IEC TR 61869-103:2012

IEC/TR 61869-103 ®
Edition 1.0 2012-05
TECHNICAL
REPORT
colour
inside
Instrument transformers – The use of instrument transformers for power quality
measurement
IEC/TR 61869-103:2012(E)
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.: +41 22 919 02 11
3, rue de Varembé Fax: +41 22 919 03 00
CH-1211 Geneva 20 info@iec.ch
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.

Useful links:
IEC publications search - www.iec.ch/searchpub Electropedia - www.electropedia.org
The advanced search enables you to find IEC publications The world's leading online dictionary of electronic and
by a variety of criteria (reference number, text, technical electrical terms containing more than 30 000 terms and
committee,…). definitions in English and French, with equivalent terms in
It also gives information on projects, replaced and additional languages. Also known as the International
withdrawn publications. Electrotechnical Vocabulary (IEV) on-line.

IEC Just Published - webstore.iec.ch/justpublished Customer Service Centre - webstore.iec.ch/csc
Stay up to date on all new IEC publications. Just Published If you wish to give us your feedback on this publication
details all new publications released. Available on-line and or need further assistance, please contact the
also once a month by email. Customer Service Centre: csc@iec.ch.

IEC/TR 61869-103 ®
Edition 1.0 2012-05
TECHNICAL
REPORT
colour
inside
Instrument transformers – The use of instrument transformers for power quality

measurement
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XC
ICS 17.220.20 ISBN 978-2-88912-073-4

– 2 – TR 61869-103  IEC:2012(E)
CONTENTS
FOREWORD . 6
1 Scope . 8
2 Normative references . 8
3 Terms and definitions . 9
4 Nature of the problem . 12
5 Power quality parameters according to IEC 61000-4-30:2008 . 13
5.1 General . 13
5.2 Power quality measurement chain . 13
5.3 Signal processing according to IEC 61000-4-30:2008 . 14
5.4 Power frequency . 15
5.5 Magnitude of the supply voltage . 15
5.6 Flicker . 15
5.7 Supply voltage dips and swells . 17
5.8 Voltage interruptions . 18
5.9 Transient voltages . 19
5.10 Supply voltage unbalance . 19
5.11 Voltage harmonics . 20
5.12 Voltage inter-harmonics . 21
5.13 Mains Signalling Voltages on the supply voltage . 21
5.14 Rapid voltage changes . 21
5.15 Measurement of underdeviation and overdeviation parameters . 21
5.16 Summary of the requirements placed by the measure of power quality
parameters . 21
6 Impact of instrument transformers on PQ measurement . 22
6.1 General . 22
6.2 Inductive instrument transformers . 24
6.2.1 Inductive voltage transformers . 25
6.2.2 Inductive CTs . 30
6.3 Capacitive voltage transformers (CVTs) . 35
6.3.1 Standard application . 35
6.3.2 Special measurement techniques . 39
6.4 Electronic instrument transformers . 42
6.4.1 General . 42
6.4.2 Common accuracy classes . 42
6.4.3 Electronic VTs . 43
6.4.4 Electronic CTs . 55
7 Tests for power quality . 67
7.1 Test procedure for VT frequency response . 68
7.2 Test set-up for VT frequency response test . 68
7.3 Test procedure for CT frequency response . 70
7.4 Test set-up for CT frequency response test . 70
7.5 Special considerations for test of electronic instrument transformers with
digital output . 72
7.6 Tests for electronic instrument transformers according to IEC Standard
60044-8 . 72
7.6.1 Test arrangement and test circuit . 73

TR 61869-103  IEC:2012(E) – 3 –
Annex A Instrument transformers and power quality measurement – open issues . 75
Annex B Transformer classes . 79
Bibliography . 81

