CISPR TR 18-3:2010

TR CISPR 18-3 ®
Edition 2.0 2010-06
TECHNICAL
REPORT
INTERNATIONAL SPECIAL COMMITTEE ON RADIO INTERFERENCE
Radio interference characteristics of overhead power lines and high-voltage
equipment –
Part 3: Code of practice for minimizing the generation of radio noise

TR CISPR 18-3:2010(E)
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TR CISPR 18-3 ®
Edition 2.0 2010-06
TECHNICAL
REPORT
INTERNATIONAL SPECIAL COMMITTEE ON RADIO INTERFERENCE
Radio interference characteristics of overhead power lines and high-voltage
equipment –
Part 3: Code of practice for minimizing the generation of radio noise

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
X
ICS 33.100.01 ISBN 978-2-88912-018-5
– 2 – TR CISPR 18-3 © IEC:2010(E)
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.8
2 Normative references .8
3 Terms and definitions .8
4 Practical design of overhead power lines and associated equipment in order to
control interference to radio broadcast sound and television reception .8
4.1 Overview .8
4.2 Corona on conductors .9
4.3 Corona on metal hardware .9
4.4 Surface discharges on insulators.9
4.4.1 Clean or slightly polluted insulators .9
4.4.2 Very polluted insulators .10
4.5 Spark and microsparks due to bad contacts, commutation effects .10
4.6 Defects on power lines and associated equipment in service.10
5 Methods of prediction of the reference level of an overhead line.11
5.1 General .11
5.2 Correlation of data given elsewhere in this publication .11
5.3 CIGRÉ formula .12
5.4 Determination of 80 % level.13
5.5 Conclusions .13
6 Preventive and remedial measures to minimize radio noise generated by bad
contacts and their detection and location.14
6.1 General .14
6.2 Preventive and remedial measures.14
6.3 Methods of detecting and locating bad contacts .15
7 Formulae for predetermination of the radio noise field strength produced by large
conductor bundles (more than four sub-conductors) and by tubular conductors .17
7.1 Basic principles .17
7.2 Calculation of corona radio noise field strengths due to large bundles .18
7.2.1 Procedure for the predetermination of the radio noise field strength .18
7.2.2 Calculation of the excitation function in heavy rain .18
7.2.3 Correction factor to evaluate the excitation function in other weather
categories .19
7.2.4 Calculation of the radio noise field strength .19
7.3 Evaluation of corona radio noise field strength due to large tubular

conductors .20
8 Figures .22
Annex A (informative) Formulae for predicting the radio noise field strength from the
conductors of an overhead line .30
Annex B (informative) Analytical procedure for the predetermination of the radio noise
field strength, at a given distance from an overhead line with large bundle conductors .38
Bibliography.45

Figure 1 – Bundle conductors .22
Figure 2 – Line with conductors in a flat configuration.23

TR CISPR 18-3 © IEC:2010(E) – 3 –
Figure 3 – Line with conductors in a delta configuration .24
Figure 4 – Line with conductors in a triangular configuration .25
Figure 5 – Line with conductors in a flat configuration.26
Figure 6 – Line with conductors in a delta configuration .27
Figure 7 – Line with conductors in a triangular configuration .28
Figure 8 – Tubular conductors of 40 cm diameter .29
Figure B.1 – Designation of the geometrical quantities for the simplified analytical
method .43
Figure B.2 – Lateral profiles of the radio noise field strengths produced by the
individual phases and of the total field, as calculated in the given example.44

Table A.1 – Empirical methods, terms of the predetermination formulae developed by
several institutions, survey.32
Table A.2 – Empirical methods, complete predetermination formulae developed by
several institutions, survey.34
Table A.3 – Predetermination formulae, examples for calculation of the absolute field
strength levels .36

