Dorman Smith PowerFormLow Voltage Factory Built Assemblies

31PowerForm Specification 2

Packaged Substations 9

Cast Resin Transformers 9

Microprocessor Based Overcurrent Releases 10

Loadline HP Circuit Breakers 11

Loadswitch Fused Devices 11

EN60439-1:1999 (IEC 60439-1:1999) Switchboard Standard 12

Internal Separation of Assemblies 14

UK National Annex Table NA1 16

EN60529:1991 (IEC 60529-1:1989) Degrees of Protection 19

Power Factor Correction 20

2500A Switchboard Specification 4

6300A Switchboard Specification 6

Loadline ACBs 10

Form 1 – 4 17

Introduction to the PowerForm Switchboard System 1

Switchboard Standards 12

Forms of Separation 17

Degrees of Protection 19

Energy Management 20

Contents

Continuous product developmentincluding new upratedspecifications have provided theopportunity for Dorman Smith toupdate their low voltage factorybuilt assembly range.

This publication gives detailedinformation on Dorman Smith’sextensive range of low voltagefactory built assemblies and isintended to assist the designengineer and installer in theselection of equipment to meettoday's stringent specifications.

Dorman Smith's world classmanufacturing facilities arededicated to answering theindividual needs of customersusing the company's own uniquerefinement of ‘Just In Time’techniques to achieve totalmanufacturing flexibility.

Such is the efficiency of theDorman Smith UK plant, it won aBritain’s Best factory award, andhas been chosen by the DTI as amanufacturing reference plant forthe UK and was also the subjectof an Open University video onmanufacturing. Dorman Smith'sability to design and manufacturereliable, durable products and togive advice on complex electrical

circuit protection, has firmlyestablished a Worldwidereputation for high quality andexpertise.

Located in Preston, Lancashire,Dorman Smith occupies apurpose built site totalling19,000m2 and is one of Britain’slargest and most well respectedmanufacturers of low voltageswitchgear, systems andassociated distributionequipment.

In addition, there are alsomanufacturing plants in Dubaiand Riyadh, which service theMiddle East markets.

Dorman Smith Switchgear Introduction

54 3The PowerForm Switchboard System has been fully tested and ASTA certified.

PowerForm is a fully type tested switchboard fully complying with

• IEC 60439-1:1999

• EN 60439-1:1999

• BSEN60439-1:1999

2

• Degree of protection to EN 60529(IEC 60529) is minimum IP3X withhigher protection available.

• Internal degree of protectionexceeds IP2X

• Functional unit interconnectionsPVC insulated

• All doors manufactured from1.6mm steel and hinged

• All rigid busbar partitions madefrom perforated 1.5mm steel

• Steel pre-treatment involves ironphosphate process for degreasing

• Paint finish in (Light Grey) PowderCoated polyester, colour RAL 7035

• Standard frames available are as shown below

Frame Frame Widths (mm)

Range Cable Access Steel (mm) Height (mm) 500 550 600 650 800 850 1000 1300

PowerForm 25 Front 2 2356 • • •

Rear 2 2356 • • •

PowerForm 63 Rear 3 2356 • • • • • • •

Certification

Standards

Mechanical Characteristics

PowerForm Specification PowerForm Specification

2500A Busbar System

• Rated voltage 415V a.c.

• Rated insulation voltage 690V a.c.

• Dielectric test voltage 2.5kV

• Nominal frequency 50 Hz

• Fully ASTA certified Busbar System

• Busbar Ratings

- 1000A

- 1250A

- 1600A

- 2000A

- 2500A

• Busbar supports are flame retardant and high temperature glass reinforced.

Max Horizontal Phase Busbar 2500A

Max Horizontal Neutral Busbar 2500A

Max Vertical Phase and Neutral Busbar 1600A

Max Short Time Current Busbars 50kA - 3 secs

Max Peak Current 105kA

6300A Busbar System

• Rated voltage 415V a.c.

• Rated insulation voltage 690V a.c.

