EN 61000-4-7:2002

SLOVENSKI SIST EN 61000-4-7:2003

STANDARD
december 2003
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
61000-4-7:2002)
ICS 33.100.20 Referenčna številka
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

EUROPEAN STANDARD EN 61000-4-7
NORME EUROPÉENNE
EUROPÄISCHE NORM October 2002

ICS 33.100.10; 33.100.20 Supersedes EN 61000-4-7:1993

English version
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 61000-4-7:2002)
Compatibilité électromagnétique (CEM) Elektromagnetische Verträglichkeit (EMV)
Partie 4-7: Techniques d'essai Teil 4-7: Prüf- und Messverfahren -
et de mesure - Allgemeiner Leitfaden für Verfahren
Guide général relatif aux mesures und Geräte zur Messung
d'harmoniques et d'interharmoniques, von Oberschwingungen und
ainsi qu'à l'appareillage de mesure, Zwischenharmonischen in
applicable aux réseaux d'alimentation Stromversorgungsnetzen und
et aux appareils qui y sont raccordés angeschlossenen Geräten
(CEI 61000-4-7:2002) (IEC 61000-4-7:2002)

This European Standard was approved by CENELEC on 2002-10-01. CENELEC members are bound to
comply with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European
Standard the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and
notified to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Czech Republic,
Denmark, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Luxembourg, Malta,
Netherlands, Norway, Portugal, Slovakia, Spain, Sweden, Switzerland and United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2002 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 61000-4-7:2002 E
Foreword
The text of document 77A/382/FDIS, future edition 2 of IEC 61000-4-7, prepared by SC 77A, Low
frequency phenomena, of IEC TC 77, Electromagnetic compatibility, was submitted to the
IEC-CENELEC parallel vote and was approved by CENELEC as EN 61000-4-7 on 2002-10-01.
This European Standard supersedes EN 61000-4-7:1993.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2003-07-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2005-10-01
Annexes designated "normative" are part of the body of the standard.
Annexes designated "informative" are given for information only.
In this standard, annex ZA is normative and annexes A, B and C are informative.
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61000-4-7:2002 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards
indicated:
IEC 61000-3 (Series) NOTE Partly harmonized in EN 61000-3 series (not modified).
IEC 61010-1 NOTE Harmonized as EN 61010-1:2001 (not modified).
__________
- 3 - EN 61000-4-7:2002
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
This European Standard incorporates by dated or undated reference, provisions from other
publications. These normative references are cited at the appropriate places in the text and the
publications are listed hereafter. For dated references, subsequent amendments to or revisions of any
of these publications apply to this European Standard only when incorporated in it by amendment or
revision. For undated references the latest edition of the publication referred to applies (including
amendments).
NOTE When an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
1)
IEC 60050-161 - International Electrotechnical - -
Vocabulary (IEV)
Chapter 161: Electromagnetic
compatibility
1) 2)
IEC 61000-3-2 - Electromagnetic compatibility (EMC) EN 61000-3-2 2000
Part 3-2: Limits - Limits for harmonic
current emissions (equipment input
current up to and including 16 A per
phase)
1) 2)
IEC 61967-1 - Integrated circuits - Measurement of EN 61967-1 2002
electromagnetic emissions, 150 kHz to
1 GHz
Part 1: General conditions and
definitions
1)
Undated reference.
2)
Valid edition at date of issue.

