Protection of High Voltage Networks (TS1)

8/12/2019 Protection of High Voltage Networks (TS1)

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DISTRIBUTION

CODE OF PRACTICE

DSS/007/001

The Protection of High Voltage

Networks (TS1)


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The Protection of High Voltage Networks (TS1)

Date of Issue : 29/03/00 Document Ref : DSS/007/001

Version : 2.0 THIS DOCUMENT MAY BE OUT OF DATE IF PRINTED Page : 1 of 30

CODE OF PRACTICE

Distribution

Code of Practice


DSS/007/001

Written : Mark Nicholson

Asset Management Engineer

Date :

16/03/00

Signature :

M Nicholson

Assured :Chris Riley

Quality Assurance

Date :

15/03/00

Signature :

C T Riley

Authorised :Reg Dixon

System Manager

Date :

20/03/00

Signature :

R Dixon

Yorkshire Electricity Group plc. 1999All rights reserved. No part of this document may be reproduced or transmitted in any form or by any means, electronic or mechanical,

including photocopying, recording or any information storage or retrieval system, nor may any design contained within this document be

reproduced in part or in whole or in any form whatsoever, without prior permission from Yorkshire Electricity Group plc.


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CODE OF PRACTICE

Revision Record

Version Date Revision Details By Authorised

2.0 29/03/00 Rewritten to represent present

practice

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CODE OF PRACTICE

Contents1. Purpose ..................................................................................................................................5

2. Scope .....................................................................................................................................5

3. Protection of High Voltage Networks ...................................................................................5

3.1 132kV Systems..................................................................................................................5

3.1.1 Feeder Main Protection .................................................................................................6

3.1.2 Transformer Main Protection ........................................................................................6

3.1.3 Transformer Feeder Main Protection ............................................................................7

3.1.4 Busbar Protection ..........................................................................................................7

3.1.5 132kV Voltage Transformers ........................................................................................7

3.1.6 Back-up Protection ........................................................................................................73.1.7 Low Frequency Protection.............................................................................................9

3.1.8 Intertripping.................................................................................................................10

3.1.9 Fault Interfering Disconnectors...................................................................................10

3.1.10 Auto Reclose............................................................................................................11

3.1.11 Local Alarms and Indications..................................................................................11

3.1.12 Application to New and Existing Equipment ..........................................................12

3.2 66kV and 33kV Systems .................................................................................................13

3.2.1 Feeder Main Protection ...............................................................................................13

3.2.2 Transformer Main Protection ......................................................................................14

3.2.3 Transformer Feeder Main Protection ..........................................................................14

3.2.4 Busbar Protection ........................................................................................................153.2.5 66kV Voltage Transformers ........................................................................................16

3.2.6 Back up Protection.......................................................................................................16

3.2.7 Intertripping.................................................................................................................18

3.2.8 Auto Reclose................................................................................................................19

3.2.9 Local Alarms and Indications......................................................................................19

3.2.10 Application to New and Existing Equipment ..........................................................20

3.3 11kV Systems..................................................................................................................21

3.3.1 Underground Feeder Protection...................................................................................21

3.3.2 Overhead Feeder Protection ........................................................................................21

3.3.3 11000/415V Transformers...........................................................................................21

3.3.4 Busbar Protection ........................................................................................................22

3.3.5 Backup Protection........................................................................................................223.3.6 Application to New and Existing Equipment ..............................................................22

3.4 Protection of Generation Connected to 66kV and Lower Voltage Systems ...................22

3.4.1 Protection Principles....................................................................................................23

3.4.2 Island Only Generation Protection ..............................................................................23

3.4.3 Short Term Parallel Generation Protection .................................................................24

3.4.4 Full Parallel Generation Protection .............................................................................24

3.4.5 Generator Earthing Requirements ...............................................................................26

3.4.6 Asynchronous Generation ...........................................................................................26

3.5 General Requirements for a Protection Scheme..............................................................26

3.5.1 General Protection Relay Requirements......................................................................26

3.5.2 Protection Relay Functionality ....................................................................................263.5.3 Testing of Protection Relays .......................................................................................27


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3.5.4 Substation Communications........................................................................................273.5.5 Provision of Voltage and Current Transformers .........................................................28

3.5.5 Scheme Diagrams ........................................................................................................28

3.5.6 Protection Relay Settings.............................................................................................28

3.5.7 Protection Relay D.C. Supplies ...................................................................................29

4. References ...........................................................................................................................29

4.1 Codes of Practice.............................................................................................................29

4.2 External............................................................................................................................29

5. Definitions ...........................................................................................................................29

5.1 Second Stage Protection Point.........................................................................................29

5.2 Fully Discriminative Protection.......................................................................................29

5.3 Primed for Reclosure.......................................................................................................29

5.4 Cascaded Intertripping.....................................................................................................30


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CODE OF PRACTICE

1. Purpose

This document details the high voltage network protection philosophy covering the 132kV,

66kV, 33kV, and 11kV systems. The requirements for the protection of private generation which

is connected at 66kV and lower voltage levels is included. Guidance on the associated settings to

be applied to this protection is given in The Setting of Protection and Associated Equipment

(TS16/17) DSS\007\007. There is a legal obligation to provide protection to meet the

requirements of the Electricity Supply Regulations (1988) and the Electricity at Work

Regulations.

This document supersedes The Protection of High Voltage Networks DSS\007\001 dated 30

September 1999 all copies of which should be destroyed.

2. Scope

This document covers all such equipment owned or operated on Yorkshire Electricity

Distribution networks.

3. Protection of High Voltage Networks

The network will be monitored by a SCADA system whose facilities are described inDSS/007/003 - Philosophy of Telecontrol Facilities Provided At Substations (TS8).

3.1 132kV Systems

All items of plant will be covered by systems of main protection and back-up protection.

The main protection will be fully discriminative i.e. cover all types of phase and earth faults

whilst disconnecting only the faulted system elements. Fault detection will occur in less than

50ms with total fault clearance achieved in 100ms to 200ms. This fault clearance time will be

irrespective of the number of ends.

This specification for fault clearance times may need to be shortened where necessary to ensure

stability of embedded generation.

The back-up protection will be arranged to limit the disruption of supplies in the event of failure

of the main protection.

On ring feeder systems zone 3 is arranged to limit disruption of supplies in the event of a circuit

breaker failing to open for a fault.

The protection scheme should conform to the grid code requirements.


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CODE OF PRACTICE

3.1.1 Feeder Main ProtectionThe main protection will be either unit protection using Yorkshire Electricity or rented pilot

circuits, or distance protection.

When zone 2 fault detection is required by the distance protection scheme, acceleration or

intertripping will be used to achieve fast clearance for remote circuit end faults. When a

transformer is teed to a feeder any intertrip facilities available will be used to achieve fast

clearance for feeder faults instead of acceleration. A shared signalling channel for acceleration or

intertripping is acceptable.

For primary circuits with no continuous earth return conductor (which is the usual case), the

earth fault feature of the distance protection will be restricted to zone 1 measurement. A

quadilateral earth fault characteristic will be used by the distance protection.