• Dielectric test voltage 2.5kV

• Nominal frequency 50 Hz

• Fully ASTA certified Busbar System

• Busbar Ratings

- 3200A

- 4000A

- 5000A

- 6300A

• Busbar supports are flame retardant and high temperature glass reinforced.

Max Horizontal Phase Busbar 6300A

Max Horizontal Neutral Busbar 10,000A

Max Vertical Phase and Neutral Busbar 1600A

Max Short Time Current Busbars 100kA - 1 sec

Max Peak Current 220kA

1

5

254

25PowerForm 25 Constructional Details

2500A Switchboard Specification

2500A Switchboard Specification

Typical Arrangements

2

Horizontal Busbar Positions

1. Typical arrangement 2500Abusbar system

• 2500A, 50kA/3sec Busbars

• Loadline HP changeover MCCBs

• Front access cabling

• High performance Loadline HPoutgoing MCCBs

2. Typical Controlgear Compartment

7

636

63 6300A Switchboard Specification

6300A Switchboard Specification

PowerForm 25 Constructional DetailsPowerForm 63 Constructional Details

3. Typical arrangement 6300Abusbar system

• 6300A 100kA/1sec Busbars.

• Selective forced air cooling to:- Busbars.- ACB Enclosure.

• 4 Pole withdrawable ACBs.

• Rear access cabling.

• High performance Loadline HP outgoing MCCBs.

4. Internal view showing 6300ABusbar

• Outgoing Connections.

• 800mm Main Cubicle.

• 500mm or 800mmCable Access Way.

5. View showing special Busbar arrangements

Typical Arrangements

3

4 5

Horizontal Busbar Positions

98

636. Insulated busbar componentsCertain essential installations mayrequire insulated Busbars within the Busbar enclosure to ensureresilience of supply. To comply withthis Dorman Smith can offer a totallyinsulated system.

To comply with EN 60439-1 (IEC 60439-1) Form 4, UK AnnexTypes 1 and 4, the Busbarseparation is achieved usinginsulated coverings.

• 6300A Busbar fully insulated.

• Joints also insulated usingshrouds.

• Insulation by means of a durablepolymeric coating.

7. Fan assisted cooling systemTo assist with cooling, high currentswitchboards, an option is to forceair cool the internal components.

• Fan will cool ACBs.

• Also can cool Busbars.

• Air flow adjusted to suit finaltemperature requirements.

• Thermostatically controlled.

• Main and standby options.

Special Arrangements

6300A Switchboard Specification

6

7

Advantages and characteristics ofcast-resin transformers.Excellent antipollution features andmaximum safetyAll constructive materials andespecially the insulating resin areself-extinguishing: they do notdevelop, in case of fire, toxic gasesand they are moisture tolerant.

PerformancesCast-resin transformers are the bestsolution for all technical installationproblems, thanks to their capabilityto withstand network impulsivevoltage peaks,dynamic short-circuit,and overloads, with the optionaladdition of cooling fans forincreasing rated capacity.

Maintenance-freeThe high stability of the physicalcharacteristics of the materials andthe state-of-the-art technologyreduce maintenance to theminimum.

Where can cast-resin transformersbe used?The electrical and physicalproperties of cast-resin transformersfit them for both civil and industrialuse: hospitals, theatres, airports,subway, mines, off-shores platforms,nuclear power plants, vessels,industrial plants, etc. That is to saywherever there are fire orenvironmental pollution risks andwhere safety is a must.

Maximum reliabilityThe product offers the maximumreliability thanks to the computerisedcontrol of thermal processes, to thecheck of the chemical and thephysical characteristics and to themeasuring of the TG (Glass-transition) temperature of resin.

Economy of installationElimination of sumps for oilcollection, reduced overalldimensions and an excellentdistribution of weights allow costreduction of the plant.

