SIST EN 61400-21:2009

SLOVENSKI STANDARD
SIST EN 61400-21:2009
01-januar-2009
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SIST EN 61400-21:2002
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Wind turbines -- Part 21: Measurement and assessment of power quality characteristics
of grid connected wind turbines
Windenergieanlagen --Teil 21: Messung und Bewertung der Netzverträglichkeit von
netzgekoppelten Windenergieanlagen
Eoliennes -- Partie 21: Mesure et évaluation des caractéristiques de qualité de puissance
des éoliennes connectées au réseau
Ta slovenski standard je istoveten z: EN 61400-21:2008
ICS:
27.180 Sistemi turbin na veter in Wind turbine systems and
drugi alternativni viri energije other alternative sources of
energy
SIST EN 61400-21:2009 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

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SIST EN 61400-21:2009

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SIST EN 61400-21:2009

EUROPEAN STANDARD
EN 61400-21

NORME EUROPÉENNE
November 2008
EUROPÄISCHE NORM

ICS 27.180 Supersedes EN 61400-21:2002


English version


Wind turbines -
Part 21: Measurement and assessment
of power quality characteristics of grid connected wind turbines
(IEC 61400-21:2008)


Eoliennes -  Windenergieanlagen -
Partie 21: Mesurage et évaluation Teil 21: Messung und Bewertung
des caractéristiques de qualité der Netzverträglichkeit
de puissance des éoliennes von netzgekoppelten
connectées au réseau Windenergieanlagen
(CEI 61400-21:2008) (IEC 61400-21:2008)




This European Standard was approved by CENELEC on 2008-10-01. 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, Bulgaria, 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


© 2008 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61400-21:2008 E

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SIST EN 61400-21:2009
EN 61400-21:2008 – 2 –
Foreword
The text of document 88/317/FDIS, future edition 2 of IEC 61400-21, prepared by IEC TC 88, Wind
turbines, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 61400-21 on 2008-10-01.
This European Standard supersedes EN 61400-21:2002.
EN 61400-21:2008 includes the following new items with respect to EN 61400-21:2002:
– interharmonics and current distortions (< 9 kHz),
– response to voltage dips,
– active power ramp rate limitation and set-point control,
– reactive power capabilities and set-point control,
– grid protection and reconnection time after grid faults.
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) 2009-07-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2011-10-01
Annex ZA has been added by CENELEC.
__________
Endorsement notice
The text of the International Standard IEC 61400-21:2008 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 61000-3-3 NOTE  Harmonized as EN 61000-3-3:2008 (not modified).
IEC 61000-4-30 NOTE  Harmonized as EN 61000-4-30:2003 (not modified).
IEC 61400-1 NOTE  Harmonized as EN 61400-1:2005 (not modified).
__________

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SIST EN 61400-21:2009
– 3 – EN 61400-21:2008

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

1) 2)
IEC 60044-1 - Instrument transformers - EN 60044-1 1999
(mod) Part 1: Current transformers


1) 2)
IEC 60044-2 - Instrument transformers - EN 60044-2 1999
(mod) Part 2: Inductive voltage transformers


1)
IEC 60050-161 - International Electrotechnical Vocabulary - -
(IEV) -
Chapter 161: Electromagnetic compatibility


1)
IEC 60050-415 - International Electrotechnical Vocabulary - -
(IEV) -
Part 415: Wind turbine generator systems


IEC 61000-4-7 2002 Electromagnetic compatibility (EMC) - EN 61000-4-7 2002
Part 4-7: Testing and measurement
techniques - General guide on harmonics and
interharmonics measurements and
instrumentation, for power supply systems
and equipment connected thereto


1) 2)
IEC 61000-4-15 - Electromagnetic compatibility (EMC) - EN 61000-4-15 1998
Part 4-15: Testing and measurement
techniques - Flickermeter - Functional and
design specifications


1) 2)
IEC 61400-12-1 - Wind turbines - EN 61400-12-1 2006
Part 12-1: Power performance measurements
of electricity producing wind turbines


IEC 61800-3 2004 Adjustable speed electrical power drive EN 61800-3 2004
systems -
Part 3: EMC requirements and specific test
methods


1) 2)
IEC 62008 - Performance characteristics and calibration EN 62008 2005
methods for digital data acquisition systems
and relevant software





1)
Undated reference.
2)
Valid edition at date of issue.

