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2009 Energy Networks Association

All rights reserved. No part of this publication may be reproduced,stored in a retrieval system or transmitted in any form or by any means,electronic, mechanical, photocopying, recording or otherwise, withoutthe prior written consent of Energy Networks Association. Specificenquiries concerning this document should be addressed to:

Engineering DirectorateEnergy Networks Association6 th Floor , Dean Bradley House

52 Horseferry RdLondon

SW1P 2AF

This document has been prepared for use by members of the EnergyNetworks Association to take account of the conditions which apply tothem. Advice should be taken from an appropriately qualified engineeron the suitability of this document for any other purpose.

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Engineering Recommendation G59/1Page 3

1991CONTENTS

1 INTRODUCTION .............................................................................................................5

2 INTERPRETATIONS .......................................................................................................5

3 LEGAL ASPECTS ............................................................................................................8

4 CONNECTION ARRANGEMENTS................................................................................9

5 SYSTEM EARTHING ASPECTS ..................................................................................10

5.1 HV System...............................................................................................................10

5.2 LV System ...............................................................................................................11

6 PARALLEL OPERATION WITH THE PUBLIC ELECTRICITY SUPPLIERSSYSTEM (INCLUDING OCCASIONAL PARALLELING) ........................................12

6.1 Operational and Safety Aspects ...............................................................................12

6.1.1 General.............................................................................................................126.1.2 Written Agreement...........................................................................................126.1.3 Responsibilities................................................................................................136.1.4 HV Operational and Safety Aspects ................................................................13

6.1.5 LV Operational and Safety Aspects.................................................................14

6.2 Technical Considerations.........................................................................................14

6.2.1 Fault Infeed ......................................................................................................146.2.2 Synchronising ..................................................................................................146.2.3 Distortion and Interference ..............................................................................156.2.4 Operational Switching .....................................................................................156.2.5 Points of Interconnection and Means of Isolation ...........................................16

6.3 Control Equipment Requirements............................................................................16

6.4 Protective Equipment...............................................................................................17

6.4.1 General.............................................................................................................176.4.2 Protective Equipment for HV Supply Arrangements ......................................176.4.3 Protective Equipment for LV Supply Arrangements.......................................186.4.4 Power Factor Correction ..................................................................................19

6.5 Testing and Commissioning ....................................................................................20

6.6 Metering...................................................................................................................20

6.7 Short Term Occasional Paralleling ..........................................................................21

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1991

RECOMMENDATIONS FOR THE CONNECTION OF EMBEDDED

GENERATING PLANT TO THE PUBLIC ELECTRICITY SUPPLIERSDISTRIBUTION SYSTEMS

1 INTRODUCTION

This Engineering Recommendation, which relates to the connection of embedded generating plant to Public Electricity Suppliers (PES) distribution systems, is intended for use where theconnection is to be made to systems at, or below, 20kV and where the output of thegenerating plant does not exceed 5MW.

The connection of generating plant of larger capacity and at higher voltages, will normallyrequire a more stringent technical appraisal and considerations not covered by this documentare likely to arise. Such generating plant is therefore outside the scope of thisRecommendation, although similar principles will apply.

This document applies to systems where the embedded generating plant may be parallelledwith PES distribution systems or where either the embedded generating plant or the PESsystems may be used to supply the same electrical load.

The basic safety and technical requirements in respect of the interface between PES systems

and embedded generating plant are specified in this document and information is given on thelegal background. Examples of the practical implementation of these requirements are givenin Engineering Technical Report (ETR) 113, however ETR 113 is a guidance document andis not intended to preclude innovation or mutual agreement on alternative means of meetingthe requirements.

Throughout this document the term Embedded Generator includes Embedded Generatorsor Suppliers as described in Section 2.

Since the first issue of this Recommendation was published in 1985, the Electricity SupplyRegulations 1988 have come into force. Many of the recommendations of the original

document have now been included in the Regulations and therefore have become statutoryrequirements. This issue of the Recommendation has been amended to include these andother changes in the legislation.

2 INTERPRETATIONS

Note: These interpretations are applicable to this document and may not be appropriate ifused out of this context.

