IEC 60076-10:2016

Power transformers - Part 10: Determination of sound levels

IEC 60076-10:2016 defines sound pressure and sound intensity measurement methods from which sound power levels of transformers, reactors and their associated cooling devices are determined. The methods are applicable to transformers, reactors and their cooling devices - either fitted to or separate from the transformer - as covered by the IEC 60076 and IEC 61378 series. This standard is primarily intended to apply to measurements made at the factory. Conditions on-site can be very different because of the proximity of objects, including other transformers. Nevertheless, this standard is applied to the extent possible for on site measurements. This edition includes the following significant technical changes with respect to the previous edition:
- additional useful definitions introduced;
- definition of distribution type transformers introduced for the purpose this standard;
- new clause for sound level measurement specification introduced;
- requirement for 1/3 octave band measurements introduced for transformers other than distribution type transformers;
- standard measurement distance changed from 0,3 m to 1 m for transformers other than distribution type transformers;
- height of measurement surface is now clearly defined to count from the reflecting plane;
- measurement surface formula unified;
- correction criteria for intensity method introduced;
- rules for sound measurements on dry-type reactors introduced;
- figures revised;
- new informative test report templates introduced (Annex B);
- IEC 60076-10-1 (application guide) revised in parallel providing worthwhile information for the use of this standard.

Transformateurs de puissance - Partie 10: Détermination des niveaux de bruit

L'IEC 60076-10:2016 définit les méthodes de mesure de la pression acoustique et de l'intensité acoustique par lesquelles sont déterminés les niveaux de puissance acoustique des transformateurs, des bobines d'inductance et de leurs dispositifs de refroidissement associés. Les méthodes sont applicables aux transformateurs, aux bobines d'inductance et à leurs dispositifs de refroidissement - qu'ils soient installés sur le transformateur ou en soient séparés - comme décrit dans les séries IEC 60076 et IEC 61378. La présente norme est principalement destinée aux mesures effectuées en usine. Les conditions sur le site peuvent être très différentes, à cause de la proximité d'autres objets, en particulier d'autres transformateurs. Néanmoins, la présente norme est appliquée dans la mesure du possible aux mesures sur le site. Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
- introduction de définitions utiles supplémentaires;
- introduction d'une définition des transformateurs de distribution pour les besoins de la présente norme;
- introduction d'un nouvel article relatif à la spécification des mesures du niveau de bruit;
- introduction d'une exigence relative aux mesures de la bande de 1/3 d'octave concernant les transformateurs autres que les transformateurs de distribution;
- modification de la distance de mesure normalisée qui passe de 0,3 m à 1 m pour les transformateurs autres que les transformateurs de distribution;
- la hauteur de la surface de mesure est désormais clairement définie à partir du plan réfléchissant;
- unification de la formule relative à la surface de mesure;
- introduction de critères de correction concernant la méthode d'intensité;
- introduction de règles relatives aux mesures du son sur des bobines d'inductance de type sec;
- révision des figures;
- introduction de nouveaux modèles de rapport d'essai informatifs (Annexe B);
- révision de l'IEC 60076-10-1 (guide d'application) en parallèle et ajout d'informations utiles relatives à l'utilisation de la présente norme.

General Information

• Status: Published
• Publication Date: 23-Mar-2016
• ICS: 27.120.20 - Nuclear power plants. Safety
• ICS: 29.180 - Transformers. Reactors
• Technical Committee: TC 14 - Power transformers
• Drafting Committee: MT 60076-10 - TC 14/MT 60076-10
• Current Stage: PPUB - Publication issued
• Start Date: 24-Mar-2016
• Completion Date: 15-May-2016

Relations

• Revises: IEC 60076-10:2001 - Power transformers - Part 10: Determination of sound levels
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 60076-10 ®
Edition 2.0 2016-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Power transformers –
Part 10: Determination of sound levels