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SIST EN 61400-21:2009

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SIST EN 61400-21:2009
IEC 61400-21
Edition 2.0 2008-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE


Wind turbines –
Part 21: Measurement and assessment of power quality characteristics of grid
connected wind turbines

Eoliennes –
Partie 21: Mesurage et évaluation des caractéristiques de qualité de puissance
des éoliennes connectées au réseau

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XA
CODE PRIX
ICS 27.180 ISBN 2-8318-9938-9
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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SIST EN 61400-21:2009
– 2 – 61400-21 © IEC:2008
CONTENTS
FOREWORD.4
INTRODUCTION.6
1 Scope.7
2 Normative references .7
3 Terms and definitions .8
4 Symbols and units .11
5 Abbreviations .13
6 Wind turbine power quality characteristic parameters .14
6.1 General .14
6.2 Wind turbine specification .14
6.3 Voltage fluctuations.14
6.3.1 General .14
6.3.2 Continuous operation .14
6.3.3 Switching operations .15
6.4 Current harmonics, interharmonics and higher frequency components .15
6.5 Response to voltage drops .16
6.6 Active power .16
6.6.1 Maximum measured power .16
6.6.2 Ramp rate limitation .16
6.6.3 Set-point control .17
6.7 Reactive power .17
6.7.1 Reactive power capability .17
6.7.2 Set-point control .17
6.8 Grid protection .18
6.9 Reconnection time.18
7 Test procedures .18
7.1 General .18
7.1.1 Test validity.19
7.1.2 Test conditions .19
7.1.3 Test equipment.20
7.2 Wind turbine specification .21
7.3 Voltage fluctuations.21
7.3.1 General .21
7.3.2 Fictitious grid.21
7.3.3 Continuous operation .23
7.3.4 Switching operations .26
7.4 Current harmonics, interharmonics and higher frequency components .27
7.5 Response to temporary voltage drop .28
7.6 Active power .30
7.6.1 Maximum measured power .30
7.6.2 Ramp rate limitation .31
7.6.3 Set point control .31
7.7 Reactive power .31
7.7.1 Reactive power capability .31
7.7.2 Set point control .32
7.8 Grid protection .32

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SIST EN 61400-21:2009
61400-21 © IEC:2008 – 3 –
7.9 Reconnection time.33
8 Assessment of power quality .34
8.1 General .34
8.2 Voltage fluctuations.34
8.2.1 General .34
8.2.2 Continuous operation .35
8.2.3 Switching operations .35
8.3 Current harmonics, interharmonics and higher frequency components .36
Annex A (informative) Sample report format.38
Annex B (informative) Voltage fluctuations and flicker.48
Annex C (informative) Measurement of active power, reactive power and voltage.56
Bibliography.58

Figure 1 – Adjustment of active power set-point.17
Figure 2 – Adjustment of reactive power set-point.18
Figure 3 – Assumed elements of measurement system .20
Figure 4 – Fictitious grid for simulation of fictitious voltage .22
Figure 5 – System with short circuit emulator for testing wind turbine response to
temporary voltage drop. .29
Figure 6 – Tolerance of voltage drop .30
Figure B.1 – Measurement and assessment procedures for flicker during continuous
operation of the wind turbine.48
Figure B.2 – Measurement and assessment procedures for voltage changes and flicker
during switching operations of the wind turbine.49
Figure B.3 – Flicker coefficient as a function of wind speed .50

