IEC TR 61000-3-6:2008

IEC/TR 61000-3-6
Edition 2.0 2008-02
TECHNICAL
REPORT
BASIC EMC PUBLICATION
Electromagnetic compatibility (EMC) –
Part 3-6: Limits – Assessment of emission limits for the connection of distorting
installations to MV, HV and EHV power systems

IEC/TR 61000-3-6:2008(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.

Droits de reproduction réservés. Sauf indication contraire, aucune partie de cette publication ne peut être reproduite
ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie
et les microfilms, sans l'accord écrit de la CEI ou du Comité national de la CEI du pays du demandeur.
Si vous avez des questions sur le copyright de la CEI ou si vous désirez obtenir des droits supplémentaires sur cette
publication, utilisez les coordonnées ci-après ou contactez le Comité national de la CEI de votre pays de résidence.

IEC Central Office
3, rue de Varembé
CH-1211 Geneva 20
Switzerland
Email: inmail@iec.ch
Web: 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.
ƒ Catalogue of IEC publications: www.iec.ch/searchpub
The IEC on-line Catalogue enables you to search by a variety of criteria (reference number, text, technical committee,…).
It also gives information on projects, withdrawn and replaced publications.
ƒ IEC Just Published: www.iec.ch/online_news/justpub
Stay up to date on all new IEC publications. Just Published details twice a month all new publications released. Available
on-line and also by email.
ƒ Electropedia: www.electropedia.org
The world's leading online dictionary of electronic and electrical terms containing more than 20 000 terms and definitions
in English and French, with equivalent terms in additional languages. Also known as the International Electrotechnical
Vocabulary online.
ƒ Customer Service Centre: www.iec.ch/webstore/custserv
If you wish to give us your feedback on this publication or need further assistance, please visit the Customer Service
Centre FAQ or contact us:
Email: csc@iec.ch
Tel.: +41 22 919 02 11
Fax: +41 22 919 03 00
A propos de la CEI
La Commission Electrotechnique Internationale (CEI) est la première organisation mondiale qui élabore et publie des
normes internationales pour tout ce qui a trait à l'électricité, à l'électronique et aux technologies apparentées.

A propos des publications CEI
Le contenu technique des publications de la CEI est constamment revu. Veuillez vous assurer que vous possédez
l’édition la plus récente, un corrigendum ou amendement peut avoir été publié.
ƒ Catalogue des publications de la CEI: www.iec.ch/searchpub/cur_fut-f.htm
Le Catalogue en-ligne de la CEI vous permet d’effectuer des recherches en utilisant différents critères (numéro de référence,
texte, comité d’études,…). Il donne aussi des informations sur les projets et les publications retirées ou remplacées.
ƒ Just Published CEI: www.iec.ch/online_news/justpub
Restez informé sur les nouvelles publications de la CEI. Just Published détaille deux fois par mois les nouvelles
publications parues. Disponible en-ligne et aussi par email.
ƒ Electropedia: www.electropedia.org
Le premier dictionnaire en ligne au monde de termes électroniques et électriques. Il contient plus de 20 000 termes et
définitions en anglais et en français, ainsi que les termes équivalents dans les langues additionnelles. Egalement appelé
Vocabulaire Electrotechnique International en ligne.
ƒ Service Clients: www.iec.ch/webstore/custserv/custserv_entry-f.htm
Si vous désirez nous donner des commentaires sur cette publication ou si vous avez des questions, visitez le FAQ du
Service clients ou contactez-nous:
Email: csc@iec.ch
Tél.: +41 22 919 02 11
Fax: +41 22 919 03 00
IEC/TR 61000-3-6
Edition 2.0 2008-02
TECHNICAL
REPORT
BASIC EMC PUBLICATION
Electromagnetic compatibility (EMC) –
Part 3-6: Limits – Assessment of emission limits for the connection of distorting
installations to MV, HV and EHV power systems

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XA
CODE PRIX
ICS 33.100.10 ISBN 2-8318-9605-3

