IEC TR 61000-3-13:2008

IEC/TR 61000-3-13
Edition 1.0 2008-02
TECHNICAL
REPORT
BASIC EMC PUBLICATION
Electromagnetic compatibility (EMC) –
Part 3-13: Limits – Assessment of emission limits for the connection of
unbalanced installations to MV, HV and EHV power systems

IEC/TR 61000-3-13:2008(E)
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IEC/TR 61000-3-13
Edition 1.0 2008-02
TECHNICAL
REPORT
BASIC EMC PUBLICATION
Electromagnetic compatibility (EMC) –
Part 3-13: Limits – Assessment of emission limits for the connection of
unbalanced installations to MV, HV and EHV power systems

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
X
CODE PRIX
ICS 33.100.10 ISBN 2-8318-9607-X

– 2 – TR 61000-3-13 © 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 voltage unbalance.14
4.1 Compatibility levels .14
4.2 Planning levels.15
4.2.1 Indicative values of planning levels.15
4.2.2 Assessment procedure for evaluation against planning levels.15
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 .19
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 unbalance emission level.20
6.3 Assessment of emission levels from unbalanced installations.21
7 General summation law .21
8 Emission limits for unbalanced installations in MV systems .22
8.1 Stage 1: simplified evaluation of disturbance emission .22
8.2 Stage 2: emission limits relative to actual system characteristics.23
8.2.1 Global emission to be shared between the sources of unbalance .23
8.2.2 Individual emission limits .24
8.3 Stage 3: acceptance of higher emission levels on a conditional basis.26
8.4 Summary diagram of the evaluation procedure .27
9 Emission limits for unbalanced installations in HV or EHV systems.29
9.1 Stage 1: simplified evaluation of disturbance emission .29
9.2 Stage 2: emission limits relative to actual system characteristics.29
9.2.1 Assessment of the total available power .29
9.2.2 Individual emission limits .30
9.3 Stage 3: acceptance of higher emission levels on a conditional basis.32

Annex A (informative) Guidance for setting planning levels and emission limits .33
Annex B (informative) Calculation examples for determining emission limits .38
Annex C (informative) List of principal letter symbols, subscripts and symbols.39

Bibliography.41

TR 61000-3-13 © 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 /U and its contribution to the
2i 1
measured unbalance at the point of evaluation. .20
Figure 4 – Example of a system for sharing global contribution at MV.23
Figure 5 – Diagram of evaluation procedure.28
Figure 6 – Determination of S for a simple HV or EHV system.29
t
Figure 7 – Determination of S for a meshed HV or EHV system .30
t
Figure A.1 – The reduction factor T as a function of the factors k k , and k .36
,
uML m s sc
Figure A.2 – Example of unbalance ratio measurement for a remote mine with largely
motor loading.36

Table 1 – Compatibility levels for voltage unbalance in low and medium voltage
systems reproduced from references IEC 61000-2-2 and IEC 61000-2-12 .14
Table 2 – Indicative values of planning levels for voltage unbalance (negative-
sequence component) in MV, HV and EHV power systems .15
Table 3 – Indicative value of exponent for the summation of general unbalanced
installations .22
Table A.1 – Portion of unbalance for accounting for the system inherent asymmetries .34
Table A.2 – Summation of unbalance from different sources .35
Table A.3 – Range of values of planning levels given different parameters .37

– 4 – TR 61000-3-13 © IEC:2008(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
ELECTROMAGNETIC COMPATIBILITY (EMC) –

Part 3-13: Limits –
Assessment of emission limits for the connection of
unbalanced 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
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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
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Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
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4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
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between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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6) All users should ensure that they have the latest edition of this publication.
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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 61000-3-13, which is a technical report, has been prepared by subcommittee 77A:
Low frequency phenomena, of IEC technical committee 77: Electromagnetic compatibility.
.
It has the status of a basic EMC publication in accordance with IEC Guide 107 [12]
This first edition of this technical report has been harmonised with IEC/TR 61000-3-6 [10] and
IEC/TR 61000-3-7 [11].
___________
Figures in square brackets refer to the bibliography.

