IEC TS 61973:2012

IEC/TS 61973 ®
Edition 1.0 2012-04
TECHNICAL
SPECIFICATION
colour
inside
High voltage direct current (HVDC) substation audible noise

IEC/TS 61973:2012(E)
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IEC/TS 61973 ®
Edition 1.0 2012-04
TECHNICAL
SPECIFICATION
colour
inside
High voltage direct current (HVDC) substation audible noise

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
PRICE CODE
XC
ICS 29.240.10; 29.240.99 ISBN 978-2-8322-0077-3

– 2 – TS 61973 © IEC:2012(E)
CONTENTS
FOREWORD . 7
1 Scope . 9
2 Normative references . 9
3 Terms and definitions . 10
3.1 Sound and noise terms . 10
3.2 Sound radiation terms . 14
3.3 Acoustic fields . 16
4 Environmental influences . 16
4.1 General . 16
4.2 Directivity of sound radiation . 16
4.3 Background noise . 17
4.4 Topography . 19
4.5 Meteorological conditions . 20
5 Noise level limits . 21
5.1 General . 21
5.2 Regulations . 22
5.2.1 Noise level limits . 22
5.2.2 Noise level measurement . 22
5.3 Land-use classifications . 22
5.4 Location of required performance limits . 23
5.4.1 General . 23
5.4.2 At the fence surrounding the HVDC substation or at the border of the
substation owner’s property . 23
5.4.3 At the given contour away from the HVDC substation (e.g. on a circle

perimeter or beyond a property border line) . 23
5.4.4 At the border of a nearby property . 23
5.5 Relationship of performance limits to time duration. 24
5.6 Typical noise performance limits . 24
5.6.1 General . 24
5.6.2 Specific A-weighted sound pressure levels . 24
5.6.3 Maximum allowable increase over background noise levels . 24
6 Sound emitting sources . 25
6.1 General . 25
6.2 Converter transformer . 25
6.2.1 Noise sources in a converter transformer . 25
6.2.2 Comparison with a.c. power transformers . 26
6.2.3 Special features of HVDC converter transformers . 26
6.2.4 Transformer winding noise. 27
6.3 Reactors . 28
6.3.1 Type and design of HVDC reactors . 28
6.3.2 Mechanism of sound generation . 28
6.3.3 AC filter reactors . 33
6.3.4 HVDC smoothing reactors . 34
6.3.5 Self-tuned filter reactors . 35
6.4 Capacitors . 36
6.4.1 Type and design of capacitors . 36

TS 61973 © IEC:2012(E) – 3 –
6.4.2 Mechanism of sound generation . 36
6.5 Cooling fans . 39
6.6 Other sound-emitting sources . 40
6.6.1 Switching devices . 40
6.6.2 Synchronous compensators . 41
6.6.3 Diesel generators . 41
6.6.4 Air conditioning plant . 41
6.6.5 Cooling circuit pumps . 41
6.6.6 Converter valves . 41
6.6.7 Air compressors . 42
6.6.8 Corona sources . 42
6.7 Typical sound power levels of sound emitting sources . 42
7 Sound reduction measures . 42
7.1 General . 42
7.2 Substation layout . 43
7.2.1 General . 43
7.2.2 Transformers and tanked reactors . 43
7.2.3 Air-cored reactors . 43
7.2.4 Capacitors . 44
7.2.5 Cooling fans . 44
7.2.6 Diesel generators . 44
7.2.7 Switching devices . 44
7.2.8 Air conditioning plant . 44
7.2.9 Corona sources . 44
7.2.10 Synchronous compensators . 44
7.3 Component design . 45
7.3.1 General . 45
7.3.2 Transformers and tanked reactors . 45
7.3.3 Air-cored reactors . 45
7.3.4 Capacitors . 45
7.3.5 Cooling fans . 46
7.3.6 Pumps and diesel generators . 46
7.3.7 Switching devices . 46
7.3.8 Air-conditioning plant . 46
7.3.9 High voltage connections . 46
7.4 Sound enclosures . 46
7.4.1 General . 46
7.4.2 Transformers and tanked-reactors . 46
7.4.3 Air-cored reactors . 47
7.4.4 Capacitors . 47
7.5 Retrofitable techniques . 48
7.5.1 Enclosures . 48
7.5.2 Damping . 48
7.5.3 Active noise and vibration mitigation . 48
8 Operating conditions . 48
8.1 General . 48
8.2 Normal operating conditions . 49
8.3 Exceptional operating conditions . 50
8.4 Operating conditions specified for verification. 51

