SIST EN IEC 61400-12-2:2023

SLOVENSKI STANDARD
01-januar-2023
Nadomešča:
SIST EN 61400-12-2:2013
SIST EN 61400-12-2:2013/AC:2016
Sistemi za proizvodnjo energije na veter - 12-2. del: Ugotavljanje elektroenergetske
zmogljivosti vetrnih turbin po načelu merjenja hitrosti vetra skozi gondolo (IEC
61400-12-2:2022)
Wind energy generation systems - Part 12-2: Power performance of electricity producing
wind turbines based on nacelle anemometry (IEC 61400-12-2:2022)
Windenergieanlagen - Teil 12- 2: Leistungsverhalten von stromerzeugenden
Windenergieanlagen auf der Grundlage der Gondelanemometrie (IEC 61400-12-2:2022)
Systèmes de génération d'énergie éolienne - Partie 12-2: Performance de puissance des
éoliennes de production d'électricité fondée sur l'anémométrie de nacelle (IEC 61400-12-
2:2022)
Ta slovenski standard je istoveten z: EN IEC 61400-12-2:2022
ICS:
27.180 Vetrne elektrarne Wind turbine energy systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 61400-12-2

NORME EUROPÉENNE
EUROPÄISCHE NORM October 2022
ICS 27.180 Supersedes EN 61400-12-2:2013;
EN 61400-12-2:2013/AC:2016-10
English Version
Wind energy generation systems - Part 12-2: Power
performance of electricity producing wind turbines based on
nacelle anemometry
(IEC 61400-12-2:2022)
Systèmes de génération d'énergie éolienne - Partie 12-2: Windenergieanlagen - Teil 12- 2: Leistungsverhalten von
Performance de puissance des éoliennes de production stromerzeugenden Windenergieanlagen auf der Grundlage
d'électricité fondée sur l'anémométrie de nacelle der Gondelanemometrie
(IEC 61400-12-2:2022) (IEC 61400-12-2:2022)
This European Standard was approved by CENELEC on 2022-10-10. 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 CEN-CENELEC
Management Centre 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 CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the
Netherlands, Norway, Poland, Portugal, Republic of North Macedonia, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland,
Türkiye and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2022 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61400-12-2:2022 E

European foreword
The text of document 88/823/CDV, future edition 2 of IEC 61400-12-2, prepared by IEC/TC 88 "Wind
energy generation systems" was submitted to the IEC-CENELEC parallel vote and approved by
CENELEC as EN IEC 61400-12-2:2022.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2023-07-10
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2025-10-10
document have to be withdrawn
This document supersedes EN 61400-12-2:2013 and all of its amendments and corrigenda (if any).
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Any feedback and questions on this document should be directed to the users’ national committee. A
complete listing of these bodies can be found on the CENELEC website.
Endorsement notice
The text of the International Standard IEC 61400-12-2:2022 was approved by CENELEC as a
European Standard without any modification.
In the official version, for Bibliography, the following note has to be added for the standard indicated:
IEC 61400-2 NOTE Harmonized as EN 61400-2
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 1 Where an International Publication has been modified by common modifications, indicated by (mod), the
relevant EN/HD applies.
NOTE 2 Up-to-date information on the latest versions of the European Standards listed in this annex is available
here: www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60688 2021 Electrical measuring transducers for converting EN IEC 60688 202X
AC and DC electrical quantities to analogue or
digital signals
IEC 61400-12-1 - Wind energy generation systems - Part 12-1: EN IEC 61400-12-1 -
Power performance measurement of electricity
producing wind turbines
IEC 61400-12-3 - Wind energy generation systems - Part 12-3: EN IEC 61400-12-3 -
Power performance - Measurement based site
calibration
IEC 61400-12-5 2022 Wind energy generation systems - Part 12-5: EN IEC 61400-12-5 2022
Power performance - Assessment of obstacles
and terrain
IEC 61400-12-6 - Wind energy generation systems - Part 12-6: EN IEC 61400-12-6 -
Measurement based nacelle transfer function of
electricity producing wind turbines
IEC 61400-50-1 - Wind energy generation systems - Part 50-1: EN IEC 61400-50-1 -
Wind Measurement - Application of
Meteorological Mast, Nacelle and Spinner
Mounted Instruments
IEC 61869-2 - Instrument transformers - Part 2: Additional EN 61869-2 -
requirements for current transformers
IEC 61869-3 - Instrument transformers - Part 3: Additional EN 61869-3 -
requirements for inductive voltage transformers
ISO 2533 1975 Standard Atmosphere - -
ISO/IEC Guide 98-3 2008 Uncertainty of measurement - Part 3: Guide to - -
the expression of uncertainty in measurement
(GUM:1995)
Under preparation. Stage at the time of publication: prEN IEC 60688:2021.
Under preparation. Stage at the time of publication: FprEN IEC 61400-50-1:2022.
IEC 61400-12-2 ®
Edition 2.0 2022-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –

Part 12-2: Power performance of electricity producing wind turbines based on

nacelle anemometry
Systèmes de génération d'énergie éolienne –

Partie 12-2: Performance de puissance des éoliennes de production d'électricité

fondée sur l'anémométrie de nacelle

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.180 ISBN 978-2-8322-5594-0

– 2 – IEC 61400-12-2:2022 © IEC 2022
CONTENTS
FOREWORD . 5
INTRODUCTION . 7
1 Scope . 9
2 Normative references . 9
3 Terms and definitions . 10
4 Symbols, units and abbreviated terms . 14
5 Overview of test method . 17
6 Preparation for performance test . 19
6.1 General . 19
6.2 Wind turbine . 19
6.3 Test site . 19
6.4 Nacelle wind speed transfer function . 20
6.5 Test plan . 20
7 Test equipment . 20
7.1 Electric power . 20
7.2 Wind speed . 21
7.3 Wind direction . 21
7.4 Air density. 21
7.5 Rotor speed . 22
7.6 Pitch angle . 22
7.7 Wind turbine status . 22
7.8 Data acquisition . 22
8 Measurement procedure . 23
8.1 General . 23
8.2 Wind turbine operation . 23
8.3 Data system(s) synchronisation . 23
8.4 Data collection . 24
8.5 Data quality check . 24
8.5.1 General . 24
8.5.2 Measured signals are in range and available . 24
8.5.3 Sensors are operating properly . 24
8.5.4 Ensure data acquisition system(s) is/are operating properly. 25
8.5.5 Sector self-consistency check . 25
8.6 Data rejection . 25
8.7 Data correction . 26
8.8 Database . 26
9 Derived results . 27
9.1 Data normalisation – Density correction . 27
9.2 Determination of measured power curve . 28
9.3 Annual energy production (AEP) . 28
9.4 Power coefficient . 29
9.5 Uncertainty analysis . 30
10 Reporting format . 30
Annex A (normative) Nacelle wind speed transfer function validity procedure . 38
A.1 General . 38

IEC 61400-12-2:2022 © IEC 2022 – 3 –
A.2 Measurement procedure: . 38
A.3 Terrain class and slope: . 38
A.4 Measurement hardware: . 38
A.5 Other turbine hardware: . 38
A.6 Turbine controls: . 39
Annex B (normative) Evaluation of uncertainty in measurement . 40
B.1 General . 40
B.2 The measurands . 40
B.3 Uncertainty components. 40
B.4 Wind direction uncertainty . 42
Annex C (normative) Theoretical basis for determining the uncertainty of
measurement using the method of bins . 43
C.1 General . 43
C.2 Propagation of uncertainty through the stages of NTF/NPC measurement . 44
C.3 Category A uncertainties . 47
C.3.1 General . 47
C.3.2 Category A uncertainty in electric power . 47
C.4 Category B uncertainties . 49
C.4.1 General . 49
C.4.2 Category B uncertainties in climatic variations . 49
C.5 Expanded uncertainty . 49
Annex D (normative) NPC uncertainty estimates and calculation . 51
D.1 Methods and assumptions. 51
D.1.1 General . 51
D.1.2 Nacelle power curve uncertainty component estimates . 51
D.1.3 Wind direction uncertainty . 54
D.1.4 Contribution factors . 55
D.2 Uncertainty example calculations . 57
D.2.1 Example description . 57
D.2.2 Example case – NTF uncertainty . 57
D.2.3 Example case – NPC uncertainty . 58
Annex E (normative) Allowable anemometry instrument types. 60
E.1 General . 60
E.2 Calibration of sonic anemometers . 60
E.2.1 General . 60
E.2.2 Step 1: Wind speed calibration (required) . 60
E.2.3 Step 2: Wind direction calibration (required) . 61
E.2.4 Step 3: Tilting test (recommended) . 61
E.3 Recalibration of sonic anemometers . 61
E.4 Uncertainty of sonic and propeller anemometers . 61
Annex F (informative) Results and uncertainty considerations . 62
F.1 General . 62
F.2 Method for calculation of measurement uncertainty . 62
F.3 Method for calculation of sampling uncertainty . 66
F.4 Combined measurement and sampling uncertainty . 66
Annex G (informative) Example multi-turbine NTF/NPC uncertainty calculation . 67
G.1 Overview. 67
G.2 Outline of procedure: . 67