INTERNATIONAL IEC
STANDARD 61000-4-7
Second edition
2002-08
BASIC EMC PUBLICATION
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 2002 Copyright - all rights reserved
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 the publisher.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
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61000-4-7 © IEC:2002 – 3 –
CONTENTS
FOREWORD . 7
INTRODUCTION .11
1 Scope .13
2 Normative references.13
3 Definitions, symbols and indices .15
3.1 Definitions related to frequency analysis.15
3.2 Definitions related to harmonics.17
3.3 Definitions related to distortion factors.19
3.4 Definitions related to interharmonics.21
3.5 Notations .23
3.5.1 Symbols and abbreviations .23
3.5.2 Indices.25
4 General concepts and common requirements for all types of instrumentation.25
4.1 Characteristics of the signal to be measured .25
4.2 Accuracy classes of instrumentation .25
4.3 Types of measurement .25
4.4 General structure of the instrument.27
4.4.1 Main instrument .27
4.4.2 Post-processing parts .29
5 Harmonic measurements .31
5.1 Current input circuit .31
5.2 Voltage input circuit .31
5.3 Accuracy requirements .33
5.4 Measurement set-up for emission assessment.35
5.5 Assessment of harmonic emissions .37
5.5.1 Grouping and smoothing .39
5.5.2 Compliance with emission limits.41
5.6 Assessment of voltage harmonic subgroups .41
6 Other analysis principles.41
7 Transitional period .43
8 General .43
Annex A (informative) Measurement of interharmonics.45
Annex B (informative) Measurements above the harmonic frequency range up to 9 kHz.49
Annex C (informative) Technical considerations for grouping method .53
Bibliography.71
Figure 1 – General structure of the measuring instrument .29
Figure 2 – Measurement set-up for single-phase emission measurement .35
Figure 3 – Measurement set-up for three-phase emission measurements.35

61000-4-7 © IEC:2002 – 5 –
Figure 4 – Illustration of harmonic and interharmonic groups (shown here for a 50 Hz
supply) .39
-1
Figure 5 – Realisation of a digital low-pass filter: z designates a time window delay,
α and β are the filter coefficients (see table 2 for values) .39
Figure 6 – Illustration of a harmonic subgroup and an interharmonic centred subgroup
(of a 50 Hz supply).41
Figure B.1 – Illustration of frequency bands for measurement, in the range 2 kHz to
9 kHz .51
Figure C.1 – Large 5th harmonic current fluctuation .59
Figure C.2 – Large 5th harmonic voltage fluctuation.59
Figure C.3 – Fluctuating 3rd harmonic current of a micro-wave appliance .61
Figure C.4 – Communication signal of 178 Hz together with 3rd and 5th harmonics .63
Figure C.5 – Interharmonic at 287 Hz, 5th and 6th harmonic .63
Figure C.6 – Modulated 5th harmonic and interharmonic at 287 Hz .67
Figure C.7 – Component vectors at frequencies of 245 Hz and 255Hz.69
Table 1 – Accuracy requirements for current, voltage and power measurements .33
Table 2 – Smoothing filter coefficients according to the window width .43

61000-4-7 © IEC:2002 – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
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
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization
comprising all national electrotechnical committees (IEC National Committees). The object of the 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, the IEC publishes International Standards. 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. The 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 the 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 National Committees.
3) The documents produced have the form of recommendations for international use and are published in the
form of standards, technical specifications, technical reports or guides and they are accepted by the National
Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the
subject of patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61000-4-7 has been prepared by subcommittee 77A: Low
frequency phenomena, of IEC technical committee 77: Electromagnetic compatibility.
This standard forms part 4-7 of IEC 61000. It has the status of a basic EMC publication in
accordance with IEC Guide 107.
This second edition cancels and replaces the first edition published in 1991, and constitutes a
technical revision.
The text of this standard is based on the following documents:
FDIS Report on voting
77A/382/FDIS 77A/387/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 3.

61000-4-7 ” IEC:2002 – 9 –
Annexes A, B and C are for information only.
The committee has decided that the contents of this publication will remain unchanged until
2005. At this date, the publication will be
x reconfirmed;
x withdrawn;
x replaced by a revised edition, or
x amended.
The contents of the corrigendum of July 2004 have been included in this copy.

61000-4-7 © IEC:2002 – 11 –
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 the 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. Other will be published with the part number followed by a dash and a second
number identifying the subdivision (example: 61000-6-1).
These publications will be published in chronological order and numbered accordingly.
This part is an International Standard for the measurement of harmonic currents and voltages
in power supply systems and harmonic currents emitted by equipment. It also specifies the
performance of a standard measuring instrument.