Distance protection will use the loss of load zone 2 acceleration feature where practicable on ring

feeder systems.

All systems of distance protection will use switch on to fault logic.

Where a ring system is run with normally open points, the distance protection at these points will

be provided with a zone 1 extension feature to reach into the remote end zone to ensure fast

clearance of end zone faults. This zone 1 extension will be switchable both locally and viatelecontrol using a telecontrol switching relay to reset the protection to a plain zone 1 reach prior

to the normally open point being closed.

Further distance protection features may be required for particular ring systems. Specific detail

can be found in the appropriate technical design manual for that ring system.

Standby main protection will be overcurrent and earth fault protection. Standby main protection

will be switched into service on failure of main protection scheme either from relay failure,

communications channel failure, or v.t failure in distance schemes.

When the feeder main protection zone excludes the 132kV circuit breaker due to the position ofits associated current transformers; the 132kV busbar protection or mesh corner protection will

be arranged to initiate the feeder intertripping or acceleration.

3.1.2 Transformer Main ProtectionThe main protection will be provided by overall bias differential protection and restricted earth

fault protection for each of the HV and LV windings.

Main and auxiliary transformer Buchholz Surge (trip) and Gas (alarm), and transformer winding

temperature trip and alarm will be provided.


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CODE OF PRACTICE

Where the main protection zone excludes the LV circuit breaker, then the busbar protection willbe arranged to clear faults in this small zone using an interlocked overcurrent scheme.

Fuses will protect auxiliary transformer LV connections.

3.1.3 Transformer Feeder Main ProtectionThe main protection provided for a transformer feeder will be the same as that provided for the

separate feeder and transformer components. Intertripping facilities will be provided as per

section 3.1.8.

The feeder main protection where permitted by the relative values of the 132kV and LV faultlevels will be highset overcurrent and compensated earth fault protection (re: EATS 41-15 Part 4

Appendix B)

3.1.4 Busbar ProtectionBusbar protection will be provided to achieve rapid and fully discriminative clearance for all

phase and earth faults occurring within the busbar zone whilst ensuring the maximum safeguard

against incorrect operation.

At grid supply points and where current transformer considerations dictate low impedance

numerical busbar protection will be provided. Two fault detecting systems will be incorporated.

Elsewhere, the scheme will be based on the unbiased differential circulating current principle

employing high impedance relays. Two independent fault detecting systems will be provided,

namely main and check zones.

The high impedance circulating current protection will not utilise in/out switching relays and will

use links in their place.

All schemes will employ current transformer supervision where detection of a faulty transformer

will initiate an alarm.

3.1.5 132kV Voltage TransformersThe 132kV wound voltage transformers will be provided with a Buchholz gas detection relay.

This relay will trip and intertrip the associated primary circuit to avoid any possibility of a

voltage transformer explosion. Modern low oil volume voltage transformers do not require a

Buchholz relay.

3.1.6 Back-up ProtectionBack up protection will be provided by inverse definite minimum time (IDMT) relays. All these

relays will be set to use the standard inverse 3/10 characteristic.


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CODE OF PRACTICE

Radial Feeders

Three pole overcurrent and single pole earth fault protection will be installed at 132kV feeder

circuit breakers at grid supply points. Earth fault protection will be directional when a voltage

transformer is installed, to significantly improve the discrimination of the back up protection.

The protection will switch to a second settings group that is non-directional with higher settings

when the protection has no voltage input.

Ring Feeders

Directional three pole overcurrent and single pole earth fault protection will be installed at

132kV feeder circuit breakers at ring feeder substations to provide both the functions of local

backup and standby main protection (SMP). The protection will switch to a second settings group

that is non-directional when the VT monitoring relay detects imbalance or loss of volts and where

appropriate when the line disconnector opens for the adjacent line.

This protection provides alternative protection in the event of a main protection failure on the

same feeder end, and provides protection in the event of an uncleared remote fault on another

feeder due to a stuck circuit breaker situation complementary to the zone 3 reach on the distance

protection.

Three stages of protection are incorporated:

SMP setting is blocked in normal service and is automatically switched into service wheneither the main protection fails or the VT supply to the main protection fails. The highsetcurrent setting with a fixed time delay applied is more sensitive and faster than the normal

backup protection. This is a non-directional protection and therefore has the same setting in

both settings groups.

Stage 2 setting is operational in normal service and consists of a high set current setting witha time delay. The time delay is longer that that of the SMP. The protection is semi-restricted

and is set to respond to faults within the particular feeder being protected. The setting is

directional and only used in the first settings group. The protection is independent of the

SMP and will operate even if the SMP fails to unblock or operate for some reason.

Stage 1 setting has a relatively low set fixed current setting that enables it to detect abnormallow level faults. The current setting is identical in both settings groups. The group 1 setting is

directional and the protection is graded with other protection on a time basis only. The timedelay is longer than SMP and stage 2 protection. The group 2 setting is non-directional is

required to clear the fault rather than grade with other protection.

Permanent relief points are required to split complex interconnected systems into simple

ring/radial systems in order to achieve grading of the backup protection. This system splitting

protection should be set to operate for a system disturbance such as a stuck circuit breaker and is

non-directional overcurrent protection with a time delay greater than the zone 3 time delay on the

distance protection.

Further back up protection features may be required for particular ring systems. Specific detail



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CODE OF PRACTICE

Transformer HV Back up Protection

Three pole overcurrent protection will be installed on the 132kV side of grid transformers. Two

stages will be provided to avoid unnecessary interruption of healthy teed transformers and two

settings groups will be provided to ensure coverage for a remote LV feeder fault when two

transformers are in service. The settings group will be changed automatically from the

transformer circuit breaker auxiliary switch. The first stage will trip the LV circuit breaker. Stage

one provides back up for uncleared LV feeder or busbar faults. The second stage will trip the LV

circuit breaker and intertrip to the remote HV circuit breaker or trip the local HV circuit breaker.

Stage two provides back up for a stuck LV circuit breaker, uncleared transformer faults, or for a

small zone fault not seen by the transformer main protection. When there is a local HV circuit

breaker present, there will be no time delay between stage 1 and stage 2. The first settings group

will be the higher of the two settings and will normally be applied when only one transformer is

in service or the LV bus section circuit breaker is open. In the event of relay field supply failure

or a hard wiring fault the settings will default to this group 1 setting. The second settings group

will be applied when both transformers are in service and the LV bus section circuit breaker is

closed.

Additionally a highset instantaneous element will be provided to ensure fast tripping for HV

terminal faults.

Standby Earth Fault Protection

Standby earth fault protection will be provided on each grid transformer. Two stages will beprovided, to avoid unnecessary interruption of healthy teed transformers. The first stage will trip

the LV circuit breaker. Stage one provides back up for stuck LV feeder circuit breakers and

uncleared LV earth faults. The second stage will trip the LV circuit breaker and intertrip to the

remote HV circuit breaker or trip the local HV circuit breaker. Stage two provides back up for

stuck LV transformer circuit breakers, faults not within the REF protected zone, and uncleared

faults in the REF protected zone. When there is a local HV circuit breaker present, there will be

no time delay between stage 1 and stage 2.