Transformateurs de puissance –
Partie 10: Détermination des niveaux de bruit

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IEC 60076-10 ®
Edition 2.0 2016-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Power transformers –
Part 10: Determination of sound levels

Transformateurs de puissance –

Partie 10: Détermination des niveaux de bruit

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 29.180 ISBN 978-2-8322-3252-1

– 2 – IEC 60076-10:2016  IEC 2016
CONTENTS
FOREWORD . 4
INTRODUCTION . 6
1 Scope . 8
2 Normative references. 8
3 Terms and definitions . 9
4 Sound power for different loading conditions . 11
4.1 General . 11
4.2 Sound power at no-load excitation . 12
4.3 Sound power of the cooling device(s) . 12
4.4 Sound power due to load current . 12
5 Sound level measurement specification . 14
6 Instrumentation, calibration and accuracy . 15
7 Principal radiating surface . 16
7.1 General . 16
7.2 Transformers with or without cooling device . 16
7.3 Transformers in enclosures with cooling devices inside the enclosure . 16
7.4 Transformers in enclosures with cooling devices outside the enclosure . 17
7.5 Cooling devices mounted on a separate structure where the distance
between the two principal radiating surfaces is ≥ 3 m . 17
7.6 Dry-type transformers . 17
7.7 Dry-type air-core reactors . 17
8 Prescribed contour . 18
9 Microphone positions . 19
10 Calculation of the measurement surface area . 19
10.1 Measurement surface area for measuring distances up to 30 m . 19
10.2 Measurement surface area for measuring distances larger than 30 m . 19
11 Sound measurement . 20
11.1 Test conditions . 20
11.1.1 Placement of test object . 20
11.1.2 Test energisation options . 20
11.1.3 Test application details . 21
11.1.4 Prevailing ambient conditions . 21
11.2 Sound pressure method . 21
11.2.1 General . 21
11.2.2 Test procedure . 21
11.2.3 Calculation of the spatially averaged sound pressure level . 22
11.2.4 Validation of test measurements with respect to background noise . 23
11.2.5 Calculation of environmental correction K . 23
11.2.6 Final correction for steady-state background noise and test environment . 25
11.3 Sound intensity method . 26
11.3.1 General . 26
11.3.2 Test procedure . 26
11.3.3 Calculation of average normal sound intensity and sound pressure level . 27
11.3.4 Measurement validation . 28
11.3.5 Final correction based on P-I index and direction flag . 28

12 Determination of sound power level by calculation . 29
13 Logarithmic addition and subtraction of individual sound levels . 29
14 Far-field calculations for distances larger than 30 m . 30
15 Presentation of results . 31
Annex A (informative) Narrow-band and time-synchronous measurements . 40
A.1 General considerations . 40
A.2 Narrow-band measurement . 40
A.2.1 General . 40
A.2.2 Post processing of narrow-band measurements to exclude background
noise . 41
A.3 Time-synchronous averaging technique . 41
Annex B (informative) Typical report of sound level determination . 42
B.1 Sound pressure method . 42
B.2 Sound pressure method – Appendix for the point-by-point procedure. 50
B.3 Sound intensity method . 51
B.4 Sound intensity method – Appendix for the point-by-point procedure . 59
Bibliography . 60

Figure 1 – Typical microphone path / positions for sound measurement on
transformers excluding cooling devices . 33
Figure 2 – Typical microphone path / positions for sound measurement on transformers
having cooling devices mounted either directly on the tank or on a separate structure
spaced < 3 m away from the principal radiating surface of the main tank . 34
Figure 3 – Typical microphone path / positions for sound measurement on transformers
having separate cooling devices spaced < 3 m away from the principal radiating
surface of the main tank . 35
Figure 4 – Typical microphone path / positions for sound measurement on cooling
devices mounted on a separate structure spaced ≥ 3 m away from the principal
radiating surface of the transformer . 36
Figure 5 – Typical microphone positions for sound measurement on dry-type
transformers without enclosures . 37
Figure 6 – Principle radiating surface and prescribed contour of dry-type air-core
reactors . 38
Figure 7 – Environmental correction, K . 39

