V supply for the PT 100 measuring trans-ducer, as well as of the 4–20mA current loop (beginning there), is alsonecessary but not shown in Figure 5.8.2.1.3.3 c for reasons of clarity.

Source

DEHN + SÖHNE: ‘Selection and installation of surge protective devices. TypeBlitzductor® CT for protection of control and instrumentation systems acc. toIEC 61312-1’. DS 656/E Aug. 1997

Figure 5.8.2.1.3.3 a Basic diagram: electrical temperature measuringequipment


5.8.2.1.3.4 Blitzductor® CT applications: Further cases. Table 5.8.2.1.3.4 alists further cases of application for different Blitzductor® CT-types.

5.8.2.1.4 Arresters for intrinsically safe measuring and control circuits andtheir application. In areas where gases, vapours, fogs or dusts are causedby treating or transporting inflammable material, which together withthe air can form a dangerous explosive atmosphere, special explosionprotection measures must be taken. To avoid the situation where the

Table 5.8.2.1.3.3 a Surge protection for electrical temperature measuringequipment: Selection procedure (SC: selectioncriterion)


Figure 5.8.2.1.3.3 b Basic circuit diagram: Blitzductor® CT, type ME 5

Table 5.8.2.1.3.3 b Blitzductor® CT, type ME 5: Technical data


Figure 5.8.2.1.3.3 c Suppressor circuit for electrical temperature measuringequipment

Table 5.8.2.1.3.4 a Examples for the use of Blitzductor® CT


electrical operating facilities become the sources of ignition in explosiveatmospheres these are designed to have different types of protection. Onetype of protection which is used worldwide in the measuring and controltechnique is Intrinsic Safety Ex(i).

‘Intrinsic safety’ protection is based on the principle of current andvoltage limitation in a circuit. Power is kept at such a low level thatneither by sparks nor by unpermissible surface heating of the electriccomponents can the surrounding explosive atmosphere be ignited. Notonly the voltage and current of the electric equipment but also the energystoring inductors and capacitors in the whole circuit must be limited tosafe maximum values. Thus, for safe operation (e.g., a measuring andcontrol circuit) neither a spark due to the opening and closing of thecircuit (e.g., at switch contacts) nor a fault (e.g., a short circuit or an earthfault) will cause ignition. Furthermore, heat ignition by the equipmentand lines in the intrinsically safe circuit must be eliminated both for thenormal state as well for the possibility of a fault.

Application of the ‘intrinsic safety’ type of protection, thus, is limitedto relatively low-performance circuits. It is achieved by limiting theavailable energy in the circuit. In contrast to other types of protection,this limitation is not only to individual devices but to the whole circuit.

This system is divided into ‘Ex-zones’ and, in general, this divisiondepends on the probability and the permanence of an explosive atmos-phere. Zones with dangerous explosive atmosphere due to gases, vapoursand fog are ranked as Ex-zones 0 to 2 and those with dangerous explosiveatmosphere due to dusts as Ex-zones 20, 21 and 22. Depending on howexplosive the different materials are, there are explosions groups I, IIA,IIB and IIC for which the corresponding minimum ignition curves arespecified. The ignition characteristics of the explosive material includea minimum ignition curve that indicates the maximum values for theoperating voltage and operating current. Explosion group IIC containsthe most explosive materials, such as hydrogen and acetylene. Whenheated, these gases have different ignition temperatures which arespecified by classifying them according to temperatures (T1–T6).

At the interface between Ex-area and non-Ex-area (safe area), safetybarriers or measuring transformers with an Ex(i)-output circuit will beinserted for separation. The safety-technical maximum values of a safetybarrier or a measuring transformer with Ex(i)-output circuit are specifiedby the test certificate of an authorized testing agency. These are, namely,(i) the maximum output voltage (U0), (ii) the maximum output current(I0), (iii) the maximum external inductance (L0) and (iv) the maximumexternal capacitance (C0). The planner/installer must examine in everysingle case whether these maximum values are met by the connectedequipment in the intrinsically safe circuit (such as field equipment, cablesand surge protective devices). Corresponding values are indicated on thetype label of the approved equipment or in the prototype test certificate.


Intrinsic safety protection entails all currents, potentials and electricenergy storage mechanisms, but not externally incoupled overvoltagesdue to atmospheric discharges, which may arise in large industrial plantsafter direct, close-up and remote lightning strikes.

In the case of direct or close-up lightning strikes the voltage dropcauses a potential increase of some 10 to 100kV at the earthing system.As a potential difference this affects all equipment connected at distantlocations. Such potential differences will exceed the insulation resist-ance of the equipment. In the case of remote lightning strikes, over-voltages are generated in lines which will damage the inputs of elec-tronic equipment as transverse voltage (voltage difference between thewires).

Thus, as protection against lightning or surge hazards the relevantarresters must be installed. Figure 5.8.2.1.4 a shows the consideration ofsurge arresters in intrinsically safe measuring and control circuits.

As an example of the Blitzductor® CT MD/Ex 24 (Figure 5.8.2.1.4 b)with a certificate from the Federal Institute for Physical Engineering(Physikalisch Technische Bundesanstalt PTB, Braunschweig), the spe-cific selection criteria for this protective device will now be explained.This surge protective device has the equipment mark ‘Eex ia IIC T6’which has the following meaning:

(i) Eex: The testing agency certifies the accordance of this electrical equip-ment with the harmonized European Standards EN 50 014 ‘ElectricalApparatus for Potentially Explosive Atmospheres. General Requirements’and EN 50 020 ‘Intrinsic Safety i’.

Figure 5.8.2.1.4 a Application of surge arresters in the intrinsically safemeasuring and control circuit, calculation of L0 and C0


(ii) Regarding the safe current and voltage limitation there are two categoriesto be considered:

• Category ib specifies that in case of a fault in the intrinsically safe circuitthe intrinsic safety must be preserved.

• Category ia requires that on the occurrence of two independent faultsthe intrinsic safety must still be preserved.

The Blitzductor® CT MD/Ex 24 is assigned to category ia with its highestdemands and so it may be installed also with other equipment which is in Ex-protection zone 0 and 20.

(iii) II C: Classification into explosion groups. Explosive gases, vapours and fogsare classified according to the spark energy necessary to ignite the mostexplosive mixture with air. Equipment is classified according to the gaseswith which it can be used.

• Group II applies for all fields of use, such as the chemical industry, coaland cereal processing, however not in underground mining.

• Danger of explosion is highest in group II C because it considers mix-tures of lowest ignition energy.

The certificate of the Blitzductor for explosion group II C therefore meets thehighest demands for a hydrogen in air mixture.

(iv) T6: Classification according to temperatures. In the case of a hot-surfaceignition of an explosive atmosphere a material-typical minimum tempera-ture is necessary. The ignition temperature is a material classification figurewhich characterizes the ignition reaction of the gases, vapours, or dusts ata hot surface. For economical reasons gases and vapours are classifiedaccording to temperatures. Temperature class T6 means that the maximumsurface temperature of the component must not exceed 85 °C in operationas well as in the case of a fault and the ignition temperature of the gases

Figure 5.8.2.1.4 b Blitzductor® CT, type MD/Ex24 (colour blue)


and vapours must be higher than 85 °C. Thus, the T6 classification is thehighest demand for the Blitzductor® CT.

In accordance with the PTB-certificate of conformity the followingelectrical parameters must be considered:

• Maximum external inductance (L0) and maximum external capacitance(C0). Owing to the special component selection in the Blitzductor® CTthe internal inductance and capacitance values of the different indi-vidual components are negligible.

• Maximum input current (Ii). The highest permissible current whichmay be supplied through the terminal parts is 500mA without cancel-ling the intrinsic safety.

• Maximum input voltage (Ui). The highest voltage with which the surgeprotective device Blitzductor® CT may be loaded is 26.8V withoutcancelling the intrinsic safety.

Concerning the practical application of arresters in intrinsically safecircuits (Figure 5.8.2.1.4 e) the requirements for the insulation resistanceneed special care. The insulation between an intrinsically safe circuitand the equipment chassis or other parts which can be earthed shouldwithstand the effective value of an AC test voltage being twice as high asthat of the intrinsically safe circuit or 500V (depending on which value ishigher). Equipment having an insulation resistance ≥ 500V AC is con-sidered as earthed.

Intrinsically safe equipment (e.g., underground lines, measuring trans-ducers, formers, sensors etc.) usually has an insulation resistance of> 500V AC. Intrinsically safe circuits must be earthed for safety reasons.They may also be earthed, if necessary, for reasons of function. Thisearthing may be realized only at one point by connection with the equi-potential bonding. Surge protective devices having a DC operating volt-age to earth < 500V DC, provide an earth of the intrinsically safe circuit.An intrinsically safe circuit is considered as not earthed if the DC operat-ing voltage of the protective device is > 500V DC. The Blitzductor® CT,Type MD/Ex 24 meets this requirement.

Figure 5.8.2.1.4 c shows how to use the Blitzductor® CT MD/Ex surgeprotective devices to protect a transducer and a sensor. In order not toworsen the arrester protective level due to voltage drop (of the interfer-ence current to be discharged), care must be taken of the consequentequipotential bonding between the equipment to be protected and thesurge protective device. In Figure 5.8.2.1.4 c this is achieved by an add-itional equipotential line between the equipment and the Blitzductor®

CT.Figure 5.8.2.1.4 d shows a special case of application. As a surge pro-

tective device in the Ex-area, the (ex-certified) Blitzductor® CT MD/Ex isused. As a surge protective device in the non-Ex-area, however, a (not Ex-


certified) Blitzductor® CT, ME is used having a protection level betweencores to earth/equipotential bonding of much less than 500V. In thelatter case this is necessary because the insulation resistance of the trans-ducer is < 500V AC.

Sources

MÜLLER, K. P.: ‘Überspannungsschutz in eigensicheren MSR-Kreisen’. de(der elektromeister + deutsches elektrohandwerk), 1997, H. 20, pp.1913–1916

Figure 5.8.2.1.4 c Application of Blitzductor® CT, type MD/Ex in theintrinsically safe measuring and control circuit of an Ex-system

Figure 5.8.2.1.4 d Application of different Blitzductor®s in an intrinsically safecircuit, which is partly in the Ex-area


EN 50 014: ‘Electrical apparatus for potentially explosive atmospheres.General requirements’ (VDE Verlag, GmbH, Berlin) March 1994EN 50 020: ‘Electrical apparatus for potentially explosive atmospheres.Intrinsic safety “i” ’ (VDE Verlag, GmbH, Berlin) April 1996

5.8.2.1.5 Arresters for cathodic protection systems. Underground metalfacilities (e.g., containers and piping) are subject to electrochemicalcorrosion, with the metals being the electrodes and the surroundingsoil the electrolyte. A characteristic of the electrochemical corrosion isthe dependence of the corrosion process on the electrodes’ potential(potential of metal in soil). If there is metal in the soil, positively chargedions enter into the soil and vice versa; also positive ions from the electro-lyte (soil) are taken up by the electrode (metal). In this context we speakof the ‘dissolution pressure’ of the metal and the ‘osmotic pressure’ ofthe electrolyte. Depending on both pressures, either the positive ions ofthe buried metal facility are increasingly dissolved (thus it becomes nega-tive with regard to the soil) or positive ions from the soil increasinglydeposit at the metal (then the metal facility becomes positive with regardto the soil). If buried facilities out of different metals are connectedoutside the soil (e.g., within the scope of equipotential bonding) thencurrent flows in the external circuit from the positive to the negativeelectrode; in the soil, however, from the negative to the positive electrode.So, the more negative metal facility delivers positive ions to the soil, thusbecoming the anode of the created galvanic element with the con-sequence of being dissolved (corroded) as time passes. Such corrosion

Figure 5.8.2.1.4 e Blitzductor® CT, type MD/Ex for the protection of a pipelinevalve station


can be avoided by current supply where a mains-operated rectifier sup-plies a current over an anode through the soil into the endangered metalfacility, thus becoming a corrosion protected cathode.

Figure 5.8.2.1.5 a shows the basic diagram of such a cathodically pro-tected system for a pipeline. The measuring sensor picks up the potentialof the pipeline to the surrounding soil, initiating the optimal value ofprotective current at the adjustable rectifier.

Cathodically protected systems can be endangered by surges due tolightning discharges and faults in high-voltage overhead lines or tractionpower supply (running in parallel to the pipeline). Protection is offeredby (Figure 5.8.2.1.5 b) Blitzductor® KKS, type AD I for the impressed-current anode circuit, and Blitzductor® KKS, type APD for the measuring

Figure 5.8.2.1.5 a Cathodic protection system: Basic design

Figure 5.8.2.1.5 b Blitzductor® KKS, type APD


sensor circuit. Technical data are provided in Table 5.8.2.1.5 a. Figure5.8.2.1.5 c shows how these surge arresters are used.

5.8.2.1.6 Arresters in Euro-card format. Arresters in Euro-card formathave an especially space-saving design (Figure 5.8.2.1.6 a). They containa graded protective circuit as shown in Figure 5.8.2.1.6 b. Such protectivecards can be inserted into individual enclosures (Figure 5.8.2.1.6 c), into19″-racks (Figure 5.8.2.1.6 d) or into complete protective cabinets(Figures 5.8.2.1.6 e).

5.8.2.1.7 Arresters in LSA-Plus-technology. Information technologydistribution boxes are often realized using LSA technology, a quick-connection system without stripping, soldering or screwing: By means ofa special tool the wires are simply pressed into the contact slots of theLSA rails. The wire insulation will be cut automatically and the coppercore will be pushed between two spring-loaded contact tags. At the sametime the tool also cuts off unnecessary wire ends.

Figure 5.8.2.1.7 a shows components of an LSA-Plus system by meansof which it is possible to construct, for example, small terminal junction

Table 5.8.2.1.5 a Blitzductor® KKS, types AD I and APD: Technical data


Figure 5.8.2.1.5 c (a) Basic diagram

Figure 5.8.2.1.5 c (b) Application of the Blitzductor® KKS in a corrosionprotection cabinet

Figure 5.8.2.1.5 c Protection of a cathodic protection system with Blitzductor®

KKS types APD and ADI


Figure 5.8.2.1.6 d 19″-drawout-unit housing for protective cards

Figure 5.8.2.1.6 a 16 pole arrester in drawout-unit design

Figure 5.8.2.1.6 b Circuit ofthe arrester shown in Figure5.8.2.6 a (shown for two singlewires)

Figure 5.8.2.1.6 c Protective cards in aluminium housing for wall mounting


boxes with the same economy as large distribution boxes or mains distri-bution frames with more than 10000 connections. Terminal blocks anddisconnection blocks are to be placed on terminal strips:

• At the terminal blocks the cable wires and the jumping wires are con-nected at opposite contacts. Between these terminal contacts there arepick-off contacts where, for example, surge protective modules can beplugged in.