Figure 1 – Measurement chain (From [8], modified) . 14
Figure 2 – Contribution of instrument transformers in overall measurement uncertainty
(from [9], modified) . 14
Figure 3 – Example of voltage fluctuation causing flicker . 16
Figure 4 – Demodulation within the IEC flickermeter . 17
Figure 5 – Example of voltage dip (courtesy of Italian distribution network monitoring
system – QuEEN) . 18
Figure 6 – Example of voltage interruption (courtesy of Italian distribution network
monitoring system – QuEEN) . 19
Figure 7 – Example of voltage unbalance (courtesy of Italian distribution network
monitoring system- QuEEN) . 20
Figure 8 – Example of voltage harmonics . 21
Figure 9 – Voltage transformer technologies frequency range according to present
experience . 23
Figure 10 – Current transformer technologies frequency range according to present
experience . 24
Figure 11 – Example of equivalent circuit for an inductive voltage/current transformer . 25
Figure 12 – Cross-section view of an inductive voltage transformer for voltages over 1
kV and up to 52 kV (courtesy of Schneider Electric) . 26
Figure 13 – Cross-section view of a freestanding High Voltage VT (courtesy of Trench
Switzerland AG) . 28
Figure 14 – Frequency response of a typical inductive VT 420 kV (courtesy of Trench
Switzerland AG) . 29
Figure 15 – First resonance peak depending on the system voltage U (courtesy of
m
Trench Switzerland AG) . 29
Figure 16 – Cross-section view of a current transformer (courtesy of Schneider
Electric) . 32
Figure 17 – Results obtained for a 245 kV CT (courtesy of Trench Switzerland AG) . 34
Figure 18 – Results obtained for a 245 kV CT: detail (courtesy of Trench Switzerland AG) . 34
Figure 19 – Cross-section view of a capacitive voltage transformer (Courtesy of Trench
Switzerland AG) . 35
Figure 20 – CVT: Equivalent circuit at power frequency . 36
Figure 21 – Simplified CVT Thevenin equivalent circuit at power frequency without
compensating reactor . 37
Figure 22 – Simplified CVT Thevenin equivalent circuit at power frequency . 37
Figure 23 – Complete CVT Thevenin equivalent circuit at power frequency . 38
Figure 24 – Measurements performed by means of a CVT with harmonic measurement
terminal . 40
Figure 25 – Comparison of different measurements with and without harmonic
monitoring terminal (Courtesy of Trench Switzerland AG, based on [16]) . 41
Figure 26 – Basic design for a bulk crystal producing a Pockels Effect (courtesy of
Alstom Grid) . 45
Figure 27 – Various solutions to apply voltage on the active crystal . 46
Figure 28 – Various methods to divide the full voltage before applying on the crystal . 46