Table 1 – Test acceptance criteria . 23
Table 2 – Approximate values of the average acoustic absorption coefficient . 25

– 4 – IEC 60076-10:2016  IEC 2016
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
POWER TRANSFORMERS –
Part 10: Determination of sound levels

FOREWORD
1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of IEC is to promote
international co-operation on all questions concerning standardization in the electrical and electronic fields. To
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6) All users should ensure that they have the latest edition of this publication.
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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is
indispensable for the correct application of this publication.
9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of
patent rights. IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 60076-10 has been prepared by IEC technical committee 14:
Power transformers
This second edition cancels and replaces the first edition published in 2001 and constitutes a
technical revision.
This edition includes the following significant technical changes with respect to the previous
edition:
– additional useful definitions introduced;
– definition of distribution type transformers introduced for the purpose this standard;
– new clause for sound level measurement specification introduced;
– requirement for 1/3 octave band measurements introduced for transformers other than
distribution type transformers;

– standard measurement distance changed from 0,3 m to 1 m for transformers other than
distribution type transformers;
– height of measurement surface is now clearly defined to count from the reflecting plane;
– measurement surface formula unified;
– correction criteria for intensity method introduced;
– rules for sound measurements on dry-type reactors introduced;
– figures revised;
– new informative test report templates introduced (Annex B);
– IEC 60076-10-1 (application guide) revised in parallel providing worthwhile information for
the use of this standard.
The text of this standard is based on the following documents:
FDIS Report on voting
14/846/FDIS 14/849/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
A list of all parts in the IEC 60076 series, published under the general title Power
transformers, can be found 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.
IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
– 6 – IEC 60076-10:2016  IEC 2016
INTRODUCTION
One of many parameters considered when specifying, designing and placing transformers,
reactors and their associated cooling devices is the sound level that the equipment is likely to
emit under defined in-service conditions. This part of IEC 60076 provides the basis for the
specification and test of sound levels.
This standard describes in a logical sequence the loading conditions, how to specify and to
test as well as how to evaluate and report sound levels for the equipment under test. A new
section for the specification of sound levels has been introduced as Clause 5.
For the purpose of this standard, the definition “distribution type transformers” was
introduced. This reflects industry’s need to maintain simpler and faster sound measurements
for this category of transformers.
The new requirement for reporting 1/3-octave band spectra for all sound levels (including the
background noise) on units for installation in substations reflects the more onerous conditions
imposed by planning authorities on the purchaser and also the improved functionality of
modern instrumentation.
When the sound intensity method was introduced in this standard limited experience was
available. During subsequent years of operating this standard levels of experience have
significantly increased and necessary changes have become evident. The equivalence of the
pressure and the intensity methods has been demonstrated within certain test limitations.
The introduction of new validation criteria for the intensity method recognises these
limitations. The permissible pressure – intensity index ∆L remains 8 dB however the
difference between measured sound pressure level and reported sound intensity level is
limited to 4 dB.
For the pressure method the correction procedure for reflections has been enhanced by
recommending the application of frequency dependent K values derived by measurement of
the reverberation time of the test facility. Where K is derived from absorption coefficients the
table for the average absorption coefficients has been rationalised to represent surfaces likely
to be found in the working environment.
Walk-around procedure and point-by-point procedure are equally applicable. The walk-around
procedure reflects the evolution of working practice allowing more time efficient
measurements mainly on large units. For distribution type transformers and in special
situations (health and safety) the point-by-point procedure is more appropriate.
In order to mitigate near-field effects the preferred measurement distance is set to 1 m with
exceptions for distribution type transformers, small test facilities, situations with low
signal-to-noise ratio and for health and safety where the distance is maintained at 0,3 m.
One single formula for the calculation of the measurement surface area S has been introduced
because the former complexity could only result in differences always smaller than 1 dB.
All figures describing the measurement surface area have been revised to be in accordance
with the enveloping method for sound power determination. The height h is always measured
from the test facility floor regardless of the height of the supports beneath the test object
unless the test object is mounted on a support with a sufficiently large surface acting as
reflecting plane.
Additional figures explain the procedure for the determination of the measurement surface
area and the prescribed contour for a number of configurations of dry-type reactors.