– 2 – TR 61000-3-6 © IEC:2008(E)
CONTENTS
FOREWORD.4
INTRODUCTION.6
ACKNOWLEDGMENT.7

1 Scope.8
2 Normative references .9
3 Terms and definitions .9
4 Basic EMC concepts related to harmonic distortion .13
4.1 Compatibility levels .13
4.2 Planning levels.14
4.3 Illustration of EMC concepts.16
4.4 Emission levels .17
5 General principles .18
5.1 Stage 1: simplified evaluation of disturbance emission .18
5.2 Stage 2: emission limits relative to actual system characteristics.19
5.3 Stage 3: acceptance of higher emission levels on a conditional basis.19
5.4 Responsibilities .19
6 General guidelines for the assessment of emission levels .20
6.1 Point of evaluation.20
6.2 Definition of harmonic emission level.20
6.3 Assessment of harmonic emission levels.21
6.4 System harmonic impedance.22
7 General summation law .24
8 Emission limits for distorting installations connected to MV systems.25
8.1 Stage 1: simplified evaluation of disturbance emission .25
8.2 Stage 2: emission limits relative to actual system characteristics.27
8.3 Stage 3: acceptance of higher emission levels on a conditional basis.31
8.4 Summary diagram of the evaluation procedure .32
9 Emission limits for distorting installations connected to HV-EHV systems .33
9.1 Stage 1: simplified evaluation of disturbance emission .33
9.2 Stage 2: emission limits relative to actual system characteristics.33
9.3 Stage 3: acceptance of higher emission levels on a conditional basis.36
10 Interharmonics .36

Annex A (informative) Envelope of the maximum expected impedance .38
Annex B (informative) Guidance for allocating planning levels and emission levels at
MV .39
Annex C (informative) Example of calculation of global MV+LV contribution .45
Annex D (informative) Method for sharing planning levels and allocating emission
limits in meshed HV – EHV systems .46
Annex E (informative) List of symbols and subscripts.54

Bibliography.57

TR 61000-3-6 © IEC:2008(E) – 3 –
Figure 1 – Illustration of basic voltage quality concepts with time/ location statistics
covering the whole system .17
Figure 2 – Illustration of basic voltage quality concepts with time statistics relevant to
one site within the whole system .17
Figure 3 – Illustration of the emission vector U and its contribution to the measured
hi
harmonic vector at the point of evaluation .20
Figure 4 – Example of a system for sharing global contributions at MV .28
Figure 5 – Diagram of evaluation procedure at MV.32
Figure 6 – Determination of S for a simple HV or EHV system.33
t
Figure 7 – Allocation of planning level to a substation in HV-EHV system .34
Figure A.1 – Example of maximum impedance curve for a 11 kV system .38
Figure B.1 – Example of an MV distribution system showing the MV transformer and
feeders 1-6.42
Figure D.1 – HV-EHV system considered for the connection of a new distorting
installation at node 1 substation .48
Figure D.2 – Harmonic Impedance at node 1 .49
Figure D.3 – Harmonic Impedance at node 5 ‘Uranus 150 kV’, when the capacitor
banks at Jupiter 150 kV are switched off .50

Table 1 – Compatibility levels for individual harmonic voltages in low and medium
voltage networks (percent of fundamental component) reproduced from
IEC 61000-2-2 [5] and IEC 61000-2-12 [6].14
Table 2 – Indicative planning levels for harmonic voltages (in percent of the
fundamental voltage) in MV, HV and EHV power systems.15
Table 3 – Summation exponents for harmonics (indicative values).25
Table 4 – Weighting factors W for different types of harmonic producing equipments.27
j
Table 5 – Indicative values for some odd order harmonic current emission limits
relative to the size of a customer installation .28
Table B.1 – Feeder characteristics for the system under consideration .43
Table B.2 – Determination of F and Sxℓ values for the feeders.43
Table C.1 – Acceptable global contribution G of the MV and LV installations to
hMV+LV
the MV harmonic voltages if the transfer coefficient from the HV-EHV system is
considered to be unity .45
Table D.1 – Influence coefficients K between node j and node 1 .49
hj-1
Table D.2 – Reduction factors.51
Table D.3 – Global contributions G at node 1.52
hB1
– 4 – TR 61000-3-6 © IEC:2008(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROMAGNETIC COMPATIBILITY (EMC) –

Part 3-6: Limits –
Assessment of emission limits for the connection of distorting
installations to MV, HV and EHV power systems

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 provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
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/TR 61000-3-6, which is a technical report, has been prepared by subcommittee 77A: Low
frequency phenomena, of IEC technical committee 77: Electromagnetic compatibility.
This Technical Report forms Part 3-6 of IEC 61000. It has the status of a basic EMC
publication in accordance with IEC Guide 107 [29] .
This second edition cancels and replaces the first edition published in 1996 and constitutes a
technical revision.
___________
Figures in square brackets refer to the Bibliography.

