SIST IEC/TR 61000-2-7:1999

SLOVENSKI STANDARD
SIST IEC/TR 61000-2-7:1999
01-april-1999
Electromagnetic compatibilty (EMC) – Part 2: Environment – Section 7: Low
frequency magnetic fields in various environments
Electromagnetic compatibility (EMC) - Part 2: Environment - Section 7: Low frequency
magnetic fields in various environments
Compatibilité électromagntique (CEM) - Partie 2: Environnement - Section 7: Champs
magnétiques basse fréquence en environnements divers
Ta slovenski standard je istoveten z: IEC/TR 61000-2-7
ICS:
33.100.99 Drugi vidiki v zvezi z EMC Other aspects related to
EMC
SIST IEC/TR 61000-2-7:1999 en
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST IEC/TR 61000-2-7:1999

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SIST IEC/TR 61000-2-7:1999
RAPPORT
CEI
TECHNIQUE – TYPE 3
IEC
61000-2-7
TECHNICAL
Première édition
REPORT – TYPE 3
First edition
1998-01
Compatibilité électromagnétique (CEM) –
Partie 2:
Environnement –
Section 7: Champs magnétiques basse fréquence
en environnements divers
Electromagnetic compatibility (EMC) –
Part 2:
Environment –
Section 7: Low frequency magnetic fields
in various environments
 IEC 1998 Droits de reproduction réservés  Copyright - all rights reserved
Aucune partie de cette publication ne peut être reproduite ni No part of this publication may be reproduced or utilized in
utilisée sous quelque forme que ce soit et par aucun any form or by any means, electronic or mechanical,
procédé, électronique ou mécanique, y compris la photo- including photocopying and microfilm, without permission in
copie et les microfilms, sans l'accord écrit de l'éditeur. writing from the publisher.
International Electrotechnical Commission 3, rue de Varembé Geneva, Switzerland
Telefax: +41 22 919 0300 e-mail: inmail@iec.ch IEC web site http: //www.iec.ch
CODE PRIX
Commission Electrotechnique Internationale
PRICE CODE V
International Electrotechnical Commission
Pour prix, voir catalogue en vigueur
For price, see current catalogue

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SIST IEC/TR 61000-2-7:1999
61000-2-7 © IEC:1998 – 3 –
CONTENTS
Page
FOREWORD . 5
INTRODUCTION . 9
Clause
1 Scope. 11
2 Normative reference. 11
3 Units. 11
4 Natural phenomena. 13
5 Power supply system environments – Power frequency magnetic fields . 21
5.1 Overhead lines. 21
5.1.1 AC, three-phase lines . 21
5.1.2 HVDC lines. 29
5.2 Underground cables. 31
5.2.1 Single-conductor cables. 31
5.2.2 Multi-conductor cables . 35
5.3 Power supply authorities' medium and high voltage premises . 37
5.4 Power supply authorities' low voltage premises . 41
6 Traction system environment . 43
7 Industrial environment. 47
7.1 Welding equipment. 47
7.2 Steel furnaces. 49
7.3 Industrial equipment in general use. 51
8 Commercial office environment . 53
9 Residential environment – Household appliances . 55
9.1 Internal wiring in residential buildings. 55
9.2 Residential appliances. 57
10 Hospital environment. 61
10.1 General. 61
10.2 Treatment of patients. 61
10.3 Ward areas . 63
11 Summary and comparisons of the magnetic fields produced by various sources . 63
12 Bibliography. 69

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SIST IEC/TR 61000-2-7:1999
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INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
ELECTROMAGNETIC COMPATIBILITY (EMC) –
Part 2: Environment –
Section 7: Low frequency magnetic fields
in various environments
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 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.
The main task of IEC technical committees is to prepare International Standards. In
exceptional circumstances, a technical committee may propose the publication of a technical
report of one of the following types:
• type 1, when the required support cannot be obtained for the publication of an
International Standard, despite repeated efforts;
• type 2, when the subject is still under technical development or where for any other
reason there is the future but no immediate possibility of an agreement on an International
Standard;
• type 3, when a technical committee has collected data of a different kind from that
which is normally published as an International Standard, for example "state of the art".
Technical reports of types 1 and 2 are subject to review within three years of publication to
decide whether they can be transformed into International Standards. Technical reports of
type 3 do not necessarily have to be reviewed until the data they provide are considered to be
no longer valid or useful.
IEC 61000-2-7, which is a technical report of type 3, has been prepared by subcommittee 77A:
Low frequency phenomena, of IEC technical committee 77: Electromagnetic Compatibility.