Table 1 – Specification of voltage drops. The specified magnitudes, duration and
shape are for the voltage drop occurring when the wind turbine under test is not
connected.16
Table 2 – Specification of requirements for measurement equipment .21
Table 3 – Specification of exponents according to IEC 61000-3-6 .37
Table B.1 – Number of measurements N and frequency of occurrence of f and f
m,i m,i y,i
for each wind speed bin in the range from cut-in wind speed to 15 m/s .51
Table B.2 – Weighting factor w for each wind speed bin.51
i
Table B.3 – Total sum of weighting factor multiplied by number of measurements for
all wind speed bins .52
Table B.4 – Weighted accumulated distribution of the flicker coefficients Pr(c each wind speed distribution.52
Table B.5 – Resulting flicker coefficient in continuous operation .53
Table B.6 – Probabilities and percentiles for different wind speeds .53

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SIST EN 61400-21:2009
– 4 – 61400-21 © IEC:2008
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________

WIND TURBINES –

Part 21: Measurement and assessment of power quality
characteristics of grid connected 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 Guidances (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 61400-21 has been prepared by IEC technical committee 88: Wind
turbines.
This second edition cancels and replaces the first edition published in 2001. This edition
constitutes a technical revision.
This edition includes the following new items with respect to the previous edition:
– Interharmonics and current distortions (<9 kHz)
– Response to voltage dips
– Active power ramp rate limitation and set-point control
– Reactive power capabilities and set-point control
– Grid protection and reconnection time after grid faults

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SIST EN 61400-21:2009
61400-21 © IEC:2008 – 5 –
The text of this standard is based on the following documents:
FDIS Report on voting
88/317/FDIS 88/326/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 of the IEC 61400 series, under the general title Wind turbines, can be found
on the IEC website.
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.

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SIST EN 61400-21:2009
– 6 – 61400-21 © IEC:2008
INTRODUCTION
The purpose of this part of IEC 61400 is to provide a uniform methodology that will ensure
consistency and accuracy in the presentation, testing and assessment of power quality
characteristics of grid connected wind turbines (WTs). The power quality characteristics here
include wind turbine specifications, voltage quality (emissions of flicker and harmonics),
voltage drop response, power control (control of active and reactive power), grid protection
and reconnection time.
This part of IEC 61400 has been prepared with the anticipation that it would be applied by:
• the WT manufacturer striving to meet well-defined power quality characteristics;
• the WT purchaser in specifying such power quality characteristics;
• the WT operator who may be required to verify that stated, or required power quality
characteristics are met;
• the WT planner or regulator who has to be able to accurately and fairly determine the
impact of a WT on the voltage quality to ensure that the installation is designed so that
voltage quality requirements are respected;
• the WT certification authority or component testing organization in evaluating the power
quality characteristics of the wind turbine type;
• the planner or regulator of the electric network who has to be able to determine the grid
connection required for a WT.
This part of IEC 61400 provides recommendations for preparing the measurements and
assessment of power quality characteristics of grid connected WTs. This part of IEC 61400
will benefit those parties involved in the manufacture, installation planning, obtaining of
permission, operation, utilization, testing and regulation of WTs. The measurement and
analysis techniques recommended in this part of IEC 61400 should be applied by all parties to
ensure that the continuing development and operation of WTs are carried out in an
atmosphere of consistent and accurate communication.
This part of IEC 61400 presents measurement and analysis procedures expected to provide
consistent results that can be replicated by others.