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Embedded Generator

A person who generates electricity and whose generating units are directly connected to aPES distribution system and includes customers with their own generating plant.

Low Voltage (LV)

A voltage normally exceeding extra-low but not exceeding 1000V ac or 1500V dc betweenconductors or 600V ac or 900V dc between conductors and earth.

Supplier

This appears in The Electricity Supply Regulations 1988 and means a person who supplies,and, where electric lines and apparatus used for that purpose are owned otherwise than bythat person, shall include the owner of those electric lines and apparatus. Thus, for the

purposes of G.59/1, Supplier includes both the PES and the Embedded Generator.

System

This appears in The Electricity Supply Regulations 1988 and means an individual electricalsystem in which all the conductors and apparatus are electrically connected to one or moresources of voltage and includes all those conductors and apparatus.

High Voltage (HV)

A voltage exceeding 1000V ac or 1500V dc between conductors, or 600V ac or 900V dc between conductors and earth.

Public Electricity Supplier (PES)

A public electricity supplier or suppliers which hold licences granted under section 6(1)(c) ofthe Electricity Act 1989 or the Electricity (Northern Ireland) Order 1992 and for the purposeof this document are also members of the Electricity Association.

PES Control Engineer

The Control Engineer at the PES Control Centre.

Point of Common Coupling

The point on the PES network, electrically nearest the generating plant installation, at whichother customers loads are, or may be, connected.

Point of Supply

The point of electrical connection between the apparatus owned by the local PES and theapparatus owned by an Embedded Generator.

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1991

Plant Types

Definitions of types of generating plant are given below; other types of plant may be suitable.

a) Synchronous Generator

A type of rotating electrical generator which operates without slip and at a speed thatis directly related to system frequency. The machine is designed to be capable ofoperation in isolation from other generating plant. The output voltage, frequency and

power factor are determined by control equipment associated with the generator.Under certain conditions, the synchronous generator may be parallelled with anetwork containing other generating plant. On disconnection of the parallel

connection, the synchronous generator will continue to generate at a voltage andfrequency determined by its control equipment.

b) Mains-excited Asynchronous Generator

A type of rotating electrical generator which operates at a speed not directly related tosystem frequency. The machine is designed to be operated in parallel with a networkcontaining other generating plant. The machine is excited by reactive power drawnonly from the network to which it is connected. The output voltage and frequency aredetermined by those of the system to which it is connected. On disconnection of the

parallel connection, the mains-excited asynchronous generator will cease generating.

c) Power Factor Corrected Asynchronous Generator

A derivative of the mains-excited asynchronous generator where the machine isexcited partly by the network to which connected and partly by a device of fixedcapacitance connected locally to the machine. On disconnection of the parallelconnection, the power factor corrected asynchronous generator may continue togenerate electrical power at a voltage and a frequency determined by the machine andsystem characteristics.

d) Self-excited Asynchronous Generator

A derivative of the mains-excited asynchronous generator where the machine isexcited purely by a device of variable capacitance connected locally to the machine.The machine is capable of operation in isolation from a network containing othergenerating plant and in this respect is similar to the synchronous generator. Undercertain conditions, the self-excited asynchronous generator may be operated in

parallel with other generators, and on failure of that connection, the machine willcontinue to generate at a voltage and frequency determined by its control equipment.

e) Self Commutated Static Invertor

An electronic device to convert direct current (dc) to alternating current (ac) in whichthe output value of ac frequency and voltage is determined by control equipment

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associated with the device. It is similar to the rotating synchronous generator in that,under certain conditions, it may be connected in parallel with a network containingother generators. On failure of that connection, the device will continue to provide

power at a voltage and frequency determined by its control equipment.

f) Line Commutated Static Invertor

A derivative of the self commutated static invertor where the output ac frequency andvoltage are determined by the network containing other generating plant to which itmust be connected. On disconnection of the parallel connection, the line commutatedstatic invertor will normally cease generating.

3

LEGAL ASPECTS

During the privatisation process of the Electricity Supply Industry all of the pre-warElectricity Acts and Part 1 and Schedule 1 to 3 of the Energy Act 1983 were repealed andreplaced by the Electricity Act 1989. The duty of a PES to supply and the power todisconnect are now to be found in this Act and the Electricity Supply Regulations 1988.

