Measurement of DC magnetic, AC magnetic and AC electric fields from 1 Hz to 100 kHz with regard to exposure of human beings - Part 2: Basic standard for measurements

IEC 61786-2:2014 provides requirements for the measurement of quasi-static magnetic and electric fields that have a frequency content in the range 1 Hz to 100 kHz, and DC magnetic fields, to evaluate the exposure levels of the human body to these fields. Specifically, this standard gives requirements for establishing measurement procedures that achieve defined goals pertaining to human exposure. Because of differences in the characteristics of the fields from sources in the various environments, e.g. frequency content, temporal and spatial variations, polarization, and magnitude, and differences in the goals of the measurements, the specific measurement procedures will be different in the various environments. Sources of fields include devices that operate at power frequencies and produce power frequency and power-frequency harmonic fields, as well as devices that produce fields independent of the power frequency, and DC power transmission, and the geomagnetic field. The magnitude ranges covered by this standard are 0,1 micro-Tesla to 200 mili-Tesla for AC (1 micro-Tesla to 10 Tesla for DC) for magnetic fields, and 1 V/m to 50 kV/m for electric fields. When measurements outside this range are performed, most of the provisions of this standard will still apply, but special attention should be paid to the specified uncertainty and calibration procedures. Examples of sources of fields that can be measured with this standard include:
- devices that operate at power frequencies (50/60 Hz) and produce power frequency and power-frequency harmonic fields (examples: power lines, electric appliances...);
- devices that produce fields that are independent of the power frequency.(Examples: electric railway (DC to 20 kHz);
- commercial aeroplanes (400 Hz), induction heaters (up to 100 kHz), and electric vehicles);
- and devices that produces static magnetic fields: MRI, DC power lines, DC welding, electrolysis, magnets, electric furnaces, etc. DC currents are often generated by converters, which also create AC components (power frequency harmonics), which should be assessed. When EMF products standards are available, these products standards should be used. With regard to electric field measurements, this standard considers only the measurement of the unperturbed electric field strength at a point in space (i.e. the electric field prior to the introduction of the field meter and operator) or on conducting surfaces. Sources of uncertainty during measurements are also identified and guidance is provided on how they should be combined to determine total measurement uncertainty.

Mesure de champs magnétiques continus et de champs magnétiques et électriques alternatifs dans la plage de fréquences de 1 Hz à 100 kHz dans leur rapport à l'exposition humaine - Partie 2: Norme de base pour les mesures

L'IEC 61786-2:2014 fournit des exigences pour la mesure des valeurs des champs magnétiques et électriques quasi-statiques avec un contenu fréquentiel compris entre 1 Hz et 100 kHz ainsi que des champs magnétiques continus, permettant d'évaluer les niveaux d'exposition du corps humain à ces champs. De manière spécifique, la présente norme donne les exigences relatives à la mise en place de procédures de mesure permettant d'atteindre les objectifs définis quant à l'exposition humaine. Compte tenu des différences de caractéristiques des champs par rapport aux sources dans les divers environnements (contenu fréquentiel, variations temporelles et spatiales, polarisation et amplitude, par exemple) et des différences d'objectifs des mesures, les procédures de mesure spécifiques sont différentes selon les environnements. Parmi les sources de champs figurent des dispositifs qui fonctionnent aux fréquences industrielles et qui produisent des champs à ces fréquences et aux fréquences harmoniques, ainsi que des dispositifs produisant des champs indépendants de la fréquence industrielle, la transmission d'énergie en courant continu, et le champ magnétique statique terrestre. Les plages d'amplitudes couvertes par la présente norme vont respectivement de 0,1 micro-Tesla à 200 mili-Tesla en alternatif (1 micro-Tesla à 10 Tesla en continu) pour les champs magnétiques et de 1 V/m à 50 kV/m pour les champs électriques. Si des mesures hors de cette plage sont réalisées, la plupart des dispositions de la présente norme s'appliquent toujours, mais il convient de veiller particulièrement à l'incertitude spécifiée et aux procédures d'étalonnage. Par exemple, les sources de champs qui peuvent être mesurées avec la présente norme sont:
- les dispositifs fonctionnant aux fréquences industrielles (50/60 Hz) et générant des champs de fréquence industrielle et des harmoniques de ces fréquences (exemples: lignes d'énergie, appareils électriques...);
- les dispositifs générant des champs indépendants de la fréquence industrielle. (Exemples: voie de chemin de fer électrifiée (du continu à 20 kHz), avions de ligne (400 Hz), les appareils de chauffage par induction (jusqu'à 100 kHz) et les véhicules électriques);
- et les dispositifs générant des champs magnétiques statiques: imagerie par résonance magnétique (IRM), lignes d'énergie à courant continu, soudage par courant continu, électrolyse, aimants, fours électriques, etc. Les courants continus sont souvent générés par des convertisseurs, qui créent également des composantes alternatives (harmoniques à fréquence industrielle), qu'il convient d'évaluer. Si des normes de produit concernant les champs électromagnétiques sont disponibles, il convient de les utiliser. Eu égard aux mesures de champs électriques, la présente norme considère uniquement la mesure du champ électrique non perturbé en un point de l'espace (c'est-à-dire le champ électrique avant l'introduction du mesureur du champ et de l'opérateur) ou sur des surfaces conductrices. Les sources d'incertitude pendant les mesures sont également identifiées, et des lignes directrices sont fournies quant à la manière dont il convient de les combiner afin de déterminer l'incertitude de mesure totale.