– 4 – TR 61869-103  IEC:2012(E)
Figure 29 – Basic design for a Pockels sensor (courtesy of Alstom Grid) . 47
Figure 30 – Industrial bulk Pockels Cell (courtesy of Alstom Grid) . 47
Figure 31 – Frequency response calculation for an optical VT (courtesy of Alstom Grid) . 48
Figure 32 – Cross-section view and electrical scheme of a resistive voltage divider
(from [22]) . 49
Figure 33 – Ratio error of an MV resistive divider (courtesy of Trench Switzerland AG) . 50
Figure 34 – Phase error of MV resistive divider (courtesy of Trench Switzerland AG) . 50
Figure 35 – Electrical scheme of a capacitive voltage divider . 51
Figure 36 – Equivalent circuit of an RC voltage divider (from [23], [24]) . 53
Figure 37 – Equivalent circuit of a balanced RC voltage divider (from [24]) . 53
Figure 38 – Frequency response of an RC voltage divider (courtesy of Trench
Switzerland AG) . 54
Figure 39 – Measurements done on an RC voltage divider with a voltage level of 145
kV with a cable length of 150 m (courtesy of Trench Switzerland AG) . 54
Figure 40 – Principle of optical CT measurement (from [22]) . 56
Figure 41 – Principle of optical CT measurement (Courtesy of Alstom Grid) . 56
Figure 42 – Frequency response calculation for an optical CT (Courtesy of Alstom
Grid) . 57
Figure 43 – Typical frequency response measurement of a LPCT (Courtesy of Trench
Switzerland AG) . 58
Figure 44 – Equivalent circuit for a Rogowski coils (Courtesy of Alstom Grid)) . 59
Figure 45 – Electrical scheme and picture of a Rogowski current transformer (Courtesy
of Alstom Grid). 61
Figure 46 – Electrical scheme of a shunt current measurement (Courtesy of Alstom
Grid) . 62
Figure 47 – Shunt for DC application (Courtesy of Alstom Grid) . 63
Figure 48 – Equivalent circuit for a compensated shunt . 63
Figure 49 – Theoretic possible bandwidth of a shunt 5 kA /150 mV (Courtesy of Alstom
Grid) . 64
Figure 50 – Hall Effect Sensor . 65
Figure 51 – Hall Effect Sensor (Courtesy of Schneider Electric – From [38]) . 66
Figure 52 – Hall Effect Sensor (Courtesy of Schneider Electric – From [38]) . 66
Figure 53 – Test circuit for VT frequency response test . 69
Figure 54 – Test circuit for VT frequency response test . 70
Figure 55 – Test circuit for CT frequency response test . 71
Figure 56 – Test circuit for CT frequency response test . 72
Figure 57 – Test set-up for electronic instrument current transformers with digital
output . 73
Figure 58 – Test set-up for electronic current transformers with analogue output . 74
Figure A.1 – Examples of “fake dips”, transients recorded at the secondary winding of
MV voltage transformers due to voltage transformers saturation (courtesy of Italian
distribution network monitoring system- QuEEN). 78

Table 1 – Power quality disturbances and measurement interval as per IEC 61000-4-
30:2008 . 15
Table 2 – Transformer parameters influencing power quality measurement . 22

TR 61869-103  IEC:2012(E) – 5 –
Table 3 – Main components of an inductive voltage transformer for voltages over 1 kV
and up to 52 kV . 26
Table 4 – Inductive voltage transformers for voltages over 1 kV and up to 52 kV:
impact on the measurements of PQ Parameters . 27
Table 5 – Inductive voltage transformers for voltages over 52 kV and up to 1 100 kV:
impact on the measurements of PQ parameters . 30
Table 6 – Main components of an inductive current transformer for voltages over 1 kV
up to 52 kV . 31
Table 7 – Inductive CTs for voltages over 1 kV up to 52 kV: impact on the
measurements of PQ parameters . 32
Table 8 – Main components of an inductive current transformer for voltages above 52
kV up to 1 100 kV . 33
Table 9 – Inductive CTs for voltages over 52 kV up to 1 100 kV: impact on the
measurements of PQ parameters . 35
Table 10 – Capacitive voltage transformers: impact on the measurements of PQ
parameters . 39
Table 11 – Capacitive voltage transformer with harmonic measurement terminal:
impact on the measurements of PQ parameters . 41
Table 12 – Capacitive voltage transformer with additional equipment for PQ
measurement: impact on the measurements of PQ parameters . 42
Table 13 – Accuracy classes for power metering. 43
Table 14 – Accuracy classes for power quality metering . 43
Table 15 – Optical voltage transformer: impact on the measurements of PQ parameters . 48
Table 16 – MV resistive divider: impact on the measurements of PQ parameters . 51
Table 17 – Capacitive voltage dividers: impact on the measurements of PQ parameters . 52
Table 18 – RC voltage divider: impact on the measurements of PQ parameters . 55
Table 19 – Optical current transformer: Impact on the measurements of PQ parameters. 57
Table 20 – Main components of LPCTs . 58
Table 21 – Main components of Rogowski sensors . 61
Table 22 – Rogowski current transformer: Impact on the measurements of PQ
parameters . 62
Table 23 – Shunt: Impact on the measurements of PQ parameters . 64
Table 24 – Hall effect sensor: Impact on the measurements of PQ parameters . 67
Table 25 – Power quality parameters and requirements for CT and VT . 68
Table 26 – Test currents and voltages for the common accuracy classes . 72
Table 27 – Test currents and voltages for special accuracy classes . 72
Table B.1 – Example of test table with possible main requirements for accuracy tests . 80

