CISPR TR 18-2:2017

CISPR TR 18-2 ®
Edition 3.0 2017-10
TECHNICAL
REPORT
colour
inside
INTERNATIONAL SPECIAL COMMITTEE ON RADIO INTERFERENCE

Radio interference characteristics of overhead power lines and high-voltage
equipment –
Part 2: Methods of measurement and procedure for determining limits

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CISPR TR 18-2 ®
Edition 3.0 2017-10
TECHNICAL
REPORT
colour
inside
INTERNATIONAL SPECIAL COMMITTEE ON RADIO INTERFERENCE

Radio interference characteristics of overhead power lines and high-voltage

equipment –
Part 2: Methods of measurement and procedure for determining limits

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 33.100.01 ISBN 978-2-8322-4894-2

– 2 – CISPR TR 18-2:2017  IEC 2017
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 10
2 Normative references . 10
3 Terms and definitions . 11
4 Measurements . 11
4.1 Measuring instruments . 11
4.1.1 Response of a standard quasi-peak CISPR measuring receiver to AC
generated corona noise . 11
4.1.2 Other measuring instruments . 12
4.2 On-site measurements on HV overhead power lines . 12
4.2.1 General . 12
4.2.2 Measurements in the frequency range 0,15 MHz to 30 MHz . 12
4.2.3 Measurements in the frequency range from 30 MHz to 300 MHz . 14
4.2.4 Measurements in the frequency range from 300 MHz to 3 GHz . 15
4.3 Statistical evaluation of the radio noise level of a line . 15
4.4 Additional information to be given in the report . 17
4.5 Measurements on HV equipment in the laboratory . 17
4.5.1 Overview . 17
4.5.2 State of the test object . 17
4.5.3 Test area . 18
4.5.4 Atmospheric conditions . 18
4.5.5 Test circuit – Basic diagram . 18
4.5.6 Practical arrangement of the test circuit . 19
4.5.7 Test circuit components . 19
4.5.8 Measuring receiver connections . 20
4.5.9 Mounting and arrangement of test object . 21
4.5.10 Measurement frequency . 21
4.5.11 Checking of the test circuit . 21
4.5.12 Calibration of the test circuit . 22
4.5.13 Test procedure . 23
4.5.14 Related observations during the test . 24
4.5.15 Data to be given in test report . 24
5 Methods for derivation of limits for HV power systems . 24
5.1 Overview. 24
5.2 Significance of CISPR limits for power lines . 25
5.3 Technical considerations for derivation of limits for lines . 26
5.3.1 Basic approach . 26
5.3.2 General . 26
5.3.3 Minimum broadcast signal levels to be protected . 27
5.3.4 Required signal-to-noise ratio . 28
5.3.5 Use of data on radio noise compiled during measurements in the field . 29
5.3.6 Use of data obtained by prediction of the radio noise from high-voltage
overhead power lines . 30
5.4 Methods of determining compliance of measured data with limits . 31
5.4.1 Long-term recording . 31