Transformer LV Back up Protection

Three pole directional overcurrent protection will be installed on each grid transformer LV

circuit breaker.

Circuit Breaker Fail Protection

Circuit breaker fail protection will be provided at grid supply points and supply points.

3.1.7 Low Frequency ProtectionLow frequency protection will be installed on all transformer circuits at supply points in

accordance with the Grid Code. There will be two sensing elements per relay to reduce the risk of

incorrect operation.


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CODE OF PRACTICE

3.1.8 IntertrippingThe remote circuit breakers should be tripped in less than 100ms after the detection of a

transformer or line fault. The intertripping schemes should be design with precautions to ensure

the schemes reliability.

Two systems of intertripping will be provided per feeder in order to maintain adequate protection

for the grid transformer should the signalling channel or equipment fail. When the first system is

voice frequency (VF) intertripping, the second system may be a fault thrower or separately routed

VF intertripping.

The first VF signalling channel will be a private circuit and the second VF signalling channelwill be a rented circuit.

Isolation transformers will protect metallic communications circuits.

The VF intertripping equipment including any telecommunications providers equipment will be

supplied from the substation d.c supplies.

One VF intertripping unit will provide intertripping facilities for two primary circuits between

the same locations, e.g. a pair of duplicate transformer feeders will have two VF intertripping

units providing four intertrip schemes.

The intertripping scheme will be monitored and insulated for 15kV.

When surge proof intertripping with YE pilots is used, a standby pilot circuit in a separate cable

will be made available and reserved for this duty.

Transformer feeders that provide mutual support for each other and use surge proof intertripping

will have the pilot circuits in separate cables.

Schemes using cascaded intertripping will be designed to achieve total fault clearance in less than

200ms. Cascade intertripping schemes will preferably have the pass on point at the grid supply

point.

3.1.9 Fault Interfering DisconnectorsThe transformer protection will intertrip to the remote circuit breaker of the transformer feeder as

well as opening the local transformer motorised disconnector. This is to assist in clearing

transformer faults in the event of an intertripping failure.

The transformer HV trip relay will initiate a timer before commencing the opening of the

disconnector. This timer is set to allow enough time for the remote circuit breaker to operate via

intertripping. If the disconnector first contact opening time is greater than 0.5s then the timer can

be set to zero, while a timer setting is required for opening times less than 0.5s.


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CODE OF PRACTICE

This mode of operation is restricted to those motorised disconnectors that are designed solely foroff load operation.

Voltage and current interlocks should be used for load switch disconnectors if they might sustain

damage that was not readily apparent and be retained in service in a dangerous condition.

3.1.10 Auto RecloseA scheme of delay auto reclose will be provided to return circuits to service after transient line

faults.

Faulty transformers will automatically be isolated before the rest of the system is re-energised.

The auto reclose sequence will be initiated by the feeder main protection or standby main

protection, for distance protection schemes this will be zones 1 and 2 only. The busbar protection

and where practicable the feeder back up protection will lock out reclosure.

The auto reclosure associated with the grid transformer is initiated by either the intertrip receive

trip (auto reset) relay, the resetting of the HV trip relay, or the directional overcurrent relay. The

line voltage is monitored through the LV VT and needs to be present before the close command

is given. Operation of either the HV transformer trip relay, transformer back up protection,

standby earth fault protection or the winding temperature trip relay will inhibit the auto reclose

cycle.

Primed for reclosure feature should be set for no longer than 15 minutes after which it should be

cancelled.

3.1.11 Local Alarms and IndicationsThe following local alarms and will be provided on the appropriate relay panel:-

Non Trip Alarm monitoring protection d.c. supplies and circuit breaker trip circuits or fortransformers the operation of main Buchholz gas, auxiliary Buchholz gas, and winding

temperature alarms.

VT Supply Fail monitoring voltage transformer circuits. Main Protection Faulty monitoring relay field (auxiliary) supply voltage and protectionrelay status. Backup Protection Faulty monitoring relay field (auxiliary) supply voltage and protection

relay status.

Trip Relay Operated / CB Auto Trip monitoring status of CB trip relays. Low Frequency Alarm monitoring low frequency protection operation. Voltage Control Faulty monitoring transformer automatic voltage control relay. Main Buchholz Alarm (routed through and displayed on the main transformer protection

relay where appropriate) monitoring main transformer Buchholz Gas operation.

Main Buchholz Trip (routed through and displayed on the main transformer protection relaywhere appropriate) monitoring main transformer Buchholz Surge operation.

Auxiliary Buchholz Alarm (routed through and displayed on the main transformer protectionrelay where appropriate) monitoring auxiliary transformer Buchholz Gas operation.


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Auxiliary Buchholz Trip (routed through and displayed on the main transformer protectionrelay where appropriate) monitoring auxiliary transformer Buchholz Surge operation.

Selector Buchholz Trip (routed through and displayed on the main transformer protectionrelay where appropriate) monitoring main transformer tapchanger Buchholz Surge

operation.

Winding Temperature Alarm (routed through and displayed on the main transformerprotection relay where appropriate) monitoring transformer winding temperature operation.

Winding Temperature Trip (routed through and displayed on the main transformer protectionrelay where appropriate) monitoring transformer winding temperature operation.

Winding Temperature Fail monitoring status of winding temperature protection relay. Main Transformer Pressure Relief Alarm monitoring main transformer pressure relief

device operation. Auxiliary Transformer Pressure Relief Alarm monitoring auxiliary transformer pressure

relief device operation.

Drycol Breather Faulty monitoring status of the transformer Drycol breather. SF6 Close Inhibit (only for SF6 circuit breakers) - indicating operation of the first stage of

low pressure monitoring.

SF6 Low Gas Pressure Lockout (only for SF6 circuit breakers) - indicating operation of thesecond stage of low pressure monitoring.

Intertrip Faulty monitoring status of intertripping equipment. Cable Pressure Low monitoring the pressure of pressure assisted cables.The following indications will be provided on the appropriate relay panel:- Disconnector Open Disconnector Closed Earth Switch Open Earth Switch Closed Circuit Breaker Open Circuit Breaker Closed Circuit Breaker Isolated HVOC High Setting Selected this is only applicable to highset overcurrent protection fitted

to transformers.

For details of SCADA alarms see DSS/007/003 - Philosophy of Telecontrol Facilities ProvidedAt Substations (TS8).

3.1.12 Application to New and Existing EquipmentAll new and modified equipment will be designed to this standard. Protection detail will be in

accordance with the relevant general protection applications documentation, relay application

documentation, and where appropriate to EATS 41-15.

Existing biased busbar protection schemes will be retained. Existing earth fault only busbar

protection schemes will be retained only until major work is carried out at the substation.


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CODE OF PRACTICE

Existing busbar protection schemes where the protection defective feature removes the trippingand short circuits the current transformers of the defective zone will be modified. The protection

defective feature will be arranged to give an alarm only and any fault detection relays that are not

continuously rated will be changed.