– 4 – TR CISPR 18-3 © IEC:2010(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION
INTERNATIONAL SPECIAL COMMITTEE ON RADIO INTERFERENCE
____________
RADIO INTERFERENCE CHARACTERISTICS
OF OVERHEAD POWER LINES
AND HIGH-VOLTAGE EQUIPMENT –
Part 3: Code of practice for minimizing
the generation of radio noise
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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2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
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3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
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5) IEC itself does not provide any attestation of conformity. Independent certification bodies provide conformity
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
The main task of IEC technical committees is to prepare International Standards. However, a
technical committee may propose the publication of a technical report when it has collected
data of a different kind from that which is normally published as an International Standard, for
example "state of the art".
CISPR 18-3, 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 second edition cancels and replaces the first edition published in 1986. It is a technical
revision.
TR CISPR 18-3 © IEC:2010(E) – 5 –
This edition includes the following significant technical changes with respect to the previous
edition: while the first edition of CISPR 18-3 only covered recommendations for minimizing the
generation of radio noise emanating from high-voltage (HV) power systems, this second
edition now also covers a new clause providing formulae for predetermination of the radio
noise field strength levels from HV overhead power lines with large conductor bundles.
Furthermore, Annex A was accomplished with a collation of predetermination formulae
developed and used by several institutions around the world. The tables also contain typical
examples of radio noise field strength levels obtained during some measurements campaigns
at several HV overhead power line constructions.
The text of this technical report is based on the following documents:
DTR Report on voting
CISPR/B/495/DTR CISPR/B/503/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 technical report 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.

– 6 – TR CISPR 18-3 © IEC:2010(E)
INTRODUCTION
This technical report forms the third of a three-part publication dealing with radio noise
generated by electrical power transmission and distribution facilities (overhead lines and
substations). It contains recommendations for minimizing the generation of radio noise
emanating from high-voltage (HV) power systems which include, but are not restricted to,
HVAC or HVDC overhead power lines, HVAC substations and HVDC converter stations,
hardware, etc., in order to promoting protection of radio reception.
The recommendations given in this part 3 of the CISPR 18 series are intended to be a useful
aid to engineers involved in design, erection and maintenance of overhead lines and HV
stations 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 18-2
contains recommendations for methods of measurement for use on-site or in a laboratory. It
furthermore recommends procedures for determination of limits for the radio noise from HV
power systems.
This second edition of CISPR 18-3 was adapted to the modern structure and content of
technical reports issued by IEC. The first edition of CISPR 18-3 underwent thorough edition
and adaptation to modern terminology. Furthermore its content was adjusted such as to allow
for use of the lateral distance y for the conduction of measurements in the field.
The CISPR 18 series does not deal with biological effects on living matter or any issues
related to exposure in electromagnetic fields.
The main content of this technical report is based on CISPR Rec. No. 57 given below:
CISPR RECOMMENDATION No. 57
CODE OF PRACTICE FOR MINIMIZING THE GENERATION OF RADIO NOISE

The CISPR
CONSIDERING
a) that the radiation of electromagnetic energy from overhead power lines causes
interference to sound and television broadcasting,
b) that the level of this noise may be reduced by the design and lay-out of a line,
c) that when defects cause unusually high levels of interference there is need to detect and
locate these faults,
RECOMMENDS
That the latest edition of CISPR Publication 18-3, including amendments, be used as guide
for minimizing the generation of radio noise caused by overhead power lines.
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.
This CISPR/TR 18-3 forms a "Code of Practice" to reduce to a minimum the production of
radio noise by power lines and equipment.

TR CISPR 18-3 © IEC:2010(E) – 7 –
It provides information which is advisable to follow both when designing various fittings and
components and when stringing the conductors and installing the hardware of the line.
It also describes methods of detecting and locating defects resulting in unusually high
interference levels, and provides prevention and correction procedures that are generally
simple to implement.
Lastly, this Part 3 provides formulae for predicting the most probable radio noise field of a line
for various weather conditions, insofar as radio noise is caused by conductor corona.