– 4 – IEC 61400-12-2:2022 © IEC 2022
G.3 Example of measurement uncertainty calculation . 70
G.4 Example of sampling uncertainty calculation . 74
G.5 Combined uncertainty . 74
G.6 Discussion of sample size and uncertainty . 74
Annex H (informative) Organisation of test, safety and communication . 76
H.1 Overview. 76
H.2 Responsibility for test . 76
H.3 Safety during test . 76
H.4 Communication . 76
H.5 Prior to test . 76
H.6 During test . 76
H.7 After test . 77
Bibliography . 78

Figure 1 – Procedural overview . 18
Figure 2 – Presentation of sample data: nacelle power performance test scatter plots . 34
Figure 3 – Presentation of sample data: binned power curve with uncertainty bands . 34
Figure 4 – Example of sample data: measured power curve and C curve . 35
p
Figure G.1 – Impact of multiple turbine testing on measurement uncertainty . 74
Figure G.2 – Impact of multiple turbine testing on sampling uncertainty . 75

Table 1 – Example of a measured power curve . 36
Table 2 – Example of estimated annual energy production . 37
Table B.1 – Uncertainty components in nacelle power curve evaluation . 41
Table B.2 – Uncertainty components in nacelle based absolute wind direction . 42
Table C.1 – Example cancellation sources . 45
Table C.2 – List of category A and B uncertainties for NPC . 48
Table C.3 – Expanded uncertainties. 50
Table D.1 – Estimates for uncertainty components from NPC measurement . 52
Table D.2 – Estimates for u for NPC terrain class . 54
V5,i
Table D.3 – Estimates for uncertainty components for wind direction . 55
Table D.4 – Estimates for contribution factors for NPC . 56
Table G.1 – List of correlated uncertainty components . 68
Table G.2 – Sample AEP and uncertainty data from three turbines . 70
Table G.3 – Component uncertainty contribution to AEP uncertainty on turbine 1 . 71
Table G.4 – Combination of uncertainty components across turbines . 72

IEC 61400-12-2:2022 © IEC 2022 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
WIND ENERGY GENERATION SYSTEMS –

Part 12-2: Power performance of electricity producing
wind turbines based on nacelle anemometry

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,
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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 itself does not provide any attestation of conformity. Independent certification bodies provide conformity
assessment services and, in some areas, access to IEC marks of conformity. IEC is not responsible for any
services carried out by independent certification bodies.
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.
IEC 61400-12-2 has been prepared by IEC technical committee 88: Wind energy generation
systems. It is an International Standard.
This second edition of IEC 61400-12-2 is part of a structural revision that cancels and replaces
the performance standards IEC 61400-12-1:2017 and IEC 61400-12-2:2013. The structural
revision contains no technical changes with respect to IEC 61400-12-1:2017 and
IEC 61400-12-2:2013, but the parts that relate to wind measurements, measurement of site
calibration and assessment of obstacle and terrain have been extracted into separate standards.
The purpose of the re-structure was to allow the future management and revision of the power
performance standards to be carried out more efficiently in terms of time and cost and to provide
a more logical division of the wind measurement requirements into a series of separate
standards which could be referred to by other use case standards in the IEC 61400 series and
subsequently maintained and developed by appropriate experts.

– 6 – IEC 61400-12-2:2022 © IEC 2022
The text of this International Standard is based on the following documents:
Draft Report on voting
88/823/CDV 88/868/RVC
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts in the IEC 61400 series, published under the general title Wind energy
generation systems, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The "colour inside" logo on the cover page of this document 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.