Directional earth fault and standby earth fault protection will not be installed retrospectively

unless other modification work is proposed or the protection is required to increase the sensitivity

and speed of the back up protection for transformers which would otherwise be dependent on one

VF intertripping scheme.

Existing arrangements of HV and LV overcurrent relays providing 2 stage protection on grid

transformers will be retained.

Circuit breaker fail protection will not be installed retrospectively.

3.2 66kV and 33kV SystemsAll items of plant will be covered by systems of main protection and back-up protection.

The main protection will be discriminative i.e. disconnect only the faulted system elements for all

likely faults on the protected plant. Fault detection will occur in less than 50ms with total fault

clearance achieved in 100ms to 200ms. This complete fault clearance time will be longer when

fault throwing switches, LV directional overcurrent, or neutral displacement protection are

necessarily employed as a means or substitute for intertripping. Clearance times exceeding200ms will also occur on feeders protected by zone 2 distance and directional earth fault

protection. However the total clearance time for any of these situations will not exceed 1s.

This specification for fault clearance times may need to be shortened where necessary to ensure

stability of embedded generation.

The back-up protection will be arranged to limit the disruption of supplies in the event of failure

of the main protection.

On ring feeder systems zone 3 is arranged to limit disruption of supplies in the event of a circuit

breaker failing to open for a fault.

3.2.1 Feeder Main ProtectionThe main protection will be fully discriminative and be by use of unit protection using Yorkshire

Electricity or rented pilot circuits. Unit protection schemes in Yorkshire Electricity pilots will be

monitored either inherently in the protection or by use of separate ones in the same pilot cable.

Unit protection schemes in rented pilots will always be monitored.

Where appropriate due to consideration of cable capacitance, paired pilot cables may be used.

When a suitable pilot circuit cannot be made available distance protection will be used.


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CODE OF PRACTICE

For primary circuits with no continuous earth return conductor (which is the usual case), theearth fault feature of the distance protection will be restricted to zone 1 measurement. A

quadilateral earth fault characteristic will be used by the distance protection.

Distance protection will use the loss of load zone 2 acceleration feature where practicable on ring

feeder systems.

All systems of distance protection will use switch on to fault logic.

Where a ring system is run with normally open points, the distance protection at these points will

be provided with a zone 1 extension feature to reach into the remote end zone to ensure fast

clearance of end zone faults. This zone 1 extension will be switchable both locally and via

telecontrol using a telecontrol switching relay to reset the protection to a plain zone 1 reach prior

to the normally open point being closed.

Further distance protection features may be required for particular ring systems. Specific detail


When the feeder main protection zone excludes the 66kV/33kV circuit breaker due to the

position of its associated current transformers; the busbar protection or adjacent zone protection

will be arranged to initiate the feeder intertripping.

Alternatively faults in the small zone between the current transformers and the switchgear

spouts will be cleared in zone 2 of the remote distance protection, or on transformer feederswithout intertripping by neutral displacement and directional overcurrent protection.

Standby Main Protection will be overcurrent and earth fault protection. Standby main protection

will be switched into service on failure of main protection scheme either from relay failure,

communications channel failure, or v.t failure in distance schemes.

3.2.2 Transformer Main ProtectionThe main protection will cover earth faults only. The protection will be provided by HV balanced

earth fault protection and 11kV restricted earth fault protection.

Main and auxiliary transformer Buchholz Surge (trip) and Gas (alarm), and transformer winding

temperature trip and alarm will be provided.

Fuses will protect auxiliary transformer LV connections.

3.2.3 Transformer Feeder Main ProtectionWhen future extensions to the primary circuit would require further zones of protection, the main

protection provided for a transformer feeder would be the same as that provided for the separate

feeder and transformer components. Intertripping facilities will be provided as per section 3.2.7.


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CODE OF PRACTICE

When the primary circuit is unlikely to be extended, the feeder main protection will be highsetovercurrent and balanced earth fault relay with low transient overreach. The transformer main

protection is as stated in 3.2.2 with the exception that balanced earth fault protection may already

form part of the feeder main protection. Intertripping facilities will be provided as per section

3.2.7.

Where the relative HV and LV faults levels do not permit highset overcurrent protection, three

methods can be considered:-

1) Star delta interposing current transformers2) Unit protection3) Phase fault distance protection with balanced earth fault protection or quadilateral earth fault


Where it is necessary to make and break parallels on air break disconnectors at 66kV/33kV (for

example to transfer a transformer to another feeder) facilities will be provided to inhibit the

balanced earth fault protection. This is to prevent a protection maloperation during the switching

operation. The feeder back up protection on these types of primary circuit must have a maximum

earth fault current setting of 120A.

Neutral Voltage Displacement Protection

Neutral displacement protection will be provided on any transformer that is supplied solely by a

feeder that contains some overhead line (including the primary circuits with a local transformer

HV circuit breaker).

Where an outage of one item of plant could result in a single, part overhead line, feeder supplying

a transformer then neutral displacement protection will be installed. Therefore even if the circuit

does not itself require neutral displacement it may be installed in order to provide interlocking to

other primary circuits. The protection ensures that broken conductors grounded on the

transformer side that could remain alive through the transformer primary windings are

disconnected. For duplicate transformer feeder circuits a two stage neutral displacement relay

will be applied, while for a single transformer a single stage neutral displacement relay will be

used. Further description of the requirements for the two stages will be as per section 3.2.7.

Relays used for neutral voltage displacement will have a third harmonic filter.

3.2.4 Busbar ProtectionBusbar protection will be provided to achieve rapid and fully discriminative clearance for all

phase and earth faults occurring within the busbar zone whilst ensuring the maximum safeguard

against incorrect operation.

At supply points and where current transformer considerations dictate low impedance numerical

busbar protection will be provided. Two fault detecting systems will be incorporated.

Elsewhere, the scheme will be based on the unbiased differential circulating current principle

employing high impedance relays. Two independent fault detecting systems will be provided,namely main and check zones.


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CODE OF PRACTICE

The high impedance circulating current protection will not utilise in/out switching relays and will

use links in their place.

All schemes will employ current transformer supervision where detection of a faulty transformer

will initiate an alarm.

At mesh substations where part of the busbars in the mesh are not included in the zone of the

adjacent feeder or transformer main protection, a single fault detecting system will be provided to

cover the unprotected busbars. The scheme will be based on the unbiased differential circulating

current principle employing high impedance relays to detect phase and earth faults.

At other substations where there are more than five circuits a busbar scheme based on the

unbiased differential circulating current principle employing high impedance relays to detect

phase and earth faults will be applied.

3.2.5 66kV Voltage TransformersThe 66kV wound voltage transformers will be provided with a Buchholz gas detection relay. This

relay will initiate an alarm. Modern low oil volume capacitor voltage transformers do not require

a Buchholz relay.

3.2.6 Back up ProtectionBack up protection will be provided by inverse definite minimum time (IDMT) relays. All these

relays will be set to use the standard inverse 3/10 characteristic.

