online_TS_3.02.04_i5

This document is for internal and contract specific use only. Disclaimer NGG and NGET or their agents, servants or contractors do not accept any liability for any losses arising under or in connection with this information. This limit on liability applies to all and any claims in contract, tort (including negligence), misrepresentation (excluding fraudulent misrepresentation), breach of statutory duty or otherwise. This limit on liability does not exclude or restrict liability where prohibited by the law nor does it supersede the express terms of any related agreements." Copyright © National Grid plc 2011, all rights reserved All copyright and other intellectual property rights arising in any information contained within this document are, unless otherwise stated, owned by National Grid plc or other companies in the National Grid group of companies. No part of this publication may by reproduced in any material form (including photocopying and restoring in any medium or electronic means and whether or not transiently or incidentally) without the written permission of National Grid plc This information should not be forwarded to third parties.

National Grid Technical Specification TS 3.02.04 Technical Specification Addendum Addendum No 3

Uncontrolled When Printed Page 1 of 2

ADDENDUM

Date Effective From 24 November 201115 July 2011

Originated by Approved by

Name Tony Westmorland David Wright

Job Title Generator & Asset Compliance Engineer

ENI Manager

Department Policy ENI

Date 24 November 2011 16 March 2012 ORIGINAL DOCUMENT DETAILS

DOCUMENT TITLE Current Transformers for Protection and General Use

DOCUMENT NUMBER TS 3.2.4

ISSUE NUMBER 5 Rev. 2

ISSUE DATE December 2003

ADDENDUM DETAILS The above document shall be read in conjunction with the following amendments: Check appropriate boxes below

Addition Replacement X Deletion

AMENDMENTS

Delete Amendment 1

Replace Schedule of Particulars - Schedule 10 with new schedule as detailed below: -

National Grid Technical Specification TS 3.02.04 Technical Specification Addendum Addendum No 3


SCHEDULE 10 TABLE OF PARTICULARS FOR 420 kV, 300 kV AND 145 kV CURRENT TRANSFORMERS

Note: For tapped current transformers the knee-point voltage, magnetising current and secondary resistance

are specified for the full winding, shown underlined.

Reference Clauses

CT Designation

Ratio

Minimum Knee-Point Voltage (Vk) or Class

Maximum Magnetising Current (mA) at Vk/2

Maximum Sec Res (ohms) at 75C

4.2 to 4.4

420 kV, 4000 A (i) PX A (ii) PX B (iv) Measurement/ Protection

1/1000/2000 1/1200/2000 1/1000/2000

3570

780

30 VA Class 1 5P20

60

24

Not Specified

4.4

2.7

3.0

4.2 to 4.4

300 kV, 3150A (i) PX A (ii) PX B (iii) Measurement/ Protection

1/600/1200/2000 1/600/1200/2000 1/600/1200/2000

2750

2000

30 VA Class 1 5P20

60

30

4.7

3.1

4.2 to 4.4

145 kV, 2000A (i) PX A (ii) PX B (iii) Measurement/ Protection + PXB + Class 1

1/500/600/1000/1200

1/500/600/1000/1200

1/500/600/1000/1200

1000

1000

30VA Class 1 5P20

800

60

30

30

2

2 2

National Grid - Internal and Contract Specific Document Number TS 3.02.04 Addendum Addendum No 2


ADDENDUM

Date Effective From 17 August 2010

Originated by Approved by

Name Tony Westmorland David Wright

Job Title Applied Policy Engineer Electricity Network Investment Manager

Department Asset Policy ENI, Asset Management

Date 17/08/2010 18/10/2010 ORIGINAL DOCUMENT DETAILS

DOCUMENT TITLE Current Transformers for Protection and General Use

DOCUMENT NUMBER TS 3.2.4

ISSUE NUMBER 5

ISSUE DATE December 2003

National Grid - Internal and Contract Specific Document Number TS 3.02.04 Addendum Addendum No 2


ADDENDUM DETAILS The above document shall be read in conjunction with the following amendments: Check appropriate boxes below

Addition x Replacement Deletion

Schedule 10 – Add new Schedule of Particulars for 400kV, 5000A Current Transformers as detailed below: -

SCHEDULE 10 TABLE OF PARTICULARS FOR 420 KV CURRENT TRANSFORMERS

TS Reference Clauses

CT Designation Turns Ratio Knee-Point Voltage (Vk)

or IEC Rating and Class

Magnetising Current (mA)

Max Sec Res (ohms)

4.2 to 4.4 420 KV, 5000 A

PXA 1/1000/2000/3000 3000/1 450(Rct + 7.5) - -

PXB 1/1000/2000/3000 3000/1 90(Rct + 5) 40 at Vk/2 5.0 at 75°C

MEASUREMENT AND PROTECTION

1/1000/2000/3000 3000/1

2000/1

1000/1

30 VA Class 1

5P20

30 VA Class 1

5P20

30 VA Class 1

5P10

Notes: 1. This specification has been issued for current transformers with a 5000A continuous current

rating with 2xPXA, 1xDual Purpose and 2PXB cores. For current transformers with a maximum continuous current rating of 4000A, refer to separate schedule of particulars.

2. The accuracy class and knee points are to be maintained for the ratios which are underlined in the table above. 3. The Current Transformer shall be assigned a short time overload rating of 2 times rated current

for 3 minutes. (refer to Table 1 of TS 2.1) 4. The Current Transformer shall be assigned a post fault continuous current rating of 1.206 times

rated current. (refer to Table 1 of TS 2.1) 5. The Current Transformer characteristics (knee point, mag current etc.) are as defined in the table above. Requirements for Dual Purpose Measurement/Protection Current Transformers

1. Current transformers intended for the dual purpose of measurement and protection shall meet the performance requirements of IEC 60044-1, Clause 4.2.1 and the above table.

2. All measurement/protection CTs shall have an extended measuring range of 200% In except CTs for Transformers and Quad Boosters which shall have an extended measuring range of 300% In.