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SIST EN 61400-21:2009
61400-21 © IEC:2008 – 7 –
WIND TURBINES –

Part 21: Measurement and assessment of power quality
characteristics of grid connected wind turbines



1 Scope
This part of IEC 61400 includes:
• definition and specification of the quantities to be determined for characterizing the power
quality of a grid connected wind turbine;
• measurement procedures for quantifying the characteristics;
• procedures for assessing compliance with power quality requirements, including
estimation of the power quality expected from the wind turbine type when deployed at a
specific site, possibly in groups.
The measurement procedures are valid for single wind turbines with a three-phase grid
connection. The measurement procedures are valid for any size of wind turbine, though this
part of IEC 61400 only requires wind turbine types intended for PCC (Point of Common
Coupling) at MV or HV to be tested and characterized as specified in this part of IEC 61400.
The measured characteristics are valid for the specific configuration and operational mode of
the assessed wind turbine type only. Other configurations, including altered control
parameters that cause the wind turbine to behave differently with respect to power quality,
require separate assessment.
The measurement procedures are designed to be as non-site-specific as possible, so that
power quality characteristics measured at for example a test site can be considered valid also
at other sites.
The procedures for assessing compliance with power quality requirements are valid for wind
turbines with PCC at MV or HV in power systems with fixed frequency within ±1 Hz, and
sufficient active and reactive power regulation capabilities. In other cases, the principles for
assessing compliance with power quality requirements may still be used as a guidance.
This part of IEC 61400 is for testing of wind turbines, though it contains information that may
also be useful for testing of wind farms.
NOTE This part of IEC 61400 uses the following terms for system voltage:
– low voltage (LV) refers to U ≤ 1 kV;
n
– medium voltage (MV) refers to 1 kV < U ≤ 35 kV;
n
– high voltage (HV) refers to U > 35 kV.
n
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, Instrument transformers – Part 1: Current transformers
IEC 60044-2, Instrument transformers – Part 2: Inductive voltage transformers

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SIST EN 61400-21:2009
– 8 – 61400-21 © IEC:2008
IEC 60050-161, International Electrotechnical Vocabulary – Part 161: Electromagnetic
compatibility
IEC 60050-415, International Electrotechnical Vocabulary – Part 415: Wind turbine generator
systems
IEC 61000-4-7:2002, Electromagnetic compatibility (EMC) – Part 4-7: Testing and
measurement techniques – General guide on harmonics and interharmonics measurements
and instrumentation, for power supply systems and equipment connected thereto
IEC 61000-4-15, Electromagnetic compatibility (EMC) – Part 4: Testing and measurement
techniques – Section 15: Flickermeter – Functional and design specifications
IEC 61400-12-1, Wind turbines – Part 12-1: Power performance measurements of electricity
producing wind turbines
IEC 61800-3:2004, Adjustable speed electrical power drive systems – Part 3: EMC
requirements and specific test methods
IEC 62008, Performance characteristics and calibration methods for digital data acquisition
systems and relevant software
3 Terms and definitions
For purposes of this document, the following terms and definitions apply.
3.1
continuous operation (for wind turbines)
normal operation of the wind turbine excluding start-up and shutdown operations
3.2
cut-in wind speed (for wind turbines)
lowest wind speed at hub height at which the wind turbine starts to produce power
[IEV 415-03-05]
3.3
flicker coefficient for continuous operation (for wind turbines)
normalized measure of the flicker emission during continuous operation of the wind turbine:
S
k,fic
c()ψ = P ×
k st,fic
S
n
where
P is the flicker emission from the wind turbine on the fictitious grid;
st,fic
S is the rated apparent power of the wind turbine;
n
S is the short-circuit apparent power of the fictitious grid
k,fic
NOTE The flicker coefficient for continuous operation is the same for a short-term (10 min) and long-term period
(2 h).
3.4
flicker step factor (for wind turbines)
a normalized measure of the flicker emission due to a single switching operation of the wind
turbine:

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SIST EN 61400-21:2009
61400-21 © IEC:2008 – 9 –
S
1
k,fic
0,31
k (ψ ) = × × P × T
f k st,fic p
130 S
n
where
T is the measurement period, long enough to ensure that the transient of the switching
p
operation has abated, though limited to exclude possible power fluctuations due to
turbulence;
P is the flicker emission from the wind turbine on the fictitious gri
...