Radial Feeders

A three pole overcurrent and single pole earth fault relay will be installed at 66kV/33kV feeder

circuit breakers.

Ring Feeders

Directional three pole overcurrent and single pole earth fault protection will be installed at132kV feeder circuit breakers at ring feeder substations to provide both the functions of local

backup and standby main protection (SMP). The protection will switch to a second settings group

that is non-directional when the VT monitoring relay detects imbalance or loss of volts and where

appropriate when the line disconnector opens for the adjacent line.

This protection provides alternative protection in the event of a main protection failure on the

same feeder end, and provides protection in the event of an uncleared remote fault on another

feeder due to a stuck circuit breaker situation complementary to the zone 3 reach on the distance

protection.

Three stages of protection are incorporated:


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CODE OF PRACTICE

SMP setting is blocked in normal service and is automatically switched into service wheneither the main protection fails or the VT supply to the main protection fails. The highset

current setting with a fixed time delay applied is more sensitive and faster than the normal

backup protection. This is a non-directional protection and therefore has the same setting in

both settings groups.

Stage 2 setting is operational in normal service and consists of a high set current setting witha time delay. The time delay is longer that that of the SMP. The protection is semi-restricted

and is set to respond to faults within the particular feeder being protected. The setting is

directional and only used in the first settings group. The protection is independent of the

SMP and will operate even if the SMP fails to unblock or operate for some reason.

Stage 1 setting has a relatively low set fixed current setting that enables it to detect abnormallow level faults. The current setting is identical in both settings groups. The group 1 setting isdirectional and the protection is graded with other protection on a time basis only. The time

delay is longer than SMP and stage 2 protection. The group 2 setting is non-directional is

required to clear the fault rather than grade with other protection.

Permanent relief points are required to split complex interconnected systems into simple

ring/radial systems in order to achieve grading of the backup protection. This system splitting

protection should be set to operate for a system disturbance such as a stuck circuit breaker and is

non-directional overcurrent protection with a time delay greater than the zone 3 time delay on the


Further back up protection features may be required for particular ring systems. Specific detail


Transformer HV Back up Protection

A three pole overcurrent and earth fault relay will be installed on the 66kV/33kV side of

transformers at busbar, mesh, and 3 circuit type substations. They will also be installed on the

66kV/33kV side of transformers at other types of substation when the setting of the IDMT relay

installed at the source exceeds 50% of the minimum fault level at the transformer LV

terminations. Two stages will be provided to avoid unnecessary interruption of healthy teed

transformers and two settings groups will be provided to ensure coverage for a remote LV feeder

fault when two transformers are in service. The settings group will be changed automatically

from the transformer circuit breaker auxiliary switch. The first stage will trip the LV circuitbreaker. Stage one provides back up for uncleared LV feeder or busbar faults. The second stage

will trip the LV circuit breaker and intertrip to the remote HV circuit breaker or trip the local HV

circuit breaker. Stage two provides back up for a stuck LV circuit breaker, uncleared transformer

faults, or for a small zone fault not seen by the transformer main protection. When there is a local

HV circuit breaker present, there will be no time delay between stage 1 and stage 2. The first

settings group will be the higher of the two settings and will normally be applied when only one

transformer is in service or the LV bus section circuit breaker is open. In the event of relay field

supply failure or a hard wiring fault the settings will default to this group 1 setting. The second

settings group will be applied when both transformers are in service and the LV bus section

circuit breaker is closed.


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CODE OF PRACTICE

Transformer LV Back up Protection

A three pole overcurrent and earth fault relay will be installed on the 11kV circuit breaker of

transformer feeders when HV overcurrent current transformers are not available.

A three pole directional overcurrent relay will be installed on each transformer 11kV circuit

breaker. This protection is for uncleared 66kV/33kV feeder faults.

Standby Earth Fault Protection

A standby earth fault relay will be provided on each transformer. Two stages will always be

provided, to avoid unnecessary interruption of healthy teed transformers. The first stage will trip

the LV circuit breaker. Stage one provides back up for stuck LV feeder circuit breakers and

uncleared LV earth faults. The second stage will trip the LV circuit breaker and intertrip to the

remote HV circuit breaker or trip the local HV circuit breaker. Stage two provides back up for

stuck LV transformer circuit breakers, faults not within the REF protected zone, and uncleared

faults in the REF protected zone. When there is a local HV circuit breaker present, there will be

no time delay between stage 1 and stage 2.

Circuit Breaker Fail Protection

Circuit breaker fail protection will be provided at new supply point substations. Operation of the

protection will trip all circuit breakers in its associated busbar protection zone. A check system

will be incorporated to reduce the risk of incorrect operation.

3.2.7 IntertrippingThe detection of a transformer fault and where necessary the detection of a feeder fault will

initiated the tripping of remote circuit breakers via intertripping.

When Yorkshire Electricity pilot cables are available 2 way 2 wire surge proof intertripping will

be used. In addition if the protected circuit has more than 2 ends then 2 way 2 wire multi-point

surge proof intertripping will be used in preference to a cascade system.

The intertripping scheme will be monitored and insulated for 15kV.

When surge proof intertripping with Yorkshire Electricity pilots is used, a standby pilot circuit in

a separate cable will be made available and reserved for this duty.

Transformer feeders that provide mutual support for each other and use surge proof intertripping,

will have the pilot circuits in separate cables.

When Yorkshire Electricity pilot cables are not available, usually on overhead line circuits,

alternative provisions for intertripping will be made. Fault throwing switches will be used to

initiate remote circuit breaker operation for transformer faults. Neutral displacement and LV

directional overcurrent will be used to trip the transformer 11kV circuit breaker for feeder faults.

The neutral displacement relay on duplicate transformer circuits will have two stages to reducethe overall clearance time using fault throwing switches for transformer faults. Stage one will be


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CODE OF PRACTICE

interlocked to enable the protection to discriminate between in zone and out zone faults. This willbe set to one second and will trip the transformer 11kV circuit breaker providing a relatively fast

clearance for a fault on any transformer teed to the feeder. Stage two will be set for 10s and will

trip the 11kV circuit breaker and close the fault thrower. The stage two is not interlocked. A

single stage neutral displacement scheme will be as described for the stage 2. Further description

is given in section 3.2.3.

Intertripping schemes that contain an unusual mixture of pilot wire intertripping, fault throwing

switches, directional overcurrent protection, and neutral displacement protection will be checked

to verify that they comply with the overall clearance times specified in section 3.2.

Fault interfering disconnectors will be applied with the requirements of section 3.1.9.

3.2.8 Auto RecloseA scheme of delayed auto reclose will be provided to return circuits to service after transient

overhead line faults. On single transformer circuits the auto reclose will not be provided on the

transformer circuit breaker unless there is intertripping provided from the source breaker.

The auto reclose sequence will be initiated by the feeder main protection or standby main

protection, for distance protection schemes this will be zones 1 & 2. The busbar protection and

the feeder back up protection will lock out reclosure.