– 6 – TR 61869-103  IEC:2012(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
_____________
INSTRUMENT TRANSFORMERS –
THE USE OF INSTRUMENT TRANSFORMERS
FOR POWER QUALITY MEASUREMENT
FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising with the IEC also participate in this preparation. IEC collaborates closely
with the International Organization for Standardization (ISO) in accordance with conditions determined by
agreement between the two organizations.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example “state of the art”.
IEC 61869-103, which is a technical report, has been prepared by IEC technical committee
38: Instrument transformers.
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
38/402/DTR 38/409/RVC
Full information on the voting for the approval of this technical report can be found in the
report on voting indicated in the above table.

TR 61869-103  IEC:2012(E) – 7 –
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all the parts in the IEC 61869 series, published under the general title Instrument
transformers, can be found on the IEC website.
The committee has decided that the contents of this publication will remain unchanged until
the stability dateindicated on the IEC web site under “http://webstore.iec.ch” in the data
related to the specific publication. At this date, the publication will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The ‘colour inside’ logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 8 – TR 61869-103  IEC:2012(E)
INSTRUMENT TRANSFORMERS –
THE USE OF INSTRUMENT TRANSFORMERS
FOR POWER QUALITY MEASUREMENT
1 Scope
This part of IEC 61869 is applicable to inductive and electronic instrument transformers with
analogue or digital output for use with electrical measuring instruments for measurement and
interpretation of results for power quality parameters in 50/60 Hz a.c. power supply systems.
This part of IEC 61869 aims at giving guidance in the usage of HV instrument transformers for
measuring power quality parameters.
The power quality parameters considered in this document are power frequency, magnitude of
the supply voltage and current, flicker, supply voltage dips and swells, voltage interruptions,
transient voltages, supply voltage unbalance, voltage and current harmonics and
interharmonics, mains signalling on the supply voltage and rapid voltage changes.
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 60044-8:2002, Instrument transformers – Part 8: Instrument transformers: Electronic
current transformers
IEC 61000-2-1:1990, Electromagnetic compatibility (EMC) – Part 2-1: Environment –
Description of the environment – Electromagnetic environment for low-frequency conducted
disturbances and signalling in public power supply systems
IEC 61000-2-2:2002, Electromagnetic compatibility (EMC) – Part 2-2: Environment –
Compatibility for low frequency conducted disturbances and signalling in public low-voltage
power supply systems
IEC 61000-4-7:2002, Electromagnetic compatibility (EMC) – Part 4-7: Testing and
measurement techniques – General guide on harmonics and interharmonics measurements
and instrumentation, for power supply systems and equipment connected thereto
IEC 61000-4-15:2010, Electromagnetic compatibility (EMC) – Part 4-15: Testing and
measuring techniques – Flickermeter – Functional and design specifications
IEC 61000-4-30:2008, Electromagnetic compatibility (EMC) – Part 4-30: Testing and
measurement techniques – Power quality measurement methods
IEC 60359:2001, Electrical and electronic measurement equipment – Expression of
performance
IEC 61557-12:2007, Electrical safety in low voltage distribution systems up to 1 000 V a.c.
and 1 500 V d.c. – Equipment for testing, measuring or monitoring of protective measures –
Part 12: Performance measuring and monitoring devices (PMD)

