IEC 61400-12:2022

Wind energy generation systems - Part 12: Power performance measurements of electricity producing wind turbines - Overview

IEC 61400-12:2022 defines procedures for assessing the power performance characteristics of wind turbines. This document provides a general introduction to the available options for power performance measurement and the contributing evaluations which are further detailed in the other parts of the IEC 61400-12 series. This first edition of IEC 61400-12 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.

Systèmes de génération d’énergie éolienne - Partie 12: Mesurages de performance de puissance des éoliennes de production d’électricité - Vue d’ensemble

L'IEC 61400-12:2022 définit les procédures d'évaluation des caractéristiques de performance de puissance des éoliennes. Le présent document fournit une introduction générale aux options disponibles des mesurages de performance de puissance et des évaluations de contribution présentes dans les autres parties de la série IEC 61400-12, avec de plus amples informations. La présente première édition de l'IEC 61400-12 fait partie d'une révision structurelle qui annule et remplace les normes de performance IEC 61400-12-1:2017 et IEC 61400‑12‑2:2013. Cette révision structurelle ne contient aucune modification technique par rapport à l'IEC 61400‑12‑1:2017 et l'IEC 61400-12‑2:2013. Toutefois, les parties relatives aux mesurages du vent, au mesurage de l'étalonnage du site et à l'évaluation des obstacles et du terrain ont été extraites vers des normes distinctes.

General Information

• Status: Published
• Publication Date: 04-Sep-2022
• ICS: 27.180 - Wind turbine energy systems
• Technical Committee: TC 88 - Wind energy generation systems
• Drafting Committee: MT 12-1 - TC 88/MT 12-1
• Current Stage: DELPUB - Deleted Publication
• Completion Date: 04-Aug-2023

Relations

• Replaces: IEC 61400-12-1:2017 - Wind energy generation systems - Part 12-1: Power performance measurements of electricity producing wind turbines
• Effective Date: 05-Sep-2023
• Replaces: IEC 61400-12-2:2013 - Wind turbines - Part 12-2: Power performance of electricity-producing wind turbines based on nacelle anemometry
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 61400-12
®

Edition 1.0 2022-09
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –
Part 12: Power performance measurements of electricity producing wind
turbines – Overview
Systèmes de génération d'énergie éolienne –
Partie 12: Mesurages de performance de puissance des éoliennes de production
d'électricité – Vue d'ensemble
IEC 61400-12:2022-09(en-fr)

---------------------- Page: 1 ----------------------
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IEC 61400-12

®


Edition 1.0 2022-09




INTERNATIONAL



STANDARD




NORME



INTERNATIONALE
colour

inside










Wind energy generation systems –

Part 12: Power performance measurements of electricity producing wind

turbines – Overview




Systèmes de génération d'énergie éolienne –

Partie 12: Mesurages de performance de puissance des éoliennes de production


d'électricité – Vue d'ensemble













INTERNATIONAL

ELECTROTECHNICAL

COMMISSION


COMMISSION

ELECTROTECHNIQUE


INTERNATIONALE




ICS 27.180 ISBN 978-2-8322-5620-6




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® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

---------------------- Page: 3 ----------------------
– 2 – IEC 61400-12:2022  IEC 2022
CONTENTS
INTRODUCTION . 5
1 Scope . 6
2 Normative references . 6
3 Terms and definitions . 7
4 Symbols, units and abbreviated terms . 8
5 Power performance method overview . 9
6 Interfaces between International Standards . 12
Bibliography . 14
Figure 1 – Overview of relationship between standards in the IEC 61400-12 and
IEC 61400-50 series . 13
Table 1 – Overview of wind measurement configurations for power curve
measurements that meet the requirements of this document . 12

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IEC 61400-12:2022  IEC 2022 – 3 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

WIND ENERGY GENERATION SYSTEMS –

Part 12: Power performance measurements
of electricity producing wind turbines – Overview

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
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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.
IEC 61400-12 has been prepared by IEC technical committee 88: Wind energy generation
systems. It is an International Standard.
This first edition of IEC 61400-12 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.

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– 4 – IEC 61400-12:2022  IEC 2022
The text of this International Standard is based on the following documents:
Draft Report on voting
88/830/CDV 88/866/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.