– 8 – TR CISPR 18-3 © IEC:2010(E)
RADIO INTERFERENCE CHARACTERISTICS
OF OVERHEAD POWER LINES
AND HIGH-VOLTAGE EQUIPMENT –
Part 3: Code of practice for minimizing
the generation of radio noise
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, excluding
the fields from power line carrier signals.
The frequency range covered is 0,15 MHz to 300 MHz.
2 Normative references
The following referenced documents are indispensable for the application of this document.
For dated references, only the edition cited applies. For undated references, the latest edition
of the referenced document (including any amendments) applies.
IEC 60050-161, International Electrotechnical Vocabulary (IEV) – Chapter 161:
Electromagnetic compatibility
CISPR/TR 18-1:2010, Radio interference characteristics of overhead power lines and high-
voltage equipment – Part 1: Description of phenomena
CISPR/TR 18-2:2010, Radio interference characteristics of overhead power lines and high-
voltage equipment – Part 2: Methods of measurement and procedure for determining limits
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 the IEC 60050-161 and
the ISO/IEC Guide 99 apply.
4 Practical design of overhead power lines and associated equipment
in order to control interference to radio broadcast sound and television
reception
4.1 Overview
This clause provides guidance on the techniques that may be applied during the design,
construction and operation of high voltage overhead power lines and associated equipment in
order to keep the various types of radio noise described in this publication within acceptable
levels.
TR CISPR 18-3 © IEC:2010(E) – 9 –
4.2 Corona on conductors
During line design, consideration should be given to the geometric parameters of the line, in
order to ensure that radio noise due to conductor corona will not exceed a specified
acceptable level. The most important parameters are conductor diameter and number of
conductors per phase. Others that could be varied, such as distance between phases, height
of conductors above ground or spacing of sub-conductors in the bundle, have a smaller effect.
In practice they are usually determined by mechanical or insulation requirements.
The quantitative laws that determine the level of radio noise caused by conductor corona are
discussed in 4.3 of CISPR/TR 18-1, and in Clause 7 below. These laws normally apply to both
stranded and smooth conductors, since the surface unevenness caused by stranding does not,
in general, substantially change the noise level, especially when conductors are damp or wet.
The existence of scratched or broken strands or deposits of extraneous substances such as
dirt or insects on the surface, on the other hand, may lead to severe localised corona
discharges, due to high local voltage gradients. This may considerably increase the noise
level of the line. For these reasons it is necessary to avoid damage to the conductor surface
during construction. It should be handled with great care in transportation and erection and
suitable techniques should be used to avoid contact of the conductor with the ground or other
objects during stringing. It is also advisable to avoid external greasing of the conductor for
protection during transportation and tensioning; when the conductor is loaded, the increase in
temperature, especially in hot weather, will cause this grease to run to the outside, gathering
dirt and leading to areas with high local gradient and consequent radio noise. When the steel
core or inside layers are greased for corrosion protection, a type of grease should be selected
that will not migrate to the surface of the conductor even at the highest temperature.
4.3 Corona on metal hardware
Radio noise due to corona on metal hardware, such as suspension clamps, dead-end clamps,
yokes, guard rings, horns, spacers, etc., can be controlled. Appropriate shapes and
dimensions may be specified during the design stage in order to avoid points of high voltage
gradient. All edges and corners should be well rounded, bolt heads should be rounded or
shielded and sharp points and protrusions should be avoided. It is also important that the
protective galvanized finish on hardware be smooth, particularly at points of maximum voltage
gradient.
Guard devices are sometimes installed to protect an insulator string from the destructive
effects of a power arc and to improve the distribution of the potential along the string. They
also contribute to the reduction of the level of radio noise from the conductor clamps, since
they screen sharp points or protrusions on the clamps. The type and dimensions of the guard
devices should be chosen in such a way that they do not themselves produce radio noise. For
example, the use of simple horns should be avoided at voltages exceeding about 150 kV, and
the diameter of tubes forming guard rings should be sufficiently large to ensure that no corona
occurs during rain.
Present knowledge seems to indicate, however, that it may be relatively difficult to design
guard rings suitable for rainy conditions, even if they are made of multiple tubes. In which
case, it may be necessary to devise special arrangements for the yoke so that the string is
screened directly by the conductor bundle and is protected from power arcs by suitable
devices on the sub-conductors of the bundle.
As in the case of conductors, it is important to avoid damage to the hardware during
manufacture, transportation, construction and maintenance by handling them with great care
at all times.
4.4 Surface discharges on insulators
4.4.1 Clean or slightly polluted insulators
The radio noise produced by these insulators under dry conditions can be controlled by:

– 10 – TR CISPR 18-3 © IEC:2010(E)
– the use of insulators of suitable design, especially as regards their geometry and the
characteristics of the material at the more critical areas, or
– the use of guard devices designed to improve the distribution of voltage on the surface of
the insulator or along the insulator string.
In insulator design, the use of conducting glaze, for example, improves the distribution of the
surface voltage gradient on the insulator. In the design of a guard device, a metal ring as
close as possible to the insulator, or to at least the first two or three insulators at the line end
of an insulator string, may considerably improve the voltage distribution on the insulator or
along the insulator string and reduce radio noise. The ring, however, shall remain compatible
with other requirements such as insulation withstand, protection of the insulators from power
arcs, screening of the clamps, etc. (see 4.3).
The radio noise produced in damp weather, fog or rain is usually more difficult to control than
the noise under dry conditions. It is, however, seldom a critical factor in line design, since the
increase in noise due to water droplets on the insulators is usually less important than the
corresponding increase in noise produced by the conductors.
4.4.2 Very polluted insulators
Under dry conditions, in addition to the phenomena that cause noise on a clean insulator,
other phenomena of the corona type may occur due to surface unevenness created by
pollution deposits, as mentioned in 6.1 of CISPR/TR 18-1. Under these conditions even
careful design of the various parts of an insulator may be of little benefit. Stress control
devices suitable for improving the voltage distribution on the insulator or along the insulator
string, however, may considerably improve the radio noise performance.
When the polluted insulator surface is wet, radio noise is generated by sparks across the dry
bands, created by the leakage currents, as discussed in 6.1 of CISPR/TR 18-1. Occasionally,
this noise has very high frequency components. It may affect both sound and television
reception and is difficult to control. The only practical remedy is to limit the leakage current
activity on the surface of the polluted insulator. This may be achieved by:
a) diminishing the voltage stress on the insulator – for example by using a longer surface
creepage path than is necessary for electrical withstand;
b) using special types of insulators such as those made of organic material or coated with
semi-conducting glaze, or designs with a longer creepage path such as fog type units,
special shapes, etc.;
c) coating the insulators with silicone grease.
4.5 Spark and microsparks due to bad contacts, commutation effects
Remedial measures for eliminating or reducing these types of radio noise are described in
Clause 5 below and in 8.4 of CISPR/TR 18-1 respectively.
4.6 Defects on power lines and associated equipment in service
Even if all possible precautions have been taken during design and construction of a power
line or substation to keep radio noise within acceptable limits, defects may occasionally occur
during operation, resulting in intolerable noise. This may be caused by breakage of strands on
the conductors, damage to clamps or insulators or accumulation of pollution on conductors
and insulators. In general, these defects shall be eliminated in order that the power system
may operate properly, whether or not they are sources of radio noise. In fact, the occasional
noise caused by such defects may result in detection and location of potential power system
faults.
These abnormal noise sources may be located by various instruments such as radio noise
measuring sets, television receivers or ultrasonic and optical detectors. Location will often be
easier when the noise affects television reception, since at very high frequencies longitudinal