TR 61869-103  IEC:2012(E) – 9 –
EN 50160:2007, Voltage characteristics of electricity supplied by public distribution networks
3 Terms and definitions
For the purpose of this document, the terms and definitions given in IEC 61000-4-30:2008 and
the following apply.
3.1
dip threshold
voltage magnitude specified for the purpose of detecting the start and the end of a voltage dip
3.2
flicker
impression of unsteadiness of visual sensation induced by a light stimulus whose luminance
or spectral distribution fluctuates with time
[SOURCE: IEC 60050-161:1990, 161-08-13]
3.3
fundamental component
component whose frequency is the fundamental frequency
[SOURCE: IEC 60050-101:1998, 101-14-49, modified definition]
3.4
fundamental frequency
frequency in the spectrum obtained from a Fourier transform of a time function, to which all
the frequencies of the spectrum are referred
[SOURCE: IEC 60050-101:1998, 101-14-50, modified definition]
Note 1 to entry: In case of any remaining risk of ambiguity, the fundamental frequency may be derived from the
number of poles and speed of rotation of the synchronous generator(s) feeding the system.
3.5
harmonic component
any of the components having a harmonic frequency
[SOURCE: IEC 61000-2-2:2002, definition 3.2.4]
Note 1 to entry: Its value is normally expressed as an r.m.s. value. For brevity, such a component may be referred
to simply as an harmonic.
3.6
harmonic frequency
frequency which is an integer multiple of the fundamental frequency
Note 1 to entry: The ratio of the harmonic frequency to the fundamental frequency is the harmonic order
(recommended notation: n) (IEC 61000 2-2, definition 3.2.3).
3.7
influence quantity
quantity which is not the subject of the measurement and whose change affects the
relationship between the indication and the result of the measurement
[SOURCE: IEC 60050-311:2001, 311-06-01]
Note 1 to entry: This quantity is generally external to the measurement equipment.
3.8
interharmonic component
component having an interharmonic frequency

– 10 – TR 61869-103  IEC:2012(E)
[SOURCE: IEC 61000-2-2:2002, definition 3.2.6]
Note 1 to entry: Its value is normally expressed as an r.m.s. value. For brevity, such a component may be referred
to simply as an interharmonic.
3.9
interharmonic frequency
any frequency which is not an integer multiple of the fundamental frequency
[SOURCE: IEC 61000-2-2:2002, definition 3.2.5]
Note 1 to entry: By extension from harmonic order, the interharmonic order is the ratio of an interharmonic
frequency to the fundamental frequency. This ratio is not an integer (recommended notation m).
Note 2 to entry: In the case where m < 1 the term subharmonic frequency may be used.
3.10
interruption
reduction of the voltage at a point in the electrical system below the interruption threshold
3.11
interruption threshold
voltage magnitude specified for the purpose of detecting the start and the end of a voltage
interruption
3.12
measurement uncertainty
parameter, associated with the result of a measurement, that characterizes the dispersion of
the values that could reasonably be attributed to the measurand
[SOURCE: IEC 60050-311:2001, 311-01-02, VIM 2.26]
3.13
nominal voltage
U
n
voltage by which a system is designated or identified
3.14
overdeviation
the absolute value of the difference between the measured value and the nominal value of a
parameter, only when the measured value of the parameter is greater than the nominal value
3.15
power quality
characteristics of the electricity at a given point on an electrical system, evaluated against a
set of reference technical parameters
[SOURCE: IEC 60050-617:2009, 617-01-05]
Note 1 to entry: These parameters might, in some cases, relate to the compatibility between electricity supplied on
a network and the loads connected to that network.
3.16
r.m.s. (root-mean-square) value
square root of the arithmetic mean of the squares of the instantaneous values of a quantity
taken over a specified time interval and a specified bandwidth
[SOURCE: IEC 60050-101:1998, 101-14-16, modified definition]

