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

IEC 61400-21:2008 covers the 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; and procedures for assessing compliance with power quality requirements, including estimation of the power quality expected from the wind turbine type. The main changes with respect to the previous edition deal with 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.

Windenergieanlagen --Teil 21: Messung und Bewertung der Netzverträglichkeit von netzgekoppelten Windenergieanlagen

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

La CEI 61400-21:2008 couvre la définition et la spécification des grandeurs à déterminer pour caractériser la qualité de puissance d'une éolienne connectée à un réseau; les procédures de mesure pour quantifier les caractéristiques; les procédures pour évaluer la conformité aux exigences de qualité de puissance, y compris l'estimation de la qualité de puissance attendue d'un type d'éolienne. Les principales modifications par rapport à l'édition précédente concernent les interharmoniques et distorsions de courant (<9 kHz); la réponse aux creux de tension; la limitation du taux de variation et la commande de la valeur de consigne de la puissance active; les capacités de puissance réactive et la commande de la valeur de consigne de la puissance réactive; la protection réseau et le temps de reconnexion après des défauts du réseau.

Sistemi generatorjev vetrne turbine - 21. del: Merjenje in ocenjevanje kakovosti napetosti vetrnih turbin prilkjučenih na omrežje (IEC 61400-21:2008)

General Information

Status
Published
Publication Date
06-Nov-2008
Technical Committee
Drafting Committee
Parallel Committee
Current Stage
6060 - Document made available
Due Date
07-Nov-2008
Completion Date
07-Nov-2008

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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.

---------------------- Page: 1 ----------------------
SIST EN 61400-21:2009
---------------------- Page: 2 ----------------------
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
---------------------- Page: 3 ----------------------
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).
__________
---------------------- Page: 4 ----------------------
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
IEC 60050-161 - International Electrotechnical Vocabulary - -
(IEV) -
Chapter 161: Electromagnetic compatibility
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
Undated reference.
Valid edition at date of issue.
---------------------- Page: 5 ----------------------
SIST EN 61400-21:2009
---------------------- Page: 6 ----------------------
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
CODE PRIX
ICS 27.180 ISBN 2-8318-9938-9
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 7 ----------------------
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

---------------------- Page: 8 ----------------------
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

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

---------------------- Page: 9 ----------------------
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
---------------------- Page: 10 ----------------------
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.
---------------------- Page: 11 ----------------------
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.
---------------------- Page: 12 ----------------------
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;
– medium voltage (MV) refers to 1 kV < U ≤ 35 kV;
– high voltage (HV) refers to U > 35 kV.
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
---------------------- Page: 13 ----------------------
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:

k,fic
c()ψ = P ×
k st,fic
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;
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:
---------------------- Page: 14 ----------------------
SIST EN 61400-21:2009
61400-21 © IEC:2008 – 9 –
k,fic
0,31
k (ψ ) = × × P × T
f k st,fic p
130 S
where

T is the measurement period, long enough to ensure that the transient of the switching

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
...

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