3. All measurement/protection CTs shall meet the short time overload ratings given in Table 1 of TS 2.1.

National Grid - - Internal and Contract Specific Technical Specification TS 3.2.4 Technical Specification Addendum Addendum No 1


TECHNICAL SPECIFICATION ADDENDUM

DOCUMENT TITLE Current Transformers for Protection and General Use DOCUMENT NUMBER TS 3.2.4 ISSUE NUMBER 5 ISSUE DATE December 2003 This Technical Specification shall be read in conjunction with the following amendments: Check appropriate boxes below

Addition Replacement X Deletion

AMENDMENTS

Schedule 10 – Replace Schedule of Particulars for 300kV Current Transformers with new schedule as detailed below: - SCHEDULE 10 TABLE OF PARTICULARS FOR 300 kV CURRENT TRANSFORMERS

TS Reference Clauses

CT Designation Turns Ratio Knee Point Voltage (Vk) or

IEC Rating Class

Magnetising Current

(mA)

Max Sec Res

(ohms)

4.2 to 4.4 300 kV, 3150A

PXA 1/600/1200/2000 2000/1

1200/1

267(Rct + 7.5)

160(Rct + 7.5)

-

-

-

-

PXB 1/600/1200/2000 2000/1

1200/1

137(Rct + 3.0)

82(Rct + 3.0)

60 at Vk/2

60 at Vk/2

2.4 at 75°C

2.4 at 75°C

MEASUREMENT AND PROTECTION

1/600/1200/2000 2000/1 30 VA Class 1

5P20

1200/1

600/1

30 VA Class 1

5P20

30VA Class 1

5P10

Date Effective From 01 January 2010

Originated by Authorised by Approved by

Name Tony Westmorland Ursula Bryan David Wright

Job Title Applied Policy Engineer Asset Policy Manager Electricity Network Investment Manager

Department Asset Policy Asset Policy ENI, Asset Management

Date 05/01/2010 05/02/2010 08/02/2010

National GridTechnical Specification

Current Transformers forProtection and GeneralUse

NGTS 3.2.4Issue 5December 2003

CONTENTS Page

Foreword ...................................................11 Scope ..............................................12 References ......................................13 General Requirements ....................24 Performance Requirements.............35 Testing Requirements .....................46 List Of Schedules ............................7Appendix A..............................................18Appendix B..............................................19

Authorised for Issue by:

Mike DeanAsset Strategy Manager

Uncontrolled when printed. This document will be valid on the day of printing only

© National Grid 2003

“No part of this publication may be reproduced, stored in a retrievalsystem, or transmitted in any form or by any means electronic,mechanical, photocopying, recording or otherwise, without thewritten permission of the National Grid obtained from the issuinglocation.

The contents of National Grid engineering documents are basedon the needs of National Grid and the conditions under which itoperates. It should not therefore be assumed that thespecifications and requirements stated therein necessarily meetthe particular circumstances and requirements of otherorganisations. The principles set out in this document are forinformation only and therefore National Grid is not liable tocustomers / suppliers for any loss or damage resulting fromreliance on the contents. It is the responsibility of such externalorganisations to check that the document is the latest version andis appropriate for their purposes.”

(National Grid Legal Services. November 1999)

Registered Office Registered in1-3 Strand England and WalesLondon No. 2366977WC2N 5EH

Published by:National GridNGT HouseWarwick Technology ParkGallows HillWarwickCV34 6DA

Uncontrolled when printed. This document will be valid on theday of printing only.

Administrative enquiries regarding this document should bedirected to:

Asset Support at Warwick, Telephone: 01926 655063

Technical enquiries regarding this document should be directed to:

Contact name: Tony WestmorlandAsset Policy

Telephone: 01926 655966

NGTS 3.2.4Issue 5

December 2003

Page 1

CURRENT TRANSFORMERS FOR PROTECTION AND GENERAL USE

FOREWORD

This Specification defines the functional and performance requirements for current transformers (CTs) forprotection and general use on The National Grid Transco (NGT) UK Transmission System (Electricity).It supports the more general requirements defined in the companion documents NGTS 1, NGTS 2.1 andNGTS 2.2.

1 SCOPE

This is a functional and performance specification for CTs used for protection and measurementapplication. For CTs used in Settlements Metering applications reference should be made toNGTS 3.2.6.

2 REFERENCES

2.1 International, European and British National Documentation

This document makes reference to, or should be read in conjunction with, the documents listedbelow. Where a standard has been harmonised into a Euronorm, only this latter reference isgiven. The issue and date of the documents detailed below shall be applicable at the time ofissue of this specification unless a specific issue date is given

IEC 60044-1 Instrument transformers- Part 1: Current Transformers

IEC 567 Guide for the sampling of gases and of oil from oil filled electrical equipmentand for the analysis of free and dissolved gases.

IEC 60044-6 Requirements for protective Current Transformers for transient performance

BS EN 60694 Common specifications for high voltage switchgear and controlgearstandards

BS 7626 Current Transformers

2.2 National Grid Technical Specifications

The following NGTS documentation is relevant to current transformers and should be read inconjunction with this document.

NGTS 1 Ratings and General Requirements for Plant, Equipment, Apparatus andServices for use on and Direct Connections to the National GridTransmission System

NGTS 2.1 Substations

NGTS 2.2 Switchgear for use on, and at Connection Points to, the National Grid System

NGTS 2.3 Transformers and Reactors for use on 132, 275 and 400 kV Systems

NGTS 2.6 Protection

NGTS 3.2.4Issue 5

December 2003

Page 2

2.3 Definitions and Abbreviations

The definitions used in NGTS1 and NGTS2.2 apply to this document.

3 GENERAL REQUIREMENTS

All CTs shall comply with NGTS 1, NGTS 2.1, NGTS 2.2 and IEC 60044-1. In addition, thefollowing clauses apply:

3.1 General Requirements for all Current Transformers

3.1.1 Additional specification and testing requirements for protection Class PX cores are given inAppendix E. For information, these requirements are identical to those given in the now obsoleteBS 3938 Class X sections.