5.4.2 Sampling method . 31
5.4.3 Survey methods . 32
5.4.4 Alternative criteria for an acceptable noise level . 32
5.5 Examples for derivation of limits in the frequency range below 30 MHz . 33
5.5.1 Radio reception . 33
5.5.2 Television reception, 47 MHz to 230 MHz . 35
5.5.3 Digital terrestrial television reception, 470 MHz to 950 MHz . 35
5.6 Additional remarks . 35
5.7 Technical considerations for derivation of limits for line equipment and
HVAC substations . 35
5.7.1 General . 35
5.7.2 Current injected by line components and hardware . 36
5.7.3 Current injected by substation equipment . 36
5.7.4 Practical derivation of limits in the l.f. and m.f. band . 37
6 Methods for derivation of limits for the radio noise produced by insulator sets . 38
6.1 General considerations . 38
6.2 Insulator types . 39
6.3 Influence of insulator surface conditions . 39
6.3.1 General . 39
6.3.2 Clean insulators . 40
6.3.3 Slightly polluted insulators . 40
6.3.4 Polluted insulators . 40
6.4 Criteria for setting up radio noise limits for insulators . 41
6.4.1 General . 41
6.4.2 Criterion for insulators to be installed in type A areas . 41
6.4.3 Criterion for insulators to be installed in type B areas . 41
6.4.4 Criterion for insulators to be installed in type C areas . 42
6.5 Recommendations . 42
7 Methods for derivation of limits for the radio noise due to HVDC converter stations
and similar installations . 44
7.1 General considerations . 44
7.2 Sources of interference . 44
7.2.1 Mechanism of radio noise generation . 44
7.2.2 Influence of station design on radio interference . 46
7.3 Radiated fields from valve halls . 46
7.3.1 Frequency spectra . 46
7.3.2 Lateral attenuation . 46
7.3.3 Reduction of the radio interference due to direct radiation from the
valve hall . 46
7.4 Conducted interference along the transmission lines . 47
7.4.1 Description of the mechanism and typical longitudinal profiles . 47
7.4.2 Reduction of the interference conducted along the transmission lines . 48
7.5 General criteria for stating limits . 48
7.5.1 Overview . 48
7.5.2 Direct radiation . 48
7.5.3 Propagation along the lines . 48
8 Figures . 50
Annex A (informative) Radio interference measuring apparatus differing from the
CISPR basic standard instruments . 64

– 4 – CISPR TR 18-2:2017  IEC 2017
Annex B (normative) List of additional information to be included in the report on the
results of measurements on operational lines . 65
Annex C (informative) Minimum radio signal levels to be protected – ITU
recommendations . 66
C.1 Broadcast radio (low frequency (l.f.) and medium frequency (m.f.) bands). 66
C.2 Broadcast radio (high frequency (h.f.) bands). 67
C.3 Amateur radio . 67
Annex D (informative) Minimum broadcast signals to be protected – North American
standards . 69
Annex E (informative) Required signal-to-noise ratios for satisfactory reception . 70
Annex F (informative) Derivation of the equation for the protected distance . 73
Bibliography . 74

Figure 1 – Transformation of pulses through a CISPR measuring receiver . 50
Figure 2 – Bursts of corona pulses generated by alternating voltage . 51
Figure 3 – Example of extrapolation to determine the radio noise field strength
reference level of a power line, here at the direct reference distance of 20 m . 51
Figure 4 – Basic test circuit . 52
Figure 5 – Standard test circuit . 52
Figure 6 – Connection to the measuring receiver by a coaxial cable . 53
Figure 7 – Connection to the measuring receiver by a balanced cable . 53
Figure 8 – Special test circuit . 53
Figure 9 – Arrangement for calibration of the standard test circuit . 54
Figure 10 – Map showing boundaries of zones A, B, and C in regions 1 and 3 . 55
Figure 11 – Illustration of the four basic parameters for a power transmission line . 56
Figure 12 – Example of typical statistical yearly "all-weather" distributions of the radio-
noise levels of a bipolar direct current line (-----) and for an alternating current line in a
moderate climate (- – -) . 57
Figure 13 – Example of radio noise voltage level V, as a function of the relative air
humidity R.H., in clean conditions and slightly polluted conditions, of a standard
insulator (-----) and a particular type of "low noise" insulator (- – -) . 57
Figure 14 – Example of frequency spectra of pulses with different rise times, simulating
commutation phenomena in mercury valves and in thyristor valves . 58
Figure 15 – Example of frequency spectra of the radio interference recorded outside
the hall of a mercury arc valve converter station with and without toroidal filters . 59
Figure 16 – Example of frequency spectra of the radio interference recorded outside
the hall of a thyristor valve converter station for different operating conditions . 59
Figure 17 – Attenuation of the field strength as a function of the distance on a
horizontal plane, for different frequencies . 60
Figure 18 – Example of frequency spectrum of the radio interference in the vicinity of a
DC line (30 m) at a short distance from the converter station . 61
Figure 19 – Example of frequency spectra of the radio interference in the vicinity of an
AC line (20 m) at a short distance from the converter station . 62
Figure 20 – Frequency spectra of radio interference at 20 m from the electrode line at
1,5 km from the Gotland HVDC link in Sweden with mercury arc groups or thyristor
groups in operation . 62
Figure 21 – Frequency spectra of radio interference at 20 m from the electrode line at
1,5 km and 4,5 km from the Gotland HVDC link in Sweden with mercury arc groups in
operation . 63