Cast-Resin Transformers IEC 726

Packaged Substations

Packaged Substations

1110

Loadline Air Circuit Breakers andtheir accessories conform to theInternational Standards IEC 947, EN 60947 (harmonised in the 17CENELEC countries), CEI EN 60947and IEC 1000, and conform to therelevant CE directives:

• Low Voltage Directives(LVD) No. 73/23EEC

• Electromagnetic compatibilityDirective” (EMC) No. 89/336EEC

The apparatus complies with thespecifications of the regulations foron-board installations and isapproved by the following NavalRegisters:

• RINA (Italian Naval Register)

• Det Norske Veritas

• Bureau Veritas

• Germanischer Lloyd

• Lloyd’s Register of Shipping

• Polskj Reiestr Statkow

The constant increase in thetechnological and functionalcomplexity of electrical installationsmakes it essential for everycomponent - particularly those suchas protection circuit breakers whichare crucial to safety - to offer thehighest levels of continuity of serviceand reliability combined withminimal maintenance requirements.

Loadline Air Circuit Breakers weredesigned in line with the advancedplant engineering requirements, andfeatures high resistance to

mechanical, electrical and thermalstresses.

Loadline Air Circuit Breakersrepresent the logical functionalcomplement to the Loadline HPmoulded case circuit breakers andhave, like them, been designed forintegration and perfect co-ordinationwith the different lines of low voltageproducts.

Loadline Air Circuit Breakers areavailable in five different models: E1, E2, E3, E4 and E6, each ofwhich benefits from theinterchangeability of the variousdifferent versions of moving parts(with different breaking and ratedcurrent capacities) for the same fixed part. The rated uninterruptedcurrents range from 800 to 6300 A.

The breaking capacities range from40kA to 150kA (380/415 V a.c.).

LV Protective Devices

Microprocessor Based Overcurrent Releases

The circuit breakers fitted withmicroprocessor-based releases offerload control, self-test and informationtransmission capabilities in additionto the traditional protection functions,enabling them to be interfaced withcentralised control and supervisionsystems. Loadline offers all thecomponents needed to build systemsthat are tailored to each installation,from field units to front ends (withstandard communication protocols),from actuators to control systems.

As a result, the work of specifiers anddesigners is considerably simplifiedwhen it comes to choosing thetechnical characteristics andperformance required.

All this is thanks to the fact that theselection criteria are common to bothfamilies of circuit breakers and useintuitive and easy-to-read codes andsymbols.

The new circuit breakers continue atradition of switchear designed andmanufactured paying particularattention to use and user interface-related aspects, with obviousadvantages in terms of ergonomics,clarity and speed of identification.

Protection PR111 PR112Functions

Overload protectionwith inverse long time-delay trip

Selective short-circuitprotection with inverseor definite short timedelay

Instantanious shortcircuit protection withadjustable trip currentsetting

Earth Fault Protection

RESIDUAL

SOURCE GROUNDRETURN

Thermal memory for functions L and S

L

S

I

G

Loadline High Performance MCCBsLoadline ACBs

Loadline HP circuit breakers andtheir accessories conform to theInternational Standards IEC 947-2,EN 60947 (harmonised in the 17CENELEC countries), CEI EN 60947and IEC 1000, while also conformingto the following EC directives:

• Low Voltage Directives (LVD)No. 73/23 EEC

• Electromagnetic CompatibilityDirective (EMC) No. 89/336 EEC

Loadline HP S4, S5, S6 and SX7circuit breakers for alternatingcurrent protection can be fitted withovercurrent releases PR211/P andPR212/P featuring mircoprocessor-based electronic technology. Thismakes it possible to obtainprotection functions which

ensure high reliability, precisetripping and immunity to theinfluence of ambient conditions. Thepower supply required for correctoperation is supplied directly by thereleases’s current transformers withone phase current ≥ 15% of theirrated curents, even with only onephase powered. Just one adjustmentis required for all the phases andneutral, and tripping of the release issimultaneous for all the poles of thecircuit breaker with operatingcharacteristics that are unaffected byambients conditions. Operation ofthe release can be checked using aTT1 portable test device poweredusing normal batteries.