TR 61000-3-6 © IEC:2008(E) – 5 –
This edition is significantly more streamlined than first edition, and it reflects the experiences
gained in the application of the first edition. As part of this streamlining process, this second
edition of IEC/TR 61000-3-6 does not address communications circuit interference. Clause 9
on this (section 10) was removed, as this did not suitably address emission limits for
telephone interference. The scope has been adjusted to point out that IEC/TR 61000-3-6 does
not address communications circuit interference. This edition has also been harmonised with
IEC/TR 61000-3-7 [30] and IEC/TR 61000-3-13 [31].
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
77A/575/DTR 77A/637/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.
A list of all parts of the IEC 61000 series, under the general title Electromagnetic compatibility
(EMC), can be found on the IEC website.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result date indicated 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.

– 6 – TR 61000-3-6 © IEC:2008(E)
INTRODUCTION
IEC 61000 is published in separate parts according to the following structure:
Part 1: General
General considerations (introduction, fundamental principles)
Definitions, terminology
Part 2: Environment
Description of the environment
Classification of the environment
Compatibility levels
Part 3: Limits
Emission limits
Immunity limits
(in so far as they do not fall under the responsibility of product committees)
Part 4: Testing and measurement techniques
Measurement techniques
Testing techniques
Part 5: Installation and mitigation guidelines
Installation guidelines
Mitigation methods and devices
Part 6: Generic standards
Part 9: Miscellaneous
Each part is further subdivided into several parts published either as International Standards
or as technical specifications or technical reports, some of which have already been published
as sections. Others will be published with the part number followed by a dash and a second
number identifying the subdivision (example: IEC 61000-6-1).

TR 61000-3-6 © IEC:2008(E) – 7 –
ACKNOWLEDGMENT
In 2002, the IEC subcommittee 77A made a request to CIGRE Study Committee C4 and
CIRED Study Committee S2, to organize an appropriate technical forum (joint working group)
whose main scope was to prepare, among other tasks, the revision of the technical report
IEC 61000-3-6 concerning emission limits for harmonics for the connection of distorting
installations to public supply systems at MV, HV and EHV.
To this effect, joint working group CIGRE C4.103/ CIRED entitled ‘’Emission Limits for
Disturbing Installations’’ was appointed in 2003. Some previous work produced by CIGRE
JWG C4.07-Cired has been used as an input to the revision, in particular the planning levels
and associated indices. In addition, using experience since the technical report IEC 61000-3-6
was initially published in 1996, WG C4.103 reviewed the procedure used to determine
emission limits and the assessment methods used to evaluate emission levels for
installations.
Subsequent endorsement of the document by IEC was the responsibility of SC 77A.

– 8 – TR 61000-3-6 © IEC:2008(E)
ELECTROMAGNETIC COMPATIBILITY (EMC) –

Part 3-6: Limits –
Assessment of emission limits for the connection of distorting
installations to MV, HV and EHV power systems

1 Scope
This Technical Report, which is informative in its nature, provides guidance on principles
which can be used as the basis for determining the requirements for the connection of
distorting installations to MV, HV and EHV public power systems (LV installations are covered
in other IEC documents). For the purposes of this report, a distorting installation means an
installation (which may be a load or a generator) that produces harmonics and/or
interharmonics. The primary objective is to provide guidance to system operators or owners
on engineering practices, which will facilitate the provision of adequate service quality for all
connected customers. In addressing installations, this document is not intended to replace
equipment standards for emission limits.
The report addresses the allocation of the capacity of the system to absorb disturbances. It
does not address how to mitigate disturbances, nor does it address how the capacity of the
system can be increased.
Since the guidelines outlined in this report are necessarily based on certain simplifying
assumptions, there is no guarantee that this approach will always provide the optimum
solution for all harmonic situations. The recommended approach should be used with
flexibility and judgment as far as engineering is concerned, when applying the given
assessment procedures in full or in part.
The system operator or owner is responsible for specifying requirements for the connection of
distorting installations to the system. The distorting installation is to be understood as the
customer’s complete installation (i.e. including distorting and non-distorting parts).
Problems related to harmonics fall into two basic categories.
• Harmonic currents that are injected into the supply system by converters and harmonic
sources, giving rise to harmonic voltages in the system. Both harmonic currents and
resulting voltages can be considered as conducted phenomena.
• Harmonic currents that induce interference into communication systems. This
phenomenon is more pronounced at higher order harmonic frequencies because of
increased coupling between the circuits and because of the higher sensitivity of the
communication circuits in the audible range.
This report gives guidance for the co-ordination of the harmonic voltages between different
voltage levels in order to meet the compatibility levels at the point of utilisation. The
recommendations in this report do not address harmonic interference phenomena in
communication circuits (i.e. only the first of the above categories is addressed). These
disturbances need to be addressed in terms of international directives concerning the
Protection of Telecommunication Lines against Harmful Effects from Electric Power and
Electrified Railway Lines, International Telecommunication Union, ITU-T Directives [1] or in
terms of locally applicable standards such as [2], [3] or [4].
___________
Figures in square brackets refer to the bibliography.