– 4 – TS 61973 © IEC:2012(E)
9 Sound level prediction . 51
9.1 General . 51
9.2 Modelling of plant . 52
9.2.1 General . 52
9.2.2 Layout . 52
9.2.3 Source . 52
9.2.4 Transmission path . 52
9.3 Calculation procedure . 53
9.3.1 Sequence of calculation. 53
9.3.2 Calculation of attenuation terms . 55
9.3.3 Results presentation . 59
10 Verification of component sound power . 61
10.1 General . 61
10.2 Calculation . 61
10.2.1 General . 61
10.2.2 Calculation of force spectrum . 62
10.2.3 Transfer function calculation . 62
10.2.4 Sound power calculation . 63
10.3 Measurement . 64
10.3.1 General aspects on sound power determination. 64
10.3.2 Sound pressure measurement . 66
10.3.3 Corrections for background noise . 67
10.3.4 Sound intensity measurement . 67
10.4 Combination of calculation and measurement . 69
10.4.1 General . 69
10.4.2 Verification of key components . 69
10.4.3 Verification of key components at site . 69
11 Verification of sound levels from the HVDC substation . 70
11.1 General . 70
11.2 Acoustic environment . 71
11.3 Conditions for verification . 71
11.4 Calculation . 71
11.5 Measurement . 72
11.6 Combination of calculation and measurement . 72
12 Parameters to be specified . 74
12.1 General . 74
12.2 Noise level measurement . 74
12.3 Data to be presented by customers, or to be investigated by contractors . 74
12.3.1 Land-use classification, noise regulation and limits . 74
12.3.2 Environmental condition . 75
12.3.3 Operation condition of HVDC substation . 77
12.4 Data to be clarified by contractors . 77
12.4.1 Noise of components . 77
12.4.2 Noise prediction of the HVDC substation . 77
12.4.3 Noise measurement on the site . 78
Annex A (normative) Procedure to correct for background noise in HVDC and SVC
plants . 79
Bibliography . 82

TS 61973 © IEC:2012(E) – 5 –
Figure 1 – Spherical spreading in a free-field from a point source . 17
Figure 2 – Hemispherical spreading from a point source . 18
Figure 3 – Quarter-spherical spreading from a point source . 18
Figure 4 – Explanation of specific and background noise . 19
Figure 5 – Example of reflecting hill and low ground. . 19
Figure 6 – Example of sound refraction with the shown wind gradient . 20
Figure 7 – Sound travels faster near the ground . 21
Figure 8 – Sound travels slower near the ground . 21
Figure 9 – Dry-type air-core reactor . 29
Figure 10 – Magnetic field of an air-core reactor winding . 30
Figure 11 – Simplified shape of the symmetrical breathing mode of a reactor winding . 31
Figure 12 – Example of flexural modes (bending modes) for a simply supported
winding layer without axial constraint . 32
Figure 13 – Example of spectrum of currents through a.c. filter reactor . 33
Figure 14 – Example of spectrum of forces acting on the reactor winding . 34
Figure 15 – Example of spectrum of currents through an HVDC smoothing reactor . 34
Figure 16 – Example of spectrum of forces acting on the reactor winding . 35
Figure 17 – Reactor for self-tuned filter applications . 35
Figure 18 – Capacitor element package with capacitor elements . 36
Figure 19 – Forces in a capacitor element . 37
Figure 20 – Example of spectrum of voltages across the capacitor . 38
Figure 21 – Example of spectrum of electrostatic forces in a capacitor. 39
Figure 22 – Explanation of AC network harmonics and converter harmonics . 50
Figure 23 – Examples of transmission paths from source to receiver . 53
Figure 24 – Grouping of point sources to one equivalent source if the measurement
distance (r) is larger than 2a . 54
Figure 25 – Definition of geometrical parameters used for calculation of screening . 56
Figure 26 – Reflecting obstacles are treated by mirror sources . 57
Figure 27 – Definition of parts for calculation of ground attenuation . 57
Figure 28 – Definition of parameters used in Equation 38 . 59
Figure 29 – Example of graphical presentation of sound pressure level calculation . 60
Figure 30 – Three steps to determine the sound power of HVDC components . 62
Figure 31 – Linear transfer function between e.g. force and vibration velocity for a
1-DOF system with the resonance frequency 500 Hz . 63
Figure 32 – Definitions of the parameters used in Equation (42) . 67
Figure 33 – Combination of calculation and measurement in determining the sound
pressure level . 72
Figure 34 – Example of layout of noise sources of an HVDC substation . 73
Figure 35 – HVDC substation and example of microphone positions for determination
of sound power levels . 73
Figure A.1 – Example of a background correction at 1/24 octave band resolution . 80