Loadswitch Fuse Combination Units

Loadswitch fuse Combination Unitsconform to EN 60947-3 (IEC 60947-3). 80kA RMS Fused Short CircuitCurrent

• 415V ac Rated Voltage

• Current ratings 32A to 800A

• 80kA RMS Fused Short-CircuitCurrent

• AC23A Utilisation Category

Loadswitch has been designed toexceed the requirements of EN 60947-3 (IEC 60947-3) and tooffer solutions demanded by ourcustomers where ease of installationsand ever increasing cable sizes arerequired.

A full uninterrupted duty ensuresthat the unit can maintain full ratedload indefinitely. A utilisation

category of AC23A and short-circuitcapacity of 80KA enables Loadswitchto be installed with confidence onany inductive or resistive load.

The door handle can be padlockedoff as standard. Up to three padlockscan be attached with ease.

LV Protective Devices

1312

Switchboard Standards Switchboard Standards

Introduction EN60439-1:1999 Fundamentals of Separation

Typical Applications

Methods of Construction

This International Standard appliesto low voltage switchgear andcontrolgear assemblies (type-testedassemblies (TTA) and partially type-tested assemblies (PTTA)), the ratedvoltage of which does not exceed1000 V a.c. at frequencies notexceeding 1000Hz, or 1500V d.c.

This standard applies to assembliesintended for use in connection withthe generation transmission,distribution and conversion ofelectric energy, and for the control ofelectric energy consumingequipment.

The object of this standard is to laydown the definitions and to state theservice conditions, constructionrequirements, technicalcharacteristics and tests for low-voltage switchgear and controlgearassemblies.

In accordance with the Standard, separation of thevarious elements of an Assembly: busbars, functionalunits, terminals, can be claimed providing one or moreof the following criteria are met:

1. Protection against contact with live parts belongingto adjacent functional units. The degree of protectionshall be at least IP2X or IPXXB.As a minimum, finger contact with live parts in adjacentfunctional units is prevented. With Assemblies suppliedby Dorman Smith Switchgear this is extended to includeprotection against finger contact between: functionalunits, adjacent busbars and busbar connections, andterminals as required for the particular form ofseparation being considered.

The requirement is proven with the standard test finger.

2. Protection against the passage of solid foreignbodies from one unit of an Assembly to an adjacentunit. The degree of protection shall be at least IP2X.The minimum requirement is proven by the standardtest finger not being able to touch live parts in adjacentunits and a 12mm ball not being able to pass betweenunits.

In practice a higher degree of protection may berequired for horizontal partitions to prevent small objectsform falling between compartments and should beidentified in the contract specification.

These two fundamental criteria are interrelated. DormanSmith Switchgear will therefore ensure all these are fullymet in respect of the particular form of separationoffered.

Form 1 - No separationTypical applications are places where the switchboard isin a secure location and where failure of the switchboardwill cause little or no additional disruption to other areasbeing fed by the switchboard.

Form 2 - Separation of busbars from functional units.Applications may well be the same as Form 1 but whereit is important that a fault in the switchboard need notaffect all functional units being fed from the samebusbar system.

Form 3 - Separation of busbars from functional unitsand the functional units from one another but nottheir terminations.Should be applied where it is important to provideprotection from internal live parts and where failure offunctional units being fed from the same busbar wouldcause unacceptable disruption.

Form 4 - Separation of busbars from functional unitsand the functional units from one another includingtheir terminations.Should be applied where it is important to provideprotection from internal live parts and where failure offunctional units being fed from the same busbar wouldcause unacceptable disruption. Because all theterminations are separated it is possible to isolate andwork on a single functional unit.

Dorman Smith have considerable experience indesigning and constructing low voltage switchboardassemblies from the simplest panelboard to the most complex multi-cubicle control and distributionswitchboard including HV/LV transformer to provide a packaged substation.