Figure 22 – Frequency spectra of the radio interference recorded along a 200 kV DC
line, at 20 m from the conductor, at different distances from the converter station. 63

Table 1 – Number of n sets of the radio noise level measurements and corresponding
values for factor k . 16
Table 2 – Minimum usable broadcast signal field strengths in the v.h.f bands according
to CCIR. 27
Table 3 – Recommendations for the radio noise voltage limits and for the test methods
for insulator sets installed in different areas . 43
Table C.1 – Minimum field strength (l.f. and m.f. radio) . 66
Table C.2 – Nominal usable field strength . 66
Table C.3 – Minimum field strength (h.f. radio) . 67
Table C.4 – Field strength limit (amateur radio) . 68
Table D.1 – Signal levels at the edge of the service area in North America . 69
Table E.1 – Summary of signal-to-noise ratios for corona from AC lines (Signal
measured with average detector, noise measured with quasi-peak detector) . 70
Table E.2 – Quality of radio reception or degree of annoyance due to RFI . 71

– 6 – CISPR TR 18-2:2017  IEC 2017
INTERNATIONAL ELECTROTECHNICAL COMMISSION
INTERNATIONAL SPECIAL COMMITTEE ON RADIO INTERFERENCE
____________
RADIO INTERFERENCE CHARACTERISTICS
OF OVERHEAD POWER LINES
AND HIGH-VOLTAGE EQUIPMENT –
Part 2: Methods of measurement
and procedure for determining limits

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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6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
CISPR 18-2, which is a technical report, has been prepared by CISPR subcommittee B:
Interference relating to industrial, scientific and medical radio-frequency apparatus, to other
(heavy) industrial equipment, to overhead power lines, to high voltage equipment and to
electric traction.
This third edition cancels and replaces the second edition published in 2010. This edition
constitutes a technical revision.

This edition includes the following significant technical changes with respect to the previous
edition:
a) updated description of the RF characteristics of spark discharges;
b) measurement method for radiated disturbances in the frequency range from 300 MHz to 3
GHz.
The text of this technical report is based on the following documents:
DTR Report on voting
CIS/B/654/DTR CIS/B/675/RVDTR
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 publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts of the CISPR 18 series can be found, under the general title Radio
interference characteristics of overhead power lines and high-voltage equipment, on the IEC
website.
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.
A bilingual version of this publication may be issued at a later date.

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.
– 8 – CISPR TR 18-2:2017  IEC 2017
INTRODUCTION
This Technical Report is the second of a three-part series dealing with radio noise generated
by electrical power transmission and distribution facilities (overhead lines and substations). It
contains recommendations for performance of on-site measurements of electromagnetic noise
fields in the vicinity of high-voltage (HV) overhead power lines and substations and for
determination of limits for protection of radio reception.
The recommendations given in this Part 2 of the CISPR 18 series are intended to be a useful
aid to engineers involved in maintenance of overhead power lines and substations and also to
anyone concerned with checking the radio noise performance of a line to ensure satisfactory
protection of radio reception. Information on the physical phenomena involved in the
generation of electromagnetic noise fields is found in CISPR TR 18-1. It also includes the
main properties of such fields and their numerical values. CISPR TR 18-3 eventually contains
a Code of Practice for minimizing the generation of radio noise.
This third edition of CISPR TR 18-2 is adapted to the modern structure and content of
technical reports issued by IEC. The second edition of CISPR TR 18-2 underwent thorough
edition and adaptation to modern terminology. This third edition now also covers an adequate
method of measurement for radiated disturbances from HV overhead power lines and
substations in the range 300 MHz to 3 GHz, since gap-type discharges can be a potential
noise source disturbing modern digital radio communication. However, because
1) there is not sufficient experience and information regarding gap-type noise and thus
further investigations regarding noise characteristics and how gap noise disturbs digital
radio communication are necessary,
2) gap noise is not persistent in normal operation of the electric power facility and tends to
emerge from defective components,
there is no discussion in this edition regarding technical considerations for derivation of limits
in the frequency range 300 MHz to 3 GHz.
The CISPR 18 series does not deal with biological effects on living matter or any issues
related to exposure to electromagnetic fields.
The main content of this technical report is based on historical CISPR Rec. No. 56 given
below:
RECOMMENDATION No. 56
METHODS OF MEASUREMENT OF RADIO INTERFERENCE CAUSED BY
OVERHEAD POWER LINES AND HIGH-VOLTAGE EQUIPMENT AND
THE PROCEDURE FOR DETERMINING LIMITS

