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EUROPEAN STANDARD
EN 61400-12-1

NORME EUROPÉENNE
June 2006
EUROPÄISCHE NORM

ICS 27.180 Supersedes EN 61400-12:1998


English version


Wind turbines
Part 12-1: Power performance measurements of
electricity producing wind turbines
(IEC 61400-12-1:2005)


Eoliennes  Windenergieanlagen
Partie 12-1: Mesures des performances Teil 12-1: Messung des
de puissance des éoliennes Leistungsverhaltens einer
de production d'électricité Windenergieanlage
(CEI 61400-12-1:2005) (IEC 61400-12-1:2005)




This European Standard was approved by CENELEC on 2006-05-01. CENELEC members are bound to comply
with the CEN/CENELEC Internal Regulations which stipulate the conditions for giving this European Standard
the status of a national standard without any alteration.

Up-to-date lists and bibliographical references concerning such national standards may be obtained on
application to the Central Secretariat or to any CENELEC member.

This European Standard exists in three official versions (English, French, German). A version in any other
language made by translation under the responsibility of a CENELEC member into its own language and notified
to the Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, the Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain,
Sweden, Switzerland and the United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels


© 2006 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61400-12-1:2006 E

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EN 61400-12-1:2006 - 2 -

Foreword
The text of document 88/244/FDIS, future edition 1 of IEC 61400-12-1, prepared by IEC TC 88, Wind
turbines, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 61400-12-1 on 2006-05-01.
This European Standard supersedes EN 61400-12:1998.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2007-02-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2009-05-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61400-12-1:2005 was approved by CENELEC as a European
Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards indicated:
IEC 60044-2 NOTE  Harmonized as EN 60044-2:1999 +A1:2000 +A2:2003 (not modified).
IEC 61400-1 NOTE  Harmonized as EN 61400-1:2005 (not modified).

__________

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- 3 - EN 61400-12-1:2006

Annex ZA
(normative)

Normative references to international publications
with their corresponding European publications

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.

NOTE  When an international publication has been modified by common modifications, indicated by (mod), the relevant EN/HD
applies.

Publication Year Title EN/HD Year

IEC 60044-1 (mod) 1996 Instrument transformers - EN 60044-1 1999
+ A1 2000 Part 1: Current transformers + A1 2000
+ A2 2002 + A2 2003


IEC 60688 1992 Electrical measuring transducers for EN 60688 1992
+ A1 (mod) 1997 converting a.c. electrical quantities to + A1 1999
+ A2 2001 analogue or digital signals + A2 2001


IEC 61400-2 1996 Wind turbine generator systems - EN 61400-2 1996
Part 2: Safety of small wind turbines


ISO 2533 1975 Standard atmosphere - -


ISO/IEC Guide 1995 Guide to the expression of uncertainty in - -
Expres measurement (GUM)

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INTERNATIONAL IEC


STANDARD 61400-12-1





First edition
2005-12


Wind turbines –
Part 12-1:
Power performance measurements
of electricity producing wind turbines

 IEC 2005  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.
International Electrotechnical Commission, 3, rue de Varembé, PO Box 131, CH-1211 Geneva 20, Switzerland
Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
PRICE CODE
Commission Electrotechnique Internationale XC
International Electrotechnical Commission
МеждународнаяЭлектротехническаяКомиссия
For price, see current catalogue

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– 2 – 61400-12-1  IEC:2005(E)
CONTENTS
FOREWORD.5
INTRODUCTION.7
1 Scope.8
2 Normative references .8
3 Terms and definitions .9
4 Symbols and units .11
5 Preparation for performance test .14
5.1 Wind turbine and electrical connection .14
5.2 Test site .14
6 Test equipment.16
6.1 Electric power .16
6.2 Wind speed .16
6.3 Wind direction .17
6.4 Air density.17
6.5 Rotational speed and pitch angle.17
6.6 Blade condition .17
6.7 Wind turbine control system .17
6.8 Data acquisition system.18
7 Measurement procedure.18
7.1 General .18
7.2 Wind turbine operation .18
7.3 Data collection .18
7.4 Data rejection.19
7.5 Data correction.19
7.6 Database.19
8 Derived results .20
8.1 Data normalization .20
8.2 Determination of the measured power curve.21
8.3 Annual energy production (AEP) .21
8.4 Power coefficient.22
9 Reporting format.23

Annex A (normative) Assessment of obstacles at the test site.33
Annex B (normative) Assessment of terrain at the test site .36
Annex C (normative) Site calibration procedure .37
Annex D (normative) Evaluation of uncertainty in measurement.39
Annex E (informative) Theoretical basis for determining the uncertainty of
measurement using the method of bins.41
Annex G (normative) Mounting of instruments on the meteorological mast.66
Annex H (normative) Power performance testing of small wind turbines.74
Annex I (normative) Classification of anemometry.77
Annex J (informative) Assessment of cup anemometry .79
Annex K (informative) In situ comparison of anemometers .88

Bibliography.90

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61400-12-1  IEC:2005(E) – 3 –