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SIST IEC/TR 61000-2-7:1999
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The text of this technical report is based on the following documents:
Committee draft Report on voting
77A/134/CDV 77A/151A/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.
This document is issued in the type 3 technical report series of publications (according to
G.3.2.3 of part 1 of the IEC/ISO Directives) as a purely informative document.
This document is not to be regarded as an International Standard.

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SIST IEC/TR 61000-2-7:1999
61000-2-7 © IEC:1998 – 9 –
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 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 sections which are to be published either as International
Standards or as technical reports.
These standards and reports will be published in chronological order and numbered
accordingly.
This section is a technical report of type 3.

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SIST IEC/TR 61000-2-7:1999
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ELECTROMAGNETIC COMPATIBILITY (EMC) –
Part 2: Environment –
Section 7: Low frequency magnetic fields
in various environments
1 Scope
Interest in magnetic fields has been stimulated in recent years by concern over the
physiological effects they may have on humans and animals and the deleterious effects they
have on the performance of some electrical equipment, particularly video display units.
Investigations have yielded results which are presented in this report as reference values.
Note 1 – The European Union EMC Directive has prompted magnetic field measurements, particularly in respect of
the commercial office environments associated with supply authority substations and electrical distribution systems
within buildings. Supply authorities have sponsored most of the work and the results are generally within the
frequency range of 50 Hz to 2 kHz, and presented as r.m.s. values. There is, however, a need to have some
knowledge about d.c. fields and the fields up to 150 kHz as they may interfere with some types of equipment.
Note 2 – Most of the magnetic field data in this report is associated with sinusoidal current sources and r.m.s.
values may be assumed unless otherwise stated.
Power supply systems operating at voltages less than or equal to 1 000 V are designated low-voltage, those above
1 000 V and up to 35 kV are designated medium-voltage, and those in excess of 35 kV are designated high-voltage.
2 Normative reference
The following normative document contains provisions which, through reference in this text,
constitute provisions of this technical report. At the time of publication, the edition indicated
was valid. All normative documents are subject to revision, and parties to agreements based
on this technical report are encouraged to investigate the possibility of applying the most recent
edition of the normative document indicated below. Members of IEC and ISO maintain registers
of currently valid International Standards.
IEC 60050(161):1990, International Electrotechnical Vocabulary (IEV) – Chapter 161: Electro-
magnetic compatibility.
3 Units
Magnetic field values in this report are either expressed in field strengths of amperes per
metre, A/m, or in flux densities of microtesla, μT. Where the older flux density unit of
milligauss, mG, has appeared in reference documents it has been converted to μT by the
following relationship:
1 μT = 10 mG ≈ 0,796 A/m
The following units are applied in the present report:
Magnetic field strength: H in A/m
Magnetic flux density: B = μ × H in T (Tesla)
–6
whereby the permeability μ =μ × μ and μ = 1,256⋅10 (Wb/Am)
r 0 0
in air the relative permeability μ = 1 and B (μT) = 1,256 H (A/m)
r
2
4 –9
NOTE – 1 T = 1 Wb/m = 10 G and B = 1,256·10 G (in air)

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SIST IEC/TR 61000-2-7:1999
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Example: Magnetic field of a single conductor
The relationship between the magnetic field strength and magnetic induction at a distance d
from a single conductor carrying a current I is given by the following expressions:
I
H = (A/m)
2πd
I
B = 1,256 (μT)
2dπ
I
d
IEC  1 527/97
An alternating current produces an alternating magnetic field, and in the case of a multi-phase
cable or overhead line, the alternating magnetic field rotates as it results from the vector sum
of the fields produced by individual phase currents.
An alternating magnetic field will induce an electromotive force in any electrical conductor to
which it is exposed. This effect is utilised by meters which have search coils. Such meters are
in common use.
Other types of meter used for low frequency measurements utilise the Hall effect. These
meters are not so good for measuring the fields from environmental sources, but they are very
useful when measuring points in space and static magnetic fields.
4 Natural phenomena
Three kinds of natural magnetic fields have to be considered:
– the earth’s magnetic field (a static field);
– magnetic fields produced by thunderstorms and solar activity (time-varying with very low
frequencies);
– magnetic fields caused by lightning strokes (pulses).
The first measurements and use of magnetic fields related to navigation and intense study of
the earth's magnetic fields has resulted in the production of field maps, an example of which is
*
given in figure 1 [1] . All unscreened conductors moving in the earth's magnetic field will
generate a voltage across their ends of a magnitude related to the speed and direction of
movement. Such voltage may disturb sensitive electronic devices in associated circuits. Static
electrical equipment is not normally affected by the earth's field.
___________
*
 Figures in square brackets refer to the bibliography.