TR 61869-103  IEC:2012(E) – 11 –
3.17
r.m.s. voltage refreshed each half-cycle
U
rms(1/2)
value of the r.m.s. voltage measured over 1 cycle, commencing at a fundamental zero
crossing, and refreshed each half-cycle
Note 1 to entry: This technique is independent for each channel and will produce r.m.s. values at successive times
on different channels for polyphase systems.
Note 2 to entry: This value is used only for voltage dip, voltage swell and interruption detection and evaluation, in
Class A.
Note 3 to entry: This r.m.s. voltage value may be a phase-to-phase value or a phase-to-neutral value.
3.18
r.m.s. voltage refreshed each cycle
U
rms(1)
value of the r.m.s. voltage measured over 1 cycle and refreshed each cycle
Note 1 to entry: In contrast to U , this technique does not define when a cycle commences.
rms(1/2)
Note 2 to entry: This value is used only for voltage dip, voltage swell and interruption detection and evaluation, in
Class S.
Note 3 to entry: This r.m.s. voltage value can be a phase-to-phase value or a phase-to-neutral value.
3.19
residual voltage
U
res
minimum value of U or U recorded during a voltage dip or interruption
rms(1/2) rms(1)
Note 1 to entry: The residual voltage is expressed as a value in volts, or as a percentage or per unit value of Udin
3.20
sliding reference voltage
Usr
voltage magnitude averaged over a specified time interval, representing the voltage preceding
a voltage-change type of event (e.g. voltage dips and swells, rapid voltage changes)
3.21
supply voltage
the voltage which a distribution undertaking maintains at the consumer’s point of supply
[SOURCE: IEC 60050-604:1987, 604-01-16]
Note 1 to entry: If a supply voltage is specified, for instance in the supply contract, then it is called “declared
(supply) voltage”.
3.22
swell threshold
voltage magnitude specified for the purpose of detecting the start and the end of a swell
3.23
underdeviation
the absolute value of the difference between the measured value and the nominal value of a
parameter, only when the value of the parameter is lower than the nominal value
3.24
voltage dip
temporary reduction of the voltage magnitude at a point in the electrical system below a
threshold
– 12 – TR 61869-103  IEC:2012(E)
Note 1 to entry: Interruptions are a special case of a voltage dip. Post-processing may be used to distinguish
between voltage dips and interruptions.
Note 2 to entry: A voltage dip is also referred to as sag. The two terms are considered interchangeable; however,
this standard will only use the term voltage dip.
3.25
voltage swell
temporary increase of the voltage magnitude at a point in the electrical system above a
threshold
3.26
voltage unbalance
condition in a polyphase system in which the r.m.s. values of the line voltages (fundamental
component), and/or the phase angles between consecutive line voltages, are not all equal
[SOURCE: IEC 60050-161:1990, 161-08-09, modified definition and notes]
Note 1 to entry: The degree of the inequality is usually expressed as the ratios of the negative- and zero-sequence
components to the positive-sequence component.
Note 2 to entry: In this document, voltage unbalance is considered in relation to 3-phase systems.
4 Nature of the problem
Instrument transformers have been used up to now for protection and metering purpose,
providing a secondary signal suitable for protection relays and measurement instruments with
the required accuracy.
Attention has been focused on the measurement of current, voltage, power frequency and
power: instrument transformers have been conceived, standardized, designed, manufactured,
tested mainly, if not exclusively, for this purpose.
Nowadays, there is a growing demand for investigating the characteristics of the electricity at
a given point on an electrical system, evaluated against a set of reference technical
parameters; in other words, for measuring the Power Quality (PQ) at that point of the system.
The development of a lot of applications sensitive to PQ issues, from domestic to industrial
field, requires technical and normative criteria, in order to protect the parts involved.
Aspects related to PQ measurement methods (and relevant accuracy classes) are defined in
detail in the Standard IEC 61000-4-30:2008. In low voltage applications, instruments are
available, able to perform measurements with a high degree of accuracy and complying with
measurement classes prescribed by IEC 61000-4-30:2008. For high voltage applications,
voltage and current transformers have to be inserted in measurement chain, but the
information available about their impact on the measurement is not yet consolidated.
For power frequency, a homogeneous behaviour within the whole instrument transformer
population belonging to the same class is expected; however, at other frequencies, the