TR CISPR 18-3 © IEC:2010(E) – 11 –
attenuation along the line is very high. When only low and medium frequency radio
broadcasts are affected, location of the noise source may require the recording of the
longitudinal attenuation of the radio noise field strength, combined with optical, ultrasonic or
ultraviolet devices, as discussed in Clause 5.
5 Methods of prediction of the reference level of an overhead line
5.1 General
This publication has been written to provide the engineer in the field with the theoretical and
practical background necessary to deal with radio interference problems. Technical aspects
have been dealt with in part 1 and many of the aspects discussed are dealt with in this clause
in a simplified manner to bring together the theoretical and practical issues.
The reference level of a line is the strength of the radio noise field at a reference frequency
of 500 kHz and at a direct distance of 20 m from the nearest conductor of the line. Where the
voltage gradient in the air at the surfaces of the conductors of a normal line is greater than
about 12 kV/cm to 14 kV/cm, depending on conductor diameter, the radio noise performance
of the line is determined by the performance of the conductors. The number and diameter of
the conductors per phase of a proposed line are often decided by the current-carrying
capacity required or by economic considerations and usually a prediction of the reference
level is required for a particular weather condition. If a line is designed with the conductors at
a high surface gradient very little can be done to reduce the noise level once the line has
been constructed.
Figure B.14 of Annex B of CISPR/TR 18-1 gives the correction to be applied to a radio noise
level relating to a measurement frequency other than 500 kHz.
Where the voltage gradient in the air at the surfaces of the conductors of a line is less than
about 12 kV/cm, the radio noise level is usually determined by the insulators and hardware. In
this case the radio noise performance of the line is inherently good and it is usually desirable
to preserve this good quality by selecting insulators and hardware of a matching quality. Most
of the methods of prediction or predetermination are concerned with the conductor noise and
do not apply to lines where the conductors are at a low surface gradient. None of the methods
applies to sparking sources at loose or imperfect contacts.
5.2 Correlation of data given elsewhere in this publication
This clause contains information about the correlation of the radio noise voltage at the line
and the resulting radio noise field strength at ground level at a certain lateral or direct
distance slant to the respective line.
a) Methods relating to noise from conductors
Subclause 5.3 of CISPR/TR 18-1 gives a survey of methods of prediction or
predetermination, both analytical or semi-empirical and empirical or comparative. The
analytical method relies on the results of measurements carried out on a short length of
sample conductor in a test cage and involves highly complex analyses. The sample
conductor can be tested with any desired surface condition and the radio noise voltage
measured by a circuit given in 4.5 of CISPR/TR 18-2. However, for a.c. lines, a reliable
prediction of the reference level due to conductor corona can be calculated only from the
wet test since in this case the number of individual corona sources per unit length is
sufficiently high to represent a statistically satisfactory sample. For d.c. lines, reference
should be made to 8.2 of CISPR/TR 18-1 for the calculation of the noise level.
The simple comparative formulae referred to in 5.3 of CISPR/TR 18-1 rely on the results
of radio noise field strength measurement carried out on an existing line of similar design.
These formulae take into account the effects of any difference between the reference and
proposed lines such as the differences in surface voltage gradient or conductor diameter.
If the design of the reference and the proposed lines are similar and the operating