When using this standard, it is recommended to frequently refer to the corresponding
application guide IEC 60076-10-1:2016 as it promotes understanding with important
background information and helpful details. IEC 60076-10 and IEC 60076-10-1 were revised
in parallel by the same maintenance team resulting in fully aligned documents.

– 8 – IEC 60076-10:2016  IEC 2016
POWER TRANSFORMERS –
Part 10: Determination of sound levels

1 Scope
This Part of IEC 60076 defines sound pressure and sound intensity measurement methods
from which sound power levels of transformers, reactors and their associated cooling devices
are determined.
NOTE For the purposes of this standard, the term "transformer" frequently means "transformer or reactor".
The methods are applicable to transformers, reactors and their cooling devices – either fitted
to or separate from the transformer – as covered by the IEC 60076 and IEC 61378 series.
This standard is primarily intended to apply to measurements made at the factory. Conditions
on-site can be very different because of the proximity of objects, including other transformers.
Nevertheless, this standard is applied to the extent possible for on-site measurements.
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 60076-1:2011, Power transformers – Part 1: General
IEC 60076-8:1997, Power transformers – Part 8: Application guide
IEC 61043:1993, Electroacoustics – Instruments for the measurement of sound intensity –
Measurements with pairs of pressure sensing microphones
IEC 61672-1, Electroacoustics – Sound level meters – Part 1: Specifications
IEC 61672-2, Electroacoustics – Sound level meters – Part 2: Pattern evaluation tests
ISO 3382-2:2008, Acoustics – Measurement of room acoustic parameters – Part 2:
Reverberation time in ordinary rooms
ISO 3746:2010, 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 9614-1:1993, Acoustics – Determination of sound power levels of noise sources using
sound intensity – Part 1: Measurement at discrete points
ISO 9614-2:1996, 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 terms and definitions given in IEC 60076-1, as well as
the following, apply.
3.1
sound pressure
p
fluctuating pressure superimposed on the static (barometric) pressure by the presence of
sound
Note 1 to entry: It is expressed in pascal, Pa.
3.2
sound pressure level
L
p
ten times the logarithm to the base 10 of the ratio of the square of the r.m.s. sound pressure
–6
to the square of the reference sound pressure (p = 20 × 10 Pa)
Note 1 to entry: It is expressed in decibels, dB.
p
L = 10 ×lg (1)
p
p
3.3
sound intensity
I
vector quantity describing the magnitude and direction of the sound power flow per unit area
at a given position
Note 1 to entry: The unit is watts per square metre, W/m .
3.4
normal sound intensity
I
n
component of the sound intensity in the direction normal to a measurement surface
Note 1 to entry: By convention, normal sound intensity is counted positive if the energy flow is directed away from
the test object and negative if the energy flow is directed towards the test object.
3.5
normal sound intensity level
L
I
ten times the logarithm to the base 10 of the ratio of the r.m.s. normal sound intensity to the
–12 –2
reference sound intensity (I = 1 × 10 Wm )
Note 1 to entry: It is expressed in decibels, dB.
I
n
L = 10 × lg (2)
I
I
Note 2 to entry: Since I can be either positive or negative, a separate direction flag F for L to indicate the
n Dir I
direction of flow of energy is to be maintained for further analysis such as calculating average and integral
quantities.
– 10 – IEC 60076-10:2016  IEC 2016
3.6
direction flag
F
Dir
indication for the direction of sound energy flow, required for sound intensity because of its
vector nature
Note 1 to entry: +1 for sound energy flow away from the test object, –1 for sound energy flow towards the test
object.
3.7
sound power
W
rate at which airborne sound energy is radiated by a source
Note 1 to entry: It is expressed in watts, W.
3.8
sound power level
L
W
ten times the logarithm to the base 10 of the ratio of a given r.m.s. sound power to the
–12
reference sound power (W = 1 × 10 W)
Note 1 to entry: It is expressed in decibels, dB.
W
(3)
L = 10 ×lg
W
W
3.9
total sound level
sound level comprising the whole frequency range under consideration
Note 1 to entry: This level is returned either directly by the measurement device or derived by logarithmic
summation of the sound levels of all individual frequency bands.
3.10
principal radiating surface
hypothetical surface surrounding the test object, assumed to be the surface from which sound
is radiated
3.11
measurement surface
S
surface enveloping the test object at the measurement distance from the principal radiating
surface on which the measurement path(s) or points are located
3.12
surface measure
L
S
ten times the logarithm to the base 10 of the ratio of the measurement surface S to the
reference surface S (1 m )
Note 1 to entry: It is expressed in decibels, dB.
S
L = 10 ×lg (4)
S
S
3.13
measurement distance
x
horizontal distance between the principal radiating surface and the measurement surface
3.14
prescribed contour
horizontal path(s) on the measuring surface on which measurements shall be made
3.15
walk-around procedure
sound level measurement obtained by continuously moving the microphone(s) along the
prescribed contour(s) at constant walking speed as the device is measuring a time averaged
and spatially averaged sound level
Note 1 to entry: Test equipment may record a digital audio file during the measuring procedure for post-
processing to determine the necessary quantities.
3.16
point-by-point procedure
sound level measurements obtained from a number of discrete microphone positions on the
prescribed contour(s), equally spaced and not more than 1 m apart
Note 1 to entry: The spatial average sound level is the average of all the point measurements.
3.17
background noise level
A-weighted sound pressure level measured along the prescribed contour with the test object
inoperative
3.18
environmental correction
K
correction that accounts for the influence of undesired sound reflections from room
boundaries and/or reflecting objects in the test room when sound pressure measurements are
used
3.19
P-I index
∆L