Merjenje enosmernih in izmeničnih magnetnih polj ter izmeničnih električnih polj od 1 Hz do 100 kHz glede na izpostavljenost ljudi - 2. del: Osnovni standard za meritve

Standard IEC 61786-2:2014 podaja zahteve za meritve navidezno statičnih magnetnih in električnih polj, katerih frekvenčni delež je v razponu od 1 Hz do 100 kHz, in enosmernih magnetnih polj, s čimer se ovrednoti ravni izpostavljenosti človeškega telesa tem poljem. Natančneje, ta standard določa zahteve za vzpostavitev merilnih postopkov, ki dosegajo določene cilje, ki se nanašajo na izpostavljenost ljudi. Zaradi razlik v lastnostih polj iz virov v različnih okoljih, npr. frekvenčne vsebine, časovnih in prostorskih sprememb, polarizacije in velikosti ter razlik v ciljih meritev, bodo posebni merilni postopki različni v različnih okoljih. Viri polj zajemajo tako naprave, ki delujejo na omrežnih frekvencah ter proizvajajo omrežne frekvence in harmonična polja omrežnih frekvenc, kot tudi naprave, ki proizvajajo polja neodvisno od omrežne frekvence in prenos moči enosmernega toka ter geomagnetno polje. Obsegi magnitude, ki jih zajema ta standard, so 0,1 mikrotesla do 200 militesla za izmenični tok (1 mikrotesla do 10 tesla za enosmerni tok) za magnetna polja in 1 V/m do 50 kV/m za električna polja. Če je meritev zunaj tega razpona, se večina določil iz tega standarda še vedno uporablja, vendar naj bi posebno pozornost posvetili določenim postopkom negotovosti in kalibriranja. Primeri virov polj, ki jih je mogoče meriti s tem standardom, so:
- naprave, ki delujejo pri omrežnih frekvencah (50/60 Hz) in proizvajajo omrežno frekvenco in harmonična polja omrežnih frekvenc (primeri: napajalni vodi, električni aparati ...);
- naprave, ki proizvajajo polja, ki so neodvisna od omrežne frekvence.(Primeri: električna železnica (enosmerni tok do 20 kHz);
- komercialna letala (400 Hz), indukcijski grelci (do 100 kHz) in električna vozila);
- in naprave, ki proizvajajo statična magnetna polja: slikanje z magnetno resonanco (MRI), napajalne vodi enosmernega toka, varjenje enosmernega toka, elektroliza, magneti, električne pečice itd. Enosmerne tokove pogosto proizvajajo pretvorniki, ki prav tako ustvarjajo komponente izmeničnega toka (obratovalna frekvenca harmonike), ki naj bi jih ocenili. Kadar so na voljo standardi izdelkov elektromagnetnega sevanja (EMF), naj bi uporabili te standarde izdelkov. Ta standard z vidika merjenja električnega polja upošteva le merjenje nespremenjene jakosti električnega polja v točki v prostoru (tj. električno polje pred uvedbo merilnika in meritelja) ali na prevodnih površinah. Opredeljeni so tudi viri negotovosti med meritvami in zagotovljena so navodila o tem, kako jih je treba združiti, da bi določili skupno merilno negotovost.