61000-4-7 © IEC:2002 – 13 –
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
1 Scope
This part of IEC 61000 is applicable to instrumentation intended for measuring spectral
components in the frequency range up to 9 kHz which are superimposed on the fundamental
of the power supply systems at 50 Hz and 60 Hz. For practical considerations, this standard
distinguishes between harmonics, interharmonics and other components above the harmonic
frequency range, up to 9 kHz.
This standard defines the measurement instrumentation intended for testing individual items
of equipment in accordance with emission limits given in certain standards (for example,
harmonic current limits as given in IEC 61000-3-2) as well as for the measurement of
harmonic currents and voltages in actual supply systems. Instrumentation for measurements
above the harmonic frequency range, up to 9 kHz is tentatively defined (see Annex B).
NOTE 1 This document deals in detail with instruments based on the discrete Fourier transform.
NOTE 2 The description of the functions and structure of the measuring instruments in this standard is very
explicit and meant to be taken literally. This is due to the necessity of having reference instruments with
reproducible results irrespective of the characteristics of the input signals.
NOTE 3 The instrument is defined to accommodate measurements of harmonics up to the 50th order.
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
IEC 61000-3-2, Electromagnetic compatibility (EMC) – Part 3-2: Limits – Limits for harmonic
current emissions (equipment input current ≤16 A per phase)
IEC 61967-1, Integrated circuits – Measurement of electromagnetic emissions, 150 kHz to
1 GHz – Part 1: Measurement conditions and definitions
___________
To be published
61000-4-7 ” IEC:2002 – 15 –
3 Definitions, symbols and indices
For the purposes of this part of IEC 61000, the definitions given in IEC 60050-161 (IEV) and
the following, apply.
3.1 Definitions related to frequency analysis
Notations: The following notations are used in the present guide for the Fourier series
development because it is easier to measure phase angles by observations of the zero
crossings:
f
m
§·
ft() c c sin ZMt (1)
01¦mm
¨¸
N
©¹
m 1
­
cb ja ab
mm m m m
°
c
°
m
C
m
°
°
°
with:  (2)
§·
® a
m
M tarctan if b 0
¨¸
mm
°
b
©¹m
°
°
§·
a
m
°MS  arctan if b 0
mm¨¸
b
°
©¹m
¯
T
­ w
2 m
§ ·
°
b f (t)u sin¨ Z t¸ dt
m 1
³
° T N
© ¹
w
°
T
°
w
° 2 § m ·
and: a f (t)ucos Z t dt (3)
¨ ¸ ®
m 1
³
T N
© ¹
w
°
°
T
w
°
c f (t) dt
°
³
T
°
w
¯
where
Z is the angular frequency of the fundamental (Z = 2Sf );
1 1 1
T is the width (or duration) of the time window (T = NT ; T = 1/f ); the time window is
w w 1 1 1
that time span of a time function over which the Fourier transform is performed;
m
c is the amplitude of the component with frequency f f ;
m 1
m
N
N is the number of fundamental periods within the window width;
c is the d.c. component;
m is the ordinal number (order of the spectral line) related to the frequency basis
(f= 1/Tw).
61000-4-7 © IEC:2002 – 17 –
NOTE 1 Strictly speaking these definitions apply to steady-state signals only.
The Fourier series is actually in most cases performed digitally, i.e. as a discrete Fourier transform (DFT).
The analogue signal f(t) to be analysed is sampled, A/D-converted and stored. Each group of M samples forms a
time window on which DFT is performed. According to the principles of Fourier series expansion, the window width
T determines the frequency resolution f = 1/T (i.e. the frequency separation of the spectral lines) for the
w w w
analysis and thus the frequency basis for the result of the transform. Therefore, the window width T must be an
w
integer multiple N of the fundamental period T of the system voltage: T = N × T . The sampling rate is in this case
1 w 1
f = M/(NT ) (where M = number of samples within T ).
s 1 w
Before DFT-processing, the samples in the time window T are often weighted by multiplying them with a special
w
symmetrical function "windowing function"). However, for periodic signals and synchronous sampling, it is
preferable to use a rectangular weighting window which multiplies each sample by unity.
The DFT-processor yields the orthogonal Fourier-coefficients a and b of the corresponding harmonic frequencies
m m
i
f = m/T , m= 0, 1, 2.2 -1. However, only m values up to half of the maximum value are useful, the other half just
m w
duplicates them.
When there is sufficient synchronisation, the harmonic order n related to the fundamental frequency f is given by