TR 61000-3-13 © IEC:2008(E) – 5 –
The text of this technical report is based on the following documents:
Enquiry draft Report on voting
77A/577/DTR 77A/616/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.
The contents of the corrigendum of April 2010 have been included in this copy.

– 6 – TR 61000-3-13 © 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 61000-3-13 © 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, a technical report concerning emission
limits for the connection of unbalanced 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. Addition survey data was also collected by the Joint Working Group in
the process of setting indicative planning levels.
Subsequent endorsement of the document by IEC was the responsibility of SC 77A.

– 8 – TR 61000-3-13 © IEC:2008(E)
ELECTROMAGNETIC COMPATIBILITY (EMC) –

Part 3-13: Limits –
Assessment of emission limits for the connection of
unbalanced installations to MV, HV and EHV power systems

1 Scope
This part of IEC 61000 provides guidance on principles which can be used as the basis for
determining the requirements for the connection of unbalanced installations (i.e. three-phase
installations causing voltage unbalance) to MV, HV and EHV public power systems (LV
installations are covered in other IEC documents). For the purposes of this report, an
unbalanced installation means a three-phase installation (which may be a load or a generator)
that produces voltage unbalance on the system. The connection of single-phase installations
is not specifically addressed, as the connection of such installations is under the control of the
system operator or owner. The general principles however may be adapted when considering
the connection of single-phase installations. 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 unbalanced load 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
installations which may cause unbalance on the system. The disturbing installation is to be
understood as the complete customer’s installation (i.e. including balanced and unbalanced
parts).
Problems related to unbalance fall into two basic categories.
• Unbalanced installations that draw negative-sequence currents which produce negative-
sequence voltages on the supply system. Examples of such installations include arc
furnaces and traction loads (typically connected to the public network at HV), and three
phase installations where the individual loads are not balanced (typically connected at MV
and LV). Negative-sequence voltage superimposed onto the terminal voltage of rotating
machines can produce additional heat losses. Negative-sequence voltage can also cause
rd
non-characteristic harmonics (typically positive-sequence 3 harmonic) to be produced by
power converters.
• Unbalanced installations connected line-to-neutral can also draw zero-sequence currents
which can be transferred or not into the supply system depending on the type of
connection of the coupling transformer. The flow of zero-sequence currents in a grounded
neutral system causes zero-sequence unbalance affecting line-to-neutral voltages. This is
not normally controlled by setting emission limits, but rather by system design and
maintenance. Ungrounded-neutral systems and phase-to-phase connected installations
are not, however, affected by this kind of voltage unbalance.

TR 61000-3-13 © IEC:2008(E) – 9 –
This report gives guidance only for the coordination of the negative-sequence type of voltage
unbalance between different voltage levels in order to meet the compatibility levels at the
point of utilisation. No compatibility levels are defined for zero-sequence type of voltage
unbalance as this is often considered as being less relevant to the coordination of unbalance
levels compared to the first type of voltage unbalance. However, for situations where a non-
zero impedance exists between neutral and earth with the system still being effectively
grounded (i.e., where the ratio between zero-sequence, X and positive sequence reactance
X is 0 < X /X ≤ 3), this type of voltage unbalance can be of concern especially when the type
1 0 1
of connection of the coupling transformer allows zero-sequence path to flow from MV to LV
and vice-versa.
NOTE The boundaries between the various voltage levels may be different for different countries (see
IEV 601 01-28) [9]. This report uses the following terms for system voltage:
– 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 purpose of this part of IEC 61000, 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
a 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
– 10 – TR 61000-3-13 © IEC:2008(E)
3.5
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 [7].
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.
3.6
(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.
3.7
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 cause voltage unbalance due to unequal currents on the three phases.
3.8
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
3.9
emission limit
maximum emission level specified for a particular device, equipment, system or disturbing
installation as a whole
3.10
generating plant
any equipment that produces electricity together with any directly connected or associated
equipment such as a unit transformer or converter
3.11
immunity (to a disturbance)
the ability of a device, equipment or system to perform without degradation in the presence of
an electromagnetic disturbance