TR 61000-3-6 © IEC:2008(E) – 9 –
NOTE The boundaries between the various voltage levels may be different for different countries (see
IEV 601-01-28 [32]). This report uses the following terms for system voltages:
– low voltage (LV) refers to Un ≤ 1 kV;
– medium voltage (MV) refers to 1 kV < Un ≤ 35 kV;
– high voltage (HV) refers to 35 kV < Un ≤ 230 kV;
– extra high voltage (EHV) refers to 230 kV < Un.
In the context of this report, the function of the system is more important than its nominal voltage. For example, a
HV system used for distribution may be given a "planning level" which is situated between those of MV and HV
systems.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60050(161), International Electrotechnical Vocabulary – Chapter 161: Electromagnetic
compatibility
3 Terms and definitions
For the purposes of this document, the following definitions apply as well as the definitions in
IEC 60050(161).
3.1
agreed power
value of the apparent power of the disturbing installation on which the customer and the
system operator or owner agree. In the case of several points of connection, a different value
may be defined for each connection point
3.2
customer
person, company or organisation that operates an installation connected to, or entitled to be
connected to, a supply system by a system operator or owner
3.3
(electromagnetic) disturbance
any electromagnetic phenomenon which, by being present in the electromagnetic
environment, can cause electrical equipment to depart from its intended performance
3.4
disturbance level
the amount or magnitude of an electromagnetic disturbance measured and evaluated in a
specified way
3.5
distorting installation
an electrical installation as a whole (i.e. including distorting and non-distorting parts) which
can cause distortion of the voltage or current into the supply system to which it is connected
NOTE For the purpose of this report, all references to distorting installations not only include linear and non-linear
loads, but generating plants, and any source of non-sinusoidal current emissions such as regenerative braking
systems,
– 10 – TR 61000-3-6 © IEC:2008(E)
3.6
electromagnetic compatibility (EMC)
ability of an equipment or system to function satisfactorily in its electromagnetic environment
without introducing intolerable electromagnetic disturbances to anything in that environment
NOTE 1 Electromagnetic compatibility is a condition of the electromagnetic environment such that, for every
phenomenon, the disturbance emission level is sufficiently low and immunity levels are sufficiently high so that all
devices, equipment and systems operate as intended.
NOTE 2 Electromagnetic compatibility is achieved only if emission and immunity levels are controlled such that
the immunity levels of the devices, equipment and systems at any location are not exceeded by the disturbance
level at that location resulting from the cumulative emissions of all sources and other factors such as circuit
impedances. Conventionally, compatibility is said to exist if the probability of the departure from intended
performance is sufficiently low. See Clause 4 of IEC 61000-2-1 [33].
NOTE 3 Where the context requires it, compatibility may be understood to refer to a single disturbance or class of
disturbances.
NOTE 4 Electromagnetic compatibility is a term used also to describe the field of study of the adverse
electromagnetic effects which devices, equipment and systems undergo from each other or from electromagnetic
phenomena.
3.7
(electromagnetic) compatibility level
specified electromagnetic disturbance level used as a reference level in a specified
environment for co-ordination in the setting of emission and immunity limits
NOTE By convention, the compatibility level is chosen so that there is only a small probability (for example 5 %)
that it will be exceeded by the actual disturbance level.
3.8
emission
phenomenon by which electromagnetic energy emanates from a source of electromagnetic
disturbance
[IEV 161-01-08 modified]
NOTE For the purpose of this report, emission refers to phenomena or conducted electromagnetic disturbances
that can distort the supply voltage waveform.
3.9
emission level
level of a given electromagnetic disturbance emitted from a particular device, equipment,
system or disturbing installation as a whole, assessed and measured in a specified manner
3.10
emission limit
maximum emission level specified for a particular device, equipment, system or disturbing
installation as a whole
3.11
generating plant
any equipment that produces electricity together with any directly connected or associated
equipment such as a unit transformer or converter
3.12
immunity (to a disturbance)
ability of a device, equipment or system to perform without degradation in the presence of an
electromagnetic disturbance
3.13
immunity level
the maximum level of a given electromagnetic disturbance on a particular device, equipment
or system for which it remains capable of operating with a declared degree of performance