Table 1 – Examples of component sound power level . 42
Table 2 – Normal operating conditions . 50

– 6 – TS 61973 © IEC:2012(E)
Table 3 – Exceptional operating conditions . 51
Table 4 – Examples of atmospheric attenuation coefficients . 56
Table 5 – Examples of attenuation coefficient values for octave bands . 59
Table 6 – Groups of noise sources . 60
Table 7 – Ranking of noise sources . 61
Table 8 – Vibration force frequency spectrum resulting from the electrical fundamental
th
frequency 50 Hz and its 11 harmonic . 62
Table 9 – Summary of different methods for sound power determination . 69
Table 10 – Land use classification . 74
Table 11 – Existence different noise limits at different times . 75
Table 12 – Existence of noise limits due to further regulation . 75
Table 13 – Definition of noise limits at different locations . 75
Table 14 – Existence of background noise limits at different locations and different
times . 75
Table 15 – Compilation of relevant topographical features . 76
Table 16 – Compilation of relevant meteorological conditions . 76
Table 17 – Compilation of further noise related weather conditions . 76
Table 18 – Existence of additional locations with relevant noise limits . 76
Table 19 – Possibility of future development . 76
Table 20 – Other sources of audible noise . 76
Table 21 – Definition of operating condition during audible noise measurement . 77
Table 22 – Further conditions relevant for audible noise measurement . 77
Table 23 – List of audible noise sources to be installed . 77
Table 24 – Contents of an audible noise prediction report . 78
Table 25 – Contents of an audible noise measurement report . 78
Table A.1 – Total sound level for the SVC example. 81

TS 61973 © IEC:2012(E) – 7 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
______________
HIGH VOLTAGE DIRECT CURRENT (HVDC)
SUBSTATION AUDIBLE 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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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 specification when
• the required support cannot be obtained for the publication of an International Standard,
despite repeated efforts, or
• the subject is still under technical development or where, for any other reason, there is the
future but no immediate possibility of an agreement on an International Standard.
Technical specifications are subject to review within three years of publication to decide
whether they can be transformed into International Standards.
IEC 61973, which is a technical specification, has been prepared by subcommittee 22F:
Power electronics for electrical transmission and distribution systems, of IEC technical
committee 22: Power electronic systems and equipment, with the participation of IEC
technical committee 115: High voltage direct current (HVDC) transmission for DC voltages
above 100 kV.
– 8 – TS 61973 © IEC:2012(E)
The text of this technical specification is based on the following documents:
Enquiry draft Report on voting
22F/243/DTS 22F/260/RVC
Full information on the voting for the approval of this technical specification 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.
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,
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• 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
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TS 61973 © IEC:2012(E) – 9 –
HIGH VOLTAGE DIRECT CURRENT (HVDC)
SUBSTATION AUDIBLE NOISE
1 Scope
This technical specification applies to the specification and evaluation of outdoor audible
noise from high voltage direct current (HVDC) substations. It is intended to be primarily for the
use of the utilities and consultants who are responsible for issuing technical specifications for
new HVDC projects with and evaluating designs proposed by prospective contractors. It is
primarily intended for HVDC projects with line-commutated converters. Part of this technical
specification can also be used for the same purpose for HVDC projects using voltage sourced
converters, and for flexible a.c. transmission systems (FACTS) devices such as static Var
compensators (SVCs) and static synchronous compensators (STATCOMs).
2 Normative references
The following documents, in whole or in part, are normatively referenced in this document and
are indispensable for its application. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any
amendments) applies.
IEC 61672-1, Electroacoustics – Sound level meters – Part 1: Specifications
IEC 61672-2, Electroacoustics – Sound level meters – Part 2: Pattern evaluation tests
ISO 1996-2, Acoustics – Description, assessment and measurement of environmental noise –
Part 2: Determination of environmental noise levels
ISO 266:1997, Acoustics – Preferred frequencies
ISO 3740, Acoustics – Determination of sound power levels of noise sources – Guidelines for
the use of basic standards
ISO 3743-2, Acoustics – Determination of sound power levels of noise sources; engineering
methods for small, movable sources in reverberant fields – Part 2: Methods for special
reverberation test rooms
ISO 3744, Acoustics – Determination of sound power levels and sound energy levels of noise
sources using sound pressure – Engineering methods for an essentially free field over a
reflecting plane
ISO 3745, Acoustics – Determination of sound power levels of noise sources using sound
pressure – Precision methods for anechoic and hemi-anechoic rooms
ISO 3746, Acoustics – Determination of sound power levels and sound energy levels of noise
sources using sound pressure – Survey method using an enveloping measurement surface
over a reflecting plane
ISO 8297, Acoustics – Determination of sound power levels of multisource industrial plants for
evaluation of sound pressure levels in the environment – Engineering method
ISO 9613-1, Acoustics – Attenuation of sound during propagation outdoors – Part 1:
Calculation of the absorption of sound by the atmosphere

