IEC TR 61869-100:2017

Instrument transformers - Part 100: Guidance for application of current transformers in power system protection

IEC TR 61869-100:2017(E) is applicable to inductive protective current transformers meeting the requirements of the IEC 61869-2 standard.
It may help relay manufacturers, CT manufacturers and project engineers to understand how a CT responds to simplified or standardized short circuit signals. Therefore, it supplies advanced information to comprehend the definition of inductive current transformers as well as their requirements.
The document aims to provide information for the casual user as well as for the specialist. Where necessary, the level of abstraction is mentioned in the document. It also discusses the question about the responsibilities in the design process for current transformers.
The contents of the corrigendum of October 2023 have been included in this copy.

General Information

• Status: Published
• Publication Date: 19-Jan-2017
• ICS: 01 - GENERALITIES. TERMINOLOGY. STANDARDIZATION. DOCUMENTATION
• ICS: 17.220.20 - Measurement of electrical and magnetic quantities
• Technical Committee: TC 38 - Instrument Transformers
• Drafting Committee: MT 40 - TC 38/MT 40
• Current Stage: PPUB - Publication issued
• Start Date: 19-Jan-2017
• Completion Date: 20-Jan-2017

Relations

• Corrected By: IEC TR 61869-100:2017/COR1:2023 - Corrigendum 1 - Instrument transformers - Part 100: Guidance for application of current transformers in power system protection
• Effective Date: 06-Oct-2023

Standards Content (Sample)

IEC TR 61869-100 ®
Edition 1.0 2017-01
TECHNICAL
REPORT
colour
inside
Instrument transformers –
Part 100: Guidance for application of current transformers in power system
protection
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

IEC Central Office Tel.: [phone]
3, rue de Varembé Fax: [phone]
CH-1211 Geneva 20 [e-mail]
Switzerland www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.

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bibliographical information on IEC International Standards, electrical terms containing 20 000 terms and definitions in
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iPad. Vocabulary (IEV) online.

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variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and

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Centre: [e-mail].
IEC TR 61869-100 ®
Edition 1.0 2017-01
TECHNICAL
REPORT
colour
inside
Instrument transformers –
Part 100: Guidance for application of current transformers in power system

protection
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.20 ISBN 978-2-8322-3808-0

– 2 – IEC TR 61869-100:2017 © IEC 2017
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 10
3 Terms and definitions and abbreviations . 10
3.1 Terms and definitions . 10
3.2 Index of abbreviations . 12
4 Responsibilities in the current transformer design process. 14
4.1 History . 14
4.2 Subdivision of the current transformer design process . 14
5 Basic theoretical equations for transient designing . 15
5.1 Electrical circuit . 15
5.1.1 General . 15
5.1.2 Current transformer . 18
5.2 Transient behaviour . 20
5.2.1 General . 20
5.2.2 Fault inception angle . 22
5.2.3 Differential equation . 23
6 Duty cycles . 25
6.1 Duty cycle C – O . 25
6.1.1 General . 25
6.1.2 Fault inception angle . 27
6.1.3 Transient factor K and transient dimensioning factor K . 28
tf td
6.1.4 Reduction of asymmetry by definition of the minimum current inception
angle . 51
6.2 Duty cycle C – O – C – O . 53
6.2.1 General . 53
6.2.2 Case A:No saturation occurs until t’ . 54
6.2.3 Case B:Saturation occurs between t’ and t’ . 56
al
6.3 Summary . 58
7 Determination of the transient dimensioning factor K by numerical calculation . 61
td
7.1 General . 61
7.2 Basic circuit . 61
7.3 Algorithm . 63
7.4 Calculation method . 63
7.5 Reference examples . 64
8 Core saturation and remanence . 70
8.1 Saturation definition for common practice . 70
8.1.1 General . 70
8.1.2 Definition of the saturation flux in the preceding standard IEC 60044-1 . 70
8.1.3 Definition of the saturation flux in IEC 61869-2 . 72
8.1.4 Approach “5 % – Factor 5” . 73
8.2 Gapped cores versus non-gapped cores . 74
8.3 Possible causes of remanence . 76
9 Practical recommendations . 80
9.1 Accuracy hazard in case various PR class definitions for the same core . 80