Section 17 of the 1989 Act allows exceptions from the duty to supply any premises.

These exceptions include the following:-

i.) Where the PES is prevented from giving a supply by circumstances beyond thecontrol of the PES.

ii.) Where circumstances exist by reason of which supplying any premises mightcause the PES to be in breach of Regulations made under Section 29 of the Act andthe PES has taken all reasonable steps to prevent those circumstances fromoccurring and having that effect. Section 29 is concerned with the need to ensure thesafety of the public and that supplies of electricity are regular and efficient.

iii.) Where it is not reasonable in all the circumstances for the PES to be required to give asupply provided that he gives 7 working days notice of his intention to discontinue thesupply.

Section 21 of the Act allows a PES to require any person requiring a supply to accept:

a) any restrictions which must be imposed to enable the PES to comply with Regulationsunder Section 29, and

b) any terms restricting any liability of the PES for economic loss resulting fromnegligence which it is reasonable in all the circumstances for that person to berequired to accept.

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1991

General conditions of supply to consumers are also covered by Regulations 27 and 28 of theElectricity Supply Regulations 1988. Under Regulation 27 no PES is compelled tocommence or continue a supply if the consumers installation may be dangerous or causeundue interference with the PES system or the supply to other consumers. Regulation 28empowers the PES to disconnect any part of the consumers installation which does notcomply with the requirements of Regulation 27. It should also be noted that each installationhas to satisfy the requirements of the Health and Safety at Work Act 1974.

Regulation 26, Interconnected Supplies, of the Electricity Supply Regulations 1988 requiresinstallations that have alternative sources of energy to satisfy the requirements of Part 1 orPart 11 of Schedule 3 of the Regulations. Part 1 of that Schedule deals with the alternativeconnection agreement as described in Section 7 of this Recommendation and Part 11

concerns parallel operation of generating plant as described in Section 6 of thisRecommendation.

It should be noted that the requirements of the Electricity Supply Regulations 1988 apply toall embedded generating plant. Any persons contemplating the operation of embeddedgenerating plant are advised to read the Regulations, particularly Schedule 3.

Under the Regulations no person may operate generating plant in parallel with a PES systemwithout the written agreement of the PES.

4 CONNECTION ARRANGEMENTS

Each installation with embedded generating plant must be designed to be compatible with thePES network to which it is to be connected. Where it is necessary for a PES to provide anyelectrical lines, or other electrical plant, or for any other works to be carried out to enable theinstallation of embedded generating plant, the PES may require payments in respect of anyexpenditure incurred in carrying out this work.

The two methods of operating embedded generating plant considered in this document aredescribed below:

a) Parallel Operation with the PES System (Including Occasional Paralleling)

The operation of embedded generating plant in parallel with the PES system incompliance with agreed technical and commercial arrangements. Occasional

paralleling allows the connection of embedded generating plant to the PES system forthe purpose of maintaining the continuity of supply when changing over from onesource of supply to the other.

The operational and technical requirements and the requirements of the ElectricitySupply Regulations 1988 (Part II, Schedule 3, Regulation 26) for both modes of

parallel operation are given in Section 6 of this Recommendation. Further advice onthe protection requirements and the circumstances under which the generating plant

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may be considered to be occasionally parallelled are given in Engineering TechnicalReport 113.

b) Operation with Alternative Connection to the PES System

The operation of embedded generating plant, as an alternative to the PES supply,arrangements being such that the generating plant cannot be parallelled with the PESsupply system.

The operational and technical requirements, and the requirements of the ElectricitySupply Regulations 1988 (Part 1, Schedule 3, Regulation 26) for this mode ofoperation are given in Section 7 of this Recommendation.

Where it is intended to change the existing method of operation to one of the above methods,the requirements of the chosen method must be met in full.

5 SYSTEM EARTHING ASPECTS

The Electricity Supply Regulations 1988 require a Supplier to ensure that every system isconnected with earth at or as near as is reasonably practicable to the source of voltage in thesystem.

5.1 HV System

For HV system neutral earthing, the PES may use direct, resistor, reactor or arc suppressioncoil methods. The magnitude of the possible earth fault current will depend inter alia onwhich of these methods is used.