General Information

Status
Published
Publication Date
19-Sep-2017
Current Stage
6060 - National Implementation/Publication (Adopted Project)
Start Date
19-Sep-2017
Due Date
24-Nov-2017
Completion Date
20-Sep-2017

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SLOVENSKI STANDARD
SIST IEC 61786-2:2017
01-oktober-2017
0HUMHQMHHQRVPHUQLKLQL]PHQLþQLKPDJQHWQLKSROMWHUL]PHQLþQLKHOHNWULþQLKSROM
RG+]GRN+]JOHGHQDL]SRVWDYOMHQRVWOMXGLGHO2VQRYQLVWDQGDUG]D
PHULWYH

Measurement of DC magnetic, AC magnetic and AC electric fields from 1 Hz to 100 kHz

with regard to exposure of human beings - Part 2: Basic standard for measurements

Mesure de champs magnétiques continus et de champs magnétiques et électriques
alternatifs dans la plage de fréquences de 1 Hz à 100 kHz dans leur rapport à
l'exposition humaine - Partie 2: Norme de base pour les mesures
Ta slovenski standard je istoveten z: IEC 61786-2
ICS:
17.220.20 0HUMHQMHHOHNWULþQLKLQ Measurement of electrical
PDJQHWQLKYHOLþLQ and magnetic quantities
SIST IEC 61786-2:2017 en

2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST IEC 61786-2:2017
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SIST IEC 61786-2:2017
IEC 61786-2
Edition 1.0 2014-12
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Measurement of DC magnetic, AC magnetic and AC electric fields from 1 Hz to
100 kHz with regard to exposure of human beings –
Part 2: Basic standard for measurements
Mesure de champs magnétiques continus et de champs magnétiques et
électriques alternatifs dans la plage de fréquences de 1 Hz a 100 kHz dans leur
rapport à l'exposition humaine –
Partie 2: Norme de base pour les mesures
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
CODE PRIX W
ICS 17.220.20 ISBN 978-2-8322-1970-6

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
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SIST IEC 61786-2:2017
– 2 – IEC 61786-2:2014 © IEC 2014
CONTENTS

FOREWORD ........................................................................................................................... 4

1 Scope .............................................................................................................................. 6

2 Normative references ...................................................................................................... 7

3 Terms and definitions ...................................................................................................... 7

4 General considerations .................................................................................................... 8

4.1 Different goals of measurement .............................................................................. 8

4.1.1 General ............................................................................................................ 8

4.1.2 Characterisation of field levels for compliance with safety standards ................ 9

4.1.3 Characterisation of spatial variations ................................................................ 9

4.1.4 Characterisation of temporal variation ............................................................ 11

4.1.5 Characterisation of frequency content in magnetic field or electric field .......... 12

4.1.6 Characterisation of population exposure to magnetic field and definition

of metric ......................................................................................................... 13

4.2 Sources with multiple frequencies ......................................................................... 14

4.2.1 General .......................................................................................................... 14

4.2.2 Sum of weighted magnitudes ......................................................................... 14

4.2.3 Weighted peak value ...................................................................................... 15

4.2.4 Impulse separation ......................................................................................... 15

4.2.5 Weighted RMS value ...................................................................................... 15

4.2.6 Highest weighted spectral line ........................................................................ 16

4.2.7 Conclusion and recommendation.................................................................... 16

4.3 Considerations before measurements ................................................................... 16

5 Measurement procedures and precaution ...................................................................... 17

5.1 AC magnetic field .................................................................................................. 17

5.2 DC magnetic field ................................................................................................. 18

