IEC 61400-11:1998

INTERNATIONAL
IEC
STANDARD
61400-11
First edition
1998-09
Wind turbine generator systems –
Part 11:
Acoustic noise measurement techniques
Aérogénérateurs –
Partie 11:
Techniques de mesure du bruit acoustique

Reference number
Numbering
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60000 series.
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available. For example, edition numbers 1.0, 1.1 and 1.2 refer, respectively, to the
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publication incorporating amendments 1 and 2.

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thus ensuring that the content reflects current technology.
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Information on the subjects under consideration and work in progress undertaken by
the technical committee which has prepared this publication, as well as the list of
publications issued, is to be found at the following IEC sources:
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• Catalogue of IEC publications
Published yearly with regular updates
(On-line catalogue)*
• IEC Bulletin
Available both at the IEC web site* and as a printed periodical
Terminology, graphical and letter symbols
For general terminology, readers are referred to IEC 60050: International Electro-
technical Vocabulary (IEV).
For graphical symbols, and letter symbols and signs approved by the IEC for
general use, readers are referred to publications IEC 60027: Letter symbols to be
used in electrical technology, IEC 60417: Graphical symbols for use on equipment.
Index, survey and compilation of the single sheets and IEC 60617: Graphical symbols
for diagrams.
* See web site address on title page.

INTERNATIONAL
IEC
STANDARD
61400-11
First edition
1998-09
Wind turbine generator systems –
Part 11:
Acoustic noise measurement techniques
Aérogénérateurs –
Partie 11:
Techniques de mesure du bruit acoustique

 IEC 1998  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
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International Electrotechnical Commission
For price, see current catalogue

– 2 – 61400-11 © IEC:1998(E)
CONTENTS
Page
FOREWORD.4

INTRODUCTION . 5

Clause
1 General. 6
1.1 Scope and object. 6
1.2 Normative references. 6
1.3 Definitions. 7
1.4 Symbols and units . 8
1.5 Abbreviations. 9
2 Outline of method . 9
3 Instrumentation. 9
3.1 Acoustic instruments. 9
3.2 Non-acoustic instruments. 10
3.3 Traceable calibration. 11
4 Measurements and measurement procedures . 11
4.1 Measurement positions. 11
4.2 Acoustic measurements. 12
4.3 Non-acoustic measurements. 15
5 Data reduction procedures. 17
5.1 Wind speed. 17
5.2 Correction for background noise. 18
5.3 Apparent sound power level . 18
5.4 Wind speed dependence. 19
5.5 Directivity. 20
5.6 Octave- or third-octave band levels. 20

5.7 Tonality. 20
6 Information to be reported. 22
6.1 Characterization of the wind turbine. 22
6.2 Physical environment. 23
6.3 Instrumentation. 23
6.4 Acoustic data. 23
6.5 Non-acoustic data. 24
6.6 Uncertainty. 24

61400-11 © IEC:1998(E) – 3 –
Page
Tables
1 Effective noise bandwidth . 14

2 Roughness length . 18

3 Bandwidth of critical bands . 21

D.1 Examples of possible values of type B uncertainty components relevant for
apparent sound power level . 37

Figures
1 Mounting of the microphone – plan view . 25
2 Mounting of the microphone – vertical cross-section . 26
3 Standard pattern for microphone measurement positions . 27
4 Illustration of the definitions of R and slant distance R . 28
0 1
5 Allowable region for meteorological mast position as a function of ß – plan view . 29
6 Allowable range for meteorological mast position – cross-section . 30
B.1 Tolerances for frequency characteristics . 33
Annexes
A Other characteristics of WTGS noise emission and their quantification . 31
B Criteria for recording/playback equipment . 33
C Assessment of turbulence . 35
D Assessment of measurement uncertainty . 36
E Bibliography .39

– 4 – 61400-11 © IEC:1998(E)
INTERNATIONAL ELECTROTECHNICAL COMMISSION

_________
WIND TURBINE GENERATOR SYSTEMS –

Part 11: Acoustic noise measurement techniques

FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising all
national electrotechnical committees (IEC National Committees). The object of the IEC is to promote international
co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and in
addition to other activities, the IEC publishes International Standards. Their preparation is entrusted to technical
committees; any IEC National Committee interested in the subject dealt with may participate in this preparatory
work. International, governmental and non-governmental organizations liaising with the IEC also participate in this
preparation. The IEC collaborates closely with the International Organization for Standardization (ISO) in
accordance with conditions determined by agreement between the two organizations.
2) The formal decisions or agreements of the IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form of
standards, technical reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any divergence
between the IEC Standard and the corresponding national or regional standard shall be clearly indicated in the
latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject of
patent rights. The IEC shall not be held responsible for identifying any or all such patent rights.
International Standard IEC 61400-11 has been prepared by IEC technical committee 88: Wind
turbine systems.
The text of this standard is based on the following documents:
FDIS Report on voting
88/96/FDIS 88/97/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.

Annexes A, B, C, D and E are for information only.
A bilingual version of this standard may be issued at a later date.

61400-11 © IEC:1998(E) – 5 –
INTRODUCTION
The purpose of this part of IEC 61400 is to provide a uniform methodology that will ensure

consistency and accuracy in the measurement and analysis of acoustical emissions by wind

turbine generator systems (WTGS). This standard has been prepared with the anticipation that it

would be applied by:
– the WTGS manufacturer striving to meet well defined acoustic emission performance
requirements and/or a possible declaration system;

– the WTGS purchaser in specifying such performance requirements;
– the WTGS operator who may be required to verify that stated, or required, acoustic
performance specifications are met for new or refurbished units;
– the WTGS planner or regulator who must be able to accurately and fairly define acoustical
emission characteristics of WTGS in response to environmental regulations or permit
requirements for new or modified installations.
This standard provides guidance in the measurement, analysis and reporting of complex acoustic
emissions from wind turbine generator systems (WTGS). The standard will benefit those parties
involved in the manufacture, installation planning and permitting, operation, utilization, and
regulation of WTGS. The technically accurate measurement and analysis techniques
recommended in this document should be applied by all parties to ensure that continuing
development and operation of WTGS is carried out in an atmosphere of consistent and accurate
communication relative to environmental concerns. This standard presents measurement and
reporting procedures expected to provide accurate results that can be replicated by others.
The consistency of results using the method for measurement of tonality will be assessed, and
future revisions will address any identified shortcomings.

– 6 – 61400-11 © IEC:1998(E)
WIND TURBINE GENERATOR SYSTEMS –

Part 11: Acoustic noise measurement techniques

1 General
1.1 Scope and object
This part of IEC 61400 presents sound measurement procedures that enable noise emissions of

a wind turbine to be characterized. This involves using measurement methods appropriate to

noise emission assessment at locations close to the machine, in order to avoid errors due to
sound propagation, but far enough away to allow for the finite source size. The procedures
described are different in some respects from those that would be adopted for noise assessment
in community noise studies. They are intended to facilitate characterization of wind turbine noise
with respect to a range of wind speeds and directions. Standardization of measurement
procedures will also facilitate comparisons between different wind turbines.
The procedures present methodologies that will enable the noise emissions of a single WTGS to
be characterized in a consistent and accurate manner. These procedures include the following:
– location of acoustic measurement positions;
– requirements for the acquisition of acoustic, meteorological, and associated WTGS
operational data;
– analysis of the data obtained and the content for the data report; and
– definition of specific acoustic emission parameters, and associated descriptors which are
used for making
...