To comply with the Electricity Supply Regulations 1988, the written agreement between thePES and the Embedded Generator must include provision for the compatibility of the meansof connecting the two systems with earth. The Embedded Generators earthing arrangementmust therefore be designed in consultation with the PES. The actual earthing arrangementswill also be dependent on the number of machines in use and the Embedded Generators ownsystem configuration and method of operation. The system earth connection shall haveadequate electrical and mechanical capability for the duty.

Where PES systems are designed for earthing at one point only, no star point or earthingtransformer should be connected by the Embedded Generator during parallel operation.Adequate precautions must be taken to ensure that the Embedded Generators HV system isearthed when operating in isolation from the PES system. Where the Embedded Generatorsupplies an unearthed isolated part of the PES system under controlled conditions, eitherthrough pre-arranged switching or the planned automatic operation of control and protection

equipment, system earthing will need to be provided at the generating plant location. Suchcontrolled conditions will be planned for in the design of the Embedded Generators and the

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1991

PES systems. All reasonable steps must be taken to avoid unearthed operation by theinstallation of suitable protection to detect the loss of the PES supply in accordance withSection 6.4.

The written agreement between the PES and the Embedded Generator must include provisionfor reasonable precautions to be taken to ensure the continuance of safe conditions if anyneutral point connected with earth in any apparatus operated at high voltage becomesdisconnected from earth.

Where the PES system is designed for multiple earthing and the generating plant is connectedto this system, earthing may be achieved by the use of a busbar earthing transformer or theuse of the star point of the generator. Engineering Technical Report 113, Figure 5.8, gives

examples of alternative neutral earthing arrangements for HV systems and generators.

5.2 LV System

PES LV systems are directly earthed, and the majority are now multiple earthed.

Where an earthing terminal is provided by the PES it may be used by an EmbeddedGenerator for earthing his installation, subject to the PES being satisfied that the existingconnection is of adequate capacity. If the embedded generating plant is intended to operateindependently of the PES supply, the installation must include an earthing system which does

not rely upon the PES earthing terminal. Where use of the PES earthing terminal is retained,the Embedded Generators earthing system and PES earthing terminal is retained, it must beconnected to the generating plant earthing system by means of a conductor at least equivalentin size to that required to connect the PES earthing terminal to the installation.Where the PES substation is on the Embedded Generators premises and adjacent to thelocation of the embedded generating plant, the PES may allow the substation earthing systemto be used in place of a separate independent earthing system. The PES written agreement isnecessary before making any connection to the PES earthing system.

Where it is intended to operate in parallel with a PES LV system with the star pointconnected to the neutral and/or earthing system, precautions will need to be taken to limit theeffects of circulating harmonics. The Supply Regulations will permit the insertion of animpedance in the supply neutral of the generating plant for this purpose, when it is parallelledwith the PES system. Other methods which will reduce the circulation of harmonics aredescribed in ETR 113. However, if the generating plant is operating in isolation from thePES system it will be necessary to have the generating plant directly earthed.

The method of earthing will affect the means of isolation required by Sections 6.2.5 and 7.3.The isolator should be selected in the following manner:

a) Where the PES LV system is multiple earthed, TN-C-S (PME) and some TN-Ssystems, and the PES earthing terminal is connected to the main earthing terminal ofthe installation in an approved manner, isolation of the phase conductors only is

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necessary. However, in the case of alternative connection, a phase and neutral isolatormay be used to avoid circulating currents (see Section 7.3).

b) For all other cases where any PES earthing terminal is connected to the installation,the PES may require isolation of phase and neutral conductors for safety reasons.(Some TN-S systems.)

c) Where a PES earthing terminal is not used or not provided (all TT Systems) phase andneutral isolation is required.

Engineering Technical Report 113, Figures 4.1 to 4.7, gives examples of alternative earthingarrangements for LV generators and systems.

Where transportable or mobile generating plant is used, it is essential that all earthconnections to the generator are efficiently made prior to making off any phase connectionsor running the generator.