– 10 – TS 61973 © IEC:2012(E)
ISO 9613-2, Acoustics – Attenuation of sound during propagation outdoors – Part 2: General
method of calculation
ISO 9614-1, Acoustics – Determination of sound power levels of noise sources using sound
intensity – Part 1: Measurement at discrete points
ISO 9614-2, Acoustics – Determination of sound power levels of noise sources using sound
intensity – Part 2: Measurement by scanning
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 Sound and noise terms
3.1.1
sound
any pressure variation in air, water or other elastic medium
Note 1 to entry: Sound is expressed as sound pressure, sound intensity or sound power (see 3.1.3).
Note 2 to entry: In this technical specification, the medium is assumed to be air.
3.1.2
sound waves in air
traveling sound pressure fluctuations
3.1.3
sound pressure
p
fluctuating pressure superimposed on the static pressure
Note 1 to entry: Sound pressure is expressed in pascal.
Note 2 to entry: Sound pressure is usually expressed through the use of a decibel scale, as sound pressure level
(see 3.1.4).
3.1.4
sound pressure level
L
p
logarithm of the ratio of the r.m.s. value of a given sound pressure to the reference sound
pressure
 
(p)  p 
 
 
L =10 lg = 20 lg
p
 
 
p
(p ) 0
 
 
where:
p  is the measured r.m.s. sound pressure in pascal;
–5
p is the reference r.m.s. pressure of 2 × 10 pascal, which corresponds to the 0 dB as
threshold of audibility.
Note 1 to entry: lg(x) means the 10th logarithm of x; this convention is used throughout the document.
Note 2 to entry: The sound pressure level (L ) is expressed in decibels (dB).
p
Note 3 to entry: Sound pressure level is measured with sound level meters, which normally incorporate a
frequency-weighting filter. For further details see 3.2.3.

TS 61973 © IEC:2012(E) – 11 –
Note 4 to entry: Since the sound level distribution measured around sound emitting objects is usually non-uniform
it is normally necessary to assess sound levels on spatial average figures gained from several measuring positions
rather than on one single discrete position.
3.1.5
average sound pressure level
L
pA
 N 
0,1L
1 pAi
 
L =10 lg 10
pA
∑
 
N
 
 i = 1 
where:
L is the average sound pressure level in dB(A);
pA
L is the measured sound pressure level at location i in dB(A), if required corrected for
pAi
the influence of background noise;
is the total number of measurement locations.
N
Note 1 to entry: The summation of several frequency bands (1/1-octave, 1/3-octave etc.) is performed in a similar
fashion:
 N 
0,1 Lp( f j)
 
L =10 lg 10
pA
∑
 
N
 
i = 1
 
where:
L pA, TOT is the total sound pressure level in dB(A);
is the sound pressure level in frequency band f in dB(A), if required, corrected for the influence of
L ( f )
j
P j
background noise;
N is the total number of frequency components.
Note 2 to entry: See 3.2.2 for more information on 1/3-octave and 1/1-octave bands.
3.1.6
sound intensity
I
I
for a plane propagating sound wave, the sound intensity, I at a given point is defined as
I
p
I =
I
ρ × c
where:
p  is the r.m.s. value of the measured sound pressure in pascal;

ρ  is the constant density of air in equilibrium in kg/m ;
c  is the speed of sound in air in m/s.
3.1.7
normal sound intensity
I
In
– 12 – TS 61973 © IEC:2012(E)
for a plane propagating sound wave, the sound intensity, I at a given point in the normal
I
direction n is defined as
p
I =
In
ρ ×c
where:
p  is the r.m.s. value of the measured sound pressure in pascal;

ρ  is the constant density of air in equilibrium in kg/m ;
c  is the speed of sound in air in m/s.
3.1.8
sound intensity level
L
I
expressed in decibels ratio of the sound intensity to the reference sound intensity
 