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IEC 61400-12:2022  IEC 2022 – 5 –
INTRODUCTION
The IEC 61400-12 series comprises a sub-set of standards which are for use in the evaluation
and measurement of the power performance characteristics of wind turbines. The power
performance characterization of wind turbines of all types and sizes is covered.
IEC TC 88 has made this revision to reduce the complexity and to improve the maintainability
of the previous version. Wind measurement procedures have been extracted from the
performance standard, recognizing that wind measurements need to be referenced from other
standards, such as in loads, noise and resource assessment measurements. IEC TC 88
recommends that the restructured standards gradually take over the previous standards before
Maintenance Cycle Reports are written on the restructured standards introducing new technical
requirements. Revision of the restructured documents should be proposed at the same time to
incorporate such technical changes, recommendations, clarifications and simplifications.
The purpose of the IEC 61400-12 series is to provide a uniform methodology that will ensure
consistency, accuracy and reproducibility in the measurement and analysis of power
performance by wind turbines. These International Standards have been prepared with the
anticipation that they would be applied by:
a) a wind turbine manufacturer striving to meet well-defined power performance requirements
and/or a possible declaration system;
b) a wind turbine purchaser in specifying such performance requirements;
c) a wind turbine operator who can be required to verify that stated, or required, power
performance specifications are met for new or refurbished units;
d) a wind turbine planner or regulator who needs to 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.
The IEC 61400-12 series provides guidance in the measurement, analysis, and reporting of
power performance testing for wind turbines. These International Standards 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 these standards 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 wind turbine performance. These standards present
measurement and reporting procedures expected to provide accurate results that can be
replicated by others. Meanwhile, a user of these standards should be aware of differences in
performance or the measurement of performance that arise from large variations in wind shear
and turbulence. Not all of the test methods specified in the IEC 61400-12 series enable
quantification of the impact of shear and turbulence. Therefore, a user should consider the
influence of these differences, the most appropriate test method/standard and the data selection
criteria in relation to the purpose of the test before contracting the power performance
measurements.
Procedures for calibration, classification and uncertainty assessment of cup anemometers and
ultrasonic anemometers are given in IEC 61400-50-1. Procedures for calibration, classification
and uncertainty assessment of remote sensing devices are given in IEC 61400-50-2. Special
care should be taken in the selection of the instruments chosen to measure the wind speed
because it can influence the result of the power performance test.

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– 6 – IEC 61400-12:2022  IEC 2022
WIND ENERGY GENERATION SYSTEMS –

Part 12: Power performance measurements
of electricity producing wind turbines – Overview



1 Scope
This part of IEC 61400 defines procedures for assessing the power performance characteristics
of wind turbines.
This document provides a general introduction to the available options for power performance
measurement and the contributing evaluations which are further detailed in the other parts of
the IEC 61400-12 series. Although this document (along with other parts of the IEC 61400-12
series) also defines the specifications of the meteorological variables (and in particular wind
speed) required for the power performance evaluation, the methods and procedures for
measuring or otherwise acquiring the wind speed data are defined in the IEC 61400-50 wind
measurement series.
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 61400-12-1, Wind energy generation systems – Part 12-1: Power performance
measurements of electricity producing wind turbines
IEC 61400-12-2, Wind energy generation systems – Part 12-2: Power performance of electricity
producing wind turbines based on nacelle anemometry
IEC 61400-12-3, Wind energy generation systems – Part 12-3: Power performance –
Measurement based site calibration
IEC 61400-12-5, 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
IEC 61400-50, Wind energy generation systems – Part 50: Wind measurement – Overview
IEC 61400-50-1, Wind energy generation systems – Part 50-1: Wind measurement –
Application of meteorological mast, nacelle and spinner mounted instruments
IEC 61400-50-2, Wind energy generation systems – Part 50-2: Wind measurement –
Application of ground-mounted remote sensing technology
IEC 61400-50-3, Wind energy generation systems – Part 50-3: Use of nacelle-mounted lidars
for wind measurements

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IEC 61400-12:2022  IEC 2022 – 7 –
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
annual energy production
AEP
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
3.2
data set
collection of data sampled over a continuous period
3.3
flow distortion
change in air flow caused by obstacles, topographical variations, or other wind turbines that
results in the wind speed at the measurement location being different from the wind speed at
the wind turbine location
3.4
hub height
height of the centre of the swept area of the wind turbine rotor above the
ground at the tower
Note 1 to entry: For a vertical axis wind turbine the hub height is defined as the height of the centroid of the swept
area of the rotor above the ground at the tower.
3.5
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
Note 1 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.
3.6
net active electric power
measure of the wind turbine electric power output that is delivered to the electrical power
network
3.7
obstacle
obstruction that blocks the wind and creates distortion of the flow
Note 1 to entry: Buildings and trees are examples of obstacles.
3.8
power performance
measure of the capability of a wind turbine to produce electric power and energy

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– 8 – IEC 61400-12:2022  IEC 2022
3.9
rotor equivalent wind speed
wind speed corresponding to the kinetic energy flux through the swept rotor area when
accounting for the variation of the wind speed with height
SEE: Equation (3)
3.10
test site
location of the wind turbine under test and its surroundings
3.11
uncertainty in measurement
parameter, associated with the result of a measurement, which characterizes the dispersion of
the values that could reasonably be attributed to the measurand
3.12
wind measurement equipment
meteorological mast or remote sensing device
3.13
wind shear
change of wind speed with height across the wind turbine rotor
3.14
wind veer
change of wind direction with height across the wind turbine rotor
4 Symbols, units and abbreviated terms
Symbol or Description Unit
abbreviated term
2
A swept area of the wind turbine rotor
m
AEP annual energy production Wh
P kinetic energy flux W
kin
RSD remote sensing device
V wind speed m/s
V wind speed at height i m/s
i
v measured equivalent wind speed m/s
eq
WME wind measurement equipment
3
ρ air density
kg/m
Φ relative humidity (range 0 % to 100 %)
–1
ω angular speed
s
φ wind direction rad
φ wind direction at hub height rad
hub
φ wind direction at height i rad
i