3.1.2 Secondary ratings and transformation ratios shall be selected from the attached Schedules andshall be specified in the contract Enquiry Document or Supplementary Agreement as appropriate

3.1.3 A single secondary terminal box shall be mounted on the transformer to accommodate thenecessary secondary terminal connections.

3.1.4 Secondary terminals and connections shall be suitable for their required purpose regardingrating, reliability and the effects of environmental conditions and corrosion.

3.1.5 Secondary terminal boxes shall comply to at least IP54 environment of BSEN60529 as requiredby NGTS 1

3.1.6 Primary and secondary terminal markings, and rating plate markings shall be inaccordance with IEC 60044�1

3.1.7 The rated continuous primary current of the current transformer shall be chosen to exceed themaximum continuous rating of the associated circuit and shall be selected from the standardvalues detailed in IEC 60044-1

3.1.8 A thermal short-time current rating (Ith) shall be assigned to all current transformers inaccordance with IEC 60044-1. The value of Ith shall not be less than the corresponding valuefor the associated switchgear or transformer primary plant.

3.1.9 Current transformer secondary terminals should allow the application of shorting/earthing linksor wiring for maintenance purposes. Separately, a terminal for earthing purposes shall beprovided within the terminal box and shall be clearly marked.

3.1.10 For all oil filled CTs the supplier shall declare the type of insulating oil being used.

3.1.11 For oil-filled equipment fitted with an external oil expansion system, means shall be provided togive a permanent visual indication of the volume of the oil. The status of the indicator should bevisible from ground level.

3.1.12 For oil filled CTs where the oil expansion system is wholly internal ie gas cushion or flexiblediaphragm, the CT shall be fitted with a permanent internal pressure indicator. The status of theindicator shall be visible from ground level.

3.1.13 All oil filled CTs shall be fitted with an oil sample valve, situated at the base of the CT, suitablefor taking oil samples for Dissolved Gas Analysis (DGA) in accordance with IEC 567. Thesample valve shall be situated on the earthed base tank of the CT. Valves where the oil isextracted by using a hypodermic needle are not suitable.

NGTS 3.2.4Issue 5

December 2003

Page 3

3.1.14 Both ends of the CT secondary windings shall be earth free.

3.2 Additional Requirements for Post-Type Current Transformers

3.2.1 An insulation test terminal (test tap) shall be provided for the purpose of performing capacitanceand dielectric loss (tan �) measurements of the primary insulation during routine maintenance.The test terminals shall be suitably identified.

3.3 Additional Requirements for Current Transformers for GIS Application

3.3.1 Current transformers may be mounted internally or externally to the GIS enclosure.

3.3.2 Adequate protection against adverse environmental conditions shall be provided for externallymounted CTs as required in NGTS 2.2.

3.4 Additional Requirements for Ring-Type Current Transformers

3.4.1 Current transformers mounted internally to power transformers shall be capable of operating inan environment as detailed in NGTS 2.3.

3.4.2 Current transformers supplied as loose equipment for power transformer application shall beequipped with secondary terminals or shall be supplied with leads of suitable length for thisapplication. Such leads shall be capable of satisfying the test requirement of Clause 5.4.3.

3.4.3 Current transformers supplied with throughwall bushings can be mounted internally or externallyto the bushing. Current transformers mounted internally shall be capable of operating within thatenvironment. Current transformers mounted externally shall be suitably protected against theeffects of adverse environmental conditions as required by NGTS 2.2.

3.4.4 Current transformers supplied as loose equipment for other switchgear applications shall becapable of operating within that environment. Current transformers for other switchgearapplications, mounted externally, shall be suitably protected against the effects of adverseenvironmental conditions as required by NGTS 2.2.

3.5 Additional Requirements for Measurement/Protection and Class PX Protective CurrentTransformers

3.5.1 Measurement/Protection and class PX protective current transformers with a rated primarycurrent of 2500 A or below and with untapped secondary windings shall have a rated secondarycurrent of 1A (as selected from IEC 60044-1). The rated secondary current for currenttransformers of this primary rating with tapped secondary windings shall be 1 A correspondingto the highest transformation ratio.

3.5.2 Measurement/Protection and class PX protective current transformers with a rated primarycurrent in excess of 2500 A shall have a rated secondary current selected from the values statedin IEC 60044-1

4 PERFORMANCE REQUIREMENTS

4.1 General

All current transformers shall comply with the performance requirements of IEC 60044-1 for theprimary ratings detailed in NGTS 1, NGTS 2.1 and NGTS 2.2. The following requirements shallalso apply as appropriate:

NGTS 3.2.4Issue 5

December 2003

Page 4

4.2 Protection Type PX-A Current Transformers

4.2.1 Protection type PX-A current transformers shall meet the additional requirements given inAppendix E providing accurate transformation up to the maximum fault current rating of theassociated main plant. This performance shall be maintained under both fault and steady-stateconditions without saturation

4.2.2 Type PX-A current transformers shall also meet the performance requirements of Schedule 10of this Specification.

4.3 Protection Type PX-B Current Transformers

4.3.1 Protection type PX-B current transformers shall meet the additional requirements given inAppendix E providing accurate steady-state transformation up to the maximum fault currentrating of the associated main plant.

4.3.2 Type PX-B current transformers shall also meet the performance requirements of Schedule 9of this Specification.

4.4 Dual Purpose Measurement/Protection Current Transformers

4.4.1 Current transformers intended for the dual purpose of measurement and protection shall meetthe performance requirements of IEC 60044-1, Clause 4.2.1 and Schedule 10 of thisSpecification.

4.5 Interposing Current Transformers

4.5.1 Short duration overload capabilities are assigned to the main current transformers and theassociated interposing current transformers shall be capable of carrying the correspondingcurrent.

4.6 Line Drop Compensation Current Transformers (as used in tap change voltage controlschemes)

4.6.1 Line drop compensation current transformers shall comply with accuracy class 5 of BS 7626.

5 TESTING REQUIREMENTS

5.1 Type Tests

5.1.1 All current transformers shall be type tested in accordance with IEC 60044-1 (type tests) andIEC 60044-1 (special tests). The additional requirements for protection class PX cores given inAppendix B. Current transformers using a gas insulation system, a leakage test on the gassystem shall be performed by the supplier to demonstrate compliance with NGTS 2.2.