IEC 61400-12-2:2022 © IEC 2022 – 7 –
INTRODUCTION
This second edition contains no technical changes with respect to the previous edition but the
parts that relate to wind measurements, measurement of nacelle transfer functions and
assessment of obstacles and terrain have been extracted into separate standards. The
separated standards comprise:
– IEC 61400-50, Wind measurements – Overview
– IEC 61400-50-1, Wind measurement – Application of meteorological mast, nacelle and
spinner mounted instruments
– IEC 61400-50-2, Wind measurement – Application of ground-mounted remote sensing
technology
– IEC 61400-12, Power performance measurements of electricity producing wind turbines –
Overview
– IEC 61400-12-1, Power performance measurement of electricity producing wind turbines
– IEC 61400-12-2, Power performance of electricity producing turbines based on nacelle
anemometry
– IEC 61400-12-3, Power performance – Measurement based site calibration
– IEC 61400-12-5, Power performance – Assessment of obstacles and terrain
– IEC 61400-12-6, Measurement based nacelle transfer function of electricity producing wind
turbines.
This procedure describes how to characterise a wind turbine’s power performance
characteristics in terms of a measured power curve and the estimated annual energy production
(AEP) based on nacelle-anemometry. In this procedure, the anemometer is located on or near
the test turbine’s nacelle. In this location, the anemometer is measuring wind speed that is
strongly affected by the test turbine’s rotor. The procedure provides guidance on determination
of measurement uncertainty including assessment of uncertainty sources and recommendations
for combining them into uncertainties in reported power and AEP.
The measured power curve is determined by collecting simultaneous measurements of nacelle-
measured wind speed and power output 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. In order to accurately measure the power curve, the nacelle-measured
wind speed is adjusted using a transfer function to estimate the free stream wind speed. The
procedure to measure such a transfer function is given in IEC 61400-12-6. The AEP is
calculated by applying the measured power curve to the reference wind speed frequency
distributions, assuming 100 % availability.
A key element of power performance testing is the measurement of wind speed. Even when
anemometers are carefully calibrated in a quality wind tunnel, fluctuations in magnitude and
direction of the wind vector can cause different anemometers to perform differently in the field.
Further, the flow conditions close to a turbine nacelle are complex and variable. Therefore
special care should be taken in the selection and installation of the anemometer. These issues
are addressed in this document.
This document will benefit those parties involved in the manufacture, installation, planning and
permitting, operation, utilisation and regulation of wind turbines. When appropriate, 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 wind
turbines is carried out in an atmosphere of consistent and accurate communication relative to
environmental concerns. This document presents measurement and reporting procedures
expected to provide accurate results that can be replicated by others.

– 8 – IEC 61400-12-2:2022 © IEC 2022
Meanwhile, a user of this document should be aware of differences that arise from large
variations in wind shear and turbulence intensity, 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 power performance
measurements.
IEC 61400-12-2:2022 © IEC 2022 – 9 –
WIND ENERGY GENERATION SYSTEMS –

Part 12-2: Power performance of electricity producing
wind turbines based on nacelle anemometry

1 Scope
This part of IEC 61400-12 specifies a procedure for verifying the power performance
characteristics of a single electricity-producing, horizontal axis wind turbine that is not
considered to be a small wind turbine per IEC 61400-2. It is expected that this document be
used when the specific operational or contractual specifications do not comply with the
requirements set out in IEC 61400-12-1. The procedure can be used for power 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 purpose of this document is to provide a uniform methodology of measurement, analysis,
and reporting of power performance characteristics for individual electricity producing wind
turbines utilising nacelle-anemometry methods. This document is intended to be applied only
to horizontal axis wind turbines of sufficient size that the nacelle-mounted anemometer does
not significantly affect the flow through the turbine’s rotor and around the nacelle and hence
does not affect the wind turbine’s performance. The intent of this document is that the methods
presented in this document be utilised when the requirements set out in IEC 61400-12-1 are
not feasible. This will ensure that the results are as consistent, accurate, and reproducible as
possible within the current state of the art for instrumentation and measurement techniques.
This document describes how to characterise a wind turbine’s power performance in terms of a
measured power curve and the estimated AEP. Guidance on uncertainty considerations relating
to the power performance of the sample of turbines tested relative to the power performance of
all turbines in a wind farm is provided. Guidance on the evaluation of the combined uncertainty
for the case where multiple turbines are tested is also provided.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements 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 60688:2021, Electrical measuring transducers for converting AC and DC electrical
quantities to analogue or digital signals
IEC 61400-12-1, Wind energy generation systems – Part 12-1: Power performance
measurements of electricity producing wind turbines
IEC 61400-12-3, Wind energy generation systems – Part 12-3: Power performance –
Measurement based site calibration
IEC 61400-12-5:2022, Wind energy generation systems – Part 12-5: Power performance –
Assessment of obstacles and terrain
IEC 61400-12-6, Wind energy generation systems – Part 12-6: Measurement based nacelle
transfer function of electricity producing wind turbines

– 10 – IEC 61400-12-2:2022 © IEC 2022
IEC 61400-50-1, Wind energy generation systems – Part 50-1: Wind measurement –
Application of meteorological mast, nacelle and spinner mounted instruments
IEC 61869-2, Instrument transformers – Part 2: Additional requirements for current
transformers
IEC 61869-3, Instrument transformers – Part 3: Additional requirements for inductive voltage
transformers
ISO 2533:1975, Standard atmosphere
ISO/IEC GUIDE 98-3:2008, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing platform: available at http://www.iso.org/obp
3.1
accuracy
closeness of the agreement between the result of a measurement and a true value of the
measurand
3.2
AEP
annual energy production
estimate of the total energy production of a wind turbine over 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
AEP-measured
measured annual energy production
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, without power curve extrapolation to higher wind speeds
3.4
AEP-extrapolated
extrapolated annual energy production
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, with power curve extrapolation to cut-out wind speed of
the turbine
3.5
complex terrain
terrain surrounding the test site that features significant variations in topography and terrain
obstacles that may cause flow distortion