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IEC 61400-12:2022  IEC 2022 – 9 –
5 Power performance method overview
Wind turbine power performance characteristics are determined from a measured power curve
and an associated estimated annual energy production (AEP) and its uncertainty. The measured
power curve, defined as the relationship between the wind speed and the wind turbine power
output, is determined by collecting simultaneous measurements of meteorological variables
(including wind speed), as well as wind turbine signals (including 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 power performance measurement method used in the IEC 61400-12 series is based on a
definition of the power curve that expresses power produced versus the wind speed that
represents effectively the kinetic energy flux in the wind flowing across the swept area of the
rotor.
The kinetic energy flux (referring to a certain point in time or period of time, typically 10 min,
assuming that the wind speed does not change within this time across the vertical capture area
is in general terms expressed as:

1
3
(1)
P = ρV dA

kin
∫
A
2

Here the wind speed V, measured at a point in space over the rotor area, is the horizontal wind
speed.
NOTE 1 Wind turbine power seems to correlate better with the horizontal wind speed definition than with a vector
wind speed definition for a one-point hub height wind speed measurement.
NOTE 2 If the wind speed changes (i.e. if the turbulence intensity is greater than zero) during a certain time period,
then the kinetic power (averaged over this time period) is higher than in the case of a constant wind speed, whereas
a wind turbine has only a limited possibility to transform this additional kinetic power into additional electric power.
This issue is not taken into further consideration in this document. As a simplification, Equations (1), (2), (3) are
considered valid here, even in the case of a turbulence intensity greater than zero. The impact of wind speed changes
on the time averaged kinetic power and the associated impact on the wind turbine power curve are treated by the
turbulence normalization procedure as included in IEC 61400-12-1.
The horizontal wind speed is defined as the average magnitude of the horizontal component of
the instantaneous wind velocity vector, including only the longitudinal and lateral (but not the
vertical) components. When we consider a horizontal axis wind turbine the wind veer is also
taken into account and the kinetic energy in the wind is corrected according to the wind direction
at hub height:

1
3
(2)
P ρV( cos(φ−φ )) dA
kin hub
∫
A
2

Here φ is the wind direction at hub height. The wind veer can vary significantly over the rotor
hub
height of large wind turbines for extreme atmospheric stability conditions and it is also
dependent on topography at the site.
In this document we do not consider wind shear and wind veer in the horizontal plane. Thus,
the energy equivalent wind speed that corresponds to the kinetic energy in the wind as derived
from the expression of kinetic energy in Equation (2) in general is described as:
=

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– 10 – IEC 61400-12:2022  IEC 2022
1

1 3
3
(3)
VV( ( cos(φ−φ )) dA)
eq i i hub i
∫
i
A

In this document, the index i refers to the height within the rotor area.
NOTE 3 When wind speed is mentioned in this document, it is by default referring to the hub height wind speed
definition unless specifically stated to be this energy equivalent wind speed definition.
Although horizontal wind speed is considered to be the influential wind speed parameter, on
sites with significant non-horizontal flow (upflow or downflow), there is additional uncertainty
associated with both the measurement of the horizontal wind speed and the response of the
wind turbine.
The wind shear and wind veer can vary significantly over the rotor height of large wind turbines
due to atmospheric stability conditions and it is also dependent on topography at the site. The
occurrence of extreme atmospheric stability conditions is a site-specific issue, and if occurring
during a power performance test the power curve can vary significantly.
At sites with low and homogeneous wind shear and wind veer over the rotor (and for turbines
with small rotor diameters in possibly more complex wind flow conditions), the wind speed
measured at hub height can be a good representation of the kinetic energy to be captured by
the rotor. Hub height wind speed is the wind speed upon which power curves have historically
been defined in all previous editions of parts of the IEC 61400-12 series. For that reason, the
wind speed measured at hub height is the default definition of wind speed and shall always be
measured and reported, even when more comprehensive measurements of wind speed are
available over the rotor height.
At sites and seasons where extreme atmospheric stability conditions are expected to be
frequent, it is recommended always to measure wind shear. Not all power curve measurement
methods can provide measurements of wind shear (e.g. the measurements described in
IEC 61400-12-2 cannot provide information on wind shear). Therefore, the choice of power
curve measurement methodology can be driven by the site-specific atmospheric stability
conditions expected.
If wind shear and wind veer are not measured over the full height of the rotor there is added
uncertainty in the rotor equivalent wind speed. This uncertainty in measurement decreases as
more wind speed and wind direction measurement heights are used. If measurements are
limited to only hub height and there is no measurement of wind shear over the most significant
parts of the rotor, then this implies an uncertainty in determination of the rotor equivalent wind
speed.
For small wind turbines (refer to IEC 61400-2), where the influence of the wind shear and wind
veer are insignificant, the wind speed shall be represented by a hub height wind speed
measurement alone without adding uncertainty due to lack of wind shear and wind veer
measurements.
For vertical axis wind turbines, where the influence of the wind veer is not present, the wind
veer shall be neglected.
As the wind conditions at the position of the test turbine and at the positi
...