5.3 AC electric field .................................................................................................... 19

6 Measurement uncertainty .............................................................................................. 21

7 Measurement report ...................................................................................................... 22

Annex A (informative) Examples of fields characteristics in typical environments ................. 24

Annex B (informative) Examples of measurement distances ................................................ 27

B.1 IEC 62110:2009 [9] ............................................................................................... 27

B.2 IEC 62233: 2005 [10] ............................................................................................ 27

B.3 IEC 62311:2007 [11] ............................................................................................. 27

B.4 IEC 62369-1:2008 [12] .......................................................................................... 27

B.5 IEC/TS 62597:2011 [14] ........................................................................................ 27

B.6 IEC 62493:2009 [13] ............................................................................................. 28

Annex C (normative) Measurement uncertainty .................................................................... 29

C.1 Overview............................................................................................................... 29

C.2 Assessment of type A uncertainty ......................................................................... 29

C.3 Assessment of type B uncertainty ......................................................................... 29

C.3.1 Non-uniform field ........................................................................................... 29

C.3.2 Pass-band limitations .................................................................................... 30

C.3.3 Temperature .................................................................................................. 30

C.3.4 Humidity ........................................................................................................ 30

C.3.5 Location of measurement............................................................................... 30

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C.3.6 Long-term drift ............................................................................................... 31

C.3.7 Instrument time constant ............................................................................... 31

C.3.8 Proximity effect of observer (for electric field) ............................................... 31

C.3.9 Correction factor ............................................................................................ 31

C.3.10 Hysteresis between scales ............................................................................ 31

Annex D (informative) Example of measurement uncertainty ................................................ 32

Bibliography .......................................................................................................................... 33

Figure 1 – Magnetic field levels under a 77 kV overhead transmission line (from [9] ) ........... 10

Figure 2 – Electric field levels under an overhead transmission line (from [9] )...................... 10

Figure 3 – Example of load variation of 735kV line due to the human activities (daily)

and outdoor temperature (seasonal) ..................................................................................... 11

Figure 4 – 50 Hz magnetic field in a high speed train in France ............................................ 12

Figure 5 – Waveform (a) and frequency spectrum (b) of magnetic field generated by a

66,04 cm (26 inches) flat-screen LCD television ................................................................... 13

Figure 6 – Example of DC magnetic field profile above DC underground cable

(calculated at a height of 1 m) ............................................................................................... 19

Figure 7 – Observer proximity effects during electric field measurements in vertical

electric field .......................................................................................................................... 20

Figure A.1 – Magnetic field exposure of typical worker (electrician) in North American

power plant (based on 3 days recording) .............................................................................. 25

Figure B.1 – Lighting equipment and measurement distances (from [13]) .............................. 28

Table A.1 – Example of field characteristics inside (workers environment) and outside

(public environment) electric substations in a North American utility ..................................... 24

Table A.2 – Field characteristics (mT) in different mass transportation system in US:

average and (maximum) ....................................................................................................... 26

Table D.1 – Example of measurement uncertainty ................................................................ 32

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SIST IEC 61786-2:2017
– 4 – IEC 61786-2:2014 © IEC 2014
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
MEASUREMENT OF DC MAGNETIC, AC MAGNETIC
AND AC ELECTRIC FIELDS FROM 1 Hz TO 100 kHz
WITH REGARD TO EXPOSURE OF HUMAN BEINGS –
Part 2: Basic standard for measurements
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

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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.

International Standard IEC 61786-2 has been prepared by IEC technical committee 106:

Methods for the assessment of electric, magnetic and electromagnetic fields associated with

human exposure.
The text of this standard is based on the following documents:
FDIS Report on voting
106/322/FDIS 106/326/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 2.