n = m/N (N = number of periods in T .).
w
NOTE 2 The fast Fourier transform (FFT) is a special algorithm allowing short computation times. It requires that
i
the number of samples M be an integer power of 2, M = 2 , with i ≥ 10 for example.
3.2 Definitions related to harmonics
3.2.1
harmonic frequency
f
n
frequency which is an integer multiple of the power supply (fundamental) frequency
(f = n × f )
n 1
3.2.2
harmonic order
n
(integer) ratio of a harmonic frequency to the power-supply frequency. In connection with the
analysis using DFT and synchronisation between f and f (sampling rate), the harmonic order
1 s
n is given by n = k/N (k = number of the Fourier component, N = number of periods T in T )
1 w
3.2.3
r.m.s. value of a harmonic component
G
n
r.m.s. value of one of the components having a harmonic frequency in the analysis of a non-
sinusoidal waveform
For brevity, such a component may be referred to simply as a 'harmonic'
NOTE 1 The harmonic component G is identical with the spectral component C with k = N × n; (G = C ). It is
n k n Nn
replaced, as required, by the symbol I for currents or by the symbol U for voltages.
n n
NOTE 2 The symbol C represents the r.m.s. value of the spectral component C for m = k in equation 2.
k m
NOTE 3 For the purposes of this standard, the time window has a width of N = 10 (50 Hz systems) or N = 12
(60 Hz systems) fundamental periods, i.e. approximately 200 ms (see 4.4.1). This yields G = C (50 Hz systems)
n 10n
and G = C (60 Hz systems).
n n
61000-4-7 © IEC:2002 – 19 –
3.2.4
r.m.s. value of a harmonic group
G
g,n
square root of the sum of the squares of the r.m.s. value of a harmonic and the spectral
components adjacent to it within the time window, thus summing the energy contents of the
neighbouring lines with that of the harmonic proper. See also equation 8 and figure 4. The
harmonic order is given by the harmonic considered
3.2.5
r.m.s. value of a harmonic subgroup
G
sg,n
square root of the sum of the squares of the r.m.s. value of a harmonic and the two spectral
components immediately adjacent to it. For the purpose of including the effect of voltage
fluctuation during voltage surveys, a subgroup of output components of the DFT is obtained
by summing the energy contents of the frequency components directly adjacent to a harmonic
with that of the harmonic proper. (See also equation 9 and figure 6.) The harmonic order is
given by the harmonic considered
3.3 Definitions related to distortion factors
3.3.1
total harmonic distortion
THD
THD (symb.)
ratio of the r.m.s. value of the sum of all the harmonic components (G ) up to a specified
n
order (H) to the r.m.s. value of the fundamental component (G ):
H
§·G
n
THD = (4)
¦¨¸
G
n=2
©¹1
NOTE 1 The symbol G represents the r.m.s. value of the harmonic component (see 3.2.3). It is replaced, as required, by
the symbol I for currents or by the symbol U for voltages.
NOTE 2 The value of H is defined in each standard concerned with limits (IEC 61000-3 series).
3.3.2
group total harmonic distortion
THD
THDG (symb.)
ratio of the r.m.s. value of the harmonic groups (g) to the r.m.s. value of the group associated
with the fundamental:
H
§·G
gn
THDG = (5)
¨¸
¦
¨¸
G
n=2
g1
©¹
61000-4-7 © IEC:2002 – 21 –
3.3.3
subgroup total harmonic distortion
THDS
THDS (symb.)
ratio of the r.m.s. value of the harmonic subgroups (sg) to the r.m.s. value of the subgroup
associated with the fundamental:
H
§·
G
sgn
THDS = (6)
¨¸
¦
¨¸
G
n=2 sg1
©¹
3.3.4
partial weighted harmonic distortion
PWHD
PWHD (symb.)
ratio of the r.m.s. value, weighted with the harmonic order n, of a selected group of higher
order harmonics (from the order H to H to the r.m.s. value of the fundamental:
min max
H
max
§·G
n
PWHD = n (7)
¦ ¨¸
G
nH=
©¹1
min
NOTE 1 The concept of partial weighted harmonic distortion is introduced to allow for the possibility of specifying
a single limit for the aggregation of higher order harmonic components.The partial weighted group harmonic
distortion can be evaluated by replacing the quantity G by the quantity G . The partial weighted subgroup
n g,n
harmonic distortion can be evaluated by replacing the quantity G by the quantity G .
n sg,n
NOTE 2 The values of H and H are defined in each standard concerned with limits (IEC 61000-3-series).
min max
NOTE 3 PWHD is defined in this standard because it is used in IEC 61000-3-4 and in IEC 61000-3-2 Ed. 2 with
amendment 1.
3.4 Definitions related to interharmonics
3.4.1
r.m.s. value of an interharmonic component
r.m.s. value of a spectral component of an electrical signal with a frequency between two