5.1.2 Radio interference voltage tests to IEC 60694 are to be performed on open-terminal currenttransformers.

5.1.3 A multi chopped impulse test shall be performed on all oil filled current transformers rated72.5 kV and above. The test method is given in Appendix D.

5.1.4 Temperature Rise - The thermal time constant of all equipment shall be determined on bothrising and falling temperature.

5.1.5 For oil filled equipment oil samples for DGA shall be taken before and after the dielectric typetests and shall comply with 5.5.3.

NGTS 3.2.4Issue 5

December 2003

Page 5

5.1.6 Accuracy at Short-Term Continuous Current Levels - Current transformers which have ameasurement specification shall have their errors determined at a current of 12000 A for 420 kVrating and 7500 A for 300 kV rating respectively. These currents shall be withstood for a periodof 3 minutes.

5.1.7 Routine tests shall be performed before and after all type tests.

5.2 Routine tests

5.2.1 All current transformers shall be routine tested in accordance with:

IEC 60044-1 (routine tests)

IEC 60044-1 (special tests)

The additional requirements for protection class PX transformers are given in Appendix B.

5.3 Additional Routine Tests

5.3.1 Accuracy Tests

a) These shall be performed in a laboratory having traceability to National/Internationalstandards.

b) The overall accuracy and uncertainty of the measurement shall be demonstrated prior totesting and shall be commensurate with the accuracy class of the transformer under test.

c) Full accuracy routine tests to IEC 60044-1.

5.3.2 Capacitance and dielectric loss angle (tan δ) measurements of the primary insulation over thevoltage range 10 kV to rated voltage shall be performed.

5.3.3 Leads for loose current transformers as detailed in Clause 3.4.2 of this Specification shallwithstand a power frequency test voltage of 5 kV (peak). For PXA application, the test levelsshall be determined by tests in Appendix B 14.2.2.

5.3.4 An oil sample for DGA shall be taken as described in 5.5 from all oil filled CTs. The sample shallbe taken at least 24 hours after the final routine electrical testing has been performed. Theresults shall be included in the routine test report as detailed in Clause 5.5.

5.4 Routine Test Reports

5.4.1 Routine test reports shall include details of all routine measurements made in accordance withthis specification. The information regarding the overall accuracy and uncertainty of theaccuracy measurements shall also be recorded.

5.4.2 During the partial discharge (PD) test, the value of measured PD at the specified test voltageshall be recorded together with the value of the PD extinction voltage. Extinction voltage isdefined as the voltage level at which measurable PD is completely extinguished upon decreasingtest voltage. The background PD level at the time of the test should also be recorded in thereport.

5.4.3 Where oil samples are taken for Dissolved Gas Analysis (DGA) the report shall contain thefollowing information:

a) Name and Address of the laboratory where the analysis was performed

b) The Accuracy, Precision and Detection Limits for the individual gas measurementexpressed in either parts per million (ppm) or percentage by volume.

NGTS 3.2.4Issue 5

December 2003

Page 6

c) The Sampling Procedure (stating the Standard Method IEC 567 if applicable).

d) The Gas Extraction Method used (stating the Standard Method IEC 567 if applicable).

e) Calibration Procedure adopted by the laboratory, including details of the number of pointsused over the range (f)and the gases used.

f) Accreditation Status of the laboratory for the purposes of DGA testing.

g) Date Sampled and Analysed.

h) Report the following:

Measurement Units No. Decimal Places

Oil Volume Tested mls 0

Total Gas Content % 2

Hydrogen ppm 0

Methane ppm 0

Ethane ppm 0

Ethylene ppm 0

Acetylene ppm 0*

Carbon monoxide ppm 0

Carbon dioxide ppm 0

Oxygen ppm 0

Nitrogen ppm 0

Moisture mg/l 0

*Note: For DGA samples associated with Type Tests, the acetylene value shall be quoted to onedecimal place

NGTS 3.2.4Issue 5

December 2003

Page 7

6 LIST OF SCHEDULES

Schedule 1 Overhead Line Feeder Circuits

Schedule 2 Synchronous Compensators Associated with Auto-Transformers

Schedule 3 Static Compensators (Reactors and Capacitors) Associated with Auto-Transformers

Schedule 4 Series Reactors

Schedule 5 Shunt Reactors

Schedule 6 Bus Sections and Couplers and other users Directly Connected via NGC busbar protection

Schedule 7 Auto-Transformer Circuits

Schedule 8 Transformer Neutral and Neutral End Current Transformer Units for use withSupergrid Auto-Transformers and Shunt Reactors

Schedule 9 Secondary ratings and rated transformation ratios for double woundtransformer current transformer circuit.

Schedule 10 Table of Particulars for 420 kV, 300 kV and 145 kV Current Transformers

NGTS 3.2.4Issue 5

December 2003

Page 8

SCHEDULE 1 OVERHEAD LINE FEEDER CIRCUITS

Class X Protection Current Transformers Measurement/Protection Current Transformers

SystemVoltage

Rated Currentof Switchgear

RatedContinuous

ThermalCurrent

Turns Ratio Extended PrimaryCurrent Rating %

kV A A Main Busbar Thermal Accuracy

RatedTransformation

Ratio

275

275

400

2000

2500

4000

2000

2500

4000

1/600/1200

1/600/1200

1/1000/2000

1/600/1200

1/600/1200

1/2000

170

210

200

420

420

500

1200/600/1

1200/600/1

2000/1000/1

NGTS 3.2.4Issue 5

December 2003

Page 9

SCHEDULE 2 SYNCHRONOUS COMPENSATORS ASSOCIATED WITH AUTO-TRANSFORMERS

Class X Protection Current Transformers Measurement/Protection Current TransformersCompensator