Figure 1 – Requirements as to distance of the meteorological mast and maximum
allowed measurement sectors.15
Figure 2 – Presentation of example database A and B: power performance test scatter
plots sampled at 1 Hz (mean values averaged over 10 min).26
Figure 3 – Presentation of example measured power curve for databases A and B .27
Figure 4 – Presentation of example C curve for databases A and B.28
p
Figure 5 – Presentation of example site calibration (only the sectors 20° to 30°, 40° to
60°, 160° to 210° and 330° to 350° are valid sectors).29
Figure A.1 – Sectors to exclude due to wakes of neighbouring and operating wind
turbines and significant obstacles .34
Figure A.2 – An example of sectors to exclude due to wakes of the wind turbine under
test, a neighbouring and operating wind turbine and a significant obstacle.35
Figure B.1 – Illustration of area to be assessed, top view.36
Figure G.1 – Example of a top-mounted anemometer and requirements for mounting .66
Figure G.2 – Example of alternative top-mounted primary and control anemometers
positioned side-by-side and wind vane and other instruments on the boom.67
Figure G.3 – Example of a top-mounted anemometer and mounting of control
anemometer, wind vane and other sensors on a boom.68
Figure G.4 – Example of top-mounted primary and control anemometers positioned
side-by-side, wind vane and other instruments on the boom .69
Figure G.5 – Iso-speed plot of local flow speed around a cylindrical mast, normalised
by free-field wind speed (from the left); analysis by 2 dimensional Navier-Stokes
computations .70
Figure G.6 – Centre-line relative wind speed as a function of distance R from the
centre of a tubular mast and mast diameter d .70
Figure G.7 – Representation of a three-legged lattice mast showing the centre-line
wind speed deficit, the actuator disc representation of the mast with the leg distance L
and distance R from the centre of the mast to the point of observation.71
Figure G.8 – Iso-speed plot of local flow speed around a triangular lattice mast with a
C of 0,5 normalised by free-field wind speed (from the left); analysis by 2
T
dimensional Navier-Stokes computation and actuator disc theory .72
Figure G.9 – Centre-line relative wind speed as a function of distance R from the
centre of a triangular lattice mast of face width L for various C values.72
T
Figure J.1 – Measured angular response of a cup anemometer compared to cosine
response.79
Figure J.2 – Wind tunnel torque measurements on a cup anemometer at 8 m/s .80
Figure J.3 – Example of bearing friction torque measurements .81
Figure J.4 – Distribution of vertical wind speed components assuming a fixed ratio
between horizontal and vertical standard deviation in wind speed.82
Figure J.5 – Calculation of the total deviation with respect to the cosine response.83
Figure J.6 – Probability distributions for three different average angles of inflow.84
Figure J.7 – Total deviation from cosine response for three different average angles of
inflow over horizontal turbulence intensity.84
Figure J.8 – Example of an anemometer that does not fulfil the slope criterion .85
Figure J.9 – Example of deviations of a Class 2.0A cup anemometer.87

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– 4 – 61400-12-1  IEC:2005(E)

Table 1 – Example of presentation of a measured power curve for database A .30
Table 2 – Example of presentation of a measured power curve for database B .31
Table 3 – Example of presentation of estimated annual energy production (database A).32
Table 4 – Example of presentation of estimated annual energy production (database B).32
Table B.1 – Test site requirements: topographical variations .36
Table D.1 – List of uncertainty components .40
Table E.1 – Expanded uncertainties.43
Table E.2 – List of categories B and A uncertainties .45
Table E.3 – Uncertainties from site calibration .53
Table E.4 – Sensitivity factors (database A).54
Table E.5 – Sensitivity factors (database B).55
Table E.6 – Category B uncertainties (database A) .56
Table E.7 – Category B uncertainties (database B) .57
Table F.1 – Example of evaluation of anemometer calibration uncertainty.62
Table G.1 – Estimation method for C for various types of lattice tower.73
T
Table H.1 – Battery bank voltage settings .76
Table I.1 – Influence parameter ranges (based on 10 min averages) of Classes A and B.78

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61400-12-1  IEC:2005(E) – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

WIND TURBINES –

Part 12-1: Power performance measurements
of electricity producing wind turbines


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
this end and in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). 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. 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 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 IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
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 61400-12-1 has been prepared by IEC technical committee 88:
Wind turbines.
This standard cancels and replaces IEC 61400-12 published in 1998. This first edition of IEC
61400-12-1 constitutes a technical revision. IEC 61400-12-2 and IEC 61400-12-3 are
additions to IEC 61400-12-1.
The text of this standard is based on the following documents:
FDIS Report on voting
88/244/FDIS 88/251/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.

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– 6 – 61400-12-1  IEC:2005(E)
IEC 61400-12 consists of the following parts, under the general title Wind turbines:
Part 12-1: Power performance measurements of electricity producing wind turbines
Part 12-2: Verification of power performance of individual wind turbines (under consideration)
Part 12-3: Wind farm power performance testing (under consideration)
The committee has decided that the contents of this publication will remain unchanged until
the maintenance result 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 standard may be issued at a later date.