TR 61000-3-6 © IEC:2008(E) – 11 –
3.14
non-linear load or equipment (see also distorting installation)
any load or equipment that draws a non-sinusoidal current when energised by a sinusoidal
voltage
3.15
normal operating conditions
operating conditions of the system or of the disturbing installation typically including all
generation variations, load variations and reactive compensation or filter states (e.g. shunt
capacitor states), planned outages and arrangements during maintenance and construction
work, non-ideal operating conditions and normal contingencies under which the considered
system or the disturbing installation have been designed to operate
NOTE Normal system operating conditions typically exclude: conditions arising as a result of a fault or a
combination of faults beyond that planned for under the system security standard, exceptional situations and
unavoidable circumstances (for example: force majeure, exceptional weather conditions and other natural
disasters, acts by public authorities, industrial actions), cases where system users significantly exceed their
emission limits or do not comply with the connection requirements, and temporary generation or supply
arrangements adopted to maintain supply to customers during maintenance or construction work, where otherwise
supply would be interrupted.
3.16
planning level
level of a particular disturbance in a particular environment, adopted as a reference value for
the limits to be set for the emissions from the installations in a particular system, in order to
co-ordinate those limits with all the limits adopted for equipment and installations intended to
be connected to the power supply system
NOTE Planning levels are considered internal quality objectives to be specified at a local level by those
responsible for planning and operating the power supply system in the relevant area.
3.17
point of common coupling (PCC)
point in the public supply system, which is electrically closest to the installation concerned, at
which other installations are, or could be, connected. The PCC is a point located upstream of
the considered installation
NOTE A supply system is considered as being public in relation to its use, and not its ownership.
3.18
point of connection (POC)
point on a public power supply system where the installation under consideration is, or can be
connected
NOTE A supply system is considered as being public in relation to its use, and not its ownership.
3.19
point of evaluation (POE)
point on a public power supply system where the emission levels of a given installation are to
be assessed against the emission limits. This point can be the point of common coupling
(PCC) or the point of connection (POC) or any other point specified by the system operator or
owner or agreed upon
NOTE A supply system is considered as being public in relation to its use, and not its ownership.
3.20
short circuit power
a theoretical value expressed in MVA of the initial symmetrical three-phase short-circuit power
at a point on the supply system. It is defined as the product of the initial symmetrical short-
circuit current, the nominal system voltage and the factor √3 with the aperiodic component
(DC) being neglected
– 12 – TR 61000-3-6 © IEC:2008(E)
3.21
spur
a feeder branch off a main feeder (typically applied on MV and LV feeders)
3.22
supply system
all the lines, switchgear and transformers operating at various voltages which make up the
transmission systems and distribution systems to which customers’ installations are
connected
3.23
system operator or owner
the entity responsible for making technical connection agreements with customers who are
seeking connection of load or generation to a distribution or transmission system
3.24
transfer coefficient (influence coefficient)
the relative level of disturbance that can be transferred between two busbars or two parts of a
power system for various operating conditions
3.25
voltage unbalance (imbalance)
in a polyphase system, a condition in which the magnitudes of the phase voltages or the
phase angles between consecutive phases are not all equal (fundamental component)
[IEV 161-08-09 modified]
NOTE In three phase systems, the degree of the inequality is usually expressed as the ratio of the negative and
zero sequence components to the positive sequence component. In this technical report, voltage unbalance is
considered in relation to three-phase systems and negative sequence only.
3.26
phenomena related definitions
the definitions below that relate to harmonics are based on the analysis of system voltages or
currents by the Discrete Fourier Transform method (DFT). This is the practical application of
the Fourier transform as defined in IEV 101-13-09 [28]
NOTE 1 The Fourier Transform of a function of time, whether periodic or non-periodic, is a function in the
frequency domain and is referred to as the frequency spectrum of the time function, or simply spectrum. If the time
function is periodic the spectrum is constituted of discrete lines (or components). If the time function is not
periodic, the spectrum is a continuous function, indicating components at all frequencies.
NOTE 2 For simplicity the definitions given in this report refer only to (inter)harmonic components, however, these
should not be interpreted as a restriction on the use of other definitions given in other IEC documents, for example,
IEC 61000-4-7 [11] where the reference to (inter)harmonic groups or subgroups are more appropriate for
measuring rapidly varying signals.
3.26.1
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. For the purpose of this technical report, the
fundamental frequency is the same as the power supply frequency
NOTE In the case of a periodic function, the fundamental frequency is generally equal to the frequency
corresponding to the period of the function itself.
3.26.2
fundamental component
component whose frequency is the fundamental frequency

