CISPR TR 18-2:2010
(Main)Radio interference characteristics of overhead power lines and high-voltage equipment - Part 2: Methods of measurement and procedure for determining limits
Radio interference characteristics of overhead power lines and high-voltage equipment - Part 2: Methods of measurement and procedure for determining limits
CISPR 18-2:2010(E), 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 is 0,15 MHz to 300 MHz. 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 300 MHz 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 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. 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. This second edition cancels and replaces the first edition published in 1986. It is a technical revision. This edition includes the following significant technical changes with respect to the previous edition:
- while the first edition of CISPR 18-2 only considered the direct distance D0 for the establishment of standard profiles for the lateral radio noise field emanating from HV overhead power lines,
- this second edition now also allows for use of the lateral distance y0 for these purposes. This way it allows for conduction of on-site measurements and simplified recording and use of measurement data obtained at lateral distances y slant to the pathway of modern HV and UHV overhead power line constructions with tall suspension towers.
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TR CISPR 18-2 ®
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 2: Methods of measurement and procedure for determining limits
TR CISPR 18-2:2010(E)
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TR CISPR 18-2 ®
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 2: Methods of measurement and procedure for determining limits
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XB
ICS 33.100.01 ISBN 978-2-88912-017-8
– 2 – TR CISPR 18-2 © IEC:2010(E)
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 a.c.
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 from 0,15 MHz to 30 MHz.12
4.2.3 Measurements in the frequency range from 30 MHz to 300 MHz.14
4.3 Statistical evaluation of the radio noise level of a line.15
4.4 Additional information to be given in the report.16
4.5 Measurements on HV equipment in the laboratory.16
4.5.1 Overview .16
4.5.2 State of the test object.17
4.5.3 Test area.17
4.5.4 Atmospheric conditions.18
4.5.5 Test circuit – Basic diagram.18
4.5.6 Practical arrangement of the test circuit.18
4.5.7 Test circuit components.19
4.5.8 Measuring receiver connections .19
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 .21
4.5.13 Test procedure .22
4.5.14 Related observations during the test.23
4.5.15 Data to be given in test report .23
5 Methods for derivation of limits for HV power systems .24
5.1 Overview .24
5.2 Significance of CISPR limits for power lines .24
5.3 Technical considerations for derivation of limits for lines .25
5.3.1 Basic approach.25
5.3.2 Scope.25
5.3.3 Minimum broadcast signal levels to be protected .26
5.3.4 Required signal-to-noise ratio.27
5.3.5 Use of data on radio noise compiled during measurements in the
field .28
5.3.6 Use of data obtained by prediction of the radio noise from high-
voltage overhead power lines .29
5.4 Methods of determining compliance of measured data with limits .30
5.4.1 Long-term recording .30
5.4.2 Sampling method.31
TR CISPR 18-2 © IEC:2010(E) – 3 –
5.4.3 Survey methods.31
5.4.4 Alternative criteria for an acceptable noise level .31
5.5 Examples for derivation of limits in the frequency range below 30 MHz .32
5.5.1 Radio reception .32
5.5.2 Television reception, 47 MHz to 230 MHz .33
5.6 Additional remarks .34
5.7 Technical considerations for derivation of limits for line equipment and
HVAC substations .34
5.7.1 General .34
5.7.2 Current injected by line components and hardware.35
5.7.3 Current injected by substation equipment .35
5.7.4 Practical derivation of limits in the l.f. and m.f. band .35
6 Methods for derivation of limits for the radio noise produced by insulator sets .37
6.1 General considerations.37
6.2 Insulator types.37
6.3 Influence of insulator surface conditions.38
6.3.1 General .38
6.3.2 Clean insulators .38
6.3.3 Slightly polluted insulators.38
6.3.4 Polluted insulators .39
6.4 Criteria for setting up radio noise limits for insulators .39
6.4.1 General .39
6.4.2 Criterion for insulators to be installed in type A areas .40
6.4.3 Criterion for insulators to be installed in type B areas .40
6.4.4 Criterion for insulators to be installed in type C areas .40
6.5 Recommendations.40
7 Methods for derivation of limits for the radio noise due to HVDC converter stations
and similar installations .42
7.1 General considerations.42
7.2 Sources of interference .43
7.2.1 Mechanism of radio noise generation .43
7.2.2 Influence of station design on radio interference.43