6 PARALLEL OPERATION WITH THE PUBLIC ELECTRICITY SUPPLIERSSYSTEM (INCLUDING OCCASIONAL PARALLELING)

6.1 Operational and Safety Aspects

6.1.1 General

Advice on the provision of safeguards for any person intending to operate or maintaininterconnected electrical systems is given in the Guidance Notes on the Safety Implicationsof the Energy Act 1983 issued by the Electricity Association with the support of the Healthand Safety Executive and the Department of Energy. Reference should also be made to theappropriate PES Safety Rules and Engineering Recommendation G.19/1.

6.1.2 Written Agreement

Under the 1988 Supply Regulations, the Embedded Generator must obtain in writing from thePES, an agreement to operate embedded generating equipment in parallel with the PESsystem. Regulation 26 requires that this agreement shall be in accordance with Schedule 3 ofthe Regulations and shall include:

a) the means of synchronisation between the Embedded Generators system and the PESsystem;

b) the responsibility for plant maintenance and failure records;

c) the means of connection and disconnection between PES and Embedded Generatorsystem;

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1991

d) reasonable precautions to be taken to ensure the continuance of safe conditions if anyneutral point connected with earth in any apparatus operated at high voltage becomesdisconnected from earth, as well as those items concerned with earthing given inSection 5 of this document;

e) marked-up drawing demonstrating the compatibility of earth connections.

6.1.3 Responsibilities

When parallel operating takes place the PES system and the Embedded Generators system become interconnected supplies under Regulation 26 of the Supply Regulations. The

Regulations put responsibilities on both parties to:-

a) ensure that all persons carrying out operations on their systems are Authorised persons and competent;

b) ensure that there are adequate and reliable means of communication between the PESand Embedded Generator;

c) inform each other of any condition, occurrence or incident which could affect thesafety of the others personnel, or the maintenance of equipment and to keep recordsof the communication of such information;

d) designate persons with authority to act and communicate on their behalf and informeach other of the names of the persons so designated and where they may be reached.

The Embedded Generator and PES must give due regard to these requirements and ensurethat all operating personnel are competent in that they have adequate knowledge andsufficient judgement to take the correct action when dealing with an emergency. Failure totake correct action may jeopardise the Embedded Generatorss or PES system. Personsoperating for Embedded Generators should be aware that many PES apply auto-reclosesystems to high voltage overhead line circuits. This may affect the operations of directlyconnected HV generators and also generators connected to LV systems supplied indirectly byHV overhead lines.

6.1.4 HV Operational and Safety Aspects

Where the point of supply provided by the PES for parallel operation is at HV, the EmbeddedGenerator must ensure:

a) that a person with authority, on his staff, is available at all times to receivecommunications from the PES Control Engineer so that emergencies, requiring urgent

action by the Embedded Generator, can be dealt with adequately. Where required bythe PES, it will also be a duty of the Embedded Generators staff to advise the PES

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Control Engineer of any abnormalities that occur on the embedded generating plantwhich have caused, or might cause, disturbance to the PES system;

b) that where it is necessary for his employees to operate the PES equipment, they have been designated in writing by the PES as an Authorised Person for this purpose.

All operations of PES equipment must be carried out to the specific instructions of thePES Control Engineer. In an emergency, the Authorised Person can open a switch orcircuit breaker without prior agreement in order to avoid danger. The operation must

be reported to the PES Control Engineer immediately afterwards.

For generating plant connection to an HV point of supply, the Embedded Generator and thePES may have to reach technical agreement on scheduling the real and reactive power outputto the PES system to ensure stability of the local distribution system. The PES may require

agreement on specific written procedures to control the bringing on and taking off of suchgenerating plant. The action within these procedures will be controlled, at all times, by thePES Control Engineer.

6.1.5 LV Operational and Safety Aspects

Where the point of supply provided by the PES for parallel operation is at LV, the PES,depending upon local circumstances, may require a similar communications procedure asoutlined in sub-paragraph (a) above.

6.2 Technical Considerations

6.2.1 Fault Infeed

When it is proposed to install embedded generating plant, consideration must be given to thecontribution which that plant will make to the fault level on the PES system. The design andsafe operation of the Embedded Generators and the PES installations depend upon accurateassessment of the fault contributions made by all the plant operating in parallel at the instantof fault and it is in the Embedded Generators interest to discuss this with the PES at theearliest possible stage.