Rating Voltage CurrentRated

Current ofSwitchgear

RatedContinuous

ThermalCurrent

Turns Ratio Extended PrimaryCurrent Rating % Rated Transformer Ratio

MVA kV A A A Main REF* UEF** Connections Thermal Accuracy BackUp Reverse Power

60 13 2665 3000 3000 1/600 1/600 1/300 1/600 - - 3000/5 3000/5

* REF - restricted earth fault** UEF - unrestricted earth fault

NGTS 3.2.4Issue 5

December 2003

Page 10

SCHEDULE 3 STATIC COMPENSATORS (REACTORS AND CAPACITORS) ASSOCIATED WITH AUTO-TRANSFORMERS

Class X Protection Current Transformers Measurement/ProtectionCurrent Transformers

CompensatorRating Voltage Current

RatedCurrent ofSwitchgear

RatedContinuous

ThermalCurrent

Turns Ratio Extended PrimaryCurrent Rating %

MVA kV A A A HVConnections

CompensatorProtection REF*

UEF** andInstantaneous

Earth FaultThermal Accuracy

RatedTransfor-mationRatio

60

30+30

13

13

2665

1335+

1335

3000

2000

3000

2000

1/600

1/600

1/600

1/1500

1/600

1/1500

1/1500 #

1/300+

1/1500#

-

-

-

-

3000/5

3000/5

* REF - restricted earth fault** UEF - unrestricted earth fault# A relay may be required+ 300/1 ratio to be specified when earth fault current is restricted to 300 A by NER.

1500/1 ratio to be specified when earth fault current is restricted by impedance of earthing transformer only.

NGTS 3.2.4Issue 5

December 2003

Page 11

SCHEDULE 4 SERIES REACTORS

Class X Protection Current Transformers Measurement/Protection CurrentTransformers

Rating SystemVoltage Current

RatedCurrent ofSwitchgear

RatedContinuous

Thermal CurrentTurns Ratio Extended Primary

Current Rating %

MVA kV A A A Main Busbar Thermal Accuracy

RatedTransformation

Ratio

90

750

750

1320

2000

132

275

275

400

400

395

1575

1575

1905

2890

800

2000

2500

4000

4000

800

2000

2500

4000

4000

1/500/1000

1/600/1200

1/600/1200

1/1000/2000

1/1000/2000

1/500/1000

1/600/1200

1/600/1200

1/2000

1/2000

-

170

210

200

200

-

170

210

200

290

1200/600/1

1200/600/1

1200/600/1

2000/1000/1

2000/1000/1

NGTS 3.2.4Issue 5

December 2003

Page 12

SCHEDULE 5 SHUNT REACTORS

Class X Protection Current Transformers Measurement/Protection CurrentTransformers

Rated ContinuousThermal Current

ATurns Ratio

Extended PrimaryCurrent Rating Thermal

and Accuracy %Rating System

Voltage CurrentRated

Current ofSwitchgear

MVA kV A A

Locatednear

Switchgear

Locatedin

Bushing

MainProtection

FeederProtection orif Applicable

ConnectionsProtection

if Applicable

Locatednear

Switchgear

Locatedin Bushing

RatedTransformation

Ratio

100 275 210 2000 2000 500 1/600/1200 1/600/1200 1/600/1200 170 - 1200/600/1 *

100 275 210 2500 2500 500 1/600/1200 1/600/1200 1/600/1200 210 - 1200/600/1 *

200 400 290 4000 4000 500 1/1000 1/1000/2000 1/2000 200 - 2000/1000/1 *

* 0.5 A relay to be specified.

NGTS 3.2.4Issue 5

December 2003

Page 13

SCHEDULE 6 BUS SECTIONS AND BUS COUPLERS

ALSO OTHER USER CT’s AT CONNECTION POINTS AND ASSOCIATED WITH NGC BUSBAR PROTECTION

Class X Protection Current Transformers Measurement/Protection Current Transformers

Turns RatioSystem Voltage Rated Current ofSwitchgear Rated Continuous

Thermal Current Extended Primary Current Rating %

kV A ABusbar

Thermal Accuracy

RatedTransformation

Ratio

275

275

400

2000

2500

4000

2000

2500

4000

1/600/1200

1/600/1200

1/1000/2000

170

210

200

420

420

500

1200/600/1

1200/600/1

2000/1000/1

NGTS 3.2.4Issue 5

December 2003

Page 14

SCHEDULE 7 AUTO TRANSFORMER CIRCUITS

Class X Protection Current Transformers Measurement/Protection Current TransformerTurns Ratio Extended Primary Current Rating %Nominal

RatingSystemVoltage Current

RatedCurrent

ofSw/gear

Rated ContinuousThermal Current

A* Thermal * Accuracy **

MVA kV A ALocated

nearSw/gear

Locatedin

Bushing

Main HV and LVConnections Busbar Back Up LV Located

nearSw/gear

Locatedin

Bushing

Locatednear

Sw/gear

Locatedin

Bushing

RatedTransform-ation Ratio

120

180

240

240

500

750

1000

275

132

275

132

275

132

400

132

400

275

400

275

400

275

250

530

380

790

500

1050

350

1050

720

1050

1080

1580

1440

2100

2500

800

2500

1250

2500

2000

4000

2000

4000

2500

4000

2500

4000

2500

2500

800

2500

1250

2500

2000

4000

2000

4000

2500

4000

2500

4000

2500

450

800

660

1200

870

1600

610

1600

1100

1600

1700

2500

2200

3200

1/600/1200

1/600/1200

1/600/1200

1/600/1200

1/600/1200

1/600/1200

1/600/1200

1/600/1200

1/600/1200

1/600/1200

1/600/1200

1/600/1200

1/600/1200

1/600/1200

1/600/1200

1/500/1000

1/600/1200

1/500/1000

1/600/1200

1/500/1000

1/1000/2000

1/500/1000

1/1000/2000

1/600/1200

1/1000/2000

1/600/1200

1/1000/2000

1/600/1200

1/600/1200

1/500/1000

1/600/1200

1/500/1000

1/600/1200

1/500/1000

1/2000

1/500/1000

1/2000

1/600/1200

1/2000

1/600/1200

1/2000

1/600/1200

1/500/1000#

1/500/1000#

1/500/1000#

1/500/1000#

1/600/1200

1/600/1200

1/600/1200

210

-

210

110

210

170

200

170

200

210

200

210

200

210

-

-

-

-

-

135

-

135

-

135

-

210

110

270

210

-

210

130

210

180

200

180

200

210

200

270

200

350

-

-

-

130

-

180

-

180

-

180

110

270

150

350

1200/600/1

1200/600/1

1200/600/1

1200/600/1

1200/600/1

1200/600/1

2000/1000/1

1200/600/1

2000/1000/1

1200/600/1

2000/1000/1

1200/600/1

2000/1000/1

1200/600/1

* Designed to cater for 150% overload** Designed to cater for 200% overload# At busbar stations where post-type CT housings are installed and LV connection protection is specified, the back-up protection is to be supplied from the