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SIST IEC/TR 61000-2-7:1999
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The earth's static magnetic field is nearly always present as a steady state background reading
at 0 Hz to site measurements. Near the poles flux densities are as high as 60 μT whilst at the
equator they are only 30 μT.
A normal value assumed for the purpose of calculations is 50 μT [1]. See figure 1.
IEC  1 528/97
Figure 1 – The earth's total magnetic field at the surface in μT
Natural phenomena, such as thunderstorms and solar activity, produce time-varying magnetic
fields in the extra-low-frequency range. Such fields are generally of low strength, up to 0,01 μT
(8 mA/m), although during intense magnetic storms, they can reach intensities of about 0,5 μT
(0,4 A/m).
Very little data is available regarding the number of lightning strokes that a particular location
may receive in a year. However the ceraunic map in figure 2 [2] does indicate the level of
activity and the probability of the highest fields being achieved.

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SIST IEC/TR 61000-2-7:1999
61000-2-7 © IEC:1998 – 17 –
IEC  1 529/97
Figure 2 – Map showing thunderstorm days per year throughout the world
NOTE – This map is based on information of the World Meteorological Organization for 1955.

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SIST IEC/TR 61000-2-7:1999
61000-2-7 © IEC:1998 – 19 –
Probability
99,99
99,95
99,9
99,8
99,5
99
98
97
95
90
80
70
60
50
Positive strokes
40
30
20
Negative strokes
10
5
2
1
0,5
0,2
0,1
0,05
0,02
1      2   3  4 5 6 7 8 10     2   3  4 5 6 7 100     2  3  4 5 6 7  1 000
Lightning stroke current in kA
IEC  1 530/97
Figure 3 – Cumulative frequency of lightning current from IEC 61024-1-1
The following reference values for the cumulative frequency of lightning current (see figure 3):
Negative stroke Positive stroke
5 % 80 kA 250 kA
50 % 33 kA 35 kA
95 % 7 kA 5 kA
The lightning stroke creates magnetic field pulses with a rise time of about 1 μs and a mid-
magnetic duration of about 100 μs.
The resulting magnetic field can be calculated according to the relationship:
I
H =  e.g. with I = 200 kA and d = 1 km: H = 32 A/m and B = 40 μT
peak
2πd

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SIST IEC/TR 61000-2-7:1999
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5 Power supply system environments – Power frequency magnetic fields
Magnetic field values relevant to power supply systems are dependent on the load current at
the time measurements are taken, the system voltage, which determines the clearances of
overhead line conductors to ground, and the depth and construction of underground cables.
Wherever possible, the values stated in this section have been referenced to the system
voltage and maximum load conditions, or expressed in terms per kiloampere, kA, of conductor
current.
5.1 Overhead lines
Magnetic fields produced by current flowing through electricity distribution overhead lines are
influenced principally by the magnitude of the current, the electrical phase configuration and
the physical configuration of the conductors. The voltage at which a power line operates is
significant because it determines the height of conductors above ground and also the phase
separation between conductors and to earthed metal used for construction purposes.
There are so many system voltages, conductor current ratings and construction standards in
use throughout the world that magnetic field data cannot be provided for every particular type
of installation. However, the typical installations and magnetic field characteristics that are
defined in the following text are good models on which to base predictions of fields for other
particular installations.
If detailed values of flux density for particular lines are required, it would be necessary to
consider the conditions of the individual lines such as wire configurations, height above ground
and line current. The following approximate formula applies:
e
e
H = 140 in A/m for 1 kA
22
hx+
where:
e is the distance between external conductors;
h
h is the height above ground;
P
x
x is the distance from central conductor to the
point P to be considered.
IEC  1 531/97
5.1.1 AC, three-phase lines
As the flux densities associated with power lines are linearly related to line current it is easy to
deduce values for particular values of current. The maximum line currents under normal
operating conditions are approximately as follows:

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SIST IEC/TR 61000-2-7:1999
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– low voltage lines 0,4 kA
– medium voltage lines 0,6 kA
– 110 kV and 220 kV lines 1,0 kA
– 380 kV lines 2,0 kA
– 750 kV lines 3,0 kA
If necessary, more accurate current values may be obtained from supply utilities and railway
companies. However, under fault conditions such as single phase or double phase short
circuits, the magnetic fields of three conductors are not balanced, and the magnetic field may
be increased by a factor of 20; such conditions may be expected to endure for a few seconds
for low and medium voltage networks and for less than 0,2 seconds for high voltage networks.
Figure 4, left side, shows the envelope of the profile of the maximum magnetic flux density per
kA of line current, for high voltage, single three-phase transmission lines, at mid-span at a
distance x from the centre of the conductor system, and at a height of 1 m from ground level
based on VDE data [3].
Figure 4, right side, shows the envelope of the profile of the magnetic flux density per kA of line
current for medium and low voltage single three-phase distribution lines operating at 20 and
0,4 kV respectively, at a distance x from the centre of the conductor system at mid-span, and
at a height of 1 m from ground level based on VDE data [3].
It can be observed that the profile curves:
– are lower at higher voltages because of the higher levels of the conductors above ground,
– and become broader at higher voltages because of the increasing distance between the
conductors.
The actual magnetic flux density depends on the line current. Referring to the envelope profiles
in figure 4 and to the maximum line currents given above, the range of the actual maximum
magnetic flux is summarized in table 1; it indicates a range of 3 μT to 44 μT.
The magnetic flux profile depends also on the line configuration. Figure 5 [4] shows practical
examples of actual high voltage lines (with an “oscillation” of the maximum value).
The 765 kV and 400 kV lines have a flat configuration of three phases and the 132 kV and
220 kV lines have a trifoil configuration. The latter configuration leads to significantly lower
magnetic field values.
Figure 6 [3] shows the dependence of the magnetic flux density on the height above ground at
mid-span of the lines considered in figure 4. It may be used to deduce the magnetic flux
density at heights above ground in excess of 1 m by application of the values given in figure 4.

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SIST IEC/TR 61000-2-7:1999
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Transmission lines Distribution lines
B μT
110 kV - 380 kV 35
0,4 kV - 20 kV
110 kV 30
(6 m)
220 kV
25
(7 m)
380 kV
(8 m)
20 kV
20
15
10
0,4 kV
5
m     40      30      20      10      0      10      20      30      40      m
Distance from the centre of the line
IEC  1 532/97
Figure 4 – Envelope of the maximum magnetic flux of single circuit, flat configuration overhead
lines measured horizontally from the centre of the line 1 m above ground level
at minimum ground clearances at mid-span
Table 1 – Range of magnitude of the maximum magnetic flux density
produced by power lines
Line voltage Maximum flux per kA Maximum current Maximum actual
magnetic flux
kV B μT kA B μT
380 22 2 44
220 25 1 25
110 30 1 30
20 20 0,6 12
0,4 7 0,4 3

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SIST IEC/TR 61000-2-7:1999
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Magnetic flux density μT
 132 kV              220 kV          400 kV                765 kV
 375 A               1 000 A         1 500 A                2 100 A
25
765 kV
20
400 kV
15
10
220 kV
5
132 kV
0
-40        -30       -20       -10        0         10        20        30        40
Distance from centre of line (metres)
IEC  1 533/97
Figure 5 – Examples of magnetic flux densities, 1 m above ground,
associated with HV lines under average load conditions

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SIST IEC/TR 61000-2-7:1999
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240
400 V
%
220
20 kV
200
110 kV
Magnetic flux
density B Factor (%)
180
220 kV
160
140
380 kV
120
100
1                1,5                 2                   2,5                    3
Height above ground 'h' (m)
IEC  1 534/97
Figure 6 – Dependence of the magnetic flux density on the height above ground up to the
minimum permitted distance from 400 V to 380 kV three-phase lines and 20 kV railway contact
wires at minimum ground clearances in mid-span referred to the maximum magnetic flux density
at 1 m above ground and valid only for flat configuration of phase conductors
5.1.2 HVDC lines
Figure 7 [3] gives magnetic flux density characteristics of typical high-voltage d.c. overhead
lines and figure 6 [3] gives the multiplying factors in terms of percentage for reference points at
height h m above ground level. All the d.c. characteristics are used in the same manner as the
a.c. line characteristics.
Earth wire
Earth wire
40
+ -
16,20 m
35
h in metres
Line measurement
Line measurement
30
Magnetic flux
25
density B
Bipolar HVDC line
Monopolar HVDC line
μT/kA
20
15
10
5
0
-50     -40     -30     -20     -10     0      10      20     30     40      50  (m)
Distance
IEC  1 535/97
Figure 7 – Curve of the magnetic flux density per kA operating current in the vicinity
of a high-voltage d.c. overhead line with an operating voltage of +450 kV or ±450 kV
at a point 1 m above the ground