The various methods of separation and constructionoffered by Dorman Smith from Form I through to Form 4 are illustrated in detail on pages 14-15 can be seen from these diagrams a modular approach

has been employed which enables the maximumnumber of permutations to be achieved within a highlycost effective frame work.

If you would like more information on Dorman Smith LowVoltage Switchgear Systems our technical Sales Teamwill be pleased to assist and can upon request organiseeducational seminars and training for your staff onEN 60439-I and the UK National Annex.

Type Tested Assemblies (TTA) Section 2.1.1.1

Partially Type Tested Assemblies (PTTA) Section 2.1.1.2

Section 2.1.1.1A low voltage switchgear andcontrolgear assembly conforming toan established type or systemwithout deviations likely tosignificantly influence theperformance, from the typicalassembly verified to be inaccordance with this standard.

Type Tests Section 8.2

Type tests include the following:

a) verification of temperature-riselimits (8.2.1):

b) verification of the dielectricproperties (8.2.2);

c) verification of the short-circuitwithstand strength (8.2.3);

d) verification of the effectiveness ofthe protective circuit (8.2.4);

e) verification of clearances andcreepage distances (8.2.5);

f) verification of mechanicaloperation (8.2.6);

g) verification of the degree ofprotection (8.2.7).

Type Tests Section 8

Section 2.1.1.2A low voltage switchgear andcontrolgear assembly, containingboth type-tested and non-type-testedarrangements, provided that thelatter are derived (e.g. bycalculation) from type-testedarrangements which have compliedwith the relevant test.

Barrier

Terminal Device Busbar

1514

Switchboard Specification Switchboard Specification

Internal Separation of Assemblies Section 7.7

Form 1 Criteria

Form 2a Criteria

Form 2b Criteria

Symbols used in Diagrams

No Separation.

Separation of busbars from the functional Units.

Terminals for external conductors not separatedfrom busbars.

Separation of busbars from the functional Units.

Terminals for external conductors separated frombusbars.

Form 3b Criteria

Form 4a Criteria

Form 4b Criteria

Form 3a Criteria

Separation of busbars from the functional unitsand separation of all functional units from oneanother. Separations of the terminals for externalconductors from the functional units, but notfrom each other.

Terminals for external conductors not separatedfrom busbars.

Separation of busbars from the functional unitsand separation of all functional units from oneanother. Separations of the terminals for externalconductors from the functional units, but notfrom each other.

Terminals for external conductors separated frombusbars.

Separation of busbars from the functional unitsand separation of all functional units from oneanother, including the terminals for externalconductors which are an integral part of thefunctional unit.

Terminals for external conductors in the samecompartment as the associated functional unit

Separation of busbars from the functional unitsand separation of all functional units from oneanother, including the terminals for externalconductors which are an integral part of thefunctional unit

Terminals for external conductors not in thesame compartment as the associated functionalunit, but in individual, separate, enclosedprotected spaces or compartments.

Terminals for externalconductors not in the samecompartment as associatedfunctional unit, but inindividual, separate,enclosed protected spacesor compartments.

1716

Separation of busbars from thefunctional units and separationof all functional units from oneanother, including the terminalsfor external conductors whichare an integral part of thefunctional unit.

Separation of busbars from thefunctional units and separationof all functional units from oneanother. Separation of theterminals for externalconductors from the functionalunits, but not from each other.

Separation of busbars from thefunctional units.

Terminals for externalconductors not separatedfrom busbars.

Terminals for externalconductors separated frombusbars.

Terminals for externalconductors in the samecompartment as theassociated functional unit.

Terminals for externalconductors not separatedfrom busbars.

Terminals for externalconductors separated frombusbars.

Form 2

Form 3a

Form 3b

Form 4a

Type 7 All separation requirements are by metallic or non-metallic rigid barriers orpartitions. The termination for each functional unit has its own integralglanding facility.

Type 6 All separation requirements are by metallic or non-metallic rigid barriers orpartitions. Cables are glanded in common cabling chamber(s).