TR 61000-3-13 © IEC:2008(E) – 11 –
3.12
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
3.13
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 disturbing installation has 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
3.14
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.
3.15
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.
3.16
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.
3.17
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.
3.18
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 61000-3-13 © IEC:2008(E)
3.19
spur
feeder branch off a main feeder (typically applied on MV and LV feeders)
3.20
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
3.21
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
3.22
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
3.23
transposition
a change of the relative positions of the phase conductors of the line
3.24
unbalanced installation
a customer’s installation as a whole (i.e. including balanced and unbalanced parts) which is
characterized according to its operation by unequal line currents, either magnitude and/or
phase angle, which can give rise to voltage unbalance on the supply system. For the purpose
of this report, all references to unbalanced installations do not only include loads, but
generating plants as well
NOTE For the purpose of this report, all references to unbalanced installations not only include loads, but also
generating plants.
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 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 unbalance are based on the analysis of system voltages or
currents by Fortescue’s transformation matrix and the Discrete Fourier Transform method
(DFT) for the purpose of extracting the fundamental frequency components for the calculation
of the unbalance factor. (The DFT is the practical application of the Fourier transform as
defined in IEV 101-13-09 [8]).
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 of the
function itself.
TR 61000-3-13 © IEC:2008(E) – 13 –
3.26.2
fundamental component
component whose frequency is the fundamental frequency
3.26.3
positive-sequence component of 3-phase voltages (or currents)
defined as the symmetrical vector system derived by application of the Fortescue’s
transformation matrix, and that rotates in the same direction as the power frequency voltage
(or current). This is given mathematically by:
1 1 3
U =  (U + a ·U + a ·U ) where and U , U , U are line to neutral
a =1∠120° = − + j
1 a b c a b c
3 2 2
voltages (fundamental component)
NOTE Phase-to-phase voltages may also be used.
3.26.4
negative-sequence component of 3-phase voltages (or currents)
defined as the symmetrical vector system derived by application of the Fortescue’s
transformation matrix, and that rotates in the opposite direction to the power frequency
voltage (or current). This is given mathematically by:
1 1 3
U = (U + a ·U + a ·U) where and U , U , U are line to neutral
2 a b c a =1∠120° = − + j a b c
3 2 2
voltages (fundamental component)
NOTE Phase-to-phase voltages may also be used.
3.26.5
zero-sequence component of 3-phase voltages (or currents)
defined as the in-phase symmetrical vector system derived by application of the Fortescue’s
transformation matrix. This is given mathematically by:
U = (U + U + U ) where U , U , U are line to neutral voltages (fundamental component).
0 a b c a b c
NOTE Phase-to-phase voltages cannot be used as the zero-sequence component in this case will be zero.
3.26.6
voltage unbalance factor (u)
defined as the ratio of the modulus of the negative-sequence to the positive-sequence
components of the voltage at fundamental frequency, expressed as a percentage
Ua +a Ub +aUc
U
u = .100 = .100 %
U
Ua +aUb +a Uc
NOTE Phase-to-phase voltages may also be used instead of line to neutral voltages
NOTE For simplicity in this document u has been used to denote the voltage unbalance factor instead of u .
An equivalent formulation is given by [3]:
4 4 4
U + U + U
ab bc ca
1− 3 − 6β
u = .100% with β =
2 2 2
1+ 3 − 6β
⎛ ⎞
U + U + U
⎜ ⎟
ab bc ca
⎝ ⎠
– 14 – TR 61000-3-13 © IEC:2008(E)
3.26.7
current unbalance factor (IUF)
defined as the ratio of modulus of the negative-sequence to the positive-sequence
components of the current at fundamental frequency
I a +a I b +a I c
I 2
i = .100 = .100 %
I 1 I a +a I b +a I c
4 Basic EMC concepts related to voltage unbalance
The development of emission limits for individual equipment or a customer’s total installation
should be based on the effect that these emissions 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 IEV 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
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 voltage unbalance in LV and MV systems are reproduced in
Table 1 from references IEC 61000-2-2 [1] and IEC 61000-2-12 [2].
Table 1 – Compatibility levels for voltage unbalance in low and medium
voltage systems reproduced from references IEC 61000-2-2 and IEC 61000-2-12
Voltage unbalance factor
C and C (%)
uLV uMV
2 %*
*Up to 3 % may occur in some
areas where predominantly single-
phase loads are connected.
NOTE 1 It is also worthwhile noting that the above compatibility levels refer to steady state heating effects of
voltage unbalance. Higher values may be recorded over a short period of time (100 % of voltage unbalance during
a short-circuit, for example), but these short-duration high unbalance levels do not necessarily produce a
significant heating effect on equipment.
NOTE 2 The specification of unbalance protection requirements within installations should take the compatibility
level and the instantaneous unbalance effects into consideration.
NOTE 3 The level of 3 % may occur typically on LV networks and MV networks which supply smaller installations
by connecting these at single-phase (or between phases).
Compatibility levels are not defined by IEC for HV and EHV systems.