• In contrast to the terminal block, the disconnection block is con-structed so that a disconnection plug can interrupt the contactsbetween the cable wire and the jumper wire side which is necessary toinclude in a protective decoupling link.

Figure 5.8.2.1.7 b shows protective devices designed especially forthe LSA-Plus system. The protection plugs for one balanced line(Figure 5.8.2.1.7 b, lower left), consisting of ‘coarse protection’, ‘de-coupling unit’ and ‘fine protection’, contain series links and must there-fore be plugged into the LSA disconnection block (Figure 5.8.2.1.7 c).There is one protection block each for 10 balanced lines (Figure 5.8.2.1.7b top right) which will also be plugged into the disconnection block.

Source

HASSE, P., and WIESINGER, J.: “EMV Blitz-Schutzzonen-Konzept’ (PflaumVerlag; München: VDE Verlag, GmbH, Berlin/Offenbach) 1994

Figure 5.8.2.1.6 e Arresters in Eurocard design, mounted in a protective cabinet


Figure 5.8.2.1.7 a LSA-Plussystem

Figure 5.8.2.1.7 b Arresters for LSA-Plussystem

Figure 5.8.2.1.7 c Connection of communication technology lines at the entry tolightning protection zone 1 of the water purification unitFrauenau/Lower Bavaria


5.8.2.2 Combined protective devices for power supply inputs andinformation technology inputs

Equipment and systems connected to power technical and informationtechnology networks, forming their own lightning protection zone andwhere the line routing leads to wide induction loops (Figure 5.8.2.2 a),will be input-protected by surge arresters which are designed for theconnection of power lines as well as for information technology lines.

The principle of protection is to realize the equipotential bondingbetween the systems in the case of overvoltage directly at the inputs ofthe device or of the system (Figure 5.8.2.2 b). It is the task of the pro-tective elements S1 and S2 to limit the transverse voltages between the

Figure 5.8.2.2 a Danger to information technology equipment connected to twosystems due to induced lightning overvoltages

Figure 5.8.2.2 b Topology of a protector for equipment or systems at twonetworks


conductors (‘differential mode protection’) and to lead the longitudinalcurrents from the conductors (‘common mode protection’) to the com-mon equipotential bonding bar.

Figure 5.8.2.2 b shows the equipment to be protected in shunt to theprotective device. This guarantees that overvoltages between the powermains and the information technology mains are limited in such a waythat the puncture voltage of the equipment between the inputs E1 and E2

will not be exceeded. Furthermore, it guarantees that the common-modecurrents can be conducted from the power mains into the informationtechnology mains and vice versa. Moreover, dangerous surges betweenthe conductors of one system cannot arise.

Figures 5.8.2.2 c and d show surge arresters for realizing such ‘protect-ive bypasses’.

Source

HASSE, P., and WIESINGER, J.: ‘EMV Blitz-Schutzzonen Konzept’ (PflaumVerlag, München; VDE Verlag, Berlin/Offenbach, 1994)

Figure 5.8.2.2 c Surgearrester for the power inputand the aerial input of a TVset/radio receiver

Figure 5.8.2.2 d Surge arrester for the powerinput and the data input of a computer terminal


5.8.2.3 Protective devices for data networks/systems

In the following Sections protective devices for different data networkswill be introduced which can be used as part of the concept oflightning protection zones at the building input (e.g., LPZ-interface0A(0B)/1), in the active distributor (HUB), in the terminal block (e.g.,LPZ-interface 1/2), or at the terminal equipment (e.g., LPZ-interface2/3).

5.8.2.3.1 Protective devices for application-neutral cabling. The EuropeanStandard EN 50173 ‘Information technology – Generic cabling systems’offers:

• a generic universally applicable cabling system and an open market forcabling components

• a flexible cabling scheme where modifications can be realized easilyand economically

• instructions to building professionals for cabling installation beforespecific requirements are known (that means early in the initial plan-ning stage of construction or renovation)

• a cabling system for industry and the standardization committees fornetwork use supporting actual products and acting as a basis forfuture product development.

This European Standard defines a universal cabling system which can beused in places with one or several buildings. It treats cablings with sym-metric copper cables and optical fibre cables. The universal cabling coversa wide range of services including speech, data, text, still and movingpictures.

Generic cabling consists of the following functional elements:

• campus distributor (CD)

• primary cable

• building distributor (BD)

• secondary cable

• floor distributor (FD)

• tertiary cable

• cable distribution cabinet (alternatively)

• information technology terminal.

Groups of these functional elements are connected to partial systems ofthe cabling.

A universal cabling system consists of three partial systems: (i) pri-mary, (ii) secondary and (iii) tertiary cabling. Together these partialsystems form a universal cabling structure as shown in Figure 5.8.2.3.1 a.By means of distribution boards any mains topologies such as bus, radialand annular topologies can be achieved.


(i) The ‘primary cabling’ partial system goes from the campus distributorto the building distributor(s) which are usually in different buildings. Itcontains any primary cables, their first points of contact (at the campusand the building distributors) and the distribution facilities in the campusdistributor.

(ii) One partial system of the ‘secondary cabling’ goes from the building dis-tributor(s) to the floor distributor(s). That partial system contains the sec-ondary cables, their mechanical points of connection (at the building andfloor distributors) and the distribution facilities in the building distributor.

(iii) The ‘tertiary cabling’ partial system goes from the floor distributor to theconnected information technology terminal(s). That partial system con-tains the tertiary cables, their (mechanical) points of connection at thefloor distributor, the distribution facility in the floor distributor and theinformation technology terminals.

The equipment terminal cabling connects the information technologyterminal with the terminal equipment. It is carried out according to localrequirements and is therefore not covered by the range of application ofthis European Standard. Between the campus and building distributoroptical fibre cables are usually used as data lines. So, no arrester from thefield side is needed. The star couplers for distributing the optical fibrecables, however, are powered by 230V and so arresters for the powerengineering system (chapter 5.8.1) may be necessary.

The secondary (building distributor to floor distributor) and tertiaryconnections (between floor distributor and terminal equipment) areoften symmetric cables (e.g., twisted pair-cables). Cable lengths (max.500 or 90m) (Figure 5.8.2.3.1 b), where high longitudinal voltages can beinduced when lightning strikes the building, would overload a HUB insu-lation strength or that of a network card in the terminal equipment.Therefore, surge protection measures must be carried out to protect both

Figure 5.8.2.3.1 a Structure of generic cabling


building/floor distributors (HUB) as well as telecommunication outlets(terminal equipment).

Protective devices used for the above purpose are specified accordingto the type of network. Usually, the following types of networks apply:

• Token Ring

• Ethernet 10 Base T

• Fast Ethernet 100 Base TX.

Figure 5.8.2.3.1 c shows where the protective devices can be used:

• Between HUB and patchpanel a NET-Protector with surge protectivemodules 4 TP (Figure 5.8.2.3.1 d, Table 5.8.2.3.1 a) is installed (Figure5.8.2.3.1 e).

• At the terminal equipment a surge arrester, type ÜGKF/RJ45 4TP(Figure 5.8.2.3.1 f, Table 5.8.2.3.1 b) can be used, where all four corepairs are protected which provides a completely neutral application.However, it must be taken into account that the power input of theterminal equipment is also protected. The combined surge protectivedevice DATA-Protector (Figure 5.8.2.3.1 g, Table 5.8.2.3.1 c), forexample, can be used, or (as shown in Figure 5.8.2.3.1 h) surge arrest-ers type ÜGKF/RJ45 for the data input and type SF-Protector (cf.Section 5.8.1.4 b, Figure 5.8.1.4 b) for the power input.

Sources

EN 50173: ‘Information technology. Generic cabling systems’ (Beuth Verlag,GmbH, Berlin) Nov. 1995DEHN + SÖHNE: ‘Surge protection: Safety for your data networks. Adviceand equipment for optimized system solutions’. DS647 Oct.1996DEHN + SÖHNE: ‘Surge protection. Main catalogue UE’98 E’. DS570/E 1998

Figure 5.8.2.3.1 b Application-neutral cabling systems


Figure 5.8.2.3.1 e NET-protector between HUB and Patchpanel

Figure 5.8.2.3.1 d NET-protector

Figure 5.8.2.3.1 c Protectors in an application-neutral cabling system


Figure 5.8.2.3.1 f(a) Surge arrester,type ÜGKF/RJ454TP

Figure 5.8.2.3.1 f(b) Basic circuitdiagram: ÜGKF/RJ45 4TP

Table 5.8.2.3.1 a NET-Protector for floor distribution boards (HUB) and othernetwork components in 19″ modular packaging system


Table 5.8.2.3.1 b Surge arrester, type ÜGKF/RJ45 4TP: Technical data

Figure 5.8.2.3.1 g(a) Combined surgeprotector DATA-Protector RJ45 4TP

Figure 5.8.2.3.1 g(b) Basic circuitdiagram


Table 5.8.2.3.1 c Combined surge protective device DATA-protector RJ 45 4TP:Technical data

Figure 5.8.2.3.1 h Surgearresters, type KF/RJ45 and SFprotector protect terminal


5.8.2.3.2 Protective devices for token ring cabling. For token ringcabling the systems are connected in the ring topology and communicateaccording to the methods specified in IEEE 802.5. As floor distributors,mostly controllable ring distributors are used to perform the networkcontrol of the different terminal equipment and the signal amplification.Long cables present no problems. The maximum data transmission rateis 16Mbps. (A Herm–Aphrodite plug, also known as an IVS connector,serves as the connector; it serves as both a plug and socket.) Figure5.8.2.3.2 a shows the principle of token ring cabling and where the neces-sary protective devices should be installed.

At the interface of lightning protection zones 0A/1 (cable input atthe building) lightning current arrester type TR8 (Figure 5.8.2.3.2 b,

Figure 5.8.2.3.2 a Protectors in token ring cabling

Figure 5.8.2.3.2 b (a) Lightning current arrester, type TR8 (surface housing) fortwo token ring lines

Figure 5.8.2.3.2 b (b)Basic circuit diagram


Table 5.8.2.3.2 a) is used. A type FS HA surge arrester (Figure5.8.2.3.2 c, Table 5.8.2.3 a), which should be mounted at the rearside ofthe floor distributor between data line and front plate as shown in Figure5.8.2.3.2 d, protects the floor distributor (interface lightning protectionzones 1 and 2). The surge arrester FS HA is a pluggable Herm–Aphroditeconnector (IVS plug) also usable to protect the terminal equipment(interface lightning protection zones 2/3) (Figure 5.8.2.3.2 e).

Table 5.8.2.3.2 a Lightning current arrester TR8 and surge arrester FS HA:Technical data


Figure 5.8.2.3.2 c(a) Surge arrester, typeFS HA (b) Basiccircuit diagram

Figure 5.8.2.3.2 d (a) Ring line distributor of atoken ring network

Figure 5.8.2.3.2 d (b) Basic diagram


Sources

IEEE Std 802 (Revision of ANSI/IEEE Std 802.5–1985): ‘Local area networks:Token ring access method and physical layer specifications’ (IEEE, NewYork, May 1989)DEHN u. SÖHNE: ‘Surge protection: Safety for your data networks. Adviceand equipment for optimized system solutions’ DS647 Oct. 1996DEHN u. SÖHNE: ‘Surge protection. Main catalogue UE’98 E’. DS570/E1998

5.8.2.3.3 Protective devices for Ethernet twisted pair cabling. For high-performance PC networks the twisted pair cabling system is used. Twotypes of cabling are specified: Ethernet 10 Base T and Fast Ethernet 100Base TX.

The structure of Ethernet 10 Base T is a ‘twisted pair’ cabling having

Figure 5.8.2.3.2 d Application of the FS HA surge arrester

Figure 5.8.2.3.2 d (c) Detail

Figure 5.8.2.3.2 e Terminal with surge protectors: (energy side) type SF-Protector; (data side) type FS HA


a tree topology with cable lengths up to 100m. The terminal equipmentcommunicating by the transmission method is specified in IEEE 802.3.Bonding elements are RJ45 connectors. HUBs located in floor distribu-tors are designed to support network management and the repeaterfunction. The data transmission rate of the system is 10Mbps. FastEthernet 100 Base TX was developed from Ethernet 10 Base T. With ahigher data transmission rate of 100Mbps this system continuouslymeets the growing requirements of data technology. The topology con-nectors and pin assignments are the same as those of the Ethernet 10Base T.

Owing to the active components in the floor distributor, large networkswith widespread cabling systems can be realized. Figure 5.8.2.3.3 a is aproposal for how to protect an Ethernet ‘twisted pair’ cabling. The floordistributor (HUB) is protected by the NET-Protector 4 TP introducedin section 5.8.2.3.1 (Figure 5.8.2.3.1 d). This surge protective deviceis suitable for both Ethernet 10 Base T and Fast Ethernet 100 BaseTX and fits the universal cabling as specified in EN 50173, class D(cat. 5).

To protect the data input of the terminal equipment, surge protecteddata socket outlets DSM-RJ45–10 Base T with shielded RJ45-sockets(Figure 5.8.2.3.3 b, Table 5.8.2.3.3 a) can be used. HUB and terminalequipment can also be protected by the pluggable surge arrester ÜGKF/RJ45 4TP (Figure 5.8.2.3.1 f, Table 5.8.2.3.1 b), as shown in Figure5.8.2.3.3 c. Data and power input of the terminal equipment can becommonly provided with the combined surge protective device DATA-Protector RJ45 4TP (Figure 5.8.2.3.1 g, Table 5.8.2.3.1 c).

Figure 5.8.2.3.3 a Protectors in Ethernet twisted-pair cabling


Sources

ANSI/IEEE 802 Edition: ‘Information technology – Telecommunications andinformation exchange between systems – Local and metropolitan area net-works – Specific requirements. Part 3: Carrier sense multiple access withcollision detection (CSMA/CD) access method and physical layer specifica-tions’ (IEEE, New York, March 1996)EN 50173:1995-11: ‘Informationstechnik. Anwendungsneutrale Verkabe-lungssysteme’. Deutsche Fassung EN 50173 (Beuth Verlag GmbH, Berlin,1995)DEHN u. SÖHNE: ‘Surge protection: Safety for your data networks. Adviceand equipment for optimized system solutions’. DS647 Oct. 1996DEHN u. SÖHNE: ‘Surge protection. Main catalogue UE’98 E’. DS570/E 1998

5.8.2.3.4 Protective devices for Ethernet coax-cabling. Coaxial cablingsystems do not require floor distributors and additional amplifiers. Twodifferent types of coaxial Ethernet networks are distinguished:

• Ethernet Thickwire according to IEEE 802.3, 10 Base 5, also called‘Yellow Cable’.