The CISPR
CONSIDERING
a) that a general description of the radio interference characteristics of overhead power lines
and high-voltage equipment has been published in CISPR 18-1,
b) that the methods of measurement of these characteristics need to be established,
c) that national authorities require guidance on the procedure for determining limits of such
radio interference.
RECOMMENDS
That the latest edition of CISPR TR 18-2, including amendments, be used for methods of
measurement of radio interference characteristics of overhead power lines and high-voltage
equipment and for procedures for determining limits.
CISPR TR 18-1 describes the main properties of the physical phenomena involved in the
production of disturbing electromagnetic fields by overhead lines and provides numerical
values of such fields.
In CISPR TR 18-2, methods of measurement and procedures for determining limits of such
radio interference are recommended.
The methods of measurement in CISPR TR 18-2 detail the techniques and procedures for use
when measuring electromagnetic fields arising from radio interference at sites close to
overhead lines and also the techniques and procedures for making laboratory measurements
of interference voltages and currents generated by line equipment and accessories.
The procedures for determining limits define the expected values of radio noise field and the
width of the "disturbed" corridor following the route of the line.
This corridor takes into account the effective field strength of the wanted signal, the signal-to-
noise ratio selected and the expected strength of the noise field for a given line.
The procedures are only valid for long and medium waves because procedures applicable to
VHF analogue television broadcasting and digital terrestrial television broadcasting have not
yet been decided, due to insufficient knowledge.
It is emphasized that this part of CISPR 18 does not specify a single set of limits to be applied
internationally. Rather it details the procedures to enable national authorities to specify limits
where it is decided that there is a need for regulations.

– 10 – CISPR TR 18-2:2017  IEC 2017
RADIO INTERFERENCE CHARACTERISTICS
OF OVERHEAD POWER LINES
AND HIGH-VOLTAGE EQUIPMENT –
Part 2: Methods of measurement
and procedure for determining limits

1 Scope
This part of CISPR 18, which is a Technical Report, applies to radio noise from overhead
power lines and high-voltage equipment which may cause interference to radio reception.
The frequency range covered by this publication is 0,15 MHz to 3 GHz.
A general procedure for establishing the limits of the radio noise field from the power lines
and equipment is recommended, together with typical values as examples, and methods of
measurement.
The clause on limits concentrates on the low frequency and medium frequency bands and it is
only in these bands where ample evidence, based on established practice, is available. No
examples of limits to protect radio reception in the frequency band 30 MHz to 3 GHz have
been given, as measuring methods and certain other aspects of the problems in this band
have not yet been fully resolved. Site measurements and service experience have shown that
levels of noise from power lines at frequencies higher than 300 MHz in normal operation are
so low that interference is unlikely to be caused to television reception.
The values of limits given as examples are calculated to provide a reasonable degree of
protection to the reception of broadcasting at the boundary of the recognized service areas of
the appropriate transmitters in the radio frequency bands used for a.m. radio broadcasting, in
the least favourable conditions likely to be generally encountered. These limits are intended
to provide guidance at the planning stage of the line and national standards or other
specifications against which the performance of the line may be checked after construction
and during its useful life.
The measuring apparatus and methods used for checking compliance with limits should
comply with the respective CISPR specifications, as e.g. the basic standards series CISPR 16,
see [1] .
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements 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 (IEV) – Chapter 161:
Electromagnetic compatibility
IEC 60060-2, High-voltage test techniques – Part 2: Measuring systems
_______________
The figures in square brackets refer to the Bibliography.