IEC 61400-12-2:2022 © IEC 2022 – 11 –
3.6
data set
collection of data sampled over a contiguous period
3.7
documentation
any information regarding the test which is kept in files or data, or both, but which will not
necessarily be presented in the final report
3.8
extrapolated power curve
extension of the measured power curve by estimating power output from the maximum
measured wind speed to cut-out wind speed
3.9
flow distortion
change in air flow caused by obstacles, topographical variations, turbine's rotor, turbine's
nacelle or other wind turbines that results in a significant deviation of the measured wind speed
from the free stream wind speed
3.10
free stream wind speed
horizontal wind speed measured upstream of the rotor of the wind turbine generator that is
unaffected by rotor aerodynamics
3.11
turbulence intensity
ratio of the wind speed standard deviation to the mean wind speed, determined from the same
set of measured data samples of horizontal wind speed, and taken over a specific period of
time
3.12
hub height
height of the centre of the swept area of the wind turbine rotor above the ground
level at the tower base
3.13
machine configuration change
change to the turbine or intervention in the turbine operation which causes a significant change
in the power performance of the turbine and which is not normal maintenance
Note 1 to entry: Examples of machine configuration change include replacements of hardware components,
especially rotor blade, gearbox or generator; a change or update of the turbine software or its parameters; unplanned
blade washing; turbine software updates.
3.14
measured power curve
table and graph that represent the measured, corrected and normalised net power output of a
wind turbine as a function of measured free stream wind speed, measured under a well-defined
measurement procedure
3.15
measurement period
period during which a statistically significant database has been collected for the power
performance test
– 12 – IEC 61400-12-2:2022 © IEC 2022
3.16
measurement sector
sector of wind directions from which data are selected for determination of:
i) the measured power curve
ii) the nacelle transfer function
3.17
measurement uncertainty
parameter, associated with the result of a measurement, which characterises the dispersion of
the values that could reasonably be attributed to the measurand
3.18
method of bins
data reduction procedure that groups test data for a certain parameter into intervals (bins)
Note 1 to entry: The method of bins is normally used for wind speed bins but is also applicable to other parameters.
Note 2 to entry: For each bin, the number of data sets or samples and their sum are recorded, and the average
parameter value within each bin is calculated.
3.19
nacelle
housing which contains the drive train and other elements on top of a horizontal axis wind
turbine generator
3.20
NPC
nacelle power curve
measured power performance of a wind turbine expressed as net active electric power output
from the wind turbine as a function of free stream wind speed
Note 1 to entry: For the NPC, the free stream wind speed is not directly measured, but rather the nacelle wind
speed is measured and a nacelle transfer function is applied to arrive at the free stream wind speed.
3.21
nacelle wind speed
horizontal wind speed measured on top of or in front of the nacelle of a wind turbine
3.22
net active electric power
measure of the wind turbine electric power output that is delivered to the electrical power
network
3.23
normal maintenance
any intervention which is done according to a defined regular maintenance program,
independent from the fact that a power performance test is being done, for example, oil change,
blade washing (if due anyway, independent from the power performance test) and any
intervention which is outside of the scope of the regular maintenance program (e.g. repair of a
failed component) and which is not a machine configuration change
3.24
obstacle
object that blocks and distorts the flow of the wind, such as a building or tree
3.25
pitch angle
angle between the chord line at a defined blade radial location (usually 100 % of the blade
radius) and the rotor plane of rotation

IEC 61400-12-2:2022 © IEC 2022 – 13 –
3.26
power coefficient
ratio of the net electric power output of a wind turbine to the power available in the free stream
wind over the rotor swept area
3.27
power performance
measure of the capability of a wind turbine to produce electric power and energy
3.28
rated power
quantity of power assigned, generally by a manufacturer, for a specified operating condition of
a component, device or equipment
3.29
report
any information regarding the test which is stated in the final documentation
3.30
roughness length
extrapolated height at which the mean wind speed becomes zero if the vertical wind profile is
assumed to have a logarithmic variation with height
3.31
site calibration
procedure that quantifies and potentially reduces the effects of
...