9.2 Limitation of the phase displacement ∆ϕ and of the secondary loop time
constant T by the transient dimensioning factor K for TPY cores . 80
s td
10 Relations between the various types of classes . 81
10.1 Overview. 81
10.2 Calculation of e.m.f. at limiting conditions . 81
10.3 Calculation of the exciting (or magnetizing) current at limiting conditions . 82
10.4 Examples . 82
10.5 Minimum requirements for class specification . 83
10.6 Replacing a non-gapped core by a gapped core . 83
11 Protection functions and correct CT specification . 84
11.1 General . 84
11.2 General application recommendations . 84
11.2.1 Protection functions and appropriate classes . 84
11.2.2 Correct CT designing in the past and today . 86
11.3 Overcurrent protection: ANSI code: (50/51/50N/51N/67/67N); IEC symbol: I> . 88
11.3.1 Exposition . 88
11.3.2 Recommendation . 90
11.3.3 Example . 90
11.4 Distance protection: ANSI codes: 21/21N, IEC code: Z< . 90
11.4.1 Exposition . 90
11.4.2 Recommendations . 92
11.4.3 Examples. 92
11.5 Differential protection . 99
11.5.1 Exposition . 99
11.5.2 General recommendations . 100
11.5.3 Transformer differential protection (87T) . 100
11.5.4 Busbar protection: Ansi codes (87B) . 105
11.5.5 Line differential protection: ANSI codes (87L) (Low impedance) . 108
11.5.6 High impedance differential protection . 111
Annex A (informative) Duty cycle C – O software code. 130
Annex B (informative) Software code for numerical calculation of K . 132
td
Bibliography . 137

Figure 1 – Definition of the fault inception angle γ . 12
Figure 2 – Components of protection circuit . 16
Figure 3 – Entire electrical circuit . 17
Figure 4 – Primary short circuit current . 18
Figure 5 – Non-linear flux of L . 19
ct
Figure 6 – Linearized magnetizing inductance of a current transformer . 20
Figure 7 – Simulated short circuit behaviour with non-linear model . 21
Figure 8 – Three-phase short circuit behaviour . 23
Figure 9 – Composition of flux . 24
Figure 10 – Short circuit current for two different fault inception angles . 26
Figure 11 – ψ as the curve of the highest flux values . 26
max
Figure 12 – Primary current curves for the 4 cases for 50 Hz and ϕ = 70° . 27
Figure 13 – Four significant cases of short circuit currents with impact on magnetic
saturation of current transformers . 28

– 4 – IEC TR 61869-100:2017 © IEC 2017
Figure 14 – Relevant time ranges for calculation of transient factor . 31
Figure 15 – Occurrence of the first flux peak depending on T at 50 Hz . 32
p,
Figure 16 – Worst-case angle θ as function of T and t’ .
...

IEC TR 61869-100 ®
Edition 1.0 2017-01
TECHNICAL
REPORT
colour
inside
Instrument transformers –
Part 100: Guidance for application of current transformers in power system
protection
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
either IEC or IEC's member National Committee in the country of the requester. If you have any questions about IEC
copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

IEC Central Office Tel.: [phone]
3, rue de Varembé Fax: [phone]
CH-1211 Geneva 20 [e-mail]
Switzerland www.iec.ch
About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.

IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
The stand-alone application for consulting the entire The world's leading online dictionary of electronic and
bibliographical information on IEC International Standards, electrical terms containing 20 000 terms and definitions in
Technical Specifications, Technical Reports and other English and French, with equivalent terms in 16 additional
documents. Available for PC, Mac OS, Android Tablets and languages. Also known as the International Electrotechnical
iPad. Vocabulary (IEV) online.

IEC publications search - www.iec.ch/searchpub IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a 65 000 electrotechnical terminology entries in English and
variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and

CISPR.
IEC Just Published - webstore.iec.ch/justpublished

Stay up to date on all new IEC publications. Just Published IEC Customer Service Centre - webstore.iec.ch/csc
details all new publications released. Available online and If you wish to give us your feedback on this publication or
also once a month by email. need further assistance, please contact the Customer Service
Centre: [e-mail].
IEC TR 61869-100 ®
Edition 1.0 2017-01
TECHNICAL
REPORT
colour
inside
Instrument transformers –
Part 100: Guidance for application of current transformers in power system

protection
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 17.220.20 ISBN 978-2-8322-3808-0