Type A 1/600/1200 CT.

NGTS 3.2.4Issue 5

December 2003

Page 15

SCHEDULE 8 TRANSFORMER NEUTRAL AND NEUTRAL END CURRENTTRANSFORMER UNITS FOR USE WITH SUPERGRID AUTOTRANSFORMERS AND SHUNT REACTORS

275/132 kV, 400/275 kV and 400/132 kV auto-transformers and 400 kV and 275 kV ShuntReactors (11 kV primary insulation)

Type Primary ConductorRating (A) (sec) Turns Ratio Function

Transformer275/132 kV(Up to 360 MVA)

82003 sec 1/600/1200

At Least 2Secondaries, NeutralEarth Fault Check,Fault recorder etc


66001 sec 1/1000/2000 "


10 6003 sec 1/1000/2000 "

Shunt Reactor275 kV(Up to 100 MVA)

21001 sec 1/600/1200 Neutral Earth Fault

Check


29001 sec 1/1000/2000 "

Table A- Neutral Current Transformers

275/132 kV, 400/275 kV and 400/132 kV auto-transformers and 400 kV and 275 kV ShuntReactors (11 kV Primary Insulation)

Type Primary ConductorCMR (Ihv - Ilv) amp Turns ratio Function


820 1/600/1200

AutoTransformer

OverallProtection


660 1/600/1200 "


1060 1/600/1200 "


210 1/600/1200Shunt Reactor

OverallProtection


290 1/1000 "

Table B - Neutral End Current Transformers (3 Single Phase Windings Starred)

NGTS 3.2.4Issue 5

December 2003

Page 16

SCHEDULE 9 SECONDARY RATINGS AND RATED TRANSFORMATION RATIOS FOR DOUBLE WOUND TRANSFORMER CURRENTTRANSFORMER CIRCUITS

Current Class X Protection Current Transformers Measurement/ProtectionCurrent Transformers

Turns RatioType Nominal

RatingSystemVoltage VT Ratio

AtNominal

RatioTap

Position

AtMeanTap

Position

RatedCurrent

ofSw/gear

RatedContinuous

ThermalCurrent

AMain Protection

Extended PrimaryCurrent Rating*

Thermal andAccuracy %

MVA kV A A A

LocatedN

earSw

/gear

LocatedN

earB

ushing

Main C

T

InterposingC

T

Back up LV

HV and LV

Connections

Busbar

LV unrestricted earthfault Located

nearSw

/gear

Located inB

ushing

Rated Transform

ationR

atio EG B

ack up HV

Star/Delta 75

27533

-33000/110

1571312

1661312

25002000

25002000

3002000

1/2001/800/1600

0.577/1.01.0/1.0/1.0

-1/1000/2000

1/600/12001/800

1/600/12001/800

-1/600/1200

210-

--

1200/600/12000/1

Star/Delta 100

27533

-33000/110

2101750

2211750

25002500

25002700

4002700

1/2001/800/1600

0.577/1.01.0/1.0/1.0

-1/1000/2000

1/600/12001/800

1/600/12001/800

-1/800/1600

210135

-135

1200/600/12000/1

Star/Delta 120

27533

-33000/110

2502100

2652100

25002500

25003200

4503200

1/4001/800/1600

0.577/0.70.7/1.0/1.0

-1/800/1600

1/600/12001/800

1/600/12001/800

-1/800/1600

210160

-160

1200/600/12000/1

Star/Star 120

27566

-66000/100

2501050

2501050

25002000

25002000

4501600

1/4001/800/1600

0.577/0.71.0/1.0/0.7

-1/800/1600

1/600/12001/800

1/600/12001/800

-1/600/1200

210170

-140

1200/600/11200/1

Star/Delta 120

27566

-66000/110

2501050

2501050

25002000

25002000

4501600

1/4001/800/1600

0.577/0.70.577/0.7

-1/800/1600

1/600/12001/800

1/600/12001/800

-1/600/1200

210170

-140

1200/600/11200/1

Star/Star 180

27566

-66000/110

3801580

3801580

25002000

25002400

7002400

1/4001/800/1600

0.577/11/1/1

-1/800/1600

1/600/12001/800

1/600/12001/800

-1/800/1600

210120

-120

1200/600/12000/1

Star/Delta 180

27566

-66000/110

3801580

3801580

25002000

25002400

7002400

1/4001/800/1600

0.577/1.00.577/1.0

-1/800/1600

1/600/12001/800

1/600/12001/800

-1/800/1600

210120

-120

1200/600/12000/1

Star/Delta 180

40066

-66000/110

2601580

2601580

40002000

40002400

5002400

1/4001/800/1600

0.577/0.71/1/1

-1/800/1600

1/1000/20001/800

1/20001/800

-1/800/1600

200120

-120

2000/1000/12000/1

Notes1 275/33 transformers’ mean tap position is -5%. 275/66 and 400/66 transformers mean tap position corresponds with the nominal ratio tap position.2 Double wound transformers, not covered by the schedule, should be referred to the General Manager, Engineering and Technology.3 For Settlement Metering CTs see NGTS 3.2.6.* Designed to cater for 150% overload.jxa/cw/may.01