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IEC 61786-2:2014 © IEC 2014 – 5 –

The committee has decided that the contents of this publication will remain unchanged until

the stability 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.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates

that it contains colours which are considered to be useful for the correct

understanding of its contents. Users should therefore print this document using a

colour printer.
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SIST IEC 61786-2:2017
– 6 – IEC 61786-2:2014 © IEC 2014
MEASUREMENT OF DC MAGNETIC, AC MAGNETIC
AND AC ELECTRIC FIELDS FROM 1 Hz TO 100 kHz
WITH REGARD TO EXPOSURE OF HUMAN BEINGS –
Part 2: Basic standard for measurements
1 Scope

This part of IEC 61786 provides requirements for the measurement of quasi-static magnetic

and electric fields that have a frequency content in the range 1 Hz to 100 kHz, and DC

magnetic fields, to evaluate the exposure levels of the human body to these fields.

Specifically, this standard gives requirements for establishing measurement procedures that

achieve defined goals pertaining to human exposure.
NOTE Requirements on field meters and calibration are described in IEC 61786-1

Because of differences in the characteristics of the fields from sources in the various

environments, e.g. frequency content, temporal and spatial variations, polarization, and

magnitude, and differences in the goals of the measurements, the specific measurement

procedures will be different in the various environments.

Sources of fields include devices that operate at power frequencies and produce power

frequency and power-frequency harmonic fields, as well as devices that produce fields

independent of the power frequency, and DC power transmission, and the geomagnetic field.

The magnitude ranges covered by this standard are 0,1 mT to 200 mT for AC (1 mT to 10 T for

DC) for magnetic fields, and 1 V/m to 50 kV/m for electric fields.

When measurements outside this range are performed, most of the provisions of this standard

will still apply, but special attention should be paid to the specified uncertainty and calibration

procedures.
Examples of sources of fields that can be measured with this standard include:

− devices that operate at power frequencies (50/60 Hz) and produce power frequency and

power-frequency harmonic fields (examples: power lines, electric appliances…)

− devices that produce fields that are independent of the power frequency. (Examples:

electric railway (DC to 20 kHz), commercial aeroplanes (400 Hz), induction heaters (up to

100 kHz), and electric vehicles.)
− devices that produces static magnetic fields: MRI, DC power lines, DC welding,

electrolysis, magnets, electric furnaces, etc. DC currents are often generated by

converters, which also create AC components (power frequency harmonics), which should

be assessed.

When EMF products standards are available, these products standards should be used.

With regard to electric field measurements, this standard considers only the measurement of

the unperturbed electric field strength at a point in space (i.e. the electric field prior to the

introduction of the field meter and operator) or on conducting surfaces.

Sources of uncertainty during measurements are also identified and guidance is provided on

how they should be combined to determine total measurement uncertainty.
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IEC 61786-2:2014 © IEC 2014 – 7 –
2 Normative references

The following documents, in whole or in part, are normatively referenced in this document and

are indispensable for its application. For dated references, only the edition cited applies. For

undated references, the latest edition of the referenced document (including any
amendments) applies.

IEC 61786-1:2013, Measurement of DC magnetic, AC magnetic and AC electric fields from

1 Hz to 100 kHz with regard to exposure of human beings – Part 1: Requirements for

measuring instruments

ISO/IEC Guide 99:2007, International vocabulary of metrology – Basic and general concepts

and associated terms (VIM)

ISO/IEC Guide 98-3:2008, Uncertainty of measurement – Part 3: Guide to the expression of

uncertainty in measurement (GUM:1995)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

NOTE Throughout this standard, the words "magnetic flux density" and "magnetic field" will be considered

synonymous.
3.1
average exposure level

spatial average over the entire human body of fields to which the individual is exposed

3.2
correction factor

numerical factor by which the uncorrected result of a measurement is multiplied to

compensate for a known error

Note 1 to entry: Since the known error cannot be determined perfectly, the compensation cannot be complete.

3.3
coverage factor

numerical factor used as a multiplier of the combined standard uncertainty in order to obtain

an expanded uncertainty

Note 1 to entry: For a quantity z described by a normal distribution with expectation m and standard deviation σ,

the interval m ± kσ encompasses 68,27 %, 95,45 %, and 99,73 % of the distribution for a coverage factor k = 1, 2,

and 3, respectively.
3.4
repeatability (of results of measurements)

closeness of agreement between the results of successive measurements of the same

measurand, carried out under the same conditions of measurement, i.e.:
− by the same measurement procedure,
− by the same observer,
− with the same measuring instruments, used under the same conditions,
− in the same laboratory,
− at relatively short intervals of time.