consecutive harmonic frequencies (see figure 4)
NOTE 1 The frequency of the interharmonic component is given by the frequency of the spectral line. This
frequency is not an integer multiple of the fundamental frequency.
NOTE 2 The frequency interval between two consecutive spectral lines is the inverse of the width of the time
window, approximately 5 Hz for the purposes of this standard.
NOTE 3 For the purposes of this standard, the interharmonic component is assumed to be the spectral
component C for k ≠ n × N.
k
3.4.2
r.m.s. value of an interharmonic group
C
ig,n
r.m.s. value of all interharmonic components in the interval between two consecutive
harmonic frequencies (see figure 4)
NOTE For the purposes of this standard, the r.m.s. value of the interharmonic group between the harmonic orders
n and n + 1 is designated as 'C '; for example, the group between n = 5 and n = 6 is designated as C .
ig,n ig,5
61000-4-7 © IEC:2002 – 23 –
3.4.3
r.m.s. value of an interharmonic centred subgroup
C
isg,n
r.m.s. value of all interharmonic components in the interval between two consecutive
harmonic frequencies, excluding frequency components directly adjacent to the harmonic
frequencies (see figure 6)
NOTE For the purposes of this standard, the r.m.s. value of the centred subgroup between the harmonic orders n
and n + 1 is designated as 'C '; for example, the centred subgroup between n = 5 and n = 6 is designated as
isg,n
C .
isg,5
3.4.4
interharmonic group frequency
f
ig,n
mean of the two harmonic frequencies between which the group is situated
3.4.5
interharmonic centred subgroup frequency
f
isg,n
mean of the two harmonic frequencies between which the subgroup is situated
3.5 Notations
3.5.1 Symbols and abbreviations
In this standard, voltage and current values are r.m.s. unless otherwise stated.
a amplitude coefficient of a sine component in a Fourier series
b amplitude coefficient of a cosine component in a Fourier series
c amplitude coefficient in a Fourier series
d distortion factor
f frequency; function
f
1 fundamental frequency
f sampling rate
s
j − 1
p value of a cumulative probability function, expressed as a percentage
t running time
x sampled value
B bandwidth
C r.m.s. value of the spectral line
D weighted distortion factor
Fc frequency component
H the order of the highest harmonic that is taken into account
Hz hertz
I current (r.m.s. value)
K number of windows in 3-s interval
M integer number; number of samples within the window width
N number of periods within the window width
P power
PCC point of common coupling
T time interval
T fundamental period
T NT (window width)
w 1
U voltage (r.m.s. value)
61000-4-7 © IEC:2002 – 25 –
ω angular frequency
ω angular frequency of the fundamental
ϕ phase angle
3.5.2 Indices
b centre-band frequency
i running-integer number
k running-integer number
m measured value; spectral content of order m (not necessarily integer)
max maximum value
min minimum value
n harmonic order: running number (integer)
g,n harmonic group order associated with harmonic order n
g,1 harmonic group order associated with the fundamental
sg,n harmonic subgroup order associated with harmonic order n
sg,1 harmonic subgroup order associated with the fundamental
ig,n interharmonic group above harmonic order n
isg,n interharmonic centred subgroup above harmonic order n
nom nominal value
r rated value
s sampled; synchronised
1 fundamental
4 General concepts and common requirements for all types of instrumentation
4.1 Characteristics of the signal to be measured
Instruments for the following types of measurement are considered:
a) harmonic emission measurement;
b) interharmonic emission measurement;
c) measurements above the harmonic frequency range up to 9 kHz.
Strictly speaking, harmonic measurements can be performed only on a stationary signal;
fluctuating signals (signals varying with time) cannot be described correctly by their
harmonics only. However, in order to obtain results that are inter-comparable, a simplified and
reproducible approach is given for fluctuating signals.
4.2 Accuracy classes of instrumentation
Two classes of accuracy (I and II) are considered, to permit the use of simple and low-cost
instruments, consistent with the requirements of the application. For emission tests, the upper
class I is required if the emissions are near to the limit values (see also note 2 of table 1).
4.3 Types of measurement
Requirements for harmonic and interharmonic measurements are given. Measurements in the
frequency range up to 9 kHz are also considered.