3.2.9 Local Alarms and IndicationsThe following local alarms and will be provided on the appropriate relay panel:-

Non Trip Alarm monitoring protection d.c. supplies and circuit breaker trip circuits or fortransformers the operation of main Buchholz gas, auxiliary Buchholz gas, and winding

temperature alarms.

VT Supply Fail monitoring voltage transformer circuits. Main Protection Faulty monitoring relay field (auxiliary) supply voltage and protection

relay status.

Backup Protection Faulty monitoring relay field (auxiliary) supply voltage and protectionrelay status.

Trip Relay Operated / CB Auto Trip monitoring status of CB trip relays. Low Frequency Alarm monitoring low frequency protection operation. Voltage Control Faulty monitoring transformer automatic voltage control relay. Main Buchholz Alarm (routed through and displayed on the main transformer protection

relay where appropriate) monitoring main transformer Buchholz Gas operation.

Main Buchholz Trip (routed through and displayed on the main transformer protection relaywhere appropriate) monitoring main transformer Buchholz Surge operation.

Auxiliary Buchholz Alarm (routed through and displayed on the main transformer protectionrelay where appropriate) monitoring auxiliary transformer Buchholz Gas operation.

Auxiliary Buchholz Trip (routed through and displayed on the main transformer protectionrelay where appropriate) monitoring auxiliary transformer Buchholz Surge operation.


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CODE OF PRACTICE

Selector Buchholz Trip (routed through and displayed on the main transformer protectionrelay where appropriate) monitoring main transformer tapchanger Buchholz Surge

operation.

Winding Temperature Alarm (routed through and displayed on the main transformerprotection relay where appropriate) monitoring transformer winding temperature operation.

Winding Temperature Trip (routed through and displayed on the main transformer protectionrelay where appropriate) monitoring transformer winding temperature operation.

Winding Temperature Fail monitoring status of winding temperature protection relay. Main Transformer Pressure Relief Alarm monitoring main transformer pressure relief

device operation.

Auxiliary Transformer Pressure Relief Alarm monitoring auxiliary transformer pressurerelief device operation.

Drycol Breather Faulty monitoring status of the transformer Drycol breather. SF6 Close Inhibit (only for SF6 circuit breakers) - indicating operation of the first stage of

low pressure monitoring.

SF6 Low Gas Pressure Lockout (only for SF6 circuit breakers) - indicating operation of thesecond stage of low pressure monitoring.

Intertrip Faulty monitoring status of intertripping equipment. Cable Pressure Low monitoring the pressure of pressure assisted cables.The following indications will be provided on the appropriate relay panel:-

Disconnector Open

Disconnector Closed Earth Switch Open Earth Switch Closed Circuit Breaker Open Circuit Breaker Closed Circuit Breaker Isolated HVOC High Setting Selected this is only applicable to highset overcurrent protection fitted

to transformers.

For details of SCADA alarms see DSS/007/003 - Philosophy of Telecontrol Facilities Provided

At Substations (TS8).

3.2.10 Application to New and Existing EquipmentAll new and modified equipment will be designed to this standard. Protection detail will be in

accordance with the relevant general protection applications documentation and relay application

documentation.

Existing protection systems are considered in general to comply with the principles of this

standard. However where existing systems are found to seriously conflict with the philosophy of

this standard they will be considered on an individual basis and modified where required.

Existing biased busbar protection, and earth fault only busbar protection will be retained.


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CODE OF PRACTICE

3.3 11kV SystemsAll plant will be protected against phase and earth faults. In general the protection will be time

graded and arranged to limit the disruption of supplies in the event of a system fault. Systems that

are required to run interconnected will be equipped with discriminative protection that will

disconnect only faulty system elements for all likely faults. The exceptions to these

interconnected systems are sections of busbars and small zones at primary substations.

If second stage protection is applied to a feeder then the feeder should be checked for generation

and intertripping provided if necessary for an islanding situation.

3.3.1

Underground Feeder Protection

Radial feeder networks that are normally run without interconnection will be protected by three

pole overcurrent and single pole earth fault relays installed at the primary substation. Second

stage protection points may be installed as required.

Interconnected or parallel feeders will be provided with unit protection or directional IDMT

protection. Unit protection will be used when there is a pilot circuit present or it is economical to

provide one. Directional IDMT protection is used if the network is suitable for the necessary time

grading.

Duplicate setting groups used for parallel feeders will be either automatically changed using the

status of the remote end bus section and feeder circuit breakers, or if these are not available thenby telecontrol.

When there are more than two parallel feeders supplying the secondary substation, then

individual consideration should be given with the objective of providing the shortest clearance

time possible compatible with DSS/007/007 - The Setting of Protection (TS16/17).

3.3.2 Overhead Feeder ProtectionThe protection of overhead feeders and connected pole mounted transformers will be in

accordance with DSS/007/010 - Protection of 11kV Overhead Networks.

3.3.3 11000/415V TransformersThe protection of 11000/415V transformers will be by time limit fuses with a.c. trip coils on a

circuit breaker. The protection will clear HV faults as fast as practical allowing for the need to

provide grading with the LV circuit protection.

The use of HV fuses should be avoided as they do not grade will source IDMT protection.

The protection will be provided by a circuit breaker fitted with 3 pole overcurrent and single pole

earth fault protection with an extremely inverse characteristic when:-

A longer time setting is required to grade with the customers protection. The transformer size is beyond the capacity of a time limit fuse on a.c. trip coils.


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CODE OF PRACTICE

The circuit is supplied from an extensible switchboard and a time limit fuse on a.c. tripprotection combination is not available.

The design of the protection and the associated settings will cover the LV terminations and

adjacent LV busbars. The HV protection should be set to cover the LV switchboard busbars up to

a maximum distance from the transformer of 15m. This distance assumes cable is used with

conductor sizes specified in DSS/005/038 Guidance on the Application of 11kV and LV

Cables, or an equivalent distance using other sizes. Where the transformer cable terminations

are longer than this distance, LV protection by a suitable circuit breaker will be installed.

3.3.4 Busbar ProtectionThe 11kV busbars at all substations will be protected by the transformer or transformer feeder

back up protection.

The busbars at secondary substations will be protected by the feeder IDMT protection installed at

the primary substation or second stage protection point. This will also apply to secondary

substations fed by two parallel feeders.

3.3.5 Backup ProtectionFeeder circuit breaker fail protection will be provided by a system of back tripping to the bus

section circuit breaker and the associated transformer circuit breaker.

3.3.6 Application to New and Existing EquipmentAll new and modified equipment at 11kV will be designed to section 3.3. Protection detail will

be in accordance with the relevant general protection applications documentation and relay

application documentation.

Existing protection systems are considered in general to comply with the principles of section

3.3. However where existing systems are found to seriously conflict with this philosophy they

will be considered on an individual basis and modified where required.

Existing 11kV busbar protection will be retained.

Existing IDMT relay protection for 11000/415V transformers using the standard 3/10

characteristic will be retained unless the application of suitable settings for grading purposes

proves difficult.