Under the Electricity Supply Regulations 1988 the Embedded Generator must ensure that hissystem is capable of withstanding the fault current associated with his equipment and anyinfeed from the PES system.

6.2.2 Synchronising

In order to operate embedded generating plant other than mains-excited asynchronousmachines in parallel with a PES system, it is necessary to synchronize the embedded

generating plant with that of the PES supply prior to making the parallel connection.

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1991

The voltage fluctuation on the PES system during synchronising should not normally exceed3% at the point of common coupling and should meet the requirements of EngineeringRecommendation P.28.

Automatic synchronising equipment is preferred. Where manual synchronising is providedthe acceptability of switching procedures and operational staff is subject to agreement withthe PES.

6.2.3 Distortion and Interference

It should be noted that the stability and electrical output of a generating plant depend upon

the source of power, and may be detrimentally affected if direct coupling is made to afluctuating source.

Where the generating plant input motive power may vary rapidly, causing correspondingchanges in the output power, for example an aero-generator, the voltage fluctuations at the

point of common coupling should not exceed 1%.

Where the generating plant is run-up to speed as a motor connected to the PES system, anyassociated disturbance must be within the limits stipulated in Engineering RecommendationP.28.

Harmonic voltages and currents produced within the Embedded Generators system maycause excessive harmonic distortion of the PES system. The Embedded Generatorsinstallation must be designed and operated to comply with the criteria specified inEngineering Recommendation G.5/3.

The level of negative phase sequence voltage at the point of common coupling on a three- phase system should not exceed 1.3% of the positive phase sequence voltage, assuming aninitially symmetrical system at this point (see Engineering Recommendation P.29).

6.2.4 Operational Switching

Circuit-breakers and switches on the PES system are not normally fitted with checksynchronising facilities. To avoid the risk of out-of-synchronism closure onto embeddedgenerating plant and also achieve the simplest method of connecting the plant in the system,the Embedded Generator will need to arrange for his plant to be disconnected from thesystem in the event of a loss of the PES supply.

The PES system may have, either now or in the future, auto-reclose or automatic sequenceswitching facilities to assist in restoring supplies after transient faults and this will affect thetime settings of the protection described in Section 6.4. During auto-reclose and sequence

switching operations, the system could be subjected to interruptions of up to one minute;

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1991Where embedded generating equipment may cause the system voltage to exceed the statutorylimit, the PES will require the installation of automatic voltage control equipment.

6.4 Protective Equipment

6.4.1 General

In addition to any generating plant protection installed by the Embedded Generator for hisown purposes the PES requires protective equipment to be provided by the EmbeddedGenerator to achieve the following objectives:

a) to inhibit connection of the generating equipment to the PES supply unless all phases

of the PES supply are energised and operating within the agreed protection settings;

b) to disconnect the generator from the system when a system abnormality occurs thatresults in an unacceptable deviation of the voltage or frequency at the point of supply;

c) to disconnect the generator from the PES system in the event of loss or one or more phases of the PES supply to the installation;

d) to ensure either the automatic disconnection of the generating plant, or where there iscompetent supervision of an installation, the operation of an alarm with audible andvisual indication, in the event of a failure of any supplies to the protective equipmentthat would inhibit its correct operation.

[Note - In some cases a system abnormality can occur which is serious but not of sufficientmagnitude for the automatic protection to operate. In such a case manual intervention may benecessary at the discretion of the PES Control Engineer.]

6.4.2 Protective Equipment for HV Supply Arrangements

Suitable protection arrangements and settings for an HV installation will depend upon the particular Embedded Generators installation and the requirements of the PES local system.These individual requirements must be ascertained in discussions with the PES. To achievethe objectives of Section 6.4, the protection must include the detection of:

a) Over Voltage b) Under Voltagec) Over Frequencyd) Under Frequencye) Loss of Mains

Achieving objective (c) of Section 6.4.1 requires some form of Loss of Mains protection as

indicated in the list above. This Loss of Mains protection will depend for its operation on thedetection of some suitable parameter, for example, rate of change of current, phase angle

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change or unbalanced voltages. This protection must enable the requirements of Section 5.1to avoid unearthed operation, and the requirements of Operational Switching in Section 6.2.4to be met.