61000-4-7 © IEC:2002 – 27 –
4.4 General structure of the instrument
New designs of instrument are likely to use the discrete Fourier transform (DFT), normally
using a fast algorithm called fast Fourier transform (FFT). Therefore this standard considers
only this architecture but does not exclude other analysis principles (see clause 6).
The general structure is represented in figure 1. An instrument may or may not comprise all
the blocks and outputs given.
4.4.1 Main instrument
The main instrument comprises
– input circuits with anti-aliasing filter,
– A/D-converter including sample-and-hold unit,
– synchronisation and window-shaping unit if necessary,
– DFT-processor providing the Fourier coefficients a and b ("OUT 1").
m m
It is complemented by the special parts devoted to current assessment and/or voltage
assessment.
NOTE 1 For further details, see 5.5.
NOTE 2 For the analysis of harmonics and interharmonics, the signal f(t) which has to be analysed is pre-treated
to eliminate frequencies higher than the operating range of the instrument.
For full compliance with this standard, the window width shall be 10 (50 Hz systems) or 12
(60 Hz systems) periods with rectangular weighting (see also clause 7). Hanning weighting is
allowed only in the case of loss of synchronisation. This loss of synchronisation shall be
indicated on the instrument display and the data so acquired shall be flagged.
The time window shall be synchronised with each group of 10 or 12 cycles according to the
power system frequency of 50 Hz or 60 Hz. The time between the leading edge of the first
sampling pulse and the leading edge of the (M+1)th sampling pulse (where M is the number of
samples; see 3.5.1) shall be equal to the duration of the specified number of cycles of the
power system, with a maximum permissible error of ±0,03%. Instruments including a phase-
locked loop or other synchronisation means shall meet the requirements for accuracy and
synchronisation for measuring at any signal frequency within a range of at least ±5% of the
nominal system frequency. However, for instruments having integrated supply sources, so
that the source and measurement systems are inherently synchronised, the requirement for a
working input frequency range does not apply, provided the requirements for synchronisation
and frequency accuracy are met.
The output (OUT 1, see figure 1) shall provide the individual coefficients a and b of the
m m
DFT, for the current or voltage, i.e. the value of each frequency component calculated.