NGTS 3.2.4Issue 5

December 2003

Page 17

SCHEDULE 10 TABLE OF PARTICULARS FOR 420 kV, 300 kV AND 145 kV CURRENTTRANSFORMERS

RatioReferenceClauses

CTDesignation

Turns Current

Knee-PointVoltage (Vk)

or IEC Ratingand Class

Magnetising

Current(mA)

Max SecRes (ohms)

4.2 to 4.4 420 kV, 4000 A

(i) Prot A 1/1000/2000 300 (Rct + 7.5)

(ii) Prot B 1/2000 60 (Rct + 5) 40 at Vk

2

5.0 at 75�C

(iii) Prot BSpecial Ratio

1/600/1200 82 (Rct +3) 60 at Vk

2

2.4 at 75�C

(iv) Measure-ment/Protection

1/1000/2000 2000/1 30 VA Class 1

5P20

1000/1 30 VA Class 1

5P10

4.2 to 4.4 300 kV, 2000 or2500 A

(i) Prot A 1/600/1200 160 (Rct + 7.5)

(ii) Prot B 1/600/1200 82 (Rct + 3) 60 at Vk

2

2.4 at 75�C


1/600/1200 1200/1 30 VA Class 1

5P20

600/1 30 VA Class 1

5P10

4.2 to 4.4 145 kV, 2000A

(i) Prot A 1/600/1200

1/500/100050 (Rct + 17)

60 (Rct + 12)

(ii) Prot B 1/500/1000 95 (Rct + 2.5) 60 at Vk

2

2.4 at 75�C


1/600/1200 1200/1 30VA Class 1

5P20

600/1 30VA Class 1

5P10

Note - For tapped current transformers the knee-point voltage, magnetising current and secondary resistance arespecified for the full winding, shown underlined.

NGTS 3.2.4Issue 5

December 2003

Page 18

APPENDIX A

MULTICHOPPED IMPULSE TYPE TEST SPECIFICATION

All oil filled CTs rated at 72.5 kV and above, shall be subjected to a 600 chopped negative polarity impulsetest at 60% of the rated BIL level for that equipment. The time to chop shall be between 2-5�s. A full setof routine electrical tests shall be performed, and oil samples for dissolved gas analysis shall be taken,both before and after this test.

The supplier shall submit to NGC details of how the test will be conducted.

The three criteria which must all be satisfied for the CT to pass the test are:

A1 The results of the routine electrical tests, performed before and after the chopped impulse test,are the same within the error specification for the test field.

A2 No evidence of degradation is found when the CT is dismantled and examined after the test.

A3 Any increases in the DGA levels are within the limits listed below.

Dissolved Gas Allowable increase after 3 days (ppm)

Hydrogen (H2) 5

Methane (CH4) 3

Ethane (C2H6) 3

Ethylene (C2H4) 2

Acetylene (C2H2) no detectable increase

The application of this test to CTs which have an ERIP or SRBP condenser core shall be subjectto agreement between NGC and the supplier.

NGTS 3.2.4Issue 5

December 2003

Page 19

APPENDIX B

ADDITIONAL REQUIREMENTS FOR PROTECTION CLASS PX TRANSFORMERS

Within the scope of IEC 60044-1 paragraph 5 additional requirements may be specified for certainprotective systems. The specification and tests for Class PX transformers was addressed in BS 3938.This document was withdrawn in June 1998. The following amendment has been tabled by theUnited Kingdom BSI PEL 38 Instrument Transformer Technical Committee for inclusion IEC 60044-1addressing these requirements.

The numbering of this section is identical to the submission made to IEC. When the amendment has beenincorporated into IEC 60044-1 this document will be revised.

B1.1 Scope

Modify 5th paragraph

For certain protective systems, ........resonant earthed networks), additional requirements aregiven in Clause 14 for class PX transformers.

After 5th paragraph add

Clause 14 covers the requirements and tests in addition to those in clauses 3 to 10 that arenecessary for current transformers for use with electrical protective relays, and in particular forforms of protection for which knowledge of the transformer secondary excitation characteristic,secondary winding resistance, secondary burden resistance and turns ratio is sufficient to assessits performance in relation to the protective relay system with which it is to be used.

B1.2 Normative references

Add

44-6 (1992) :instrument transformers, Part 6 : Requirements for protective current transformersfor transient performance

B2 Definitions

B2.1 General definitions

Add

B2.1.32 rated resistive burden (Rb) : For definition see IEC Publication 60044-6 Clause 3.11.

B2.1.33 secondary winding resistance (Rct) : For definition see IEC Publication 60044-6Clause 3.12.

B2.3 Additional definitions for protective current transformers.

B2.3.10 Excitation characteristic : A graphical or tabular presentation of the relationship between ther.m.s value of the exciting current and a sinusoidal r.m.s e.m.f applied to the secondaryterminals of a current transformer, the primary and other windings being open circuited, over arange of values sufficient to define the characteristics from low levels of excitation up to the ratedknee point e.m.f.

B2.3.12 Rated knee point e.m.f (Ek) : That minimum sinusoidal e.m.f. (r.m.s) at rated power frequencywhen applied to the secondary terminals of the transformer, all other terminals being open-circuited, which when increased by 10% causes the r.m.s exciting current to increase by no morethan 50%.

Note: - The actual knee point e.m.f will be � the rated knee point e.m.f.

NGTS 3.2.4Issue 5

December 2003

Page 20

B2.3.13 Rated turns ratio : The required ratio of the number of primary turns to the number of secondaryturns eg

Example 1: 1/ 600 (one primary turn with six hundred secondary turns)

Example 2: 2/1200 (a current transformer of similar ratio to example 1 but employing twoprimary turns).

B2.3.14 Turns ratio error: The difference between the rated and actual turns ratios. expressed as apercentage.