• Ethernet Thinwire according to IEEE 802.3, 10 Base 2, also called‘Cheaper Net’.

Their data transmission rate is 10Mbps.The yellow coated ‘Ethernet Thickwire’ cable (rigid inner conductor,

four shielding layers) has excellent electrical characteristics and can havea segment length up to 500m. Connections to the cable segment arepossible by means of a transmission/receiver unit (transceiver). Trans-ceivers are connected by N-connectors or crimp snap-in connectors tothe coaxial bus cable. It is possible to connect up to 100 transceiverstations in a 500m segment. Up to 50m long cable sets connect trans-ceivers and stations. These sets are also called ‘drop-cables’.

Figure 5.8.2.3.3 b (a) Data socket outlet(with surge arrester) DSM-RJ45-10 Base T protectsdata input of the terminal

Figure 5.8.2.3.3 b(c) Basic circuitdiagram

Figure 5.8.2.3.3 b(b) DSM-RJ45-10 Base T


By contrast ‘Ethernet Thinwire’ cable only has a shield and single-stranded conductor which is shielded by an outer wire fabric and so it ismuch more flexible than the ‘Ethernet Thickwire’ cable. The segmentlength of the thin Ethernet cable, however, is limited to 185m withonly 30 connections to be made at one cable segment. External trans-ceivers are not necessary for these connections, but BNC-T connectors or

Table 5.8.2.3.3 a Surge arrester DSM-RJ45–10 Base T: Technical data


EAD outlets can be used as the Ethernet-connection cards in the stationsalready have integrated transceivers.

The coaxial cables of both systems consist of wire and shield, theshield being earthed at one point (mostly at the server of the system).The shield is also a common return for the data transmission. Figure5.8.2.3.4 a shows a proposal of how to protect a system.

Ethernet Thickwire only allows two protectors per segment. Theseshould be installed at the building entrance or at the floor entrance. Anynumber of protectors can be used with Ethernet Thinwire and it isrecommended to protect every network card.

The Ethernet Thickwire cable 10 base 5 in Figure 5.8.2.3.4 b (Table5.8.2.3.4 a) is protected by a ÜGKF/N-L protector, whereas theÜGKF/B-L surge arresters are used in the Ethernet Thinwire system10 Base 2 in the Figure 5.8.2.3.4 c (Table 5.8.2.3.4 a).

Sources

ANSI/IEEE 802 Edition: ‘Information technology – Telecommunications andinformation exchange between systems – Local and metropolitan area net-works – Specific requirements. Part 3: Carrier sense multiple access withcollision detection (CSMA/CD) access method and physical layer specifica-tions’ (IEEE, New York, March 1996)

Figure 5.8.2.3.3 c Compact-HUB and terminal are protected by typeÜGKF/RJ45 surge arresters. There is an SF-Protectorto protect the power input of the terminal.


Figure 5.8.2.3.4 a Protectors in Ethernet coax-cabling

Table 5.8.2.3.4 a Surge arresters, types ÜGKF/N-L and ÜGKF/B-L: Technicaldata


DEHN u. SÖHNE: ‘Surge protection: Safety for your data networks. Adviceand equipment for optimized system solutions’. DS64 Oct.1996DEHN u. SÖHNE: ‘Surge protection. Main catalogue UE’98 E’. DS570/E1998

5.8.2.3.5 Protective devices for standard cabling. Interfaces V.24 (RS 232C), V.11 (RS 422) and Twinax for IBM hardware are often used toconnect EDP systems such as terminals and printers. Interfaces RS 232 C(V.24) and RS 422 (V.11) are used with usual telephone cables in the star-topology. Consider the following notes:

(i) V.24 (RS 232 C). This is a serial interface with a data transmission rate ofup to 19.2kbps. Standard bus drivers are able to support data transmission

Figure 5.8.2.3.4 b (a) Ethernet thickwire segment connected to the star couplerby an ÜGKF/N-L protector

Figure 5.8.2.3.4 b (b) Surge arrester,type ÜGKF/N-L with N-plug/socket

Figure 5.8.2.3.4 b (c) Basiccircuit diagrams of the surgearresters ÜGKF/N-L and ÜGKF/B-L (indirect shield-earthingpossible by gas-filled surgearresters)


lines of up to 15m length, while special bus drivers are able to cover adistance of up to 300m line length. By the use of an interface converterfor RS 232 to TTY transmission, distances of more than 300m can bereached. Usually 25-pole D-subminiature sockets and 9-pole connectorsare used as connectors.

(ii) V.11 (RS 422) This is a serial interface using two balanced lines for datatransmission rates of up to 2Mbps. Line lengths up to 1000m are possible.The 15-pole D-subminiature socket is often used for mechanicalconnection.

Figure 5.8.2.3.4 c (a) Application of surge arresters in the T-branch of anEthernet-thinwire segment

Figure 5.8.2.3.4 c (b) Surge arresterÜGKF/B-L to protect the network cardin a workstation

Figure 5.8.2.3.4 c (c) Surgearrester ÜGKF/B-L withBNC-plug/socket


(iii) Twinax cabling. The IBM standard is carried out with a shielded Twinaxcable comprising a wire pair. In one Twinax line up to eight terminals canbe connected in the bus topology. A data transmission rate of up to 1Mbpsis possible. The Twinax connector is used at the host computer (e.g., AS400) as well as at the terminal.

Figure 5.8.2.3.5 a shows cabling protection with V.24(RS 232 C) andV.11(RS 422) interfaces. Figure 5.8.2.3.5 b shows the basic circuit dia-gram for data transmission in an IBM Twinax system. Figure 5.8.2.3.5 cshows the corresponding protection arrangement.

Figure 5.8.2.3.5 a Protectors in a cabling system with V.24 (RS 232 C) andV.11 (RS 422) interfaces

Figure 5.8.2.3.5 b Data transmission in the IBM Twinax system


Figure 5.8.2.3.5 c Protectors in an IBM Twinax system

Figure 5.8.2.3.5 d (a) Surge arresters, type FS 25 E protect control unit (everyterminal cable is protected)

Figure 5.8.2.3.5 d (b) Surge arrester, typeFS 25 E protects terminal input

Figure 5.8.2.3.5 d (c) Surge arrester, type FS 25 E


The lightning current arrester Blitzductor® CT, type BE, 5 V, isinstalled to protect the V.24 (RS 232 C) / V.11 (RS 422) cabling at thebuilding input. Surge arresters type FS 15 E (15-pole) or type FS 25 E(25-pole) protect the sockets (Figure 5.8.2.3.5 d, Table 5.8.2.3.5 a). If

Table 5.8.2.3.5 a Surge arresters, types FS 25 E and FS 15 E: Technical data


there are TTY interface converters in such a system, then a type ÜSD-25-TTY/B-KS surge arrester (Figure 5.8.2.3.5 e, Table 5.8.2.3.5 b) can beapplied.

The IBM Twinax system can be protected by type ÜGKF/Twinaxsurge arresters (Figure 5.8.2.3.5 f, Table 5.8.2.3.5 c).

Table 5.8.2.3.5 b Surge arrester, type ÜSD-25-TTY/B–KS: Technical data


Sources

DEHN + SÖHNE: ‘Surge protection: Safety for your data networks. Adviceand equipment for optimized system solutions’. DS647 Oct. 1996DEHN + SÖHNE: ‘Surge protection. Main catalogue UE’98 Ed’. DS570/E1998

5.8.2.3.6 Protective devices for data telecontrol transmission by an ISDNbase terminal. Different services are offered across common publicnetworks using ISDN (‘integrated services digital network’). Voice

Table 5.8.2.3.5 c Surge arrester, type ÜGKF/Twinax: Technical data


Figure 5.8.2.3.5 e (a) Surge arrester, type ÜSD-25-TTY/B-KS for TTY-interface

Figure 5.8.2.3.5 f (b)Basic circuit diagram

Figure 5.8.2.3.5 f (b) ÜGKF/Twinax

Figure 5.8.2.3.5 f (a) Surge arrester, type ÜGKF/Twinax protects IBM-terminal

Figure 5.8.2.3.5 f(c) Basic circuit diagram


frequencies as well as data can be transmitted digitally using ISDN. Thesupply line of the digital local exchange is a balanced line. A networkterminal (NT) is the transfer interface for the user. The terminal base has2 B-channels with 64kbps each and a D-channel with 16kbps. The NT issupplied with interface Uk0, the user’s interface is S0. A four-line bustopology can be up to 150m long, a direct connection from point topoint can be up to 1000m long. Digital terminal equipment such astelephones, faxes or extensions may be connected to this interface.

Figure 5.8.2.3.6 a shows where to use what type of protector.When protective devices are installed before the NT (Uk0 interface),the requirements of the telecommunication companies are to beobserved.

The Blitzductor® CT, type B arrester described in section 5.8.2.1.1 isinstalled at the lightning protection zone interface 0A/1 (Figure 5.8.2.3.6 b,Table 5.8.2.1.3.2 b).

At the user’s interface (So interface) of the NT the pluggable surgearrester ÜGKF/RJ45 ISDN S0 (Figures 5.8.2.3.6 c, Table 5.8.2.3.6 a) isinstalled.

There are one or two-pole data sockets (with surge protection) DSM-1 × RJ45 ISDN So or DSM-2 × RJ45 ISDN So for ISDN terminals(Figures 5.8.2.3.6 d, Table 5.8.2.3.6 b).

Systems with LSA-PLUS-terminals are protected by surge arresterssuch as type DPL 10 F/ISDN So (Figure 5.8.2.3.6 e, Table 5.8.2.3.6 c).

Figure 5.8.2.3.6 a Protectors for long-distance data transmission with an ISDN-base terminal


Figure 5.8.2.3.6 c (b) Surge arrester ÜGKF/RJ45 ISDN So

Figure 5.8.2.3.6 b Lightningcurrent arrester Blitzductor® CT,type B

Figure 5.8.2.3.6 c (a) Surge arresterÜGKF/RJ45 ISDN So on the user side ofthe NTBA

Figure 5.8.2.3.6 c (c)Basic circuit diagram


Table 5.8.2.3.6 a Surge arrester, type ÜGKF/RJ45 ISDN So: Technical data

Figure 5.8.2.3.6 d (a) Data socket outlet (with surge arrester) DSM–2 × RJ45ISDN So protects ISDN terminals (Fax and telephone)


Figure 5.8.2.3.6 d (b) Data socket outlets (with surge arresters) types DSM–1 × RJ45 ISDN So and DSM-2 × RJ45 ISDN So

Figure 5.8.2.3.6 d (c) Basic circuit diagrams

Figure 5.8.2.3.6 e (a) Surge protective block,type DPL 10F/ISDN So for 10 double wires toplug into LSA-PLUS disconnection block

Figure 5.8.2.3.6 e(b) Basic circuit diagram


Table 5.8.2.3.6 b Data socket outlets (with surge arresters), types DSM-1 × RJ45 ISDN SO and DSM-2 × RJ45 ISDN So: Technicaldata


Sources

DEHN + SÖHNE: ‘Surge protection: Safety for your data networks. Adviceand equipment for optimized system solutions’. DS647 Oct. 1996DEHN + SÖHNE: ‘Surge protection. Main catalogue UE’98 E’. DS570/E 1998.

5.8.2.3.7 Protective devices for data telecontrol transmission by ISDN pri-mary multiplex terminal. The primary multiplex terminal has 30 B chan-nels with 64kbps each and a D channel with 64kbps. Data transmissionsup to 2.048Mbps can be carried out via a primary multiplex terminal.The NT is supplied with interface U2m; the user’s interface is S2m. Large

Table 5.8.2.3.6 c Surge protective block, type DPL 10 F/ISDN So: Technicaldata


extension units or data lines with high data volumes are connected to thisinterface. The S2m interface is operated using normal telephone lines.

Figure 5.8.2.3.7 a shows the basic arrangement of the protectivedevices. At the interface of lightning protection zone 0A/1 again a light-ning current arrester Blitzductor® CT, type B (introduced in Section5.8.2.1) (Figure 5.8.2.3.7 b) is used.

In the user’s system surge arresters Blitzductor® CT, type MD/HF(also described in Section 5.8.2.1.1) (Figure 5.8.2.3.7 c, Table 5.8.2.3.7 a)are applied.

Figure 5.8.2.3.7 a Protectors for long-distance data transmission with ISDN-primary–multiplex terminal equipment

Figure 5.8.2.3.7 b Lightningcurrent arrester Blitzductor®

CT, type B to protect the U2m

interface

Figure 5.8.2.3.7 c Surge arresterBlitzductor® CT, type MD/HF ( forhigh-frequency applications)


Sources

DEHN + SÖHNE: ‘Surge protection: Safety for your data networks. Adviceand equipment for optimized system solutions’. DS647 Oct. 1996DEHN + SÖHNE: ‘Surge protection. Main catalogue UE’98 E’. DS570/E1998

5.8.2.3.8 Protective devices for data telecontrol transmission by analoguea/b-wire terminal. In industrial as well as in private sectors, analoguelong-distance data transmission via modem is commonly used. The datatransmission rate is determined by hardware components of the modem.The TAE system with N coding is specified by the German Telecomas a plug-in connector. The exchange lines as well as branch exchangelines are mostly carried via terminals blocks. The LSA-PLUS terminals

Table 5.8.2.3.7 a Surge arrester Blitzductor® CT-type MD/HF: Technical data


Figure 5.8.2.3.8 c (a) Surge arresters,type DPL 1F/ALD, 110V, protect therank distributor

Figure 5.8.2.3.8 c(c) Basiccircuitdiagram

Figure 5.8.2.3.8 a Protectors for long-distance data transmisssion with analoguea/b-wire connection

Figure 5.8.2.3.8 b (a) Lightningcurrent arrester, type DPL 10G in LSA-PLUS technique for protection of10 double wires

Figure 5.8.2.3.8 c(b) Surge arrester,type DPL 1F/ALD,110V

Figure 5.8.2.3.8.b (b) Basiccircuit diagram


described in Section 5.8.2.1.7 are widely used for this purpose. Terminalequipment is often connected via TAE sockets with F coding.

Figure 5.8.2.3.8 a shows the arrangement of protective devices in sucha system. Lightning current arresters (e.g. Blitzductor® CT, type B)(Figure 5.8.2.3.7 b) or DPL 10 G (at LSA-PLUS terminals) (Figure5.8.2.3.8 b, Table 5.8.2.3.8 a) are installed at the interface of the light-ning protection zones 0A/1 (line input of the lightning protectedbuilding).

The lines at the disconnection block are protected by surge arrestersDPL 1F/ALD, 110V (Figure 5.8.2.3.8 c, Table 5.8.2.3.8 b).

The telephones are connected to TEA sockets (with surge protection)DSM-TAE-3x6 NFN-PWM (Figure 5.8.2.3.8 d , Table 5.8.2.3.8 c).