TR 61000-3-6 © IEC:2008(E) – 13 –
3.26.3
harmonic frequency
frequency which is an integer multiple of the fundamental frequency. The ratio of the harmonic
frequency to the fundamental frequency is the harmonic order (recommended notation: “h”)
3.26.4
harmonic component
any of the components having a harmonic frequency. For brevity, such a component may be
referred to simply as a harmonic
3.26.5
interharmonic frequency
any frequency which is not an integer multiple of the fundamental frequency
NOTE 1 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 In the case where m < 1 the term subharmonic frequency may be used.
3.26.6
interharmonic component
component having an interharmonic frequency. For brevity, such a component may be
referred to simply as an “interharmonic”
3.26.7
total harmonic distortion – THD
ratio of the r.m.s. value of the sum of all the harmonic components up to a specified order (H)
to the r.m.s. value of the fundamental component
H
⎛ ⎞
Q
h
⎜ ⎟
THD =
∑
⎜ ⎟
Q
⎝ 1⎠
h=2
where
Q represents either current or voltage,
Q is the r.m.s. value of the fundamental component,
h is the harmonic order,
Q is the r.m.s. value of the harmonic component of order h,
h
H is generally 40 or 50 depending on the application.
4 Basic EMC concepts related to harmonic distortion
The development of emission limits (voltage or current) for individual equipment or a
customer’s installation should be based on the effect that these emission limits will have on
the quality of the voltage. Some basic concepts are used to evaluate voltage quality. In order
for these concepts to be used for evaluation at specific locations, they are defined in terms of
where they apply (locations), how they are measured (measurement duration, sample times,
averaging durations, statistics), and how they are calculated. These concepts are described
hereafter and illustrated in Figures 1 and 2. Definitions may be found in IEC 60050(161).
4.1 Compatibility levels
These are reference values (see Table 1) for co-ordinating the emission and immunity of
equipment which is part of, or supplied by, a supply system in order to ensure the EMC in the
whole system (including system and connected equipment). Compatibility levels are generally
based on the 95 % probability levels of entire systems, using statistical distributions which
represent both time and space variations of disturbances. There is allowance for the fact that

– 14 – TR 61000-3-6 © IEC:2008(E)
the system operator or owner cannot control all points of a system at all times. Therefore,
evaluation with respect to compatibility levels should be made on a system-wide basis and no
assessment method is provided for evaluation at a specific location.
The compatibility levels for harmonic voltages in LV and MV systems are reproduced below
from references IEC 61000-2-2 [5] and IEC 61000-2-12 [6]. These compatibility levels shall be
understood to relate to quasi-stationary or steady-state harmonics, and are given as reference
values for both long-term effects and very-short-term effects.
– The long-term effects relate mainly to thermal effects on cables, transformers, motors,
capacitors, etc. They arise from harmonic levels that are sustained for 10 min or more.
– Very short-term effects relate mainly to disturbing effects on electronic devices that may
be susceptible to harmonic levels sustained for 3 s or less. Transients are not included.
With reference to long-term effects, the compatibility levels for individual harmonic
components of the voltage are given in Table 1. The compatibility level for the total harmonic
distortion is THD = 8 %.
Table 1 – Compatibility levels for individual harmonic voltages in low and medium
voltage networks (percent of fundamental component) reproduced from
IEC 61000-2-2 [5] and IEC 61000-2-12 [6]
Odd harmonics Odd harmonics
Even harmonics
non-multiple of 3 multiple of 3
Harmonic Harmonic Harmonic Harmonic Harmonic Harmonic
order voltage order voltage order voltage
h % h % h %
5 6 3 5 2 2
7 5 9 1,5 4 1
11 3,5 15 0,4 6 0,5
13 3 21 0,3 8 0,5
17 10
2,27 ⋅ − 0,27 0,2 0,25 ⋅ + 0,25
17≤ h ≤ 49 21< h ≤ 45 10 ≤ h ≤ 50
h h
NOTE The compatibility level for the total harmonic distortion is THD = 8 %.