– 12 – TR CISPR 18-3 © IEC:2010(E)
conditions, such as air pollution, etc., are also similar a fairly accurate prediction may be
obtained of the reference level to be expected from the proposed line due to conductor
corona. The effects of weather may also be determined by taking measurements on the
reference line in a variety of weather conditions.
In 5.4 and Annex B of CISPR/TR 18-1 is given a catalogue of radio noise field strength
profiles resulting from conductor corona for certain designs of single circuit overhead line.
The profiles are correct when the value of the voltage gradient in the air at the surfaces of
the conductors of the lines are sufficiently high to produce radio noise and the values of
the field strength, at a measurement frequency of 500 kHz, are given for both heavy rain
and average fair weather conditions; the heavy rain conditions producing a higher field
strength of between 17 dB and 25 dB. The profiles show the attenuation of the field with
distance normal to the lines for distances out to 150 m.
b) Method relating to noise from insulators and/or fittings
Subclause 6.2 of CISPR/TR 18-1 gives a correlation between the radio noise voltage
generated by a hardware or component of a line, when measured in accordance with the
procedure given in 4.5 of CISPR/TR 18-2, and the level of the reference field. This
correlation applies where the line has a single noise source, for example a broken
insulator, or where multiple sources are uniformly distributed along the line. The method,
which includes a semi-empirical formula, is particularly useful where the conductors of a
proposed line are to operate at a low surface gradient and a prediction is required of the
reference level to be expected from the insulators of the line. When the measurement
procedure given in 4.5 of CISPR/TR 18-2 is carried out on insulators they are usually in a
clean and dry condition, since this condition is normally specified, but the procedure is not
restricted to measurements on clean and dry objects and specially polluted sample
insulators could be tested when damp and when dry and the results inserted into the
formula to predict the reference level of a proposed line.
c) Methods relating to aggregate noise from the conductors, insulators and/or hardware.
Subclause 5.2 of CISPR/TR 18-1 gives information on the use of test lines. Where
conditions relating to a new design of line are such that they cannot be related to data
available from an existing line the expected performance is sometimes studied on a
relatively short test line. Such test line studies are particularly useful when a new system,
for operation at a much higher voltage than hitherto, is in the planning stage. The radio
noise performance of the experimental line is monitored in a range of weather and
atmospheric conditions so that the performance of the proposed line can be assessed
under the conditions which it will experience in service. This could also include the effects
of insulator pollution. Other important data, such as corona loss and acoustic noise
performance, can also be obtained from the test line at the same time.
In 5.4 of CISPR/TR 18-2 a method is given whereby the reference level of a line may be
found which will protect a given broadcast signal strength at a given distance from the line
for 80 % of the time with 80 % confidence.
5.3 CIGRÉ formula
A simple direct formula has also been evolved for predicting the level of the radio noise field
strength to be expected from the conductors of a line. The formula, which is empirically based,
gives the most probable level to be expected from aged conductors in fair weather at a direct
distance D of 20 m from the nearest conductor at a measurement frequency of 500 kHz. The
formula is derived from lines operating at voltages between 200 kV and 765 kV and at
maximum voltage gradients between 12 kV/cm and 20 kV/cm. Strictly, the formula gives the
noise from one phase conductor or bundle of a line and the effects of the other conductors
may be taken into account by a summation process; however, for a number of designs of lines
within these ranges, it is found that only a small error is introduced if only the conductor
producing the highest noise at the measuring point of a three-phase line is considered;
usually this is the nearest conductor but not necessarily so in all cases.
The formula is
TR CISPR 18-3 © IEC:2010(E) – 13 –
E = 3,5 g + 12 r – 30,   in dB(μV/m)
max
where
E is the level of the radio noise field strength in dB(μV/m) at a direct distance D of 20 m
from nearest conductor of proposed line;
g is the maximum gradient of the r.m.s. voltage at the conductor surface, in kV/cm;
max
r is the radius of conductor or sub-conductor, in cm.
This matter is considered in more detail in Annex A.
5.4 Determination of 80 % level
*
The 80 % level for a line may be predicted by calculation [2, 3] or, if the line exists, the 80 %
level may be determined with a high degree of confidence, by measurement. Methods of
determining the 80 % level are as follows:
1) for an existing line the 80 % level may be determined, with a high degree of confidence,
from the all-weather distribution curve obtained by measurements made over a period of
one year.
2) if the all-weather distribution curve is not available, or in the case of a proposed line, the
results of measurements made one line of similar design in a similar climate and pollution
environment could be used.
3) from the figures mentioned in 4.3.4 of CISPR/TR 18-1 it is seen that, on average, the
80 % level for a line is 10 dB greater than the 50 % level. Therefore, if the 50 % level is
known the 80 % level may be estimated.
4) the 80 % level may be predicted by adding 5 dB to 15 dB, depending on the climate, to the
fair-weather level estimated from the simple formula given in 5.3 above.
5.5 Conclusions
The particular method of prediction to use in the case of a particular proposed line will depend
on whether the interest is in conductor corona or noise due to insulators and/or hardware that
is whether the conductors are to operate at a voltage gradient greater than about 14 kV/cm or
less than about 12 kV/cm. For voltage gradients in between these values both the conductors
and the insulators may contribute to the noise level of the proposed line.
The simple comparative formula referred to in item a) of 5.2, the catalogue of radio noise field
strength profiles referred to also in item a) of 5.2 and the CIGRÉ formula given in 5.3 are all
simple to use and, provided they are used within their inherent limitations, they should give
reasonably accurate indications of the reference level to be expected from the conductors of a
proposed line. It should be borne in mind that owing to the variable nature of radio noise and
its dependency on the effects of weather, atmospheric conditions, pollution, etc., it is often
difficult to measure the reference level of a line with any high degree of accuracy and
reproducibility.
The method referred to in item b) of 5.2 relating to noise from insulators and/or hardware has
not, as yet, become established practice for the case of specially polluted test insulators but
the method would appear to have promise for this case. If a test line, referred to in item c) of
5.2, is available, together with the time required to carry out experimental work, the likely
reference level from a proposed line may be obtained with a good degree of accuracy for the
particular conductor, insulators and hardware proposed.
—————————
*
The figures in square brackets refer to the Bibliography.