7.3 Radiated fields from valve halls .44
7.3.1 Frequency spectra.44
7.3.2 Lateral attenuation.44
7.3.3 Reduction of the radio interference due to direct radiation from the
valve hall.44
7.4 Conducted interference along the transmission lines .45
7.4.1 Description of the mechanism and typical longitudinal profiles.45
7.4.2 Reduction of the interference conducted along the transmission lines.45
7.5 General criteria for stating limits.46
7.5.1 Overview .46
7.5.2 Direct radiation .46
7.5.3 Propagation along the lines .46
8 Figures .48
Annex A (informative) Radio interference measuring apparatus differing from the
CISPR basic standard instruments.62
Annex B (normative) List of additional information to be included in the report on the
results of measurements on operational lines .63
– 4 – TR CISPR 18-2 © IEC:2010(E)
Annex C (informative) Minimum broadcast signal levels to be protected – ITU
recommendations .64
Annex D (informative) Minimum broadcast signals to be protected – North American
standards.65
Annex E (informative) Required signal-to-noise ratios for satisfactory reception.66
Annex F (informative) Derivation of the formula for the protected distance.69
Bibliography.70
Figure 1 – Transformation of pulses through a CISPR measuring receiver .48
Figure 2 – Bursts of corona pulses generated by alternating voltage.49
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 .49
Figure 4 – Basic test circuit.50
Figure 5 – Standard test circuit .50
Figure 6 – Connection to the measuring receiver by a coaxial cable .51
Figure 7 – Connection to the measuring receiver by a balanced cable .51
Figure 8 – Special test circuit.51
Figure 9 – Arrangement for calibration of the standard test circuit.52
Figure 10 – Map showing boundaries of zones A, B, and C in regions 1 and 3 .53
Figure 11 – Illustration of the four basic parameters for a power transmission line .54
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 (- - -) .55
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 (- - -) .56
Figure 14 – Example of frequency spectra of pulses with different rise times, simulating
commutation phenomena in mercury valves and in thyristor valves.56
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 .57
Figure 16 – Example of frequency spectra of the radio interference recorded outside
the hall of a thyristor valve converter station for different operating conditions.57
Figure 17 – Attenuation of the field strength as a function of the distance on a
horizontal plane, for different frequencies .58
Figure 18 – Example of frequency spectrum of the radio interference in the vicinity of
a d.c. line (30 m) at a short distance from the converter station .59
Figure 19 – Example of frequency spectrum of the radio interference in the vicinity of
an a.c. line (20 m) at a short distance from the converter station .60
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 .60
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 .61
Figure 22 – Frequency spectra of the radio interference recorded along a 200 kV d.c.
line, at 20 m from the conductor, at different distances from the converter station .61
Table 1 – Number of n sets of measurement of the radio noise level and
corresponding values for factor k .16
TR CISPR 18-2 © IEC:2010(E) – 5 –
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.42
Table C.1 – Minimum field strength.64
Table C.2 – Nominal usable field strength.64
Table D.1 – Signal levels at the edge of the service area in North America .65
Table E.1 – Summary of signal-to-noise ratios for corona from a.c. lines (Signal
measured with average detector, noise measured with quasi-peak detector).66
Table E.2 – Quality of radio reception or degree of annoyance due to RFI .67
– 6 – TR CISPR 18-2 © IEC:2010(E)
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
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
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9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
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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 second edition cancels and replaces the first edition published in 1986. It is a technical
revision.
TR CISPR 18-2 © IEC:2010(E) – 7 –
This edition includes the following significant technical changes with respect to the previous
edition: while the first edition of CISPR 18-2 only considered the direct distance D for the
establishment of standard profiles for the lateral radio noise field emanating from HV
overhead power lines, this second edition now also allows for use of the lateral distance y for
these purposes. This way it allows for conduction of on-site measurements and simplified
recording and use of measurement data obtained at lateral distances y slant to the pathway of
modern HV and UHV overhead power line constructions with tall suspension towers.