Type 5 Busbar separation is by metallic or non-metallic rigid barriers or partitions.Terminals may be separated by insulated coverings and glanded in commoncabling chamber(s).

Type 4 Busbar separation is achieved by insulated coverings, e.g. sleeving, wrapping or coatings. Cables may be glanded elsewhere.

Type 3 Bushbar separation is by metallic or non-metallic rigid barriers or partitions. The termination for each functional unit has its own integral glanding facility.

Type 2 Busbar separation is by metallic or non-metallic rigid barriers orpartitions. Cables may be glanded elsewhere.

Type 1 Busbar separation is achieved by insulated coverings,e.g. sleeving, wrapping or coatings. Cables may be glanded elsewhere.

Type 1 Busbar separation is achieved by insulated coverings,e.g. sleeving, wrapping or coatings

Type 2 Busbar separation is by metallic or non-metallic rigidbarriers or partitions.

Type 1 Busbar separation is achieved by insulated covering,e.g. sleeving, wrapping or coatings

Type 2 Busbar separation is by metallic or non-metallic rigidbarriers or partition.

FormForm 1

Type of ConstructionSub criteriaMain criteriaNo separation

UK National Annex Table NA.1

The internal separation ofAssemblies by barriers or partitionsis specified in 7.7 and is subject toagreement between themanufacturer and the user.

Table NA.1 gives additionalinformation regarding different types

of construction, based on typicalpractice in the United Kingdom.Other types of construction are notprecluded, and it is not essential toadopt any of the listed types in orderto comply with the requirements ofthe Standard.

However, in order to achieveagreement between manufacturersand users, it is recommended toadopt one of the listed types ofconstruction.

Forms of Separation Table NA.1

Form 2b Type 2 Internal Separation of Assemblies Section 7.7

Switchboard Standards Switchboard Standards

Form 3b Type 2 Internal Separation of Assemblies Section 7.7

IncomingUnit

OutgoingUnits

OutgoingUnits

OutgoingUnits

IncomingUnit

OutgoingUnits

OutgoingUnits

OutgoingUnits

IncomingCable

OutgoingCables

OutgoingCables

Form 4a Type 2 Internal Separation of Assemblies Section 7.7

IncomingUnit

OutgoingUnits

OutgoingUnits

OutgoingUnits

IncomingCable

OutgoingCables

OutgoingCables

1918

Switchboard Standards

Form 4b Type 5 Internal Separation of Assemblies Section 7.7

Form 4b Type 6 Internal Separation of Assemblies Section 7.7

Form 4b Type 7 Internal Separation of Assemblies Section 7.7

IncomingUnit

OutgoingUnits

OutgoingUnits

OutgoingUnits

IncomingCable

OutgoingCables

OutgoingCables

IncomingUnit

OutgoingUnits

OutgoingUnits

OutgoingUnits

IncomingCable

OutgoingCables

OutgoingCables

Compartmentfor future use

IncomingUnit

OutgoingUnits

OutgoingUnits

OutgoingUnits

IncomingCable

OutgoingCables

OutgoingCables

Compartmentfor future use

Degrees of Protection

No protection. non-protected

Protection of personsProtection against solid against access to

IP Example foreign objects - Tests hazardous parts with:

0

Full penetration of 50mm diametersphere allowed.Contact with hazardous parts notpermitted.

back of handIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII

IIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIII

501

Full penetration of 12.5mmdiameter sphere not allowed. Thejointed test finger shall haveadequate clearance fromhazardous parts.

finger

IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIIIIIIII IIIIII

IIII

IIIIIIIIIIIIIIIIIIIIII I IIIIIIIIIIIIIIII

12.52

The access probe of 2.5mmdiameter shall not penetrate.

tool3

The access probe of 1.0mmdiameter shall not penetrate.

wire4

Limited ingress of dust permitted(no harmful deposit).

wire5

Totally protected against ingress ofdust.

wire6

EN 60529 : 1991

EN 60529 : 1991 describes a system forclassifying degrees of protection providedby enclosures of electrical equipment with arated voltage not exceeding 1000V ac and1500V dc.