61000-4-7 © IEC:2002 – 29 –
Sampling
frequency
generation
Input
Preprocessing
voltage
Sampling
Main instrument
DFT
Out 1
conversion
Input
Preprocessing
current
Grouping
Input for
active power
Out 2a
see note 1
Smoothing
Out 2b
Check for
compliance
Out 3
IEC  1950/02
Figure 1 – General structure of the measuring instrument
A further output, not necessarily from the DFT, shall provide the active power P evaluated
over the same time window used for the harmonics. For the harmonic emission measurements
according to IEC 61000-3-2, this power shall not include the d.c. component.
NOTE 3 The active power P is provided as input to the smoothing process, not to the grouping process.
NOTE 4 Measurement of the d.c. components and of the power associated with them may be included as an
option but is not required by this standard.
4.4.2 Post-processing parts
As required by emission standards, additional operations on the raw data like smoothing and
weighing of the raw results are performed in successive parts of the instrument.
If output values are to be related to a corresponding value (fundamental, declared or nominal
values), this normalization shall be performed only after these additional smoothing
procedures.
61000-4-7 © IEC:2002 – 31 –
5 Harmonic measurements
5.1 Current input circuit
The input circuit shall be suitable for the currents to be analysed. It shall provide a direct
measurement of the harmonic currents and, in addition, should have a low-voltage high-
impedance voltage input which may be associated with external resistive shunts (or a
combination of current transformers with resistive shunts). Appropriate input circuit
sensitivities range from 0,1 V to 10 V, with 0,1 V being the preferred value, provided they
comply with the requirements given in 5.3.
NOTE For current measurements directly in the circuit, it may be advisable, but is not required, to provide the
following nominal r.m.s. input current measurement ranges I : 0,1 A ; 0,2 A ; 0,5 A ; 1 A ; 2 A ; 5 A ; 10 A ; 20 A ;
nom
50 A ; 100 A.
The power absorption of the current input circuit shall not exceed 3 VA for class II
instrumentation. For class I instrumentation, the r.m.s. input voltage drop shall not exceed
0,15 V.
Each current input circuit shall be able to be continuously stressed by 1,2 I and a
nom
stressing by 10 I for 1 s shall not lead to any damage.
nom
The instrument shall be able to accept input signals with a crest factor up to 4 for the ranges
up to 5 A r.m.s., 3,5 for the 10 A r.m.s. range and 2,5 for higher ranges.
An overload indication is required.
The overall accuracy requirements are stated in table 1.
For other requirements, see clause 8.
NOTE A d.c. component is often associated with the distorted current to be measured; such a d.c. component
may produce large errors in input current transformers. The manufacturer should indicate in the instrumentation
specifications the maximum allowed d.c. component so that the additional influence error does not exceed the
stated accuracy.
5.2 Voltage input circuit
The input circuit of the measuring instrument shall be suitable for the maximum voltage and
the frequency of the supply voltage to be analysed and shall keep its characteristics and
accuracy unchanged up to 1,2 times the maximum voltage. A crest factor of at least 1,5 is
sufficient for measurements, except for highly distorted voltages in industrial networks, for
which a crest factor of at least 2 may be necessary. An overload indication is required in any
case.
Stressing the input for 1 s by an a.c. voltage of four times the input voltage setting or 1 kV
r.m.s., whichever is less, shall not lead to any damage in the instrument.
Many nominal supply voltages between 60 V and 690 V exist, depending on local practice. To
permit a relatively universal use of the instrument for most supply systems, it may be
advisable for the input circuit to be designed for the following nominal voltages:
U : 66 V, 115 V, 230 V, 400 V, 690 V for 50 Hz systems
nom
U : 69 V, 120 V, 240 V, 277 V, 347 V, 480 V, 600 V for 60 Hz systems.
nom
61000-4-7 © IEC:2002 – 33 –
NOTE 1 In association with external voltage transformers, additional ranges may also be useful (100 V, 100/√3 V,
110/√3 V)
NOTE 2 Inputs with higher sensitivity (0,1 V; 1 V; 10 V) are useful for operation with external sensors. The input
circuit should be capable of accepting an input signal with a crest factor of at least 2.
The power absorption of the input circuit shall not exceed 0,5 VA at 230 V. If high-sensitivity
inputs (less than 50 V) are provided, their input resistance shall be at least 10 kΩ/V.
Care should be taken that the high value of the fundamental (supply frequency) voltage as
compared to the other voltage components to be measured does not produce overload
causing damage or intermodulation signals in the input stages of the instrument. Errors so
caused shall be below the stated accuracy. An overload indication shall be provided.
5.3 Accuracy requirements
Two classes of accuracy are suggested for instrumentation measuring harmonic components.
The maximum allowable errors given in table 1 refer to single-frequency and steady-state
signals, in the operating frequency range, applied to the instrument under rated operating
conditions to be indicated by the manufacturer (temperature range, humidity range, instrument
supply voltage, etc.).
NOTE When testing appliances according to IEC 61000-3-2, the uncertainty terms are related to the permissible
limits (5 % of the permissible limits) or to the rated current (I ) of the tested appliance (0,15 % I ), whichever is
r r
greater. This should be considered when choosing the proper input current range of the measuring instrument.
Table 1 – Accuracy requirements for current, voltage and power measurements
Class Measurement Conditions Maximum error
Voltage
U ≥ 1% U ±5% U
m nom m
U < 1% U
m nom
±0,05% U
nom
I Current
I ≥ 3% I ±5% I
m nom m
I < 3% I
m nom
±0,15% I
nom
Power
P ≥ 150 W ±1% P
m nom
P < 150 W ±1,5 W
m
Voltage
U ≥ 3% U ±5% U
m nom m
U < 3% U
m nom ±0,15% U
II
nom
Current
I ≥ 10 % I ±5% I
m nom m
I < 10 % I
m nom
±0,5% I
nom
I : Nominal current range of the measurement instrument
nom
U : Nominal voltage range of the measurement instrument
nom
U and I : Measured values
m m
NOTE 1 Class I instruments are recommended where precise measurements are
necessary, such as for verifying compliance with standards, resolving disputes, etc. Any
two instruments that comply with the requirements of Class I, when connected to the
same signals, produce matching results within the specified accuracy (or indicate an
overload condition).
NOTE 2 Class I instruments are recommended for emission measurements, Class II is
recommended for general surveys, but can also be used for emission measurements if
the values are such that, even allowing for the increased uncertainty, it is clear that the
limits are not exceeded. In practice, this means that the measured values should be
lower than 90% of the allowed limits.
NOTE 3 Additionally, for Class I instruments, the phase shift between individual
channels should be smaller than n × 1º.