3.4 Protection of Generation Connected to 66kV and Lower Voltage SystemsThis section specifies the protection requirements for private generation, generating at LV,

connected to Yorkshire Electricity Distribution systems at 66kV, 33kV, 11kV, and LV levels.

All HV connected generation, generating at HV, should be the subject of detailed studies

although the principles contained in this section may be applied.


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CODE OF PRACTICE

All groups of LV generation connected at HV where the total generation capacity is greater than

10MW should be the subject of more detailed stability and voltage studies in order to specify the

protection scheme.

This does not cover connections to the 132kV systems, which should be the subject of detailed

studies although the principles contained in this section may be applied.

The guidance detailed here summaries and supplements the information contained in Engineering

Recommendation G59, Engineering Recommendation G75, Engineering Technical Report

TR113, and the IMP/001/007 Code of Practice for the Connection of Generation Plant.

3.4.1 Protection Principles

The Yorkshire Electricity protection and the generators protection is required to achieve the

following objectives:-

To ensure that any generation connected to the Yorkshire Electricity Distribution systems isprevented from operating outside agreed parameters of voltage and frequency.

To prevent any possibility of automatic reclosure out of synchronism i.e. to primarily protectthe generator from damage.

To prevent the operation of any system without a neutral earth i.e. to comply with theElectricity Supply Regulations.

To clear any fault current into the Yorkshire Electricity system from the generator. To clear any earth fault that occurs subsequent to the loss of the system neutral earth. To prevent islanded operation of part of the Yorkshire Electricity network i.e. to disconnect

the generation in the event that the part of the network to which it is connected, becomes

disconnected from the rest of the network.

3.4.2 Island Only Generation Protection

In an island only scheme the generation is available as a back up or alternative to the Yorkshire

Electricity supply. The generation will never be connected to the Yorkshire Electricity supply for

any length of time.

The generation should be treated as a load connection so that the minimum protection at theYorkshire Electricity interface is HV fuses, time limit fuses with a.c. trip coils on a circuit

breaker, or an overcurrent and earth fault relay. This will protect against phase and earth faults on

the customers installation.

The requirement for interlocking between the generation and Yorkshire Electricity supplies will

be considered on an individual basis.

Where there is an auto-changeover facility for example on mains fail, this will be witnessed on

commissioning and operation proved in so far is reasonable.


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CODE OF PRACTICE

3.4.3 Short Term Parallel Generation Protection

Short term parallel schemes are essentially island schemes but with the capability to parallel to

the Yorkshire Electricity system for short periods. This will enable a no-break change over from

the Yorkshire Electricity supply to the generator or vice versa. Positioning of the synchronising

facilities will affect the exact change over capabilities. These schemes will not allow export at

any time.

Short term parallel generation may be connected for 5 minutes once per month for testing

purposes in accordance with Engineering Recommendation G59.

A Yorkshire Electricity timer will be started by the closure of the generator synchronising circuitbreaker and will be arranged to disconnected the Yorkshire Electricity supply if the customer

does not open a switch to break the connection. This timer will be set to 5 minutes.

The customer is recommended to install a similar system that will disconnect the generator in a

controlled manner after 4 minutes.

The generation should be treated as a load connection so that the minimum protection at the

Yorkshire Electricity interface is HV fuses, time limit fuses with a.c. trip coils on a circuit

breaker, or an overcurrent and earth fault relay. This will protect against phase and earth faults on

the customers installation.

The customer will be required to fit over voltage, under voltage, over frequency, and underfrequency protection.

3.4.4 Full Parallel Generation Protection

A full parallel scheme is one where the connection agreement allows the generator to be

permanently connected to the Yorkshire Electricity network. This is irrespective of the operating

regime proposed (e.g. schemes not covered by short term paralleling) or whether there is any

export.

Full parallel schemes can be categorised as:

Generator installations over 1MW Generator installations less than 1MW fed by overhead lines where the amount of overhead

line and customers present on the feeder would necessitate the installation of auto reclose to

improve the quality of supply to the customers.

Generator installations less than 1 MW fed by underground cablesThis is the generation capacity not the export capacity.

Feeder Protection at Yorkshire Electricity Substation

The feeder protection at the Yorkshire Electricity substation should be checked to determine

whether the fault infeed from the generator installation does not significantly shorten the reach,

lengthen the clearance times or effect the discrimination of the protection.

Yorkshire Electricity Interface Protection


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CODE OF PRACTICE

For all parallel connections, the generation should be treated as a load connection so that theminimum protection at the Yorkshire Electricity interface is HV fuses, time limit fuses with a.c.

trip coils on a circuit breaker, or an overcurrent and earth fault relay. This will protect against

phase and earth faults on the customers installation.

If the generator installation is capable of supporting in island mode the remaining connected load

after operation of any remote circuit breaker on that part of the network, then protection will be

fitted on the YE interface circuit breaker to ensure disconnection of the generation. The

capability to support the load in an island mode is defined as the connected generation capacity

being equal to or greater than half the minimum load remaining. Generation not fulfilling this

criteria will be disconnected following operation of the customers protection.

The additional protection fitted on the Yorkshire Electricity interface circuit breaker will be

dependent on the generator capacity and connection.

Generator installations over 1MW intertripping scheme. Generator installations less than 1MW fed by overhead lines intertripping scheme. Generator installations less than 1 MW fed by underground cables neutral voltage

displacement relay to protect against earth faults, directional overcurrent relay to protect

against phase faults on the Yorkshire Electricity network.

Intertripping Scheme for Yorkshire Electricity Network

The interface protection will normally be provided with an intertrip command from the protection

at the Yorkshire Electricity fault infeed point. Where the generator is capable of supporting boththe load on the feeder and the load at the substation supplying that feeder, then the intertripping

will be required from the protection at the previous stages in the network.

Customer Protection

The customers installation requires a loss of mains protection and a back up protection.

Generators below 1MW may use RoCoF/REED/Vector Shift based protection schemes as the

loss of mains protection. Yorkshire Electricity place no reliance on these protection schemes as

they have been known to be unreliable both failing to operate when required and also operating

causing nuisance tripping.

Generators above 1MW are required to install loss of mains protection where an intertripping

signal will be provided by Yorkshire Electricity.

The loss of system earth scheme provides the customer with the intertripping signal. The scheme

operates for a two transformer substation due to the opening of one transformer circuit breaker

and the bus section circuit breaker or the opening of both transformer circuit breakers. Other

types of substation scheme will operate on the same principle.

The customer will be required to fit over voltage, under voltage, over frequency, and under

frequency protection referred to the Yorkshire Electricity supply terminals as back up.


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CODE OF PRACTICE

3.4.5 Generator Earthing Requirements

A generator running in island mode or short term parallel mode may have its own star point earth

connection, whereas a generator running in full parallel will normally rely on an earth provided

by the Yorkshire Electricity supply.

A full parallel generator with island mode capability will require an isolatible star point earth

connection, which will normally run open. The closure of the generator neutral earth switch

should be initiated from the opening of the Yorkshire Electricity interface circuit breaker or the

customers interface circuit breaker.