Other protection could be required and may include the detection of:

a) Neutral Voltage Displacement b) Over Currentc) Earth Faultd) Reverse Power

The settings of relays should be agreed with the PES, and it is a requirement of the Electricity

Supply Regulations 1988 that the settings shall not be altered without the express agreementof the PES.

Further advice on the protection arrangements to meet the objectives of Section 6.4.1 aregiven in Engineering Technical Report 113 Notes of Guidance for the Protection ofEmbedded Generating Plant up to 5MW for Operation in Parallel with Public ElectricitySuppliers Distribution Networks.

6.4.3 Protective Equipment for LV Supply Arrangements

a) Small Generating Plant Below 150kVA

Small asynchronous generating plant (

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1991

TABLE 1 - PROTECTIVE EQUIPMENT AND SETTINGS FOR LV SUPPLYARRANGEMENTS

Protection Phases TripSetting

Total * Tripping

Time

Under VoltageOver VoltageUnder FrequencyOver Frequency

AllAllOneOne

- 10% (phase-neutral)+ 10% (phase-neutral)- 6%+ 1%

0.5s0.5s0.5s0.5s

* The total tripping time includes any integration or timing period of the protectionrelay as well as relay and circuit-breaker operating time.

b) Large Generating Plant Exceeding 150kVA

As the generating plant size increases, its likely adverse effects on the distributionsystem also increase. Additional protection to that stated above may be requiredsimilar to that suggested for HV installations. Engineering Technical Report 113gives advice on protection systems for these higher power installations.

The protective equipment to meet the requirements of this Section must be located in asuitable cabinet that affords immediate visual inspection of the relays but is secure frominterference by unauthorised personnel.

The requirement under the Supply Regulations for agreement of the PES to any changes in protection settings equally applies to LV connections.

6.4.4 Power Factor Correction

Power factor correction equipment is sometimes used with asynchronous generators todecrease reactive power flows on the supply systems. Where the power factor correctionequipment is of a fixed output, stable operating conditions in the event of loss of the PESsupply are extremely unlikely to be maintained.

Therefore, for small LV installations as described in 6.4.3(a) the protection in Table 1 would be adequate for mains-excited generators.

Where an installation contains power factor correction equipment controlled to meet thereactive power demands, the probability of sustained generation is increased. For LVinstallations, additional protective equipment provided by the Embedded Generator, is

required as in the case of self-excited asynchronous machines.

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For larger LV and HV installations the effect of any power factor correcting equipment willhave to be taken into account in the design of individual protection requirement. ETR 113shows by example how the power factor of load influences the fault current contribution fromgenerators on which protection requirements are based.

6.5 Testing and Commissioning

Full tests on the protective equipment shall be agreed in order to meet the requirements ofthis document . These tests are the responsibility of the Embedded Generator and must becarried out by him. Where the installation is connected to the PES HV system, the tests must

be witnessed by a representative of the PES who shall be given adequate opportunity and

reasonable notice to witness the tests.

Where the installation is connected to the PES LV system the tests need not be witnessed bythe PES. In this case the full results of the tests must be submitted to the PES for approval.

Appendix B gives a Schedule of Tests to be carried out, but further tests may be required bythe PES depending on the protection arrangements of the particular installation.

The tests must be carried out on site; tests performed before delivery and installation are notacceptable.

The Embedded Generator must keep a written record of all protection settings and testresults. A copy of this record should be available for inspection at the metering position or asrequired by the PES or other interested parties such as representatives of the Department ofEnergy.

Periodic testing of the protection is recommended at intervals to be agreed in discussion between the PES and the Embedded Generator. Tests may be required to determine:

i.) voltage dip on synchronising;

ii.) harmonic voltage distortion;

iii.) voltage levels as a result of the connection of the generator remain within thelimits laid down in the Supply Regulations.

6.6 Metering

Metering equipment must be installed at the point of supply to record measurements to therequirements of the PES. These may include both the export and import of active andreactive electrical energy to and from the Embedded Generators network. Where the

metering is to be supplied and owned by the PES, the Embedded Generator must provide thefacilities for the equipment to be installed by the PES.