The modem is protected by a combined surge protective device, typeFAX-Protector TAE/N (Figure 5.8.2.3.8 e, Table 5.8.2.3.8 d).

Table 5.8.2.3.8 a Lightning current arrester, type DPL 10 G: Technical data


Table 5.8.2.3.8 b Surge arrester, type DPL 1 F/ALD, 110V: Technical data

Figure 5.8.2.3.8 d (a) TAE-socket outlet(with integrated surge arrester for a/b wires)type DSM-TAE-3 × 6 NFN–PWM withthree TAE-sockets with N/F/N coding

Figure 5.8.2.3.8 d(b) Basic circuitdiagram


Table 5.8.2.3.8 c TAE socket outlet (with surge arrester), type DSM–TAE-3 × 6NFN-PWM

Figure 5.8.2.3.8 e (a) Combined surgeprotector, type FAX-protector TAE/N protectsa/b-wire-input and 230V-energy supply of themodem


Figure 5.8.2.3.8 e(b) Combined surge protector,type FAX-protector TAE/N

Figure 5.8.2.3.8 e (c) Basic circuitdiagram

Table 5.8.2.3.8 d FAX-Protector TAE/N: Technical data


Sources

DEHN + SÖHNE: ‘Surge protection: Safety for your data networks. Adviceand equipment for optimized system solutions’. DS647 Oct. 1996DEHN + SÖHNE: ‘Surge protection. Main catalogue UE’98 E’. DS570/E 1998


Chapter 6

Application in practice:Some examples

Here are some practical examples of how the protective measuresdescribed are carried out and how the protective devices introduced areused in electrical systems with sensitive electronic equipment. These arealso systems which were seriously interfered with or even damagedby lightning previously. Since protective measures were completed thewell-targeted application of protective devices has been working trouble-free for years, even during violent thunderstorms and direct lightningstrikes.

It is now over 20 years since the development of surge limiters forhighly sensitive electronic systems was initiated. At that time structureswere equipped with the new protective devices and with ‘lightning cur-rent counters’. Today, there is more than a decade of reliable informationon the efficiency of these surge protective devices, including those sys-tems that failed five times and more per year in the previouslyunprotected stage.

A lightning/surge current counter which can also register the responseof surge protective devices is shown in Figure 6 a. This is designedaccording to the current transformer principle (Figure 6 b) and registerssurge currents with peak values exceeding 200A. Such a counter can beinstalled directly into the down conductor of a lightning protection sys-tem (Figure 6 c) or the earth bonding line of a protective device withoutreducing the cross section. Often it is necessary to carry out surgevoltage/surge current tests not only in the laboratory or during the pro-duction of protective devices but also in the field. Here the portable‘hybrid generator’ shown in Figure 6 d has been proven. In the case of ashort circuit it emits a standardized 8/20μs surge current with a max-imum peak value of 10kA, whereas in open circuit it generates thestandardized surge voltage wave 1.2/50 μs with a peak value up to10kV.

Figure 6 a Lightning/surge current counter

Figure 6 b Lightning/surge current counter: Layout and interior circuit

Figure 6 c Lightning/surge current counter installed at a down conductor

Figure 6 d Portable hybrid generator


6.1 Industrial plants

As explained in Section 4.1.1, the necessary protective measures and therequired lightning protection levels for a particular industrial plant aredetermined by means of risk analysis as a first step. In a second step thelightning protection zones will be determined according to the manage-ment plan introduced in Section 4.1.3 (in accordance with IEC 61312–1)(Figure 6.1 a).

Modern construction techniques using steel skeletons, reinforced con-crete and often metal facings allow integration of these metal partsinto the lightning protection system. If lightning protection matters havebeen considered during the construction planning stage, advantageousarchitectural solutions can often be found.

6.1.1 Fabrication hall

A step-by-step procedure for a factory hall built of prefabricated con-crete elements (Figure 6.1.1 a) follows:

• Connection lines bonding the reinforcement of the foundation socket(for the hall pillars) with the reinforcement of the pillars and with aring type earth electrode are laid around the hall (Figure 6.1.1 b).

• Reinforcement of the pillars is interconnected and the connection linesare brought out at the bottom and top (Figures 6.1.1 c and d).

• Figure 6.1.1 e shows a finished pillar with the brought out reinforce-ment basket connection, ready to be placed into the foundationsocket.

Figure 6.1 a Industrial plant: lightning protection levels = PL (acc. to a riskanalysis) and lightning protection zones = LPZ (in accordance withthe LEMP-management plant)

Application in practice: Some examples 295

• Floor reinforcement mats are interconnected by continuous steel wires(Figure 6.1.1 f ), brought out near the pillars for final connection withthe ring equipotential bonding bar (Figure 6.1.1 g).

• Reinforcement connection wires brought out on top of the pillars(Figure 6.1.1 h) are to be connected with the steel construction of theattic (Figures 6.1.1 i and j).

• All piping or lines entering the factory building (such as water, heating,oil, compressed air pipes or power, telephone, data and signal lines)enter through a reinforced cable duct (the reinforcement of which willbe connected with the hall reinforcement) at a point where the light-ning protection equipotential bonding will also be carried out.

• All foundation reinforcements will be included into the earthing sys-tem (Figure 6.1.1 k), the individual reinforcement mats being intercon-nected by a continuous wire and corresponding clamps (Figure 6.1.1 l).Earthing systems of individual buildings of the whole structure to beprotected shall be interconnected to a meshed surface earthing (Figure6.1.1 m).

6.1.2 Store and dispatch building

In this example the building is a computer-controlled high-bay ware-house (Figure 6.1.2 a) with dispatch area (Figure 6.1.2 b), made out ofreinforced concrete supports, reinforced prefabricated concrete wallelements and a metal roof (Figure 6.1.2 c). The following Figures showhow lightning protection measures are realized during the progress ofconstruction:

Figure 6.1.1 a Factory hall made out of prefabricated concrete parts, where themetal reinforcements are integrated into the lightning protectionsystem (total view)


Figure 6.1.1 f Continuouslyinterconnected reinforcement mats ofthe floor

Figure 6.1.1 c Reinforcement basketof a hall pillar (lying down, duringfabrication) with connection line

Figure 6.1.1 d Detail of Figure 6.1.1 c

Figure 6.1.1 e Finished hall pillar(lying) with brought out reinforcementconnection line

Figure 6.1.1 g Brought outconnection wire of the reinforcementmats provided for later connection tothe ring equipotential bonding bar

Figure 6.1.1 b Foundation socket withbrought out reinforcement connectionwire


• Reinforcements of the foundations for the building supports are to beinterconnected and provided with connection wires to the outside(Figure 6.1.2 d); the reinforcement baskets will then be interconnected.

• Steel reinforcements of the supports are to be continuously connected(Figure 6.1.2 e).

Figure 6.1.1 j Connection of the atticsupport construction

Figure 6.1.1 l Terminal to connectreinforcement mats with steel strip

Figure 6.1.1 k Foundationreinforcement is included in theearthing system

Figure 6.1.1 h Reinforcementconnection wire brought out at thepillar head

Figure 6.1.1 i Connection of thereinforcement with the attic supportconstruction


• Reinforcements of foundation and support are to be connected (Figure6.1.2 f ).

• Support reinforcements are to be connected with the metal roof con-struction by clamps made to carry lightning currents (Figures 6.1.2 g).

• Steel reinforcements of the prefabricated wall elements for the

Figure 6.1.1 m Building earthings interconnected to a meshed surfaceearthing

Figure 6.1.2 a High-baywarehouse

Figure 6.1.2 b Dispatch area


high-bay warehouse (lightning protection zone 2) are already continu-ously connected by the producer (for later shielding purposes) and areprovided with fixed earthing terminals (at which the wall elements thenwill be interconnected) (Figures 6.1.2 h).

• Figure 6.1.2 i shows such interconnected wall elements.

• Reinforcement steel mats in the store floor are to be interconnected;connection wires (for the ring equipotential bonding bar) are broughtout at the walls (Figure 6.1.2 j).

Figure 6.1.2 c Dispatch building

Figure 6.1.2 d Reinforcement baskets with brought out connection wires


• This is the way to create in the building (lightning protection zone 1) acompletely shielded room (lightning protection zone 2) for the com-puter controlled high-bay warehouse.

• Metal piping for water, heating, and compressed air entering the build-ing through a supply duct are to be included into the lightning protec-tion equipotential bonding by pipe clamps (made to carry lightningcurrents) on entering lightning protection zone 1 (Figure 6.1.2 k).

Figure 6.1.2 e Continuouslyinterconnected support reinforcement

Figure 6.1.2 f Reinforcement steelsof foundation and support areconnected

Figure 6.1.2 g Connection of the support reinforcement with the metal roofconstruction


• Power lines are to be provided with lightning current arresters onentering lightning protection zone 1 of the building (Figure 6.1.2 l).

• Information technology lines will be connected across the protectivecabinet shown in Figure 6.1.2 m on entering the building (lightningprotection zone 1).

• On entering the high-bay warehouse (lightning protection zone 2) allelectric lines are to be provided with surge arresters in the distribution(outside at the store wall) (Figure 6.1.2 n).

6.1.3 Factory central heating

The central heating system of a factory, shown in Figures 6.1.3 a, hastwo 20m high metal chimneys the protected area of which (lightning

Figure 6.1.2 i Reinforcementsof two wall elementsinterconnected at brought outfixed earthing terminals

Figure 6.1.2 j Interconnection of the steelmats in the floor with brought out connectinglugs for ring equipotential bonding bar

Figure 6.1.2 h Continuous reinforcementsteels of the wall elements are prepared forshielding purposes


Figure 6.1.2 m Informationtechnology lines (e.g. telephonelines, fire-alarm lines, control lines)are taken over a protective cabinetat the building input

Figure 6.1.2 k Inclusion of metalpipings into the lightning protectionequipotential bonding at the entry intolightning protection zone 1

Figure 6.1.2 l Lightning currentarrester at the input of power lines intolightning protection zone 1


protection level III, α = 45°) is not sufficient (as shown in the side view ofFigure 6.1.3 a, C) to avoid direct lightning strikes into the centralheating.

Also in this example it will be demonstrated step-by-step howlightning/surge protection is going to be carried out for a central heatingsystem with steel pillars, sheet steel walls and a metal roof construction.Consider the following:

• Figure 6.1.3 b shows the reinforcement of the ground plate (all struc-tural steel mats being interconnected) and the metal plate foundationsfor the tubular steel pillars which are to be interconnected for reasonsof earthing and shielding.

• The tubular steel pillars serve as down conductors (Figure 6.1.3 c).

• Figure 6.1.3 d shows how the reinforcement baskets of the metal chim-neys’ foundations are interconnected.

• The tubular steel of the chimneys is to be bonded with the foundationreinforcement (Figure 6.1.3 e) to serve as ‘air terminations/downconductor/earthing’.

• Metal roof and sheet steel wall elements are to be bonded with thetubular steel pillars and the metal roof-supporting construction, thus

Figure 6.1.2 n Electrical lines entering lightning protection zone 2 of the high-bay warehouse are connected with surge arresters


serving as ‘air terminations, down conductors and shield’ (Figure 6.1.3 f)and forming an inside lightning protection zone 1.

• All metal aggregates are to be connected with the base reinforcement(as directly as possible) via preinstalled fixed earthing terminals(chapter 5.2, Figure 5.2 g) (Figure 6.1.3 g).

• Electrical lines, on entering lightning protection zone 1, are to be pro-vided with lightning current arresters in the switchgear cabinet (Figure6.1.3 h).

• Figure 6.1.3 i shows the electrical line protected by surge arresters on

Figure 6.1.3 a Central heating

(d) Internal view

(b) Front view (a) External view

(c) Side view


Figure 6.1.3 f Metal roof and wall elements are interconnected

Figure 6.1.3 d Reinforcementbaskets of the chimney foundations

Figure 6.1.3 e Metal chimneysconnected with the foundationreinforcement

Figure 6.1.3 b Continuousground plate reinforcementand metal plate foundations

Figure 6.1.3 c Steel tube supportsconnected with the ground platereinforcement as down conductors


entering the control cabinet of the central heating unit which is light-ning protection zone 2.

6.1.4 Central computer

The central computer (Figure 6.1.4 a) of the factory is in the office build-ing and is used for accounting, book-keeping, operations scheduling,

Figure 6.1.3 h Lightning currentarresters at the entry of electrical linesinto lightning protection zone 1

Figure 6.1.3 i Surge arresters at thecrossing of electrical lines from lightningprotection zone 1 into lightningprotection zone 2 (control cabinet)

Figure 6.1.3 g Metal aggregates sets are connected as closely as possible with theground reinforcement by fixed earthing terminals


material tracking, production control and stock control. A long fail-ure of this computing centre (e.g., due to surges) would not only paralysethe automatic operating process but also would mean an immeasurablefinancial loss for the company.

Data transfer occurs over a four-wire current loop 20mA currentinterface. 25-pole D-subminiature plugs are used as terminal facilities.The office building has been structured according to the concept oflightning protection zones where the interfaces of incoming lines aretreated accordingly at the lightning protection zone boundary 0/1. Thecomputer room in the office building is designated as lightning protectionzone 2, as described below.

The power cable is connected to surge arresters at the boundary oflightning protection zone 1/2 (Figure 6.1.4 b). For the datalines, surgeprotected data socket-outlets are installed at this zone crossing. They aremechanically and electrically compatible with the computer interfaces.These socket-outlet type surge arresters have a front-side ‘protected out-put’. They are installed into a 19 inch protective cabinet where they offerthe possibility to jump, thus this cabinet can also serve as a terminal block(Figures 6.1.4 c and 6.1.4 d).

Sources

HASSE, P., and WIESINGER, J.: ‘EMV Blitz-Schutzzonen-Konzept’ (PflaumVerlag, München, VDE Verlag, Berlin/Offenbach, 1994)

Figure 6.1.4 a Computer centre of a factory


HASSE, P.: ‘EMV- orientiertes Blitz-Schutzzonen-Konzept mit Beispielen ausder Praxis’. Aus: ‘Elektromagnetische Verträglichkeit’ (VDE Verlag, Berlin/Offenbach, 1991), pp. 59–150

6.1.5 European installation bus (EIB)

Just as with any other electrical lines the bus network will also be includedin the lightning/surge protection measures, that is lightning currentarresters will be installed at the boundary of lightning protection zone

Figure 6.1.4 c Front view ofthe 19 ″-protective cabinet fordata lines

Figure 6.1.4 b Connection of mains and data lines of a computer centre at theinterfaces of lightning protection zones 1/2 with surge arresters

Figure 6.1.4 d Detail of Figure 6.1.4 c


0A/1 (Figure 6.1.5 a). For surge protection of the bus line (Figure 6.1.5 b)there is an EIB surge-arrester terminal (Figures 6.1.5 c, Table 6.1.5 a)which, for example, can be mounted in a switch box (as Figures 6.1.5 dshow).