– 14 – TR CISPR 18-3 © IEC:2010(E)
6 Preventive and remedial measures to minimize radio noise generated by
bad contacts and their detection and location
6.1 General
Radio noise generated by sparking at bad, that is loose or imperfect, contacts occurs mainly
in dry weather since in wet weather the comparatively small gaps involved usually became
bridged with moisture.
6.2 Preventive and remedial measures
When constructing high voltage equipment it is important
1) to ensure that all fixing bolts are securely tightened, and
2) to bond conducting elements, as far as is possible, either to earth or conductor potential.
On distribution lines, bonding adjacent metal surfaces is important but bonding to earth or
conductor potential is not required for spark suppression. If bonding to one side is not
possible (for example at the pin and clevis, or ball and socket, couplings of an insulator string),
the adjacent conducting elements should have good metal-to-metal contact and the whole
assembly should be well insulated from other metallic parts of the equipment. It should be
borne in mind that even when equipment is new, galvanized metallic parts can have a
corrosion coating of zinc carbonate. When the surfaces have weathered, additional oxides
and sulphides may be present and an imperfect contact may result leading to the possibility of
gap-type discharges. The phenomenon may occur when suspension insulator strings have
inadequate mechanical loading.
The following preventive and remedial measures have been found to be effective:
a) Conductive grease and paste
A quick and economical method is the application of conductive grease to the socket or
clevis area of insulators. This is a temporary cure, however, and it is necessary to re-
apply the grease at a later date. The use of a copper paste, instead of conductive grease,
promises to be a more lasting remedy but care shall be taken to ensure that the grease or
paste does not find its way on to an insulating surface.
Ordinary, non-conductive grease applied to freshly galvanized surfaces will inhibit
corrosion.
b) Bonding brush
The application of a bonding brush, with stainless steel bristles, is a temporary cure,
lasting for some three to five years, by providing metal-to-metal contact in the pin and
clevis, or ball and socket, area.
c) Bonding clip
Where pin and clevis type insulators are used, bonding clips can easily be installed in the
pin and clevis area. It is especially important that these be installed in the conductor
clamp connection with the line end insulator. There are several types of clip suitable for
insertion between ball and socket which maintain sufficient pressure to break down the
oxide film.
d) Permanent bonding
The best results are likely to be obtained with a permanent flexible bon
...