The text of this technical report is based on the following documents:
DTR Report on voting
CISPR/B/494/DTR CISPR/B/502/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.
– 8 – TR CISPR 18-2 © IEC:2010(E)
INTRODUCTION
This technical report forms the second 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 conduction 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 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 second edition of CISPR/TR 18-2 was adapted to the modern structure and content of
technical reports issued by IEC. The first edition of CISPR 18-2 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 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.
TR CISPR 18-2 © IEC:2010(E) – 9 –
The methods of measurement in CISPR/TR 18-2 detail the techniques and procedures for use
when measuring fields on site near to an overhead line 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 as the procedures applicable to
VHF frequency-modulation 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 there is a need for regulations.
– 10 – TR CISPR 18-2 © IEC:2010(E)
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 is 0,15 MHz to 300 MHz.
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 300 MHz 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 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. 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 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
IEC 60060-2, High-voltage test techniques – Part 2: Measuring systems
—————————
*
The figures in square brackets refer to the Bibliography.
TR CISPR 18-2 © IEC:2010(E) – 11 –
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
CISPR 16-4-3, Specification for radio disturbance and immunity measuring apparatus and
methods – Part 4-3: Uncertainties, statistics and limit modelling – Statistical considerations in
the determination of EMC compliance of mass-produced products
CISPR/TR 18-1:2010, Radio interference characteristics of overhead power lines and high-
voltage equipment – Part 1: Description of phenomena
CISPR/TR 18-3:2010, Radio interference characteristics of overhead power lines and high-
voltage equipment – Part 3: Code of practice for minimizing the generation of radio noise
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 Measurements
4.1 Measuring instruments
4.1.1 Response of a standard quasi-peak CISPR measuring receiver to a.c. 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 a.c. 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.
– 12 – TR CISPR 18-2 © IEC:2010(E)
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. Then 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
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 Δf, 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 r.m.s. 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 clause. 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 from 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.
TR CISPR 18-2 © IEC:2010(E) – 13 –
NOTE 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
(x,y,z), i.e. x = place along the line at mid-span where the measurements are made, y = 0 m
and z = 0 m corresponding to the vertical projection to ground of the outmost sub-conductor)
to the centre of the antenna used for the measurements. For determination of the overall
typical lateral field strength profile of the radio noise field of a given overhead HV power
transmission line it may be sufficient to consider lateral distances y in the range from 0 m to
200 m.
– 14 – TR CISPR 18-2 © IEC:2010(E)
In order to allow for comparison of measured lateral profiles of the radio noise fields
generated by several individual HV power transmission lines of the same type or by several
HV power transmission lines of different types it is necessary to determine a reference
distance at which the observed profile curves converge through the same indication level.
Practice proved that this is the case for a distance of 15 m taken laterally from the vertical
projection to ground of the outmost sub-conductor (i.e. the reference point) of the
transmission line concerned. That is why this 15 m distance is defined as the lateral reference
distance y for comparison of different lateral profiles.
In order to allow for subsequent comparison with other lateral radio noise field profiles,
normalised profiles should either be related directly to that lateral reference distance of 15 m
or, in case that measurements could not be performed at that distance, the obtained results
should be normalised to the reference distance by means of the interpolation described in the
next paragraph.
NOTE 1 In case of most of already operated conventional overhead HV power transmission lines the normalised
versions of lateral profiles of the radio noise fields obtained in a direct distance of 20 m from the nearest conductor
converge through the same indication level as those obtained in the new lateral reference distance of 15 m, due to
the usual height of the conductors above ground. It should however be kept in mind that the direct distance of 20 m
used so far may prove impractical for prediction of the radio noise for transmission lines utilising higher voltages
and for which high towers may be used. In order to allow for measurements at ground level also in these conditions
the CIS
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