CISPR 16-1-1, Specification for radio disturbance and immunity measuring apparatus and
methods – Part 1-1: Radio disturbance and immunity measuring apparatus – Measuring
apparatus
ISO IEC Guide 99, International vocabulary of metrology – Basic and general concepts and
associated terms (VIM)
NOTE Informative references are listed in the Bibliography.
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-161 and the
ISO IEC Guide 99 apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
4 Measurements
4.1 Measuring instruments
4.1.1 Response of a standard quasi-peak CISPR measuring receiver to AC generated
corona noise
CISPR 16-1-1 specifies the response characteristic of a measuring receiver to periodically
repeated pulses, according to their repetition frequency, for a number of different frequency
ranges and bandwidths including the range 0,15 MHz to 30 MHz and a resolution bandwidth
of 9 kHz.
Figure 1 indicates the form these pulses take as they progress through the various stages of
the measuring receiver. However, in the special case of corona pulses generated by high-
voltage AC power systems, the individual pulses are not equally spaced throughout a cycle
but occur in closely packed groups or bursts around the peak of the voltage waveform. A burst
has a duration not exceeding 2 ms to 3 ms and this is followed by a quiescent no-corona
period.
Owing to its inherent time constants, a standard quasi-peak CISPR measuring receiver is
unable to respond to individual pulses within a burst, which is seen as a single pulse whose
amplitude is discussed below.
Hence, the pulse repetition frequency, in the meaning of the CISPR definition, is constant at
2 f (where f is the power system frequency) for single phase and 6 f for three-phase single or
multi-circuit systems, provided that the individual circuits are part of the same system.
Figure 2 indicates the usual case where individual corona pulses generated around the
positive peaks of the voltage waveform are much greater in amplitude than those generated
around the negative peaks. Hence in a three-phase power line there are three bursts of higher
amplitude and three burst of lower amplitude noise during each period of 1/f.
Also, in the measurement of the radio noise field strength in close vicinity of an operational
line, the antenna of the measuring receiver is not located at the same distance from all the
phase conductors. Because a quasi-peak detector responds only to the higher amplitude
bursts and disregards the lower ones, rules of summation of the radio noise generated by the
individual phases of a line can be formulated which are specific to the CISPR characteristics