[SOURCE: IEC 60050-311:2001, 311-06-06, modified –The note to entry has been deleted.]

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3.5
reproducibility (of measurements)

closeness of agreement between the results of measurements of the same value of a quantity,

when the individual measurements are made under different conditions of measurement:

− principle of measurement,
− method of measurement,
− observer,
− measuring instruments,
− reference standards,
− laboratory,

− under conditions of use of the instruments, different from those customarily used,

− after intervals of time relatively long compared with the duration of a single measurement

[SOURCE: IEC 60050-311:2001, 311-06-07, modified –The notes to entry have been deleted.]

3.6
standard uncertainty
uncertainty of the result of a measurement expressed as a standard deviation
3.7
uncertainty of measurement

parameter, associated with the result of a measurement, that characterises the dispersion of

the values that could reasonably be attributed to the measurand

Note 1 to entry: Uncertainty of measurement generally comprises many components. Some of these components

may be estimated on the basis of the statistical distribution of the results of series of measurements, and can be

characterised by experimental standard deviations. Estimates of other components can be based on experience or

other information.
4 General considerations
4.1 Different goals of measurement
4.1.1 General

Magnetic and electric fields can be characterised according to a number of parameters, i.e.

magnitude, frequency, polarization, etc. (see IEC 61786-1:2013, Annex C). Characterisation

of one or more of these parameters and how they might relate to human exposure may serve

as possible goals of a measurement programme. As an aid for readers interested in

developing a field measurement protocol, this subclause provides a list of such possible

measurement goals and possible methods for their accomplishment.

Except in the vicinity of high voltage sources, there is no need to measure the power

frequency electric field, because the electric field will be, at most, a few tens of volts per

metre [3; 22] .

Annex A gives examples of typical field characteristics in different environments.

The goals of a measurement programme, such as those considered below, shall be clearly

defined. A clear definition of goals is required for the determination of instrumentation and

calibration requirements, e.g. instrumentation pass-band, magnitude range, frequency

calibration points, etc. Once the goals have been identified and appropriate instrumentation

has been acquired, a pilot study in the measurement environment of interest may be desirable

___________
Numbers in square brackets refer to the Bibliography.
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IEC 61786-2:2014 © IEC 2014 – 9 –

before decisions are made as to the final measurement methods and associated protocol. The

protocol will describe the step-by-step procedure to follow, using the possible methods

indicated, to accomplish the measurement goals. The protocol may explicitly indicate such

things as instrument requirements (e.g. pass-band, probe size, magnitude range), location of

measurements and duration of measurements. It should then be possible, using the same

protocol, to compare with confidence measurement results obtained in similar electrical

environments.

Possible measurement goals and possible methods for their accomplishment are given in

4.1.2 to 4.1.6.
4.1.2 Characterisation of field levels for compliance with safety standards

Limits on permissible electric or magnetic field levels expressed as resultant values and as a

function of frequency have been indicated in a number of documents, such as [17-19; 21]

necessitating the determination of field levels with the maximum value or spatial value in

specified areas. The choice of measurement location shall be done in consideration of the

possible location of people.

Method: Three-axis meters shall be used to make such measurements of the resultant

magnetic and electric fields. Standards and guidance exist for such measurements near

power lines [4; 9; 15] and electric appliances [10] .

Measurements of magnetic fields near power lines should be correlated with load currents.