The markings used to indicate the degree ofprotection consist of the letter IP (IngressProtection) followed by two characteristicnumerals.

The first characteristic numeral designatesthe degree of protection with regards tosolid objects.

The second numeral designates the degreeof protection against the ingress of liquid.

It is intended to provide indication of:

a) Protection of persons againstaccess to hazardous parts inside

enclosures and protection of theequipment inside the enclosureagainst the ingress of solid foreignobjects.

b) Protection of the equipmentinside the enclosure againstharmful ingress of water.

First Number - Protection Against Solids Second Number - Protection Against Liquids

No protection No protection

Protection againstvertically falling drops of water.

dripping up to 15° fromthe vertical

limited spraying

splashing from alldirections

hosing jets from alldirections

strong hosing jets fromall directions

temporary immersion

continuous immersion

Protection againstIP Example Liquids - Tests Protection from water

Protection against vertically falling drops of water.

Protection against vertically fallingdrops of water with enclosure tilted 15° from the vertical.

Protection against sprays to 60° fromthe vertical - limited ingresspermitted.

Protection against water splashedfrom all directions - limited ingresspermitted.

Protected against low pressure jets ofwater from all directions - limitedingress permitted.

Protected against strong jets of water, eg. for use on shipdeckslimited ingress permitted.

Protected against the effects ofimmersion between 15cm and 1m.

Protected against long periods ofimmersion under pressure.

15cm min.

0

1

2

3

4

5

6

7

8

Second Characteristic NumeralProtection against harmful ingress of water

1 2 3 4 5IP21IP31 IP32

IP42 IP43IP53 IP54 IP55

IP64 IP65

First Characteristic NumeralProtection against contact and protection

against ingress of solid foreign23456

For switchboard assemblies intended for indoor useEN60439-1 : 1999 states that there is no requirement for protectionagainst ingress of water (clause 7.2.1.1) and that the IP referencespreferred for assemblies designated for indoor use are:

IP00 IP2X IP3X IP4X IP5X

Where some degree of protection against ingress of water is required thefollowing table gives the preferred IP combination numbers:-

EN 60529 : 1991

List of Preferred IP References

2120Introduction

Power Factor Correction

Electrical installation sizing must becarried out according to the apparentpower S which, defined as theproduct of the voltage and thecurrent (V x I) is expressed in [VA].

When there are ohmic loads, theapparent absorbed power is utilisedcompletely as active power and isdissipated in heat, whereas whenthere are other loads, such asmotors. welders, fluorescent lamps.transformers. etc., a part of theapparent absorbed power, calledreactive power Q, is utilised only toenergise the magnetic circuits. Itcannot therefore be used as activepower to carry out work.

The ratio between the active powerand the apparent power expressesthe power factor (cosφ) or thedephasing between voltage andcurrent when the user absorbsreactive power.

The power factor is equal to 1 whenall the apparent absorbed power isactive, whereas it is less than 1 whenthe apparent absorbed powerconsists of partly active power andpartly reactive power.

This means that user equipment witha low power factor requires moreapparent power from the network(and therefore more current) than a

user with a higher power factor.Therefore the voltage drops andenergy losses are higher, the lowerthe power factor.

To keep down voltage drops andpower losses it is therefore necessaryto size the installations consideringthe higher current due to the lowpower factor, and this is to thedetriment of the installation’s cost-effectiveness.

For these reasons, companiessupplying electrical energy increasethe price of electricity for users witha low power factor.

Types of Power Factor Correction

Distributed power factor correction Distributed power factor correctionis, in fact, the best technical solutionsince capacitor and user equipmentfollow exactly the same path duringdaily service of loads, so the cosφsetting becomes automatic andsystematic.