61000-4-7 © IEC:2002 – 35 –
Frequencies outside the measuring range of the instrument shall be attenuated so as not to
affect the results. To obtain the appropriate attenuation, the instrument may sample the input
signal at a frequency much higher than the measuring range. For example, the analysed
signal may have components exceeding 25 kHz, but only components up to 2 kHz are taken
into account. An anti-aliasing low-pass filter, with a –3 dB frequency above the measuring
range shall be provided. The attenuation in the stop-band shall exceed 50 dB.
NOTE For example, a 5th order Butterworth filter achieves 50 dB attenuation at approximately three times the
-3 dB frequency.
When it is necessary to assess harmonics with an order greater than 15 and with a rated
current greater than 5 A with the minimum uncertainty, it is advisable to use external shunts
or current sensors matched to give a range equal to the rated current of the tested equipment.
For instrumentation intended for measuring harmonics only, the accuracy requirements apply
to harmonic components only.
To achieve the accuracy stated in table 1 some simple adjustment of the instrument,
according to clear indications to be given by the manufacturer, by means of an internal or
external calibrator may be required. The uncertainty of the calibrator (if internal) shall be
specified.
The errors due to the most important influence factors (temperature, auxiliary mains supply
voltage, etc.) shall be indicated by the manufacturer for the instrument itself and for the
internal calibrator if it is provided.
5.4 Measurement set-up for emission assessment
The measurement set-up is given in figures 2 and 3.
Key
U
∆
L
U Source voltage line-neutral
S
L
S
U EUT terminal voltage
O
Z
L
U E
Z Impedance of wiring and current sensing part
L,N
U
U
S
R U
EUT Equipment under test
Z
N
C T
E
∆U Voltage drop across Z and Z (∆U=∆U +∆U )
N L N L N
∆U
N
L Line connection
IEC  1951/02
N Neutral connection
Fig
...