– 2 – IEC TR 61869-100:2017 © IEC 2017
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 10
3 Terms and definitions and abbreviations . 10
3.1 Terms and definitions . 10
3.2 Index of abbreviations . 12
4 Responsibilities in the current transformer design process. 14
4.1 History . 14
4.2 Subdivision of the current transformer design process . 14
5 Basic theoretical equations for transient designing . 15
5.1 Electrical circuit . 15
5.1.1 General . 15
5.1.2 Current transformer . 18
5.2 Transient behaviour . 20
5.2.1 General . 20
5.2.2 Fault inception angle . 22
5.2.3 Differential equation . 23
6 Duty cycles . 25
6.1 Duty cycle C – O . 25
6.1.1 General . 25
6.1.2 Fault inception angle . 27
6.1.3 Transient factor K and transient dimensioning factor K . 28
tf td
6.1.4 Reduction of asymmetry by definition of the minimum current inception
angle . 50
6.2 Duty cycle C – O – C – O . 53
6.2.1 General . 53
6.2.2 Case A:No saturation occurs until t’ . 54
6.2.3 Case B:Saturation occurs between t’ and t’ . 56
al
6.3 Summary . 58
7 Determination of the transient dimensioning factor K by numerical calculation . 61
td
7.1 General . 61
7.2 Basic circuit . 61
7.3 Algorithm . 62
7.4 Calculation method . 63
7.5 Reference examples . 64
8 Core saturation and remanence . 69
8.1 Saturation definition for common practice . 69
8.1.1 General . 69
8.1.2 Definition of the saturation flux in the preceding standard IEC 60044-1 . 69
8.1.3 Definition of the saturation flux in IEC 61869-2 . 71
8.1.4 Approach “5 % – Factor 5” . 72
8.2 Gapped cores versus non-gapped cores . 73
8.3 Possible causes of remanence . 75
9 Practical recommendations . 79
9.1 Accuracy hazard in case various PR class definitions for the same core . 79

9.2 Limitation of the phase displacement ∆ϕ and of the secondary loop time
constant T by the transient dimensioning factor K for TPY cores . 79
s td
10 Relations between the various types of classes . 80
10.1 Overview. 80
10.2 Calculation of e.m.f. at limiting conditions . 80
10.3 Calculation of the exciting (or magnetizing) current at limiting conditions . 81
10.4 Examples . 81
10.5 Minimum requirements for class specification . 82
10.6 Replacing a non-gapped core by a gapped core . 82
11 Protection functions and correct CT specification . 83
11.1 General . 83
11.2 General application recommendations . 83
11.2.1 Protection functions and appropriate classes . 83
11.2.2 Correct CT designing in the past and today . 85
11.3 Overcurrent protection: ANSI code: (50/51/50N/51N/67/67N); IEC symbol: I> . 87
11.3.1 Exposition . 87
11.3.2 Recommendation . 89
11.3.3 Example . 89
11.4 Distance protection: ANSI codes: 21/21N, IEC code: Z< . 89
11.4.1 Exposition . 89
11.4.2 Recommendations . 91
11.4.3 Examples. 91
11.5 Differential protection . 98
11.5.1 Exposition . 98
11.5.2 General recommendations . 99
11.5.3 Transformer differential protection (87T) . 99
11.5.4 Busbar protection: Ansi codes (87B) . 104
11.5.5 Line differential protection: ANSI codes (87L) (Low impedance) . 107
11.5.6 High impedance differential protection . 109
Annex A (informative) Duty cycle C – O software code. 128
Annex B (informative) Software code for numerical calculation of K . 130
td
Bibliography . 135

Figure 1 – Definition of the fault inception angle γ . 12
Figure 2 – Components of protection circuit . 16
Figure 3 – Entire electrical circuit . 17
Figure 4 – Primary short circuit current . 18
Figure 5 – Non-linear flux of L . 19
ct
Figure 6 – Linearized magnetizing inductance of a current transformer . 20
Figure 7 – Simulated short circuit behaviour with non-linear model . 21
Figure 8 – Three-phase short circuit behaviour . 23
Figure 9 – Composition of flux . 24
Figure 10 – Short circuit current for two different fault inception angles . 26
Figure 11 – ψ as the curve of the highest flux values . 26
max
Figure 12 – Primary current curves for the 4 cases for 50 Hz and ϕ = 70° . 27
Figure 13 – Four significant cases of short circuit currents with impact on magnetic
saturation of current transformers . 28

– 4 – IEC TR 61869-100:2017 © IEC 2017
Figure 14 – Relevant time ranges for calculation of transient factor . 31
Figure 15 – Occurrence of the first flux peak depending on T at 50 Hz . 32
p,
Figure 16 – Worst-case angle θ as function of T and t’ .
...