Figures 6.1.5 e show further application of this bus surge arrester forprotection of bus devices in a factory. Figure 6.1.5 f shows the com-prehensive protection of EIB lines crossing several buildings.

Figure 6.1.5 a Inclusion of the bus network into the lightning protectionequipotential bonding (Source: ZVEI/ZVEH)

Figure 6.1.5 b Application of surge arresters at bus devices

Figure 6.1.5 c (a) EIB-surge arresterBUStector

Figure 6.1.5 c (b) Basiccircuit diagram


Table 6.1.5 a EIB-surge arrester BUStector: Technical data

Figure 6.1.5 d (a) Basic diagram

Figure 6.1.5 d (a, b and c) Mounting of the EIB-surge arrester in a switch box(Source: ZVEI/ZVEH)

Figure 6.1.5 d (c) Practical executionFigure 6.1.5 d (b) Practical execution


Figure 6.1.5 e (a) at the connector

Figure 6.1.5 e (b) at the line coupler

Figure 6.1.5 e (a and b) Mounting examples for EIB-surge arresters(Source: ZVEI/ZVEH)

Figure 6.1.5 f Lightning/surge protection of factory buildings with EIB-systems


6.1.6 Other bus systems

Other bus systems are equally integrated in the lightning protection con-cept by lightning current and surge arresters. It must always be con-sidered that the local surge protection of the bus components (e.g., in alocal lightning protection zone) includes both the power lines and the buslines (Figure 6.1.6 a). This is shown, for example, by the SIMATIC ET100 bus system (interface RS 485) in Figure 6.1.6 b.

6.1.7 Fire and burglar alarm system

Fire and burglar alarm systems need long conductor loops throughbuildings and structures, encountering a considerable danger (especially

Figure 6.1.6 a Surge protection for mains supply and bus lines: (left) SPS-protector; (right) Blitzductor®

Figure 6.1.6 b Surge protection for SIMATIC ET 100


to the central alarm) due to surges. The minimum interference immunityof such systems is standardized in EN 50 130, prescribing the selectionof the arresters to be used.

There are two kinds of examining principles for fire and burglar alarmsystems:

• DC line technique. According to the closed-circuit principle everysignal line (which has several detectors) is continuously controlled.If a detector gives an alarm, the corresponding signal line will beinterrupted and thus the alarm is given in the central alarm. Hereonly the signal line can be identified: not, however, the signallingdetector.

• Impulse line technique. Here the information of a signalling detectorwill be transmitted in digital signals. By means of the transmissionprotocol the signalling detector can be identified.

The lines, just as those for any other network in buildings and systems,must be included in the lightning/surge protection:

• At the boundary of lightning protection zone 0A/1 the Blitzductor®

CT, type BE, for example, is used for lines which cross severalbuildings (selected according to the operating voltage of the signalline).

• At the central alarm (which is mostly designed as the local zone ofprotection) all inputs and outputs (signal line inputs, optical/acoustical signal line outputs) will be equipped, for example, with asuitable Blitzductor® CT, where it should be taken into account thatthe nominal current of these arresters (at system operation) is notexceeded. In case of nominal currents > 1A, for example, the surgeprotection device DEHNrail with adequate nominal voltage should beused.

The Blitzductor® CT, type BD, 110V, for example, is recommended toprotect telecoms lines (for the self-dial device). The power supply lineof the central alarm will be protected as usual by the lightning currentarrester (e.g., DEHNport® , 250V), decoupling element (e.g., in the caseof insufficient line length, DEHNbridge) and surge arrester (e.g.,DEHNguard®).

Figure 6.1.7 a shows a typical fire alarm system in the DC line tech-nique; here, also, are the necessary protective devices. Figure 6.1.7 bshows the protection of a burglar alarm system using the DC linetechnique.

The surge protection for the lightning protection zone crossing 1/2 forthe Siemens fire central alarm, type BMS, is shown in Figure 6.1.7 c andin Figure 6.1.7 d for the Siemens burglar central alarm, type IT. Forboth of these protection proposals it is pointed out that the Blitzductor®s


CT, type ME/C, are energy coordinated with the protective device type,8 P/G, recommended by Siemens for such systems (Figure 6.1.7 e).

Source

EN 50130–4: ‘Alarm systems. Part 4: Electromagnetic compatibility –Product family standard: Immunity requirements for components of fire,intruder and social alarm systems’ (International Electrotechnical Commis-sion, Geneva, 1995)

Figure 6.1.7 a Protection of a fire-alarm system using DC line-technique

Figure 6.1.7 b Protection of a burglar alarm system using DC line-technique


6.1.8 Video control system

Video systems are used in industrial plants for object monitoring andaccess control. Figure 6.1.8 a shows the basic structure of such systems.They are included in lightning/surge protection systems as describedbelow:

• Location of the video camera must not be subject to direct lightning(lightning protection zone 0B): for example, at the outer façade of

Figure 6.1.7 c (a) Surge protection of the SIEMENS fire-alarm system,type BMS

Figure 6.1.7 c (b) Example for the surge protection of a fire-alarm system


the building in the protection zone of the air terminations of thebuilding’s lightning protection system, or the camera mast will be pro-vided with an air termination rod. The system cable between cameraand terminal box will be run in the shaft of the metal mast.

• Connection between terminal box (or transmitter) and monitor (orreceiver) can, for example, be realized by the existing telephone net-work (symmetric two-wire line) of the industrial plant, or there is aseparate coaxial line network. As shown in Figure 6.1.8 b the choice oflightning and surge arresters will depend on the requirements (at thelightning protection zone interfaces).

Figure 6.1.7 d Surge protection of the SIEMENS burglar alarm system, type IT

Figure 6.1.7 e Energy coordinated application of Blitzductor® CT, type ME/Cand SIEMENS ÜSS, type 8 P/G


The protective devices ÜGK/B and ÜGKF/BNC, mentioned in Figure6.1.8 b, are shown in Figures 6.1.8 c with their technical data beingsummarized in Tables 6.1.8 a and b.

For surge protection of a video control centre where several monitor-ing lines arrive, the protective devices for the 19 inch case mounting,shown in Figure 6.1.8 c (c), can be used (technical data equal to ÜGKF/BNC).

6.1.9 Radio paging system

A radio paging system, as used in an industrial area, is shown in Figure6.1.9 a. Note that: (i) the actuator, with microphone and selective call

Figure 6.1.8 a Video-monitoring system: Basic construction

Figure 6.1.8 b Protection for video-monitoring system


generator, is in the control room or in the keeper’s lodge; (ii) one or twodouble wires transmit the signal to the amplifier which is installedtogether with the omni-directional antenna in the roof area of anexposed building; and (iii) the amplified signal will be led to the antennaby a coaxial cable.

Figure 6.1.8 c (a) Lightning current arrester ÜGK/B (b) Surge arrester ÜGKF/BNC (c) Surge arrester ÜGKF/BNC III

Figure 6.1.8 c (a)

Figure 6.1.8 c (b)

Figure 6.1.8 c (c)


Figure 6.1.9 a also shows what protective measures shall be taken:

• Lightning current arresters are to be used at the lines which are cross-ing several buildings. For example:

Blitzductor®s CT, type BE (according to the signal voltage) for thesignal line double wires; coaxial arresters, type ÜGK (according to thetype BNC, N, or UHF attachment) for the aerial coaxial line; DEHN-port® for the 230V supply (such lightning current arresters certainlyare installed anyhow, if there is a lightning protection system).

• Actuator and amplifier will be protected at the 230 V input by surgearresters, for example, DEHNguard®, type 275 (which must be suf-ficiently decoupled from the lightning current arresters).

6.1.10 Electronic vehicle weighbridge

As explained in the example in Section 5.8.2.1.3.1, electronic vehicleweighbridges are powered using the four or six-wire technique: that is,two wires each for the supply voltage, for measuring and for compensa-tion purposes.

Table 6.1.8 a Arresters for video systems: Technical data

(a) Lightning current arrester, type ÜGK/B


(b) Surge arrester ÜGKF/BNC

Figure 6.1.9 a Protection of a radio/paging system


Earthing and equipotential bonding measures for the weighbridge(with the pressure gauges) are shown in Figure 6.1.10 a.

Figure 6.1.10 b shows how the protective devices are to be used:

Figure 6.1.10 a Earthing and equipotential bonding measures for a vehicleweighbridge

Figure 6.1.10 b Protection of an electronic vehicle weighbridge


• There are lightning current arresters Blitzductor® CT, type BE, 12V, atthe voltage supply, the measuring and compensation lines as well as atthe weighbridges and also at the evaluating electronics.

• Data transfer between evaluating electronics and large-digital displayusually travels by symmetric interfaces. For example, V.11 (RS 422),thus Blitzductor® CT, type BE/C, 12V, is used here.

• Control and monitoring of the weighing system in this example isrealized by a personal computer (PC) having the asymmetric interfaceV.24 (RS 232). A type FS 25 E surge arrester protects this input to theevaluating electronics (since the PC is in the same building).

• The 230V input of the evaluating electronics will be protected by surgearresters DEHNguard®, type 275 (since this line is already providedwith a lightning current arrester, for example, DEHNport® at thebuilding input).

6.2 Peak-load power station

Using the example of the peak-load power station St. Veit of theAllgäuer Überlandwerk (AÜW) in Kempten it can be demonstrated hownew buildings with electronic equipment already in the existing struc-tures can obtain the best protection according to the lightning protectionzone concept, and how these measures are made compatible with thosealready existing.

A new engine hall with gas turbines has been joined to the engine hallwith diesel generators and the lightning protection system has beenintegrated into the comprehensive lightning protection concept (Figure6.2 a). The volume to be protected is defined as lightning protectionzone 1 and comprises:

• the engine hall of the gas turbines

• the four underground gas tanks with the tank domes and the gaspipelines

• the external gas distribution station

• the corresponding connection routes with power cables and telecom-munication cables.

The transition from lightning protection zone 0 to lightning protectionzone 1 shall be explained in detail by considering the construction of theengine hall. The flat roof and the façades consist of usual reinforcedconcrete elements with welded reinforcement (Figure 6.2 b). At the fourcorners of the prefabricated concrete elements there are threaded bush-ings which are welded to the reinforcement. At these bushings the indi-vidual concrete elements can be bonded (Figure 6.2 d). The defined downconduction of the lightning protection system from the roof to thefoundations has been realized here by additional round steel in the con-crete pillars. Additional bonding points are provided to connect the


Figure 6.2 a General plan of the peak-load power station

Figure 6.2 b Steel reinforcementof the prefabricated concrete parts

Figure 6.2 c Threaded bushing welded tothe reinforcement


reinforcement of the façade elements to down conductors. The wall sideadjoining the already existing engine hall with the diesel generators hasbeen covered by continuous wire netting to guarantee a closed, electro-magnetic shield.

In the floor of the engine hall a net of strip iron is welded to thereinforcement and bonded with the reinforcement of the cartridge-typefoundations (Figure 6.2 e). By these simple and rather favourable measuresit was possible to obtain an appreciable basic shielding of the engine hallinterior against the electromagnetic field from a lightning discharge.

• Only shielded cables have been used inside the volume to protect inlightning protection zone 1, thus leading to a further reduction inexisting residual fields of interference for the electrical lines. Allshielded cables from the engine hall area are run to the informationtechnology cabinets, realized using closed sheet metal boxes, of thedirectly neighbouring control room. Inside the information technologycabinets and the connected cables a lightning protection zone 2 hasthus been created. There is further cable routing to two protective cabi-nets where cable shields are connected and the active cores are protectedby Blitzductor® KT (predecessor of Blitzductor® CT) surge arresters.These protective cabinets (Figures 6.2 f) are the central interfacebetween the protected volume of the engine hall and the outer area.

There turned out to be a special problem in that the underground gastanks and gas pipelines had to be cathodically protected. Here twodifferent levels of equipotential bonding had to be created:

• the equipotential bonding on the level of the mentioned direct earthingby the foundation earth electrodes

• the equipotential bonding on the level of the cathodical protectionpotential.

Figure 6.2 d Electrical bondingof the reinforcement of theprefabricated concrete parts

Figure 6.2 e Bonding of the reinforcementsteel by means of steel strips


Figure 6.2 g shows the line treatment inside and around the gas distrib-ution station. Those cable shields leading to equipment on the cathodicprotection potential are connected to a cathodic corrosion protectionequipotential bus bar (CCP–EBB). The gas tank bodies and the pipescoming from the tanks are directly connected to this equipotential bond-ing bar. The bushing of the cable shields and the gas pipes must be insu-lated from the earthed reinforcement of the gas distribution station. Asthe gas pipe in the distribution station is at earth potential, an insulatingflange had to be inserted at the entrance and the output of the station.

Equipment at earth potential and the corresponding cable shields havebeen bonded with the equipotential bonding bar (EBB) which is directlyearthed. For the purpose of lightning protection equipotential bondingthe equipotential bus bar lying at cathodic protection potential (CCP-EBB) and the equipotential bus bar lying at earth potential (EBB) areinterconnected by suitable explosion-protected disconnection spark gaps(Figure 6.2 h).

A corresponding solution has been implemented at the entrance of thecables and gas pipes into the engine hall area.

Sources

HASSE, P., and WIESINGER, J.: ‘EMV Blitz-Schutzzonen-Konzept’ (PflaumVerlag, München VDE Verlag, Berlin/Offenbach, 1994LANG, U., and WIESINGER, J.: ‘Eine Methode des Blitzschutzes für nach-richtentechnische Anlagen – Das Denken in Blitz-Schutzzonen’, de derelektromeister + deutsches elektrohandwerk, 1990, (11), pp. 39–45

Figure 6.2 f Protective cabinets: control room (Source: P. Biebl); total view ofthe protective cabinets; cable input into the protective cabinet witharresters (Source: P. Biebl)


Figure 6.2 g Equipotential bonding in the gas distribution station

Figure 6.2 h An explosion protected disconnection spark gap connects theequipotential bonding bar at cathodic protection potential withthe equipotential bonding bar at earth potential


6.3 Mobile radio systems

Mobile radio systems are often installed on existing buildings (in a radiotechnically favourable site). For these systems class III (according toDIN V ENV 61024–1) lightning protection is mostly provided. This mustbe independent of the host building’s systems so that they will not beadditionally endangered.

Determination of class III protection means a radius R = 45m (of therolling sphere) for the rolling sphere method to specify the position andheight of the air terminations. A sphere with radius R = 45m willbe rolled over that part of the building where the components of themobile radio system are located (Figure 6.3 a). Thus, there are lightningprotection zones with different levels of potential lightning danger:

• LPZ 0A. Direct strike is possible, undamped electromagnetic lightningfields (e.g., antenna masts).