– 12 – CISPR TR 18-2:2017  IEC 2017
and are given in Clause 4 of CISPR TR 18-3:__ . It should be noted that the loudspeaker of a
radio receiver, and consequently the listener, perceives the overall generated noise.
To examine the response of the CISPR measuring receiver to a given burst of pulses, it
should be borne in mind that each individual pulse becomes, at the output of the amplifier of
Figure 1 of pass-band ∆f, a damped oscillation whose duration can be taken as approximately
2/RBW (i.e. 0,5 times its IF amplifier resolution bandwidth), or 0,22 ms for 9 kHz. When there
are a large number of pulses distributed at random within a burst, the resulting oscillations will
overlap randomly and the overall quasi-peak signal will be approximately equal to the
quadratic sum of the individual quasi-peak values. This statement, which is difficult to prove
mathematically, has been well proven by experience and justifies the use, in quasi-peak
detection, of the quadratic summation law which would moreover be rigorous if the noise
levels were expressed in RMS values.
4.1.2 Other measuring instruments
Measuring instruments differing from standard CISPR instruments are referred to in Annex A
although measuring instruments having detectors other than quasi-peak are also referred to in
CISPR 16-1-1.
4.2 On-site measurements on HV overhead power lines
4.2.1 General
On-site measurements in the vicinity of HV overhead power lines should be carried out in
accordance with the instructions given in this subclause. Further information about a possible
assessment and documentation of measured data is found in 5.3.5 and 5.4.
4.2.2 Measurements in the frequency range 0,15 MHz to 30 MHz
4.2.2.1 Reference frequency
The reference measurement frequency is 0,5 MHz. It is recommended that measurements are
made at a frequency of 0,5 MHz ± 10 % but other frequencies, for example 1 MHz, may also
be used. The frequency of 0,5 MHz (or 1 MHz) is preferred because, usually, the level of radio
noise at this part of the spectrum is representative of the higher levels and also because
0,5 MHz lies between the low and medium frequency broadcast bands.
Because of the possibility of error due to the presence of standing waves, it is inadvisable to
rely on the measured value of the radio noise field strength at a single frequency but to draw
a mean curve through the results of a number of readings throughout the noise spectrum.
Measurements should be made at, or near, the following frequencies: 0,15 MHz, 0,25 MHz,
0,5 MHz, 1,0 MHz, 1,5 MHz, 3,0 MHz, 6,0 MHz, 10,15 MHz and 30 MHz although, clearly,
frequencies at which interference to the wanted noise is received, should be avoided.
4.2.2.2 Measurement antenna
The antenna used for the measurements shall be an electrically-screened vertical loop, whose
dimensions are such that the antenna will be completely enclosed by a square having a side
of 600 mm in length. The balance shall be such that in a uniform field the ratio between the
maximum and minimum indications on the measuring receiver when the antenna is rotated
shall not be less than 20 dB. The base of the loop should be about 2 m above ground. The
antenna shall be rotated around a vertical axis and the maximum indication noted. If the plane
of the loop is not effectively parallel to the direction of the power line, the orientation should
be stated.
_______________
Under preparation. Stage at the time of publication: CISPR/RPUB 18-3:2017.

According to the ANSI/IEEE Standard 430 (1986) [4], the antenna height using measurement
vehicle is recommended as below:
If a vehicle-mounted antenna is used, the antenna should be at least 2 m above the roof of
the vehicle. The effects of vehicles on vehicle-mounted antennas have been found to be
negligible if this minimum height of 2 m is maintained; however, the vehicle and antenna
combination should be calibrated to confirm the antenna factors and to check for existence of
azimuthal asymmetries in the antenna pattern, as described in Section 5 of
IEEE Standard 473 (1985) [5].
A check shall be made to ensure that the supply mains, if used, or other conductors
connected to the measuring apparatus do not affect the measurements.
4.2.2.3 Selection of measurement points along the pathway of the overhead
HV power transmission line
To determine the radio noise performance of a line, certain positions of measurement should
be avoided; but these restrictions would not apply when an investigation into a case of
interference is being carried out.
Measurements should be made at mid-span between the towers and preferably at several
such positions. Measurements should not be made near points where lines change direction
or intersect.
Sites at an abnormal height of span should be avoided. The measuring site should be flat,
free from trees and bushes and remote from large metal structures and other overhead power
and telephone lines.
Ideally the measuring site should be at a distance greater than 10 km from a line termination,
in order to avoid reflection effects and consequently inaccurate results, but lower voltage
distribution lines are sometimes too short to enable this condition to be met. However, the
results of measurement (see reference [6]) indicate that the level of the radio noise field
strength in the absence of reflections corresponds to the geometric mean of the maximum and
minimum values, in microvolt per metre (µV/m), of the frequency spectrum from a line
subjected to reflections.
If the line is transposed, the measuring site should be located as far as possible from the
transposition towers.
The atmospheric conditions should be approximately uniform along the line. Measurements
under rain conditions will be valid only if the rain extends over at least 10 km of the line on
either side of the measuring site.
Annex B gives a list of such information.
4.2.2.4 Selection of measurement points lateral to the pathway of the overhead
HV power transmission line
Measurements are performed e.g. for determination of the lateral field strength profile of the
radio noise field generated by overhead HV power transmission lines. In these conditions, a
number of measurement points at mid-span in between two towers should be chosen along a
straight line departing perpendicular from the pathway of the overhead HV power transmission
line under test. The distances of measurement shall be taken laterally from the vertical
projection to ground of the outmost sub-conductor of the transmission line (reference point
...