transformers behaviour may change, not only from type to type, but even between different
samples of the same type.
The present technical report aims to provide the relevant information available at the present
about the subject, to give, where possible, indications about the methods and the
arrangements to be used and to define the issues that have to be solved and the aspects to
be investigated.
In the following chapter, power quality parameters according to IEC 61000-4-30:2008 are
described. The possible impact of instrument transformers on the measurement chain is also
considered.
TR 61869-103  IEC:2012(E) – 13 –
5 Power quality parameters according to IEC 61000-4-30:2008
5.1 General
The IEC 61000 family of standards on electromagnetic compatibility standardizes most
aspects of power quality. Namely, these standards provide definition for the various
disturbances, acceptable emission, susceptibility and compatibility levels as well as
measurement methods. The most relevant standards necessary to understand the influence of
instrument transformers on power quality parameters are:
• IEC 61000-2-1:1990, Electromagnetic compatibility (EMC) – Part 2-1: Environment –
Section 1: Description of the environment – Electromagnetic environment for low-
frequency conducted disturbances and signalling in public power supply systems
• IEC 61000-2-2:2002, Electromagnetic compatibility (EMC) – Part 2-2: Environment –
Compatibility for low-frequency conducted disturbances and signalling in public low-
voltage power supply systems
• IEC 61000-4-7:2002, Electromagnetic compatibility (EMC) – Part 4-7: Testing and
measurement techniques – General guide on harmonics and interharmonics
measurements and instrumentation, for power supply systems and equipment connected
thereto
• IEC 61000-4-15:2010, Electromagnetic compatibility (EMC) – Part 4-15: Testing and
measurement techniques – Flickermeter – Functional and design specifications
• IEC 61000-4-30:2008, Electromagnetic compatibility (EMC) – Part 4-30: Testing and
measurement techniques – Power quality measurement methods
• IEC 60359:2001, Electrical and electronic measurement equipment – Expression of
performance
• IEC 61557-12:2007, Electrical safety in low voltage distribution systems up to 1 000 V a.c.
and 1 500 V d.c. – Equipment for testing, measuring or monitoring of protective measures
– Part 12: Performance measuring and monitoring devices (PMD)
The first two standards listed provide a definition of the power quality disturbances and their
acceptable levels in power system. The remaining three documents define how these
disturbances are measured. IEC 61000-4-30:2008 is the main document and is completed by
IEC 61000-4-7:2002 and IEC 61000-4-15 which address the specific requirements for
harmonics and flicker. It is important to note that IEC 61000-4-30:2008 addresses
disturbances relevant to voltage only, while IEC 61000-4-7:2002 also includes current. This
implies that, at present, voltage transformers influence has to be considered taking into
account the measurement of all quantities identified by IEC 61000-4-30:2008, while the
analysis of the impact of current transformers could be limited to harmonics and
interharmonics.
5.2 Power quality measurement chain
To determine and quantify the influence of instrument transformers on the overall uncertainty
on power quality measurements, it is necessary to simultaneously consider the electrical
behaviour of an instrument transformer for a given disturbance and the measurement method
as they constitute a measurement chain. This is shown schematically in Figure 1.
NOTE The measurement chain shown in Figure 1 is the same illustrated in clause 4.2 of IEC 61000-4-30:2008,
where “Measurement transducers” has been replaced with “Instrument transformers”, in order to be consistent with
the terminology used by IEC TC 38.

– 14 – TR 61869-103  IEC:2012(E)
Instrument Measurement Evaluation unit
transformers unit
Electrical input Input signal to be Measurement Measurement
signal measured result evaluation

IEC  735/12
Figure 1 – Measurement chain (From h) , modified)
The impact of instrument transformers on the overall uncertainty can be quantified as an
added uncertainty that combines with the uncertainty of the measuring system as illustrated in
Figure 2.
Operating uncertainty
of external sensors +
impedance of wires
Variations due
to external influence
quantities
(temperature, …)
Variations due
Overall system uncertainty
to power system
(cf IEC 61557-12)
electrical parameters
(harmonics, …)
Operating uncertainty
(cf IEV and IEC 60359)
Uncertainty
under
Measurement uncertainty
reference
(cf IEC 61000-4-30)
conditions
Intrinsic uncertainty
(cf IEV and IEC 60359)
IEC  736/12
Figure 2 – Contribution of instrument transformers in overall
measurement uncertainty (from i), modified)
5.3 Signal processing accor
...