Turns ratio error (%) = (actual turns ratio - rated turns ratio) × 100rated turns ratio

B6 Classification of tests

B6.1 Type tests

Modify as follows :

(f) determination of errors (see 11.4 and/or 12.4, 11.6, 12.5, 14.3)

B6.2 Routine tests

Modify as follows :

(d) power-frequency withstand test on secondary winding ( see 8.3 or 14.4.4);

(e) power-frequency withstand tests, between sections ( see 8.3 or 14.4.4 );

(f) inter-turn over voltage test (see 8.4 or 14.4.5);

(g) determination of errors (see 11.5 and/or 12.4, 11.6, 12.6, 14.4)

B10.2 Rating plate markings

Modify as follows :

(e) The rated output and the corresponding accuracy class, together with additionalinformation specified in the later parts of these recommendations (see 11.7 and/or 12.7,13.8, 14.5).

B14 Additional requirements for Class PX protective current transformers

B14.1 Specification of performance for Class PX protective current transformers:

The performance of class PX current transformers shall be specified in terms of the following:

(a) rated primary current (Ipn)

(b) rated secondary current (Isn)

(c) rated turns ratio. The turns ratio error shall not exceed ± 0.25%

(d) rated knee point e.m.f. (Ek)

(e) maximum exciting current (Ie) at the rated knee point e.m.f. and / or at a statedpercentage thereof

(f) maximum resistance of the secondary winding at a temperature of 75°C (Rct)

NGTS 3.2.4Issue 5

December 2003

Page 21

(g) rated resistive burden (Rb)

(h) dimensioning factor (Kx)

Note - The rated knee point e.m.f. is generally determined as follows:

� � snbctxk IRRKE ��

B14.2 Insulation requirements for class PX protective current transformers.

B14.2.1 Insulation requirements for secondary winding

The secondary winding insulation of class PX current transformers having a rated knee pointvoltage Ek ≥ 2 kV shall be capable of withstanding a rated power frequency withstand voltageof 5 kV r.m.s for 60 s. For Ek < 2 kV the withstand voltage shall be 3 kV r.m.s for 60 s.

B14.2.2 Inter-turn insulation requirements

For Class PX transformers having a rated knee point e.m.f of 450 V or less the rated withstandvoltage for inter-turn insulation shall be 4.5 kV peak. For those with a rated knee point e.m.f ofgreater than 450V, the rated withstand voltage for the inter-turn insulation shall be a peakvoltage of 10 times the r.m.s value of the specified knee point e.m.f, or 10 kV peak, whicheveris the lower. Note: For some EHV transmission systems a higher limiting value of peak voltagemay be agreed between the manufacturer and the purchaser.

B14.3 Type tests for class PX protective current transformers

Class PX current transformers shall in addition to the requirements of clause 7 be tested asbelow.

B14.3.1 Proof of low reactance type

An inspection of drawings shall be made in accordance with the requirements of IECPublication 60044-6 Clause 7.3.1 a) in order to establish proof of low leakage reactance design.If compliance with the requirements of low leakage reactance design cannot be established tothe mutual satisfaction of the manufacturer and purchaser by reference to drawings then thecomposite error shall be determined for the complete secondary winding using either of thedirect methods of test given in Appendix A Clause A.5 or A.6 of this document, at a secondarycurrent of Kx. Isn and with a secondary burden Rb. Proof of low leakage reactance design shallbe considered to have been established if the value of composite error from the direct methodof test is less than 1.1times that deduced from the secondary excitation characteristic.

Note - The value of primary current required to perform direct composite error tests on certaintransformer types may be beyond the capability of facilities normally provided by manufacturers.Tests at lower levels of primary current may be agreed between the manufacturer and purchaser.

B14.4 Routine tests for class PX protective current transformers

Class PX current transformers shall in addition to the requirements of clause 8 be tested asbelow:

B14.4.1 Rated knee point e.m.f. (Ek) and maximum exciting current (Ie)

A sinusoidal e.m.f. of rated frequency equal to the rated knee-point e.m.f. shall be applied to thecomplete secondary winding, all other windings being open-circuited and the exciting currentmeasured.

NGTS 3.2.4Issue 5

December 2003

Page 22

The e.m.f. shall then be increased by 10% and the exciting current shall not increase by morethan 50%. All measurement shall be performed using r.m.s. measuring instruments. Due to thenon sinusoidal nature of the measured quantities the measurements should be performed usingr.m.s measuring instruments having a crest factor ≥3.

The excitation characteristic shall be plotted at least up to the rated knee point e.m.f. Theexciting current (I'e) at the rated knee-point e.m.f. and at any stated percentage, shall not exceedthe rated value. The number of measurement points shall be agreed between the manufacturerand the purchaser.

B14.4.2 Secondary winding resistance (Rct)

The resistance of the complete secondary winding shall be measured. The value obtained whencorrected to 75°C shall not exceed the specified value.

B14.4.3 Turns ratio error ( t)

The turns ratio shall be determined in accordance with IEC publication 60044-6 Annex E. Theturns ratio error shall not exceed the value given in Clause 14.1 (c).

Note - A simplified test involving measurement of the ratio error with zero connected burden maybe substituted by agreement between the manufacturer and purchaser.

B14.4.4 Insulation tests

Tests shall be performed to demonstrate compliance with Clause 14.2.1 . For test method referto Clause 8.3.

B14.4.5 Inter-turn insulation tests

Tests shall be performed to demonstrate compliance with Clause 14.2.2. For test methodrefer to Clause 8.4

B14.5 Marking of rating plate of Class PX current transformers

B14.5.1 Principal marking : See Clauses 10.2.

B14.5.2 Special marking

(a) rated turns ratio

(b) rated knee point e.m.f. (Ek)

(c) maximum exciting current (Ie) at the rated knee point e.m.f. and/or at the statedpercentage thereof.

(d) maximum resistance of the complete secondary winding at a temperature of 75°C (Rct)

The following may also be required by the purchaser:

(e) dimensioning factor (Kx)

(f) rated resistive burden (Rb)

RECORD OF REVISION

DOCUMENT NO: NGTS 3.2.4

ISSUE NO: 5

This issue has been revised and amended as follows:

DATE DETAILS OF REVISION AUTHORISATION

December 2003 Editorial changes

Documents

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