3.4.6 Asynchronous Generation

Asynchronous generators can have their fields excited by the mains supply or be self excited by

using a capacitor bank. Mains excited generators will normally cease generation if the mains

supply fails as the required magnetising current will not be available, and so no special

protection is required. However generation could continue by self excitation if the capacitance of

the connected network is sufficient, and in these circumstances the protection should be selected

as for synchronous generators. An assessment will be made at the design stage to establish if

generation by self excitation is possible.

If power factor correction is installed such that the generator can run self excited either at no-

load or at any load then the generation will be treated as synchronous.

3.5 General Requirements for a Protection Scheme3.5.1 General Protection Relay Requirements

All measuring relays will be of modern design offering a wide range of settings, timing

characteristics, and additional facilities including self-supervision.

The relay self-supervision will include power-on diagnostics and continuous self monitoring with

the operation of an alarm upon any failures detected.

The voltage supply for relay input contacts will be monitored.

Protection at distribution substations can be of the electromechanical type where it is

uneconomical to provide battery supplies.

3.5.2 Protection Relay FunctionalityThe following protection functions can be utilised in a single multi-functional relay.

Feeder highset overcurrent and compensated earth fault protection. Feeder overcurrent and earth fault protection incorporating directional, non-directional,

highset, and standby main protection stages.

Feeder highset overcurrent and balanced earth fault protection.

Feeder backup overcurrent and earth fault protection.


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CODE OF PRACTICE

Low frequency stage 1 and stage 2 protection. Feeder neutral voltage displacement protection stage 1 and stage 2. Transformer HV 2 stage overcurrent and balanced earth fault protection. Transformer bias differential, HV restricted earth fault, and LV restricted earth fault

protection.

Transformer standby earth fault protection stage 1 and stage 2. Transformer LV directional overcurrent, restricted earth fault, and overcurrent protection. 11kV feeder overcurrent and earth fault protection.

3.5.3 Testing of Protection RelaysAdequate test and isolation facilities will be provided to facilitate all necessary maintenance andtesting without the need to remove wired connections.

All test facilities will be normally accessible from the front of the panel.

Sufficient maintenance test points will be provided to allow main protection, back up protection,

control and alarm equipment to be tested and maintained using the Yorkshire Electricity standard

automatic test equipment. As a minimum relay test blocks will be provided on a per protection

relay basis and two blocks will be provided for distance protection relays.

Protection relays will be of a withdrawable design to allow relay or module replacement without

the need to remove wired connections.

3.5.4 Substation CommunicationsProtection and control relays will have remote data communications facilities appropriate to the

type of relay. These data communications facilities will be used by the SCADA system RTU.

The SCADA and remote data communications will be capable of being in service at the same

time.

Transformer and feeder analogue measurements from the specified protection relays will be

displayed and accessed via the communications bus.

The communications will be capable of operating in a normal substation environment under

normal operating conditions, and will continue to operate during fault conditions if this is

necessary for the correct operation of the protection and control scheme.

The communications facilities of all protection and control relays will be marshalled in, or

adjacent to, the existing telecontrol marshalling kiosk. An interface unit will be provided at this

point, powered from the substation telecontrol battery, so that all relays can be interrogated from

a standard PC and remotely via the modem associated with the disturbance recorder installation.

Suitable communications branching facilities will be provided so both the relays and the

disturbance recorder installations can be remotely interrogated using suitable software packages.


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CODE OF PRACTICE

3.5.5 Provision of Voltage and Current Transformers

The VT supply for protection relays will be supervised for all types of loss of VT input to the

protection relay.

One set of CTs will be provided per protection function with the exclusion of 11kV feeder

protection where both the overcurrent and earth fault protection will be driven from the same set

of CTs.

The detailed requirements for current transformers as applied to specific protection and metering

functions at the different system voltages will be in accordance with the GAPP Current

Transformer Specifications 11kV 132kV.

Feeder Overcurrent and Earth Fault Backup Protection on 132kV Ring Systems

For single switch substations, the CTs in the 132kV bus section and the CTs on the HV side of

the transformer are summated to enable true feeder current measurement. If a dedicated set of

CTs can not be provided then before being summated, the transformer HV CTs will also feed

the two stage HV overcurrent protection.

3.5.5 Scheme DiagramsThe following diagrams should be approved by the client engineer prior to construction of the

relay panels.

Logic Diagrams

In general these diagrams will show a schematic of the primary system connections along with

the relevant protection and control functions. Four types of diagram are required:-

Protection logic diagram showing the operation of protection to initiate both the localcircuit breaker tripping and any intertripping.

Alarms logic diagram showing local alarms/controls/analogues/indications. Telecontrol logic diagram showing remote alarms/controls/analogues/indications. Auto reclose logic diagram showing the details of any auto reclose and auto close schemes.Connections and Protection Diagrams

These diagrams will show a schematic of the primary system connections along with the

associated plant information and details of the protection relay panels along with the associated

v.t and c.t. connections. A number of these diagrams will be required depending upon the size of

the substation.

3.5.6 Protection Relay SettingsThe setting of protection and control relays will be in accordance with the procedures and

formats specified in DSS/007/007 - The Setting of Protection (TS16/17).


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CODE OF PRACTICE

3.5.7 Protection Relay D.C. SuppliesAll d.c supplies to protection and control relays will be monitored. The last device in a d.c.

supply spur to protection and control relays will be either a self supervised protection and control

relay or a supply supervision relay.

Remote indication of the d.c. supply supervision will be in accordance with DSS/007/003 -

Philosophy of Telecontrol Facilities Provided At Substations (TS8).

4. References

4.1 Codes of PracticeDSS/005/038 - Guidance on the Application of 11kV and LV Cables

DSS/007/003 - Philosophy of Telecontrol Facilities Provided At Substations (TS8)

DSS/007/007 - The Setting of Protection (TS16/17)

DSS/007/010 - Protection of 11kV Overhead Networks

IMP/001/007 Code of Practice for the Connection of Generation Plant

4.2 External

Electricity Supply Regulations (1988)

Electricity at Work RegulationsEATS 41-15 Standard Circuit Diagrams for 132kV Substations

Grid Code

Engineering Recommendation G59 (1991)

Engineering Recommendation G75 (1996)

Engineering Technical Report TR113 (1995)

5. Definitions

5.1 Second Stage Protection PointA suitable circuit breaker on an 11kV network feeder which has been fitted with IDMTprotection to improve customer quality of supply.

5.2 Fully Discriminative ProtectionProtection that is able to select and disconnect only the faulty plant in the power system, leaving

all others in normal operation in so far as possible.

5.3 Primed for ReclosureWhere a circuit breaker will automatically close without external initiation once one side has

become energised.


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CODE OF PRACTICE

5.4 Cascaded IntertrippingCascaded intertripping is a system where the intertrip signal is re-transmitted to initiate the

remote tripping of a further circuit breaker.

Documents

Protection of High Voltage Networks (TS1)