With reference to the very-short term effects (3 s or less), the compatibility levels for
individual harmonic components of the voltage are the values given in Table 1 multiplied by a
factor k , where k is calculated as follows:
hvs
hvs
0,7
k = 1,3 + ⋅ (h − 5 )
(1)
hvs
The compatibility level for the total harmonic distortion for very short-term effects is THD =
11 %.
Compatibility levels are not defined in IEC for HV and EHV systems.
4.2 Planning levels
4.2.1 Indicative values of planning levels
These are harmonic voltage levels that can be used for the purpose of determining emission
limits, taking into consideration all distorting installations. Planning levels are specified by the
system operator or owner for all system voltage levels and can be considered as internal
quality objectives of the system operator or owner and may be made available to individual

TR 61000-3-6 © IEC:2008(E) – 15 –
customers on request. Planning levels for harmonics are equal to or lower than compatibility
levels and they should allow co-ordination of harmonic voltages between different voltage
levels. Only indicative values may be given because planning levels will differ from case to
case, depending on system structure and circumstances. Indicative values of planning levels
for harmonic voltages are shown in Table 2.
Table 2 – Indicative planning levels for harmonic voltages (in percent of the
fundamental voltage) in MV, HV and EHV power systems
Odd harmonics Odd harmonics
Even harmonics
non-multiple of 3 multiple of 3
Harmonic
Harmonic voltage Harmonic voltage
Harmonic Harmonic Harmonic
voltage
% %
order order order
%
h h h
MV HV-EHV MV HV-EHV MV HV-EHV
5 5 2 3 4 2 2 1,8 1,4
7 4 2 9 1,2 1 4 1 0,8
11 3 1,5 15 0,3 0,3 6 0,5 0,4
13 2,5 1,5 21 0,2 0,2 8 0,5 0,4
17 17 10 10
1,9 ⋅ − 0,2 0,2 0,2 0,25 ⋅ + 0,22 0,19 ⋅ + 0,16
17≤ h ≤ 49 1,2 ⋅ 21< h ≤ 45 10 ≤ h ≤ 50
h
h h h
The indicative planning levels for the total harmonic distortion are
THD = 6,5% and THD = 3 %
MV HV-EHV
NOTE 1 For some higher order harmonics, care should be exercised when specifying very low values such as
0,2 % because of practical limitations of measurement accuracy mainly at HV-EHV. Furthermore, depending on
system characteristics a margin should exist between MV, HV and EHV planning levels in order to allow
coordinating emission of disturbances between different voltage levels (measurement results can be used as a
basis to determine appropriate margin).
NOTE 2 The planning levels in Table 2 are not intended to control harmonics arising from exceptional events such
as geomagnetic storms, etc.
NOTE 3 In some countries, planning levels are defined in national standards or guidelines.
NOTE 4 Voltage characteristics that are quasi-guaranteed levels exist in some countries for MV and HV systems.
They are generally selected to be higher than the planning levels [7].
With reference to very short term effects of harmonics (3 s or less), planning levels for
individual harmonics should be multiplied by a factor k as given by Equation (1).
hvs
Where national circumstances make it appropriate depending on system characteristics,
intermediate values of planning levels may be needed between the MV, HV and EHV values
due to the possibly wide range of voltage levels included in HV-EHV (>35 kV). Additionally, an
apportioning of planning levels between HV and EHV may also be necessary to take account
of the impact on HV systems of disturbing installations connected at EHV. In this case,
planning levels at EHV
...