TR 61000-3-13 © IEC:2008(E) – 15 –
4.2 Planning levels
4.2.1 Indicative values of planning levels
These are voltage unbalance levels that can be used for the purpose of determining emission
limits, taking into consideration all unbalanced 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
customers on request. Planning levels for voltage unbalance are equal to or lower than
compatibility levels and they should allow coordination of voltage unbalances 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 voltage unbalance are shown in Table 2.
Table 2 – Indicative values of planning levels for voltage unbalance
(negative-sequence component) in MV, HV and EHV power systems

Planning level
Voltage level
L (%)
u2
MV 1,8
HV 1,4
EHV 0,8
NOTE 1 The above indicative values allow that a contribution from LV customers and unbalanced installations
can be accommodated for a compatibility level of 2 % at LV (see Table 1). For MV systems where a 3 %
compatibility level applies (i.e.1,5 times the 2 % compatibility level), the value of the planning level can be selected
as 1,5 times the planning level indicated in Table 2 (i.e. a value of 2,7).
NOTE 2 The above indicative values are based on transfer coefficients of 0,9 from MV to LV and of 0,95 from HV
to MV, and a summation law exponent of 1,4. The allocation is based on an equal share of unbalance contribution
at each of the voltage levels. A discussion is provided in Annex A on how more appropriate planning levels can be
defined for a specific system. In some countries, the allocation may not be equal between voltage levels.
NOTE 3 The planning levels in Table 2 are not intended to control unbalance arising from uncontrollable or
exceptional events such as equipment malfunctions, short-circuits, switching operations, etc.
NOTE 4 In some countries, planning levels are defined in national standards or guidelines.
NOTE 5 Voltage characteristics exist in some countries for MV, HV and EHV systems that are quasi-guaranteed
levels (e.g. 2 % for HV and MV systems and 1,5 % for EHV systems). These should be coordinated with the
planning levels. In considering these, the nature of the system should be taken into consideration (e.g. HV AC
traction supplies).
NOTE 6 For the purpose of rating equipment or apparatus in a customer’s installation, the declared supply voltage
characteristics have to be considered.
Where national circumstances make it appropriate depending on system characteristics,
intermediate values of planning levels may be needed between the MV and HV values, and
between HV and EHV values as well due to the possibly wide range of voltage levels included
in those.
The remainder of this report outlines procedures for using these planning levels to establish
the emission limits for individual customers unbalanced installations.
4.2.2 Assessment procedure for evaluation against planning levels
The measurement method to be used for voltage unbalance measurements is the class A
method specified in IEC 61000-4-30 [3]. The data flagged in accordance with this standard
should be removed from the assessment. For clarity, where data is flagged the percentile
used in calculating the indices defined below is calculated using only the valid (unflagged)
data.
– 16 – TR 61000-3-13 © IEC:2008(E)
The minimum measurement period is one week with normal business activity. The monitoring
period should include some part of the period of expected maximum voltage unbalance levels.
One or more of the following indices may be used to compare the actual unbalance levels with
the planning levels. More than one index may be needed for planning levels in order to
assess the impact of higher emission levels allowed for short periods of time such as during
bursts or start-up conditions.
− The 95 % weekly value of u (voltage unbalance factor at fundamental frequency over
2sh
"short" 10 min periods) should not exceed the planning level.
− The greatest 99 % probability daily value of u (voltage unbalance factor at fundamental
2vs
frequency over "very short" 3
...