• LPZ 0B. Direct strike impossible, undamped electromagnetic lightningfields (e.g., parts of the roof surface).

• LPZ 1: Direct strike impossible, damped electromagnetic lightningfields (e.g., interior of the base station).

If an electrical line crosses a zone interface, it must be protected at thecrossing point. For coaxial cables this is realized by connecting theshields to earthing couplings and by their equipotential bonding.

Active power and telecommunication wires will be protected by light-ning current arresters at the lightning protection zone boundary 0A/1 andby surge arresters at the zone boundaries 0B/1 and higher. According toclass III lightning protection there is a total lightning current loading of50kA (10/350μs) for the power and telecommunication cables.

To avoid uncontrolled arcing due to a lightning strike, all mobile

Figure 6.3 a Determination of the protected zone by means of the rolling spheremethod (LPZ: lightning protection zone)


radio systems on the roof such as metal installations of electrical sys-tems and the lightning protection and earthing system (if there is any),must be interconnected by a meshed functional equipotential bonding(MFEB).

This MFEB shall include the metal components of the base station,the antenna masts, cable racks and the lightning protection system of thehost building (which might already exist). For the MFEB in the area ofthe components of a mobile radio system, a mesh width of about 5 × 5 mshall be kept, thus obtaining a network of low impedance. The line crosssections of the MFEB can be taken from Table 6.3 a. An example of real-izing the meshed functional equipotential bonding for a host buildingwithout a lightning protection system is shown in Figure 6.3 b (a).

Figure 6.3 b (b), for example, shows the integration of the meshedequipotential bonding for host buildings with an existing lightningprotection system. The antenna mast must be connected as directly aspossible with the MFEB.

When using sector or radio relay antennas they must be placed in theprotective area of the mast (Figures 6.3 c). At the mast foot the incomingcoaxial cables must be screwed to a ground coupling, thus obtaining anelectrically conductive connection (lightning current proof) between thephase of the coaxial cable and the antenna mast.

The antenna cables are to be run in steel cable conduits (cable racks,cable gutters). This prevents the cables from direct lightning strikes andthe lightning field influence on the aerial cable will be damped in the caseof close-up strikes. It is necessary to ensure that there is a continuousbonding of the cable gutters. This is realized by screwing the cable racksor by bonding them by lightning current proof bridging ropes (Figures6.3 d (b) ). In addition, ground couplings are used to integrate the aerialcable at the base station into the MFEB.

The meshed functional equipotential bonding of buildings with exist-ing lightning protection system will be earthed by connection to the airterminations (Figure 6.3 b (b) ). The meshed functional equipotentialbonding of buildings without lightning protection will be earthed by anantenna earthing according to EN 50 083–1:1993–09. As the bondingconductor (earth conductor) between the MFEB on the roof and theantenna earthing, the following can be used:

Table 6.3 a Minimum cross section of MFEB line


• single solid wire, 16mm2 copper

• single solid wire, 25mm2 insulated aluminium

• 50mm2 steel.

As the earth conductor, the following can be also used:

• metal installations such as continuous metal water pipes, continuousmetal heating pipes on condition that: (i) there is permission inaccordance with the local regulations, (ii) there is permanent continuityof the different parts, and (iii) the cross sections are at least equal tothose of the above mentioned materials.

Figure 6.3 b Meshed functional equipotential bonding for a mobile radio systemon the roof of the host building: (a) without lightning protectionsystem; (b) with lightning protection system

Figure 6.3 b (a)

Figure 6.3 b (b)


• metal frame of the building

• continuous reinforcement steel of the concrete building

• façades, railings, and subconstructions of metal façades on conditionthat: (i) their cross sections are at least equal to those of the abovementioned materials and their thickness is at least 0.5mm and (ii) thereis safe vertical continuity.

Figure 6.3 c Sector antenna in the protected zone of the antenna mast

Figure 6.3 c (a) Principle: protected zone

Figure 6.3 c (b) Arrangement in practice


Antenna earthing is to be carried out using one of the followingmeans: (i) foundation earth electrode, (ii) earth electrode rod 2.5m long,or (iii) two horizontal earth electrodes at least 5m long, laid at least0.5m deep and a distance of 1m from the foundations. The minimumcross section of every earth electrode is 50mm2 Cu or 80mm2 steel.

Usually the base station, subdistribution and cable junction formlightning protection zone 1 (Figure 6.3 d (a) ).

The electrical supplying conductors (power line, telecommunication

Figure 6.3 d Protection of base station, subdistribution (SD) and cablejunction (CJ)

Figure 6.3 d (a) Basic circuit diagram

Figure 6.3 d (b) Practical arrangement


line) entering this lightning protection zone 1 must be included in themeshed functional equipotential bonding by lightning current arrestersat the zone crossing (Figure 6.3 d (a) ). Application of lightning currentand surge arresters is adjusted to the low-voltage system (TT, TN–C orTN–S system) taking into account the sufficient energy coordination ofboth arrester types. Practical examples of the arresters and decouplinginductances introduced in Section 5.8.1 are shown in Figures 6.3 e.Owing to narrow spaces the complete protective circuit for the 230Vsupply is often gathered in a service entrance box (Figure 6.3 f ).

All telecommunication lines entering lightning protection zone 1 at thecable junction must also be included in the meshed lightning protectionequipotential bonding by lightning current arresters (Figure 6.3 d (a) ).Often, a combination of a lightning current and surge arrester (e.g.,Combi-Arrester Blitzductor® CT, Type BD), depending on the telecominterface is applied:

• Analogue connection (a/b-wire): Blitzductor® CT BD, 110V

• ISDN Uko- interface: Blitzductor® CT BD, 110V

• ISDN U2m-interface: Blitzductor® CT BD / HF, 5V

• ISDN S2m-interface: Blitzductor® CT BD / HF, 5V

Conductors between base station, subdistribution and cable junction areusually run in metal conduits on the roof (on both sides connected withthe MFEB) so that they remain in lightning protection zone 1, notneeding special protective devices.

Sources

ENV 61024–1 (VDE V 0185 Teil 100): ‘Protection of structures againstlightning. Part 1: General principles’. Central Secretariat: rue de Stassart 35,B-1050 Brussels Aug.1996EN 50 083 Teil 1: ‘Cabled distribution systems for television and soundsignals. Part 1: Safety requirements’ (International Electrotechnical Commis-sion, Geneva, 1993)

Figure 6.3 d (b) Practical arrangement


6.4 Television transmitter

TV transmitters (Figure 6.4 a) are usually located at high altitude or onmountain tops (Figure 6.4 b), so they are particularly endangered bylightning. Power for the transmitter is taken from the public mains.

Figure 6.3 e Energy coordinated application of lightning current- and surge-arresters to protect the power supply input of mobile radio systemsat different network configurations

Figure 6.3 e (c) TN–S system

Figure 6.3 e (a) TT system Figure 6.3 e (b) TN–C system

Figure 6.3 f Power connection box for TN–S system (compare Figure 6.3 e, C)


Figure 6.4 a Transmitter mast

Figure 6.4 b Television transmitter on a mountain


Often an overhead line from the valley is changed into an undergroundcable at high altitude or on a mountain top. The protective insulation inthe power input circuit and safe electrical insulation by a disconnectiontransformer is often the protective measure in the transmitter.

An especially remarkable event involving lightning damage occurredat a transmitter of the Austrian Broadcasting Service (ORF) in Styria. Atthe time (1981) surge arresters with a nominal discharge capability of5kA (8/20 μs) according to IEC 99.1 were used to protect the transmit-ter. Such arresters are only designed for surge currents due to distantlightning strikes. In this case the surge arresters were damaged due to adirect lightning strike on the TV transmitter (Figure 6.4 c), leaving onephase of the power supply conductively connected to the station earth.Owing to the fact that in a totally insulated power input the neutral con-ductor is not connected to the station earth, a short-circuit current torelease the back-up fuses could not be generated. A current of about30A had, in fact, been flowing through the station earth resistance ofabout 7 Ω for several months without being noticed. During that time allaccessible parts of the transmitter station which were connected to thestation earth (transmitter cabin, mast and associated equipment) carriedmains voltage.

Apart from the danger to personnel from the hazardous contact volt-ages at all conductive parts of the transmitter, there was also a consider-able increase in the current consumption of the installation. Thisundesirable condition was only identified when the current consumptionof the plant was subsequently analysed.

Figure 6.4 c Surge arresters (having a rated discharge capacity of 5kA, 8/20μs)of the ORF TV transmitter ‘Braunhuberkogel’ in Styria damagedby lightning strike


This example clearly demonstrates that, in the quest to attain total‘protective insulation’, only arresters which are extremely robust (able tocarry lightning currents non-destructively) and absolutely reliable interms of their insulation should be used.

After having turned the transmitter cabin into a lightning protectionzone 1 new protective devices, namely, quenching spark gaps and high-current spark gaps, were installed in this installation in autumn 1982(Figures 6.4 d to 6.4 f). Lightning current counters were installed in the

Figure 6.4 d Power supply of the ORF TV transmitter ‘Braunhuberkogel’.Lightning current-proof surge protection at the crossing ‘overheadline/underground cable’

Figure 6.4 e Power input with protective insulation and lightning current-proofsurge protection of the transmitter cabin of the ORF TV transmitter‘Braunhuberkogel’


corresponding earth connection line of the arresters at the overhead linemast and in the transmitter cabin. These had recorded 29 lightningcurrents at the overhead line mast and 59 lightning currents in the trans-mitter up to the end of 1997. These lightning strikes have been controlledwithout damage or interference to the transmitter.

Sources

HASSE, P., and WIESINGER, J.: ‘EMV Blitz-Schutzzonen-Konzept’ (PflaumVerlag, München VDE Verlag, Berlin/Offenbach, 1994)FELDHÜTTER, W., HASSE, P., and PIVIT, E.: ‘Überspannungsschutz desNetzeinganges eines Fernsehfüllsenders auch be direken Blitzeinschlägen’.17th International Conference on Lightning Protection (ICLP), Den Haag,1983, Paper 3.2 EN 60099–1: ‘Surge arresters. Part 1: Non linear resistor type gapped surgearresters for AC systems’ (International Electrotechnical Commission,Geneva, 1991)

Figure 6.4 f (a) Transmitter cabin Figure 6.4 f (b) Detailed view ofFigure 6.4 f (a)


6.5 Mobile telecommunication facility

A mobile facility (Figures 6.5 a) must be protected against dangerouscontact voltages and surges. In this present case surge protection of thepower connection (with total insulation) was required to guarantee safeuninterrupted operation in the event of direct lightning strikes andnuclear electromagnetic pulses (NEMP).

Turning the facility into a lightning protection zone 1 and a NEMPprotection zone 1 was the solution to the problem. All cable entries wereprotected at the interface of the lightning or NEMP protection zones 0and 1.

The lightning and NEMP interferences on the power connection side

Figure 6.5 a Transportable, metal encased telecommunication facility with lineinputs protected against lightning and NEMP (1 to 5)


must be limited by an arrester circuit so that the protective insulation willnot be endangered. A suitable arrester circuit is shown in Figure 6.5 b. Agroup of lightning current arresters (Figure 6.5 c) out of five spark gapswhich can quench the mains follow-current (quenching spark gaps) and ahigh current spark gap as a disconnection spark gap is installed betweenthe phases (L1, L2, L3, N and PE) and the shielding case of the mobilefacility. The minimum AC operating voltage of this arrangement ofarresters is about 5kV and the minimum impulse operating voltageabout 10kV. The insulation between the power input circuit and the

Figure 6.5 b Basic circuit diagram of a surge protected power connection of amobile operating facility with protective insulation in the inputcircuit

Figure 6.5 c Lightning current arrester arrangement out of five quenching sparkgaps and one high current spark gap


shielding case of the mobile facility as well as the insulation between theinput and output circuit of the isolating transformer are adjusted tothese operating voltages. Surges below this level, such as switching surges,are carried by the insulation.

During undisturbed operation, this group of arresters ensuresdouble insulation. The basic insulation is provided by the quenchingspark gaps which have a quenching capacity according to DIN VDE0675 Part 6; the additional insulation will be realized by the high currentspark gap.

Voltage peaks will arise at the arrester arrangement before and duringactivation, the level of which depends on the steepness of the surges.Increasing voltage steepness makes the operating voltage of the group ofarresters rise according to its impulse characteristic. Owing to theenclosed spike chokes, very steep voltage peaks will be damped and thusreliably protecting the insulation of the isolation transformer (Figure6.5 d). In the internal network of the facility in lightning and NEMPprotection zone 1, on the secondary side of the isolating transformer, theTN-C-S-system is used. Any surges arising on the secondary side priorto the reaction of the arresters will be limited by varistors. For protectionagainst very high frequency surges, especially due to NEMP effects,additional RFI bushing filters are provided.

The protective conductor PE of the power cable is not necessary ifprotective insulation is applied. However, by using standard power cablesand plugs, the protective conductor PE will be automatically carried tothe coupling socket of the cable at the transportable facility. It must notterminate here in an open circuit condition because in the event of asurge a sparkover would occur in the plug and socket facility. Therefore,the protective conductor PE should be treated as if it were a live con-ductor and is equipped with a quenching spark gap.

Figure 6.5 d Coordinated surge characteristics of the arrester arrangement andthe isolating transformer insulation


In the case of a direct lightning strike into a facility on a non-definitively earthed vehicle the worst case condition occurs when theentire lightning current enters through the power supply. Therefore, anarrester arrangement is required to meet the lightning currents accordingto protection class III (compare Table 4.1.1 c):

• Insulation resistance and minimum operating voltage must notchange considerably even after multiple lightning current loadings(this guarantees a long-term protective insulation of the powerinput).

• After activation of the arresters by a surge, the ensuing mains follow-current must be quenched automatically.

As shown in Figure 6.5 b, these requirements are distributed amongseveral spark gaps. In terms of their insulation characteristics thesequenching spark gaps correspond to the basic insulation. They will beconnected at their lower end and wired via the high-current spark gap tothe casing of the power connection. This spark gap, working like a dis-connection spark gap, can control the entire lightning current and hasexcellent and very reliable insulation characteristics corresponding to therequirements of additional insulation.

The series connection of quenching and high current spark gapsthus constitutes a double insulation with lightning current conductivesurge protection. The spark gaps are installed in a service entrance boxwhich can be easily inserted into the mobile facility, as shown in Figure6.5 e.