Load currents for appliances are either constant or, typically, periodic through a fixed range in

a relatively short time, enabling the determination of the largest resultant magnetic field with

relatively few measurements.
4.1.3 Characterisation of spatial variations

Magnetic and electric fields are not constant around sources. For example, variations of

magnetic or electric fields below power lines are typical (Figures 1 and 2) and can be

calculated.
In Figure 1, non-uniformity is defined by [4; 9] as the maximum value of
( B − B ) / B ×100 (%)
h avg avg
Where
B is the magnetic field level at heights of 0,5 m, 1,0 m and 1,5 m above ground;
B is the arithmetic mean of the three levels.
avg
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SIST IEC 61786-2:2017
– 10 – IEC 61786-2:2014 © IEC 2014
100
untransposeduntransposed
5,0
1,1,5 m5 m
4,5 90
A A
1,1,0 m0 m
AA AA
4,0 0,0,5 m5 m
B B
BB BB
Non-uniformity 70
3,5 C C
CC CC
3,2 m 3,2 m
3,0
2,5
40 3,0 m
2,0
3,5 m 3,5 m
1,5
1,0
3,0 m
0,5
0 3,8 m 3,8 m
–10
0,0
–30 –20 –10 0 10 20 30
Distance (m)
Conductor
transposedtransposed
7,0
100
1,1,5 m5 m
phase sequencephase sequence
6,0 1,1,00m m
AAA CC
6,0 m
0,0,5 m5 m
B B
BB BB
non -
Non-uniformity
5,0 70
C A
CC AA
4,0
1,0 m
3,0
G.L.
2,0
Distance (m)
1,0
0,0
–30 –20 –10 0 10 20 30
77 kV, double-circuit, vertical configuration
Distance (m)
IEC

Figure 1 – Magnetic field levels under a 77 kV overhead transmission line (from [9])

3,2 m 3,2 m
Phase sequence
phase sequencphase sequencee
3,0 m
AAA AAA A C
AA CC
900
3,5 m 3,5 m
Electric Field (V/m)
900
BBB BBB B B
BB BB
800 C C C A
CC CC CC AA
800
3,0 m
UntranspoUntransposedsed transposetransposedd
700
700 3,8 m 3,8 m
600
600
500
500
Conductor
400
400
11,0 m
300
300
200
200
100
100
1,0 m
G.L.
–30 –20 –10 0 10 20 30
- 30 - 20 - 10 0 10 20 30
Distance x (m)
Distance (m)
distance x (m)
77 kV, double-circuit, vertical configuration
IEC
Figure 2 – Electric field levels under an overhead transmission line (from [9])

The spatial distribution of magnetic fields away from power lines or single identifiable sources

is typically unknown.

Alternating magnetic fields in most environments will be non-uniform because of the spatial

dependence of the fields from the source currents. It is noteworthy that static magnetic fields

also show considerable spatial variability in residences [29].

Method: The magnetic field components shall be recorded as a function of coordinate position

when characterising spatial variation. Standards exist for carrying out such measurements

Electric field (V/m)
Magnetic field (mT) Magnetic field (mT)
Non-uniformity (%) Non-uniformity (%)
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SIST IEC 61786-2:2017
IEC 61786-2:2014 © IEC 2014 – 11 –

near power lines [4; 9; 15] and electric appliances [[9]]. While such measurements can be

made with survey meters, instrumentation incorporating "measurement wheels" is available

for characterising spatial distributions of magnetic fields in environments where physical

obstructions do not hinder the movement of the wheel. As the wheel rotates, it periodically

triggers a three-axis magnetic field meter to record the resultant magnetic field. Software

provided with such instrumentation permits the generation of plots of magnetic field profiles,

equifield contours, statistical analyses of the field levels, etc [2; 26]. As for characterisation of

field levels for compliance with safety limits, such data will not take the temporal variations of

the field profiles into account without repeated measurements.
4.1.4 Characterisation of temporal variation

Because magnetic fields are produced by load currents and ground return currents that can

vary greatly with time, the temporal variations of magnetic fields can easily exceed a factor of

Under a power line, the magnetic field depends on the load of the line. For single circuit lines

or double circuit lines operated in parallel, the magnetic field is directly proportional to the

load of the line. Figure 3 gives an example of the load of a 735 kV line and the outdoor

temperature. In this case, the load is influenced by human activities (daily cycle) and by

outdoor temperature (season cycle) and by the place of the line in the network. Moreover, the

magnetic field level can vary with the sagging of the conductors because of heating due to

large current loads and environmental conditions [16] .
IEC
Figure 3 – Example of load variation of 735kV line due to
the human activities (daily) and outdoor
...

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