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SIST IEC/TR 61000-2-7:1999
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Table 2 – Magnetic flux density in μT per kA operating current of high-voltage overhead lines
at various line voltages and tower heights
Monopolar line Bipolar line
Voltage Height Max. Distance Distance Max. Distance Distance
kV m
–10 m –20 m ±10 m ±20 m
250 23 31 25 13 31 15 5
450 30 25 23 14 25 19 8
600 30 21 21 10 21 18 9
5.2 Underground cables
5.2.1 Single-conductor cables
Table 3 gives typical environment flux densities for locations associated with supply networks
having single-conductor cable systems.
Table 3 – Typical magnetic flux density in μT, associated
with supply network single-conductor cable systems
Horizontal distance from installation
Supply network 0 m 10 m 20 m 30 m
240/415 V house supplies 1,3 0,3
Less than 0,1 μT
66 kV distribution supply 2,1 0,7 0,3 0,1
220 kV cable 15,0 0,6 0,2 Less than 0,1
220 kV overhead double circuit 5,0 1,2 0,2 Less than 0,1
For the flat configuration shown in figure 8, and for different depths (h) and spacings (a)
between the individual cables, without taking account of the screening effect on the cable
sheaths, the magnetic flux densities shown in table 4 are representative of typical values
associated with an operating current of 500 A per phase. The reference point x = 0 m, from
which location distances are measured, is assigned to the centre cable.

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SIST IEC/TR 61000-2-7:1999
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0
+ x
- x
h
a
IEC  1 536/97
Figure 8 – Configuration of single-conductor cables laid in flat formation
Similar fields to those defined in this section occur in the vicinity of low-voltage flat
configuration cables connected to medium voltage transformers installed within buildings, and
main distribution cables forming part of consumers' electrical installations.
Figure 9 [3] gives a qualitative curve of magnetic flux densities on the basis of values in
table 4, line 5, and demonstrates the reductions achieved by laying cables at greater depth and
reduced spacing.
200
%
180
160
140
2   = 0,7 mh
Magnetic flux
120
density B
100
1   = 1,0 mh
80
60
40
3   = 1,7 mh
20
0
10     8      6     4     2     0     2      4     6      8     10
-    Distance (metres)    +x x
IEC  1 537/97
Figure 9 – Comparison of magnetic flux density characteristics of single core cables laid at
depths of 0,7 m (curve 2), 1,7 m (curve 3), with a cable laid at a depth of 1 m (curve 1)
Magnetic flux densities are expressed as a percentage of the maximum value associated with
curve 1. The cable configuration is as figure 9 with dimensions corresponding to table 4, line 5.

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SIST IEC/TR 61000-2-7:1999
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Table 4 – Magnetic flux densities of three-phase systems with single-conductor cables
in flat configuration at operating currents of 500 A (figure 8 refers)
Cable Depth Spacing between Magnetic flux density
h μT
diameter the individual
conductor cables
a
at distance +x or –x from the centre of the cable
mm m
m
024 68 10
1 0,02 8,6 1,7 0,5 0,2 0,1 0,09
0,03 0,7 0,02 17,6 1,9 0,5 0,2 0,1 0,09
(LV 1 0,05 13,8 2,8 0,8 0,4 0,2 0,1
MV) 0,7 0,05 28 3,1 0,8 0,4 0,2 0,1
1* 0,07* 17,2 3,5 1 0,5 0,3 0,2
0,7 0,07 34,7 3,9 1,1 0,5 0,3 0,2
0,1 1,7 0,18 17,5 7,6 2,8 1,3 0,8 0,5
(HV) 1 0,18 48,5 10,5 3,1 1,4 0,8 0,5
* See figure 9.
The magnetic flux densities can be converted on a linear basis for other operating currents.
With bundled single-conductor cables in a triangular configuration, the magnetic flux densities
are approximately the same as multi-conductor cables with three-phase conductors.
5.2.2 Multi-conductor cables
Tables 5 and 6 [3] contain magnetic flux densi
...