Figure 6.5 e Mains connection box, installed into a mobile operating facility


Sources

HASSE, P., and WIESINGER, J.: ‘EMV Blitz-Schutzzonen-Konzept’ (PflaumVerlag, München;: VDE Verlag, Berlin/Offenbach, 1994)HASSE, P., MEUSER, A., PIVIT, E., and WIESINGER, J.: ‘Überspan-nungsschutz eines Netzanschlusses für transportable Betriebsstätten mitSchutzisolierung bei direkten Blitzeinschlägen’, etz Elektrotechn. Z, 1982,103, (2), pp. 52–54E DIN VDE 0675 Teil 6: ‘Überspannungsableiter zur Verwendung in Wech-selstromnetzen mit Nennspannungen zwischen 100V und 1000V’ (VDEVerlag, GmbH, Berlin/Offenbach) Nov. 1989

6.6 Airport control tower

The planning of the new control tower of Nuremberg Airport shall beused as an example for the application of LEMP management (IEC61312–1) introduced in chapter 4.1.3.1.

In accordance with the first step of the LEMP protection managementplan (cf. Table 4.1.3 a), LEMP-protection planning was executed by theplanner Dr R. Frentzel (TÜV South Germany, Munich) in coordinationwith

• the operator and owner of the airport who provides the new towerincluding all technical installations

• air traffic control as a user of the new tower with its own electronicequipment,

• the architect (construction planning)

• the engineering office (electrotechnical planning).

The defined target of protection was to safeguard failure-free oper-ation of the electrical and electronic systems of the air traffic control inthe case of lightning interference as far as possible. As, in this stage ofplanning, no data about the electromagnetic surge immunity of the dif-ferent electric and electronic devices and systems of the air traffic controlwere available, the requirement was to achieve the utmost protection forthese devices and systems against the impact of lightning and againstinternal interferences, by means of the structural possibilities and by theguidelines for the system installation. Correspondingly the structure wasrated as a lightning protection class I project (according to IEC 61024–1).

The new control tower and the corresponding operations buildingwere then subdivided into lightning protection zones and interferenceprotection zones, in order to define rooms of different degrees of severitywith regard to conducted and field interference. Such a subdivision alsomakes it possible to determine local equipotential bonding points at thelightning protection zone boundaries.


For the planning of the air terminations by which lightning protectionzones 0A and 0B are determined, an existing CAD-3D-Tower-Model(scale 1:100) was used. As Figure 6.6 a shows, a sphere (corresponding tolightning protection class I) with radius 20m is used for the rolling spheremethod.

The second step, ‘LEMP-protection’ according to Table 4.1.3 a,involves determining the strike-protected areas (lightning protectionzone 0B) in the outer area by means of suitable sectional drawings of thestructure.

Owing to the defined target of protection and the structural condi-tions, two lightning protection zones of graded interference levels weredetermined in the inner area of the control tower and the operationbuilding. All rooms which contain electronic systems and the cables thatare important for the operation of the air traffic control were classified aslightning protection zone 2, where conducted and field interference arestrongly reduced. All other rooms were classified as lightning protectionzone 1 for which an effective electromagnetic shield is not realizable. Inlightning protection zone 1, therefore a high residual lightning field andthe resulting electromagnetic coupling on lines and devices must be takeninto account. The malfunction and failure of equipment in lightningprotection zone 1, for example of office PCs, are accepted. By a con-sequent realization of the planned zone division, however, interferencefrom devices and systems in lightning protection zone 1 on those inlightning protection zone 2 will be avoided.

The power technical system rooms in the basement were classified asbeing in interference protection zone 1, which is comparable to lightningprotection zone 1 with regard to the prevalent interference level. All

Figure 6.6 a Tower model (1:100) and to scale rolling sphere (r=20m)(Source: Frentzel, R., TÜV South Germany)


rooms of lightning protection zone 2 also belong to interference protec-tion zone 2. The interference in interference zone 1 is due to powertechnical switching operations and feedback from the mains. In defininglightning protection zone 1 it was considered that the metal housingsof the devices, such as switching cabinets out of sheet steel, alreadyattenuate the high frequency field interference. The interior of the metalhousings is therefore considered as being in interference protection zone0. Figure 6.6 b shows the division into protection zones.

Functions of lightning protection and EMC (such as air terminations,down conductors, foundation earth electrodes, lightning protection andsurface equipotential bonding, shielding of buildings and rooms againstelectromagnetic fields, and earthing of information technology systems)have been attributed to the metal parts of the control tower and theoperation building, as there are reinforcement mats, steel pillars, metalfaçades, metal roof coverings, lattices, railings, stilted floors, elevatorconstructions etc. The basis for these functions is an electrically conduct-ive and possibly low-impedance connection of all metal parts. For thetower this is realized by an additional netting which is put into thereinforced floors, ceilings and walls (Figure 6.6 c). The welded nettingconsists of flat steel strips 30mm × 3.5mm with a grid size of about 5m ×5m and is welded to the reinforcement every 2m. For the purpose ofequipotential bonding with other metal parts, fixed earthing terminals orconnection lugs are made to project from the concrete at the necessarypoints.

Lightning protection zone 2 contains the systems of the air trafficcontrol with the highest protection requirements. The electromagneticshield of lightning protection zone 2 essentially consists of a multilayerreinforcement of usual mesh size 10–15cm. For the basement, forexample, it was quite easy to plan an effective shield because the floor, thewalls and the ceiling are reinforced all over. Thus, sufficient shielding inlightning protection zone 2 against rooms with lightning protection orinterference protection zone 1 as well as against lightning protection

Figure 6.6 b Subdivision of the basement into protected zones (Source: Frentzel,R., TÜV South Germany)


zone 0 (outer area) is achieved. The window openings in the basementare shielded by the conductive bonding of the gratings which cover the(reinforced) light shafts. If non-metallic doors are planned inside theshield of lightning protection zone 2, a shielding will be realized byinserting metal sheets into the doors. These metal sheets will also bebonded with the reinforcement via the metal door frames.

Not quite as easy, however, was the planning of the shield of light-ning protection zone 2 in the air traffic controller cabin (Figure 6.6 d)where, due to the panoramic glass, intensive electromagnetic fields, dueto lightning, must be taken into account. Shielding lattices in front ofthe windows or shielded panes were not accepted by the air-traffic con-trol, as these measures would lower the visibility. Therefore, the innerair-traffic controller cabin has been divided into lightning protectionzone 1 and lightning protection zone 2. Lightning protection zone 2comprises the space under the false floor where the entire cabling islaid. This volume is shielded by a conductive false floor and lateralsheeting. The base plate under the control bench is reinforced concrete.All shielding elements are low-impedance interconnected. This light-ning protection zone 2 is extended to the control desks of the air trafficcontrollers. The necessary shielding effect will be reached by the use ofdesk casings the insides of which are covered by metal foil. These met-allized plates will be contacted with the metal base frame of the deskswhich again will be low-impedance integrated into the conductive falsefloor.

Figure 6.6 c Schematicrepresentation of the additionalmeshed network (Source: Frentzel,R., TÜV South Germany)

Figure 6.6 d Subdivision of theair traffic controller cabin intoprotected zones (Source: Frentzel,R., TÜV South Germany)


The down conductors in the control tower shaft have been planned asadditional netting, as already described. In the area of the operationbuilding which contains an office section, the partly reinforced walls withadditional netting, the metal façades, and in the case of steel–glass con-structions, the steel pillars are used as down conductors. By using thenatural elements it is not necessary to install the usual externallymounted down conductors.

For the tower a common earthing system has been planned to realize ahigh-voltage protective earth, low-voltage operational earth, functionalearth and lightning protection earth. The earthing system will be realizedby using a mesh-type earth electrode within the foundation plate, thusfulfilling the requirements of DIN 18 014. Also here the nettingdescribed is used to which the flat steel strips of the additional netting inthe walls as well as the down conductors are bonded. The foundationreinforcement of the 1m thick base plate is also included into the earth-ing measure by welding in order to reduce the earthing resistance and toachieve close-meshed shielding.

Within the scope of the lightning protection equipotential bondingall metal installations, the electrical systems, the down conductors andthe earthing system are interconnected in the basement. This bonding inthe basement represents, at the same time, the equipotential bonding atthe boundary from lightning protection zone 0 (0A or 0B) to lightningprotection zone 1 or lightning protection zone 2. The following con-struction principles are also applicable for installations which will enterlightning protection zone 1 or lightning protection zone 2 in the otherfloors from the external area. All metal installations which enter thebuilding will be included into the lightning protection equipotentialbonding directly at their point of entrance. For this purpose reinforce-ment terminal points have been provided at the corresponding points onthe inside of the outer walls. Piping will be bonded directly or via isolat-ing spark gaps. In the case of electrical cables from the external area it isthe lightning current conductive shield itself or the wires of the cableswhich will be connected via lightning current or surge arresters. Theshield connection and the earthing of the arresters must be carried outwith low-impedance.

The selection of the protective devices must, on the one hand, takeinto account the probable threat, while, on the other hand, therequirements of the respective zone boundary and the immunity of theequipment to be protected. Generally, lightning current arresters shouldbe installed at the crossing from lightning protection zone 0A into light-ning protection zone 1 and surge arresters between lightning protectionzone 1 and lightning protection zone 2. Sometimes there is a directchange over from lightning protection zone 0A to lightning protectionzone 2. In such cases the corresponding combi-arresters (chapter 5.8)must be installed. From the producer of the arresters it is required that


the lightning current and surge arresters be coordinated and harmon-ized with regard to their sparkover characteristic and dischargecapability.

It is also in the basement where the lightning protection equipotentialbonding of the larger installations inside the building must be carriedout, as there are cable tray systems, heating pipes, ventilation or air-conditioning lines, fire extinguishing conduits and guide rails of eleva-tors. Corresponding terminals are also provided for these installations.Equipotential bonding must also be carried out at the boundaries oflightning protection zones 1 and 2 for all electrically conductive partswhich cross the boundaries as well as for metal parts inside the lightningprotection zone.

With the above-described measures a low-impedance equipotentialbonding network is obtained from which it is possible to realize asurface-covering earthing of the electronic systems at the commonearthing system. The use of concrete reinforcement together with addi-tional netting as down conductor/equipotential bonding means thatproximities for these structural parts of the tower can be neglected.For other structural parts the safety distance must be calculatedaccording to the proximity formula indicated in IEC 61024–1. Withregard to the calculations for the area of the air-traffic controllercabin it should be considered that the next equipotential bonding levelfor the electric lines is the floor of the air-traffic controller cabin, seeFigure 6.6 d.

Apart from lightning discharge as an external source of interferencethere are switching operations within the power plants which are a dan-gerous internal source of interference for electronic systems. Suchswitching operations generate high-frequency field and line-conductedinterference which can influence the electronic systems in different modesof coupling. As a measure to control such interference the already-described interference protection zones have been defined. The shields atthe boundaries of the interference protection zones (i.e., the metalequipment casings at the boundary of the interference protection zones0/1 and the structural shielding measures at the boundary of the inter-ference protection zones 1/2) have a sufficient damping effect on thefields which are radiated by the equipment itself, under the condition thatthe equipment casings are included with low-impedance into the equi-potential bonding. Conducted interference due to switching operationsis effectively limited by using shielded cables in interference protectionzone 2 and by the protection measures at interference protection zoneboundary 1/2.

To avoid undesired influence on electronic systems by power cables,defined distances between cables of different voltage levels are main-tained. For example, consider a three-layer rack pile; the followingconfiguration might be provided:


• Level 1 (bottom): signal cables < 30V

• Level 2 (middle): control, measuring, telecommunication cables< 60V, control cables < 1kV

• Level 3 (top): low-voltage cables < 1kV.

Protection management against electromagnetic lightning pulsesmeans new requirements for the construction. Additional functions suchas the carrying of lightning current, earthing and shielding of the build-ing, and equipotential bonding are attributed to the metal structures ofthe building. Thus, an economic realization of an effective protectionsystem is possible. The main difficulty is that after the construction phasemost of the metal structures are no longer accessible. It is, therefore,absolutely necessary to guarantee that those parts which will be coveredby concrete or soil meet the regulations and so stringent control is neces-sary during the construction phase.

Sources

IEC 61312–1: ‘Protection against lightning electromagnetic impulse. Part 1:General principles’. Centrel de la Commission Electrotechnique Inter-nationale. 3, rue de Varembe, Genève Jan. 1995ENV 61024–1: ‘Protection of structures against lightning. Part 1: Generalprinciples’. European Committee for Electrotechnical Standardization, Cen-tral Secretariat, rue de Stassart 35, B-1050 Brussels Jan. 1995DIN 18 014: ‘Fundamenterder’ (Beuth Verlag, Berlin) Feb.1994FRENTZEL, R.: ‘Massnahmen des Blitzschutzes und der EMV für den neuenTower am Flughafen Nürnberg’: DEHN u. SÖHNE Druckschrift Nr. 657 6.Forum für Versicherer: Blitz und Überspannungsschutz – Massnahmen derEMV, April 1998 pp. 79–85


Chapter 7

Prospects

The requirement for electronic information technology systems not to bedisturbed or even damaged by direct or close-up lightning strikes has ledto new quality requirements and a new dimension in the area of lightningprotection engineering. Lightning protection has been integrated into theworld of electromagnetic compatibility (EMC). The so-created conceptof lightning protection zones has turned out to be a very efficient man-agement method and is proven as a universal organizing principle innumerous complex problems. Meanwhile, the concept of lightning pro-tection zones has been specified as generally the method most appropriatefor the protection of any kind of structure with electronic equipment. Tothis end the Technical Committee (TC) 81 of the International Electro-technical Commission (IEC) has elaborated upon the standard whichshows the principles for protection against ‘electromagnetic lightningpulses’. This has been published as IEC 61312–1.

This book has introduced practice-proven components and protectivedevices by which it is possible to plan and realize complete lightning/surge protection concepts for many kinds of complex systems and struc-tures. The protective measures exemplified and devices available areapplicable, not only in new projects but also in existing systems whichcan be retrofitted so that a sufficient protection can still be attained.Subsequent installation, however, will be at higher cost and with a lowerefficiency.

The standards committees are currently working on standards whichtreat the following subjects:

• risk analysis as to the failure of electronic systems due to lightning

• electromagnetic shielding effects of existing metal structure com-ponents against lightning fields

• coordinated application of lightning current and surge arresters at theinterfaces of the lightning protection zones

• application of the concept of lightning protection zones to existingstructural systems with electronic equipment.

Along with the practical protection requirements, producers areaccompanying these activities with improvements to protection devices.As a guiding example of such an improvement the lightning currentarrester DEHNport® Maxi now safely extinguishes mains follow-currents of up to 50 kA.