Apart from this, with local powerfactor correction it is not only thesupply authority which benefits fromreactive energy saving, but also thewhole internal distribution system ofthe user. ln industrial installations,for example, the saving which can bemade with distributed power factorcorrection, is not just a question oftariffs, but is also noted in sizing allthe MV/LV substations with the

corrected loads

Another advantage with regard todistributed power factor correction, isits simple and cost-effective installationsince the capacitor and load areconnected and disconnectedsimultaneously and can use the sameprotections against overloads aridshort-circuits.

Centralised power factor correction Centralised power factor correction iscost-effective in the case of installationswith several heterogenous loadsoperating on an occasional basis, sothere is high installed power and fairlyIow average energy absorption by loadsin simultaneous service. Withcentralised power factor correction, thebank power is notably less than the

overall power which would be requiredfor distributed power factor correction,taking into account, too, that the kVARcost of a high-powered capacitor is lessthan that of small capacitors.

The bank can be connectedpermanently only if the reactiveenergy absorption is fairly regularduring the day, otherwise it must beswitched to prevent having cosφ inadvance.

When the reactive power absorptionis highly variable during operation ofthe installation, automatic regulationis required with the bank split upinto several steps.

Energy Management Energy Management

Introduction

Manufacturers are increasingly beingasked to provide for oversized neutralcapabilities in their products. This is to cater for all anticipated increasedcurrent in the neutral system.

The increased current is a result ofharmonics being introduced onto thesystem, by modern day equipmentsuch as, variable speed drives, static

rectifiers, microwave ovens, personalcomputers, etc. This can result insevere overheating e.g. in cabIes,busbar, enclosures, transformer coils,etc.

Therefore, Industry, commercialpremises, offices and homes, may allbe affected, and with the growth ofuse of such equipment, the problemwill escalate.

BSRIA (Building Services ResearchAssociation) has been working withthe industry to find the extent andseverity of power quality problemsrelated to harmonic currents. It hasfound widespread problems andbelieves that unless designers andoperators are more aware of theproblems, and take action to avoidthem, they will become critical.

Recommendations

• Obtain information about theharmonic current for all equipmentto be installed;

• Consider the effect of sourceimpedance of ups and standbygenerator systems - they can bemuch higher than the impedanceof the main transformer and causemore severe voltage distortion;

• Eliminate the source of harmonicsby specifying low harmonicversions of switch mode powersupplies, variable speed drives andhigh frequency ballasts;

• Calculate the harmonic voltage andcurrent at critical parts of thesystem, phase and neutralconductors;

• Design the installation, includingproper sizing of neutralconductors, to accommodateharmonic currents where theyoccur;

• Separate circuits supplyingharmonic generating loads fromthose supplying loads which aresensitive to harmonics;

• Specify transformers and filters toremove harmonics;

• Follow guidelines for identificationof harmonic problems includingsurveys, measurement methodsand diagnosis;

• Safety considerations areparamount and the correct choiceof instruments is also emphasisedso that they will measure harmonicfrequencies.

The Effects of Harmonics

The effects of harmonic voltages aremalfunctions in sensitive equipmentsuch as the sensing circuits of circuitbreakers and ups switches. Theeffects of harmonic current areoverheating in conductors,transformers, motor coils andcapacitors.

When harmonic loaded single phasecircuits on different phases arebrought together in a distributionboard, the third harmoniccomponents and all the odd

multiples (triplen harmonics) addtogether in the neutral. In severecases the neutral current can exceedtwice the phase currents. In suchcases a double size neutral busbar isoften specified.

However, it may be necessary todouble rate busbar and circuitbreakers in the main distributionboard as well. In a large installationthe main circuit breaker could berated at 4000 A. Finding an acb totake an 8000A neutral conductorcan be difficult.

Fortunately, diversity of the harmonicloads leads to a certain amount ofcancellation since the harmoniccurrents of different loads are rarelyin perfect phase. The solution mayrequire modelling software to predictthe neutral current. A range ofsolutions is available, from U.P.S. toavoid interruptions, through isoIatingand phase shift transformers topassive and active filters.

Harmonics

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