difference between uncorrected spatially averaged sound pressure level and spatially
averaged sound intensity level
Note 1 to entry: A-weighted values shall be used.
3.20
distribution type transformers
transformers for installation other than in substations with rated power typically lower than
5 000 kVA
Note 1 to entry: This definition is made for the purpose of this standard.
Note 2 to entry: This definition applies to both liquid-immersed and dry-type transformers.
4 Sound power for different loading conditions
4.1 General
There are three components of sound potentially contributing to the overall transformer sound
power level in service:
– 12 – IEC 60076-10:2016  IEC 2016
• sound power at no-load excitation;
• sound power of the cooling device;
• sound power due to load current.
The representation of the sound power level of a transformer at a certain service condition is
given by the logarithmic sum of the three sound power components at this service condition.
For details see Clause 13.
4.2 Sound power at no-load excitation
Sound power due to no-load excitation has to be regarded for all types of transformer. The
excitation voltage shall be of sinusoidal or practically of sinusoidal waveform and rated
frequency. The voltage shall be in accordance with 11.5 of IEC 60076-1:2011. In the case of
reactors a no-load condition does not exist since rated current will flow as soon as rated
voltage is applied. For more information on reactor sound testing see IEC 60076-6.
The usual condition for sound power level determination of transformers at no-load excitation
refers to rated voltage at an untapped winding. Other excitation conditions may occur in
service leading to lower or higher sound power levels and might also be the condition for a
guarantee and if so shall be specified by the purchaser. For transformers designed to operate
with variable flux, the sound power at no-load excitation is strongly impacted by the tapping
position. The tapping position for the sound measurement has therefore to be agreed between
manufacturer and purchaser during tender stage.
If a transformer is fitted with reactor-type on-load tap-changer equipment where the reactor
may on certain tap-changer positions be permanently energized, the measurements shall be
made with the transformer on a tapping which involves this condition and which is also as
near to the principal tapping as possible.
The selected test conditions shall be clearly indicated in the test report.
NOTE DC bias magnetization of the core can cause a significant increase in the measured sound levels. Its
presence is indicated by the existence of odd harmonics of the excitation frequency in the sound spectrum and this
can be identified by a narrow band analysis. The DC bias impact on no-load sound level measurements during
factory testing can be practically eliminated by an over excitation run for some minutes. When over excitation is not
a practical option, as in on-site measurements, DC bias elimination after a transformer inrush event can take
several hours or even days.
4.3 Sound power of the cooling device(s)
The usual condition for sound power level determination is to have all cooling devices
necessary to operate the transformer at its rated power running.
In case of a water cooling device, the water flow need not be maintained during sound level
testing.
In case of variable speed cooling devices (usually fans) the speed during sound level testing
has a significant effect on the sound power level. The speed of the cooling device selected for
the sound level measurement shall be the speed necessary to operate the transformer at its
rated power under the most onerous external cooling medium conditions.
The selected test conditions shall be clearly indicated in the test report.
4.4 Sound power due to load current
The main component of the sound power level due to load current, for most transformers, is of
double the power frequency.
The magnitude of the load current sound power level can be roughly estimated by
Equations (5) and (6):
S
r
for 50 Hz power frequency (5)
L ≈ 39 +18× lg
WA, Ir
S
p
S
r
for 60 Hz power frequency (6)
L ≈ 44 +18× lg
WA, Ir
S
p
where
L is the estimated A-weighted sound power level of the transformer at rated current
WA,Ir
and rated frequency at short-circuit condition;
S is the rated power in MVA;
r
S is the reference power (1 MVA).
p
For auto-transformers and three winding transformers, the equivalent two-winding rated power
is used instead of S , in accordance with 3.2 of IEC 60076-8:1997.
r
NOTE 1 The predictions with Equations (5) and (6) are usually within ±6 dB of the measured sound power level
due to rated load current.
A guideline to estimate the significance of the sound power due to load current is given by
Equations (5) and (6). When the calculated values are 10 dB or more below the sound power
level estimated at no-load excitation, its contribution will be negligible and therefore need not
be tested, unless the purchaser has specified the test.
NOTE 2 Distribution type transformers usually do not require consideration of sound power due to load current.
When this measurement is required, one winding shall be short-circuited and the rated current
at rated frequency shall be injected into the other winding.
Unless otherwise specified, the tests shall be carried out with the tap-changer (if any) on the
principal tapping. However, this tap position may not give the maximum sound level in service
due to variations of the magnetic stray field distributions in the windings, the core and the
tank shielding elements.
The selected test conditions shall be clearly indicated in the test report.
The sound power level at a current different from the rated current can be calculated by
Equation (7):
I
T
L = L + 40× lg (7)
WA, IT WA, Ir
I
r
where
L is the calculated or measured A-weighted sound power level at rated current;
WA,Ir
L is the calculated A-weighted sound power level at actual current;
WA,IT
I is the rated current;
r
I is the actual current.
T
The equation is valid for currents in the range of 60 % to 130 % of rated current. It shall also
be applied to calculate the sound power level due to rated load current if, in case of test bay
limitations, testing is agreed to be done at a current lower than rated current.