Sources

HASSE, P., and WIESINGER, J.: ‘EMV Blitz-Schutzzonen-Konzept’ (PflaumVerlag, München; VDE Verlag, Berlin/Offenbach, 1994)IEC 61312–1: ‘Protection against lightning electromagnetic impulse – Part 1:General principles’ (International Electrotechnical Commission, Geneva)Feb. 1995


Index

abattoir 22aerials 27–29, 31, 329air termination 127–129

rods 128roof superstructures 128, 129wires 128

air termination systems 69, 78, 79, 84, 85,87

air traffic control 343–346aircraft, damage 36–38airport control tower, protection 343–349airports, damage 37alarm systems 68, 313–317

protection 313–317analogue a/b-wire terminal 286–292angle of protection 78animal breeding farm 17, 21

automatic feeding 17, 21ventilators 17, 21

antenna mast 328, 329, 331, 332Apollo 12 space ship 38application-neutral cabling 255–261arrester backup fuses 196–204arrester classes 109, 115, 117, 120–122,

154–156, 160arrester disconnecting devices 117–120arrester tests 115–119, 227

disconnecting devices 117–119operating duty 117, 118test currents 115–117thermal stability 117

arresters 24, 26, 79, 98–101, 113–126,153–292

breaking capacity 120combined 214, 228, 253, 254coordination 120, 121, 125, 218, 220cut-off frequency 217, 218, 226decoupling 180–183discharge capability 120, 124, 223limiting voltage 215–217

N-PE 121, 122nominal current 124, 217, 218, 226nominal voltage 124, 214, 216, 226,

227operating frequency range 124protection level 119, 124, 215, 227rated voltage 119, 124standards 113–126test values 99, 116valve-type 167, 168

arresters, application in different systemconfigurations 182–197

IT-system 184, 185, 196, 197TN-system 184, 185, 188–192, 333, 334TT-system 184, 185, 193–195, 333,

334arresters for cathodic protection systems

246–249arresters for equipment inputs 175, 176,

208arresters for information technology

122–125, 206–292arresters for lightning protection

equipotential bonding 157–167arresters for measuring and control

systems 209–252arresters for overhead lines 155–159arresters for permanent building

installations 167–174, 208arresters for power engineering 113–122,

155–205arresters for socket outlets 174–176, 208arresters, graded application 178–183,

206arresters in Euro-card format 248, 250,

251arresters in LSA-Plus technology 248,

251, 252arresters, selection 119, 120, 124, 125,

223–228

atmospheric overvoltages 45–61magnitude 60, 61

backup fuses for arresters 196–204Blitzductor® 208–249

construction and mode of functioning210–222

examples of application 228–240selection criteria 223–228

building installations, protection167–174, 208

building regulations 69, 70building services control system 22, 23buildings 39, 40, 69, 76, 77, 81–85, 88–92,

295–304metal components 83, 84, 90, 92protection 295–304room shielding 84, 88–92

burglar alarm systems 313–315, 317bus systems 309–313

cable coupling resistance 57cable television 32cables 56, 57, 61, 95–97, 138–143

ducts 95–97, 140, 141shielding 138–143supporting structures 142

cabling systems 255–257generic 255, 256primary 255, 256secondary 255, 256tertiary 255, 256

catastrophic damage 39–41cathodic protection systems 246–249,

326, 327central computer, protection 307–309central heating, protection 302, 304–307cereal processing 243chemical industry 196, 243chemical plant 11–13close-up strike 45, 242cloud-to-cloud lightning 45coal processing 243common mode protection 254computer integrated business 1computer integrated manufacturing 1computers, damage 5, 6, 16–20, 32, 34, 35computers, protection 55, 207, 209, 254,

307–309connection components, standards 113consequential damage 77contact voltage 184coordination between arresters and

equipment to protect 178–183, 220

coordination characteristics 220–222,227

corrosion protection 246–249coupling of surge currents on signal lines

57–60capacitive 59, 60inductive 58, 59ohmic 58

coupling path 43, 44

damage statistics 5–10, 70data networks, protection 255–292data telecontrol transmission 277–292

by analogue a/b-wire terminal 286–292by ISDN base terminal 277–284by ISDN primary multiplex terminal

284–286DC line technique 314, 315decoupling elements 206decoupling of arresters 180–183

decoupling choke 180–183decoupling length 180, 181, 183

differential mode protection 254direct strike 45, 60, 242, 328, 336disconnection 61, 62disconnection spark gap 326, 327, 340,

342disconnectors 167, 168, 170, 171

remote indication 170, 171dissolution pressure 246distribution cabinet 30distributors 255–257, 262–264down conductor systems 78, 79, 84, 85drop-cable 267

earth bus 92, 131, 135, 146earth electrode 90, 332earth-fault current 193earth ring bus 146–149earthing systems 78, 79, 84, 85, 90, 111,

295, 296, 298, 299, 347electrical systems of buildings 103–110

protection 103–110surge protection standards 103–110

electrochemical corrosion 246, 247electromagnetic cage 129, 130electromagnetic compatibility (EMC) 2,

3, 43, 63, 68, 112, 114, 115, 351standards 112, 114, 115

electromagnetic interference 67, 68electromagnetic lightning fields 328

damped 328undamped 328

electronic data processing systems 1, 9

354 Index

electronic equipment protection 80electrostatic discharge 7, 17, 20, 43engine hall 323–325equipment inputs, protection 175, 176,

208, 253, 254equipotential bonding 13, 16, 48, 69,

78–81, 90–95, 97, 99, 111, 145–149,190–192, 194, 195, 197, 207, 244,302, 303, 310, 322, 325–329, 345,347, 348

meshed functional equipotentialbonding 329, 330

equipotential bonding bar 90–93,147–149, 253, 296, 297, 326,327

equipotential bonding lines 141, 147equivalent earth resistance 47, 48equivalent surface 76Ethernet 10 Base T 265, 266Ethernet coax-cabling 267–272

thickwire 267, 269, 271thinwire 267–269, 272

Ethernet twisted pair cabling 265–269European Installation Bus (EIB)

309–313Ex-zones 241, 243–245explosion-protected spark gap 150–152,

326, 327explosions 10–13, 24, 27, 241, 243

nuclear 44, 68explosive atmosphere 238, 241–243external lightning protection 16, 69, 78,

79

factories, protection 295–323factory hall, lightning protection

295–299Faraday cage 13, 16Faraday hole 13, 16Fast Ethernet 100 Base TX 265, 266fault voltage-operated protective device

185, 193, 196Fax machine 281field-bus systems, lightning/surge

protection 231–236financial loss 1, 8, 13, 16, 17, 22, 308fire alarm systems 313–316flashover 10, 16, 22follow-current 199–204, 342, 352fuses 196–204

gas discharge arresters 215–217, 224, 225gliding spark gap 161, 163, 165, 166, 199,

200

hazardous areas, damage 10–15high current spark gap 151–153, 337,

340–342hospitals 39houses, damage 27–36hybrid generator 293, 294

impulse earth resistance 45, 48, 49voltage drop 48, 49

impulse line technique 314incoupling 22, 58induced voltages in metal loops 49–56, 58

square-wave 49–54transverse 50–52, 58

industrial plants, damage 15–24industrial plants, protection 295–323information technology equipment

protection 73, 122–125, 206–292insulation coordination 105, 106, 178insulation monitoring device 185, 196insulation resistance 244, 245, 342insurance 9, 10interference model 43interference protection zones 344, 345,

348interference sources 43, 44internal lightning protection 16, 69, 78,

79intrinsic safety 241–244intrinsically safe measuring and control

circuits 238–246ISDN base terminal 277–284ISDN primary multiplex terminal

284–286

kerosene tank 10–12

lightning current 2, 17, 27, 28, 32, 45–49,55, 56, 67

components 46parameters 46, 78, 160partial 46, 47rate of rise 49, 50

lightning current arresters 153–155,157–167, 177–183, 188–203, 206,207, 211, 222, 228, 234, 262, 263,275, 280, 285, 287, 288, 307, 314,319, 320, 323, 328, 340, 341, 352

lightning current counter 293, 294, 337,338

lightning damage 7, 8, 10–41direct 7, 8, 34examples 10–41indirect 7, 8, 34, 35

Index 355

lightning discharge 2, 3, 68lightning electromagnetic impulse 43lightning electromagnetic impulse

protection (LEMP) 80, 82–102, 343,344, 351

costs 101, 102inspection 100, 101installation 99, 100planning 83–97realization 97–99supervision 99, 100

lightning interference standards 64lightning protection levels 74, 75, 77, 78,

83, 155, 158, 194, 295lightning protection systems 16, 67–102,

223–225, 351building integrated 84–86cable routing and shielding 94–98efficiency 77equipotential bonding networks 90–94external 16, 69, 78, 79flow diagram 75, 76internal 16, 69, 78, 79isolated 84–86, 128partly isolated 84–86, 128planning 83–97protection levels 74, 75, 77, 78, 83room shielding 84, 88–91standards 69–103zones 79–85, 92–99, 102

lightning protection zones 79–85, 92–99,102, 177–179, 255, 295, 303, 304,307–309, 323, 325, 328, 343–348,351, 352

lightning strikes 45–57, 60, 242, 328, 336close-up 45, 242direct 45, 60, 242, 328, 336remote 45, 56, 57, 60, 242

longitudinal current 254low-voltage overhead lines 155–159LSA-Plus technology 248, 251, 252

measuring and control systems,protection 209–252

meshed functional equipotential bonding(MFEB) 329, 330, 333

line cross section 329mesh width 329

military applications 152military installations 68mobile radio systems, protection 328–334mobile telecommunication facility,

protection 339–343modem 286, 288, 290

N-PE arresters 121, 122, 166, 167, 193,194

NET-Protector 257–259, 266network card 269, 272network terminal 279, 284NH fuses 200–204

explosion 201, 202melting 200, 201no melting 200

nuclear electromagnetic pulse (NEMP)44, 339, 341

nuclear power station 68

oil refinery 10, 13, 14optical fibre transmission system 144,

145, 256optocoupler 145, 146optoelectronic connection 143–146osmotic pressure 246overcurrent protective device 185,

187–189, 193, 196, 203overhead lines, protection 155–159overvoltage category 105–108

peak-load power station 323–327petrol tanks 10, 11, 13, 15

temperature control 10, 11pipeline 247, 249pipeline valve station 246potentially susceptible equipment 43,

44power engineering systems, protection

113–122, 155–205power stations, protection 323–327power supply systems, damage 24–27printing press 22–24protection against direct contact 182, 184protection in case of indirect contact

182, 184–188, 193, 196, 202protection levels 74, 75, 77, 78, 83, 155,

158, 194, 295angle of protection 78efficiency 77, 78lightning current parameters 78mesh size 78rolling sphere radius 78

protective bypass 254protective circuit 206protective devices for analogue a/b-wire

terminal 286–292protective devices for application-neutral

cabling 255–261protective devices for data networks/

systems 255–292

356 Index

protective devices for Ethernet coax-cabling 267–272

protective devices for Ethernet twistedpair cabling 265–269

protective devices for ISDN baseterminal 277–284

protective devices for ISDN primarymultiplex terminal 284–286

protective devices for power supplyinputs and information technologyinputs combined 253, 254

protective devices for standard cabling271–278

protective devices for token ring cabling262–265

protective insulation 340, 341

quench gap 166, 167quenching spark gap 337, 340–342

RADAX-flow technology 161, 164, 203,204

radio paging system, protection 318–321radio systems 29, 31, 32, 39, 254,

318–321, 328–334rated surge voltage 105, 107, 108reactive current compensation system 22reinforcement 129–134remote strike 45, 56, 57, 60, 242residual current circuit breaker 17, 22

false tripping 17residual current device 17, 22, 185–189,

193, 194, 196, 202resistance thermometer 236risk analysis 74–78, 80, 351risk of failure 67rockets 36, 38rolling sphere method 84, 87, 128, 328,

344drawing 87scale models 87, 344

safety clearances 78shielding 84, 88–92, 129–143, 351

buildings 129–138cables 138–143electronic cabinets 137lines 138–141metal façades 131, 136rooms 84, 88–92, 130, 131steel reinforcements 129–134

short-circuit current 193socket outlets, protection 174–176, 208spark gaps 150–153, 155, 157–159,

161–166, 198, 199, 200, 203, 204,326, 327, 337, 340–342

explosion-protected 150–152, 326, 327gliding 161, 163, 165, 166, 199, 200high-current 151–153, 337, 340–342isolating 150–153quenching 337, 340–342RADAX-flow technology 161, 164,

203, 204sparkover voltage 150, 151

standard cabling 271–278standards 67–126

arresters for information technology122–125

arresters for power engineering113–122

connection components 112, 113electromagnetic compatibility 112,

114, 115European 67international 67lightning protection 69–103protective devices 113–126surge protection of electrical systems

of buildings 103–110surge protection of

telecommunications systems110–112

state of limited overvoltage 105, 106in-system 106protective 106

store and dispatch building, lightningprotection 296–304

strain gauges 229, 230surge arresters 153–159, 167–197,

206–208, 211, 228, 234, 242, 253,254, 257, 259–261, 263–272,274–290, 307–314, 319–323, 328,336

surge current 45, 46, 56–60, 63cables 56, 57coupling 57–60

surge current counter 293, 294surge damage 5–10surge immunity 207, 218, 219surge limiter 123surge protection 67, 68, 103–112, 224,

225electrical systems of buildings

103–110longitudinal 224, 225standards 103–112telecommunications systems 110–112transverse 224, 225

Index 357

surge protective devices 153, 154, 178,206, 257, 260, 261, 266: see alsoarresters

surge voltage 45, 46, 63surge withstand voltage 105, 107switchbays 24, 26switching electromagnetic impulse 43switching overvoltage 6, 7, 22, 61–64

disconnection of a capacitance 61,62

disconnection of a transformer 62earth fault in the floating network 62

telecommunication systems, protection53, 54, 110–112, 146–149, 223, 224,279, 339–343

equipotential bonding 146–149mobile 339–343surge protection standards 110–112

telephone systems 17, 28, 31, 32, 34, 35,39–41, 210

telephones 281, 288television sets 32, 254television transmitter, protection

334–339temperature measuring equipment, surge

protection 236–240textile industry 16token ring cabling 262–265

traffic lights 28, 32, 34transceivers 267–269transformer substation 24, 25, 27transmitter mast 335, 336, 338transverse voltage 50–52, 58, 253Twinax cabling 273, 274, 276–278

valve-type arresters 167–170disconnectors 167, 168, 170protection characteristic 169voltage and current characteristics

167, 169varistors 170–174

U/I characteristic 172, 173zinc oxide 170–172

vehicle weighbridge, lightning/surgeprotection 229–233, 320, 322, 323

video control system, protection316–321

vital infrastructure 40, 41

warehouse protection 296–304weighbridge 229–233, 320, 322, 323wind power stations, damage 38–40

rotor blades 38, 39

zinc oxide varistors 170–173discharge capability 172, 173U/I characteristic 172, 173

358 Index

over voltage

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