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The direct operation of circuit-breakers or contactors must not result in the defeat of theinterlocking system. For example, if a circuit-breaker can be closed mechanically, regardlessof the state of any electrical interlocking, then it must have mechanical interlocking inaddition to electrical interlocking. Where an automatic mains fail type of generating plant isinstalled, a conspicuous warning notice should be displayed and securely fixed.

7.2 Changeover Operated at HV

Where the changeover operates at HV in order to meet the Supply Regulation requirements,the following provisions may be adopted although each has limitations:

a) an electrical interlock between the closing and tripping circuits of the changeovercircuit-breakers;

b) a mechanical interlock between the operating mechanisms of the changeover circuit- breakers;

c) an electro-mechanical interlock in the mechanisms and in the control circuit of thechangeover circuit-breakers;

d) a system of mechanical interlocks operated by a transferable key system.

Although any one method meets the minimum requirement, it is recommended that twomethods of interlocking are used.

7.3 Changeover Operated at LV

Where the changeover operates at LV, the following provisions may be adopted to meet theSupply Regulation requirements:

a) manual break-before-make changeover switch;

b) two separate switches or fuse switches mechanically interlocked so that it isimpossible for one to be moved when the other is in the closed position;

c) an automatic break-before-make changeover contactor;

d) two separate contactors which are both mechanically and electrically interlocked.

e) a system of locks with a single transferable key.

The PES must be satisfied that any other arrangement will fulfil its obligations under the

Regulations and also those of the Embedded Generator.

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1991

14 Engineering Recommendation P.29 - EA Engineering andPlanning Limits for Voltage Unbalance in the UK for Safety Division132kV and Below

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APPENDIX B

EMBEDDED GENERATION TEST RECORD

Ref No.

1 OWNERS/COMPANY DETAILS

Name and Address......................................................................................................................................................

......................................................................................................................................................

......................................................................................................................................................

..Telephone Number(s)......................................................................................................................................................

2 GENERATING PLANT DETAILS

Location of Generator

......................................................................................................................................................

......................................................................................................................................................

......................................................................................................................................................

Type (synchronous, asynchronous, inverter) .....................................................................

Manufacturer.....................................................................Rated: Voltage.....................................................................Frequency.....................................................................Capacity (kVA).....................................................................Current.....................................................................Power Factor.....................................................................

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1991

3 SUPPLY FROM PUBLIC ELECTRICITY SUPPLIER

Voltage.....................................................................Service Details.....................................................................Capacity (kVA).....................................................................Max Fault level.....................................................................Point of Common Coupling.....................................................................

Protection.....................................................................

.

.

.

.

.

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Ref

4 PROTECTION TESTS

Test Results

Protection Manufacturer Type

Setting 1 2

Over VoltageR-N or R-YY-N or R-BB-N or R-B

Volts%

Sec Volts%

Sec Volts%

Sec Volts%

Under VoltageR-N or R-YY-N or Y-BB-N or R-B

Volts%

Sec Volts%

Sec Volts%

Sec Volts%

Over FrequencyUnder Frequency

Hz Sec Hz Sec Hz Sec Hz

NeutralVoltageDisplacement

Volts Sec Volts Sec Volts Sec Volts

AdditionalProtectionForSynchronous orSimilar Plant

NB. In addition to protection tests it may be necessary to carry out other tests described in Section 6.5.

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1991Ref No

5 CERTIFICATION

On behalf of `The Generator I certify that the generating equipment specified in Section 2has been installed and tested and complies with the requirements of EngineeringRecommendation G59/1.

Signed......................................

Date........................................

On behalf of the Public Electricity Supplier I have witnessed the tests in Section 4.

Signed......................................

Date........................................

Notes

a) The tests are to safeguard the Public Electricity Suppliers system. They do notcertify that the whole installation has been tested, or meets the requirements of the Wiring

Regulations, or any statutory requirements.

b) The over voltage and under voltage protection should be tested using an externalvariable voltage supply.

c) Where the frequency of the plant is dependent on the mains frequency an externalvariable frequency audio signal generator, with suitable voltage and current output,should be used for the under and over frequency protection tests.

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