– 14 – IEC 60076-10:2016  IEC 2016
In service, the direction of load flow and the power factor can impact the sound power level
due to a superposition of the flux at no-load condition and the stray flux partly entering the
core. This effect cannot be replicated by factory testing.
Special transformers such as industrial, SVC and HVDC converter transformers as well as
specific types of reactor experience load currents with high harmonic content and
subsequently produce sound harmonics of higher frequency. The injection of such currents
requires special test equipment and test configurations which usually are not available for
transformer testing. For reactors such tests are more common, see IEC 60076-6. Where
testing is not possible, it is necessary to agree on predictions of the sound power level due to
load current including its harmonics based upon calculations. For detailed information see
4.2.5 and 7.6 as well as Annex A of IEC 60076-10-1:2016.
5 Sound level measurement specification
When sound level measurements are specified, the acoustic performance of a transformer
shall be indicated by its A-weighted sound power level.
In exceptional cases, an average sound pressure level at a certain distance is allowed to be
specified by the purchaser. The determination of that pressure level can either be obtained
from a measurement of the spatially averaged sound pressure level at that distance or derived
from the sound power determined at a different distance.
As a minimum, the sound power level at no-load excitation at rated voltage and frequency on
an untapped winding shall be specified. For variable flux applications see 4.2.
If the transformer is equipped with a cooling device having pumps and/or fans then the
cooling device’s sound power level corresponding to the transformer’s rated power shall also
be specified. Duties other than that required for rated power can be specified by the
purchaser.
Alternatively, the combined sum of the transformer no-load excitation and cooling device
sound power level can be specified.
If the calculated sound power level due to load current according Equations (5) and (6) is
considered significant by the purchaser, it is recommended to specify a measurement of the
sound power level due to rated load current in order to report the transformer sound power
level as in service.
NOTE 1 Distribution type transformers usually do not require consideration of sound power due to load current.
The purchaser may also specify a value for the sum of the sound power levels
• at no-load excitation,
• of the cooling device and
• due to load current,
all at the before mentioned rating.
Conditions other than those mentioned above, which might better reflect the likely service
condition, can be agreed for sound measurements.
NOTE 2 It is in the purchaser interest to notify the manufacturer on any special service conditions, such as the
presence of harmonics and/or d.c. bias in the network for the impact to the in service sound power level to be
assessed.
In case of phase segregated transformers forming a three-phase bank the sound level
specification shall be per phase segregated unit.