I
 
L = 10 lg
I
 
I
 
−12 −2
where, I = 1×10 Wm
3.1.9
normal sound intensity level
L
In
ratio of the normal sound intensity to the reference sound intensity
 
I
n
 
L = 10 lg
In
 
I
 
−12 −2
where, I = 1×10 Wm
Note 1 to entry: Normal sound intensity level is expressed in decibel.
Note 2 to entry: I may be negative if there is a sound wave into the enclosing surface, which may happen in the
n
acoustical near-field. The level is then expressed as – “xx” dB. The equation in 3.1.6 however assumes a plane
propagating wave in the far-field of a sound source, in the direction defined as positive.
3.1.10
sound power
W
rate at which sound energy is radiated by a source
Note 1 to entry: Sound power is a scalar quantity and is expressed in watt.
Note 2 to entry: The total sound power is defined as:

TS 61973 © IEC:2012(E) – 13 –
W = I d A
∫
A
where:
A is a closed surface of integration;
I is the vector of sound intensity on an elementary surface d A .
3.1.11
sound power level
L
W
 
W
 
L = 10 lg
W
 
W
 0 
where:
W is the emitted sound power in watt;
−12
W is a reference sound power of 1×10 W and corresponding to 0 dB as the threshold
of audibility.
Note 1 to entry: The sound power level is expressed in decibel.
Note 2 to entry: The A-weighted sound power level (L ) of an object may be determined from the surface sound
WA
pressure level (L ) according to ISO 3744.
pA
 
S
 
L = L + 10 lg
WA pA
 
S
 0 
where:
S  is the area of the “measurement surface” enclosing the object (in m );
S is a reference area of 1 m .
Note 3 to entry: The sound power within an enclosing surface is independent of the distance to the sound source,
but the sound pressure depends on the distance, reflections etc.
3.1.12
sound propagation
for hemispherical propagation over a reflecting plane, the sound pressure level at a given
point depends on the distance from the source, the source sound power and the geometry
involved as expressed by the following equations
L = L −10 lg (2πr )
p w
or alternatively
L = L −10 lg (2π ) − 20 lg (r)
p w
Note 1 to entry: This expression is sometimes called “the law of distance” in acoustics, when dealing with sound
propagation from stationary sources. The law of distance implies that the sound pressure level decreases by six
decibels (6 dB) for each doubling of distance from the sound source, provided that the measurements are
performed in the far-field of the sound source. The boundary of the far-field depends among other things on the
size of the sound source, the spatial complexity of the sound field and on the radiated frequency. For example; for

– 14 – TS 61973 © IEC:2012(E)
a large transformer, the far-field may begin at a distance of 30 m from the transformer. For a small reactor which
radiates sound at e.g. 1 kHz, the far-field may begin at a distance of 5 m.
The law of distance is strictly speaking only valid for point sources. Many sources can however be treated as point
sources at a sufficient distance from the source. Care must however be taken when applying the formula on real
sources.
3.1.13
noise
unwanted sound
3.1.14
audible noise
unwanted sound with frequency range from 20 Hz to 20 kHz
3.2 Sound radiation terms
3.2.1
directivity of sound radiation
4π r
L = L −10 lg
p
W
Q
where:
L is the sound pressure level at distance r from the sound source;
p
L is the sound power of the sound source;
W
r  is the distance between the source and the receiver;
Q  is the directivity factor of the sound radiation, e.g.
Q = 1 for spherical sound propagation (see Figure 1);
Q = 2 for hemispherical sound propagation (see Figure 2);
Q = 4 for quarter spherical sound propagation (see Figure 3).
Note 1 to entry: The directivity of sound radiation may also be expressed in decibel and is then called directivity
index (DI) which is defined by
DI = 10 lg Q
Q = 2 ⇒ DI = 3 dB, or for Q = 4 ⇒ DI = 6 dB.
For example, for
Note 3 to entry: The directivity index is a correction index (dB-adder) which quantifies the deviation of the sound
propagation from uniform spherical spreading. The sound pressure level may then be calculated from:
L = L + DI −10 lg 4π r
p
W
3.2.2
sound measurement filters
standard filters used for sound measurement equipment and measuring the total level of
sound pressure in a defined frequency band
Note 1 to entry: Usually “1/1-octave” or “1/3-octave” filters are used for these measurements. One 1/1-octave
band contains three 1/3 octave bands. For example, the 31,5 Hz 1/1-
...