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61400-12-1  IEC:2005(E) – 7 –
INTRODUCTION
The purpose of this part of IEC 61400 is to provide a uniform methodology that will ensure
consistency, accuracy and reproducibility in the measurement and analysis of power
performance by wind turbines. The standard has been prepared with the anticipation that it
would be applied by:
– a wind turbine manufacturer striving to meet well-defined power performance requirements
and/or a possible declaration system;
– a wind turbine purchaser in specifying such performance requirements;
– a wind turbine operator who may be required to verify that stated, or required, power
performance specifications are met for new or refurbished units;
– a wind turbine planner or regulator who must be able to accurately and fairly define power
performance characteristics of wind turbines in response to regulations or permit
requirements for new or modified installations.
This standard provides guidance in the measurement, analysis, and reporting of power
performance testing for wind turbines. The standard will benefit those parties involved in the
manufacture, installation planning and permitting, operation, utilization, and regulation of wind
turbines. The technically accurate measurement and analysis techniques recommended in
this standard should be applied by all parties to ensure that continuing development and
operation of wind turbines 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.
Meanwhile, a user of the standard should be aware of differences that arise from large
variations in wind shear and turbulence, and from the chosen criteria for data selection.
Therefore, a user should consider the influence of these differences and the data selection
criteria in relation to the purpose of the test before contracting the power performance
measurements.
A key element of power performance testing is the measurement of wind speed. This standard
prescribes the use of cup anemometers to measure the wind speed. This instrument is robust
and has long been regarded as suitable for this kind of test. Even though suitable wind tunnel
calibration procedures are adhered to, the field flow conditions associated with the fluctuating
wind vector, both in magnitude and direction, will cause different instruments to potentially
perform differently.
Tools and procedures to classify cup anemometers are given in Annexes I and J. However
there will always be a possibility that the result of the test can be influenced by the selection
of the wind speed instrument. Special care should therefore be taken in the selection of the
instruments chosen to measure the wind speed.

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– 8 – 61400-12-1  IEC:2005(E)
WIND TURBINES –

Part 12-1: Power performance measurements
of electricity producing wind turbines



1 Scope
This part of IEC 61400 specifies a procedure for measuring the power performance
characteristics of a single wind turbine and applies to the testing of wind turbines of all types
and sizes connected to the electrical power network. In addition, this standard describes a
procedure to be used to determine the power performance characteristics of small wind
turbines (as defined in IEC 61400-2) when connected to either the electric power network or a
battery bank. The procedure can be used for performance evaluation of specific turbines at
specific locations, but equally the methodology can be used to make generic comparisons
between different turbine models or different turbine settings.
The wind turbine power performance characteristics are determined by the measured power
curve and the estimated annual energy production (AEP). The measured power curve is
determined by collecting simultaneous measurements of wind speed and power output at the
test site for a period that is long enough to establish a statistically significant database over a
range of wind speeds and under varying wind and atmospheric conditions. The AEP is
calculated by applying the measured power curve to reference wind speed frequency
distributions, assuming 100 % availability.
The standard describes a measurement methodology that requires the measured power curve
and derived energy production figures to be supplemented by an assessment of uncertainty
sources and their combined effects.
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 60044-1:1996, Instrument transformers – Part 1: Current transformers
Amendment 1 (2000)
1
Amendment 2 (2002)
IEC 60688:1992, Electrical measuring transducers for converting a.c. electrical quantities to
analogue or digital signals
Amendment 1 (1997)
2
Amendment 2 (2001)
IEC 61400-2:1996, Wind turbine generator systems – Part 1: Safety of small wind turbines
ISO 2533:1975, Standard atmosphere
ISO Guide to the expression of uncertainty in measurement, 1995, ISBN 92-67-10188-9
___________
1
There exists a consolidated edition 1.2 (2003) that includes edition 1 and its amendments 1 and 2.

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61400-12-1  IEC:2005(E) – 9 –
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
accuracy
closeness of the agreement between the result of a measurement and a true value of the
measurand
3.2
annual energy production
AEP
estimate of the total energy production of a wind turbine during a one-year period by applying
the measured power curve to different reference wind speed frequency distributions at hub
height, assuming 100 % availability
3.3
complex terrain
terrain surrounding the test site that features significant variations in topography and terrain
obstacles that may cause flow distortion
3.4
data set
collection of data that was sampled over a continuous period
3.5
distance constant
indication of the response time of an anemometer, defined as the length of air that must pass
the instrument for it to indicate 63 % of the final value for a step input in wind speed
3.6
extrapolated power curve
extension of the measured power curve by estimating power output from the maximum
measured wind speed to cut-out wind speed
3.7
flow distortion
change in air flow caused by obstacles, topographical variations, or other wind turbines that
results in a deviation of the measured wind speed from the free stream wind speed and in a
significant uncertainty
3.8
hub height (wind turbines)
height of the centre of the swept area of the wind turbine rotor above the ground at the tower
NOTE For a vertical axis wind turbine the hub height is the height of the equator plane.
3.9
measured power curve
table and graph that represents the measured, corrected and normalized net power output of
a wind turbine as a function of measured wind speed, measured under a well-defined
measurement procedure
3.10
measurement period
period during which a statistically significant database has been collected for the power
performance test

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