Methods used for the determination of sound power levels can be either sound pressure or
sound intensity and are normally chosen by the purchaser. If not specified by the purchaser,
the manufacturer shall choose the method and it shall be stated in the tender.
Sound measurements for distribution type transformers shall provide the total sound level as
per definition 3.9 only, unless otherwise specified by the purchaser.
NOTE 3 This applies also to reactors with rated power lower than 1 MVA.
Sound measurements for all other transformers shall be executed with 1/3-octave band
filtering, unless an alternative band width (octave-band or narrow-band) or a total sound level
only is specified by the purchaser. For more details on narrow-band measurements see 5.4
and Annex A of IEC 60076-10-1:2016.
Sound measurements on all transformers and reactors shall be executed with an active part
temperature close to ambient test bay conditions, unless the purchaser has specified sound
measurements at close to service temperature conditions (usually performed at the end of a
temperature rise test).
Unless otherwise specified by the purchaser, the choice between the use of the walk-around
or the point-by-point procedure shall be at the discretion of the manufacturer.
NOTE 4 The difference in measured sound level due to the chosen method is negligible based on manifold
comparisons but the walk-around procedure is less time consuming, especially in the case of large units.
The point-by-point procedure shall be applied when safety considerations dictate.
The point-by-point procedure is the logical choice in situations where there are a small
number of measuring points. This normally applies to distribution type transformers.
6 Instrumentation, calibration and accuracy
The available frequency response of the measuring instrument shall range from below the
rated power frequency to above the upper limit of the human ear capability of 20 kHz.
In case of transformers with a power frequency lower than 25 Hz and when the measuring
device is limited in its lower frequency end then it is acceptable to have double the power
frequency as the lower frequency end.
The upper limit for the actual measurement shall be chosen in accordance with the highest
emitted significant frequency, usually below 10 kHz. The selected frequency range for
background noise measurements and the test measurement shall be the same.
Sound pressure measurements shall be made using a type 1
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