Wind energy generation systems - Part 12-6: Measurement based nacelle transfer function of electricity producing wind turbines

IEC 61400-12-6:2022 specifies a procedure for measuring the nacelle transfer function of a single electricity-producing, horizontal axis wind turbine, which is not considered to be a small wind turbine in accordance with IEC 61400-2. It is expected that this document be used when a valid nacelle transfer function is needed to execute a power performance measurement according to IEC 61400-12-2. This document specifies how to characterise a wind turbine's nacelle transfer function. The nacelle transfer function is determined by collecting simultaneous measurements of nacelle‑measured wind speed and free stream wind speed (as measured on a meteorological mast) 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 procedure also provides guidance on determination of measurement uncertainty including assessment of uncertainty sources and recommendations for combining them.
This first edition of IEC 61400-12-6 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 12-6: Fonction de transfert de la nacelle fondée sur le mesurage des éoliennes de production d'électricité

IEC 61400-12-6:2022 spécifie une procédure de mesure de la fonction de transfert de la nacelle d’une éolienne simple de production d’électricité à axe horizontal, qui n’est pas considérée comme un petit aérogénérateur selon l’IEC 61400-2. Il est attendu que le présent document soit utilisé lorsqu’il est nécessaire d'employer une fonction de transfert de la nacelle valide pour mesurer la performance de puissance conformément à l’IEC 61400-12-2. Le présent document décrit la façon de déterminer la fonction de transfert de la nacelle d’une éolienne. La fonction de transfert de la nacelle est déterminée en collectant simultanément des valeurs de mesure de la vitesse du vent mesurée à la nacelle et de la vitesse du vent en écoulement libre (mesurée sur un mât météorologique) pendant une période suffisamment longue pour créer une base de données statistiquement significative sur une certaine plage de vitesses du vent et dans des conditions de vent et des conditions atmosphériques variables. Cette procédure fournit également des recommandations relatives à la détermination de l’incertitude de mesure, incluant l’évaluation des sources d’incertitude et des recommandations qui permettent de les combiner.
La présente première édition de l’IEC 61400-12-6 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
29-Aug-2022
Current Stage
PPUB - Publication issued
Completion Date
30-Aug-2022
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IEC 61400-12-6
Edition 1.0 2022-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –
Part 12-6: Measurement based nacelle transfer function of electricity producing
wind turbines
Systèmes de génération d'énergie éolienne –
Partie 12-6: Fonction de transfert de la nacelle fondée sur le mesurage des
éoliennes de production d'électricité
IEC 61400-12-6:2022-08(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 61400-12-6
Edition 1.0 2022-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –
Part 12-6: Measurement based nacelle transfer function of electricity producing
wind turbines
Systèmes de génération d'énergie éolienne –
Partie 12-6: Fonction de transfert de la nacelle fondée sur le mesurage des
éoliennes de production d'électricité
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.180 ISBN 978-2-8322-5604-6

Warning! Make sure that you obtained this publication from an authorized distributor.

Attention! Veuillez vous assurer que vous avez obtenu cette publication via un distributeur agréé.

® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale
---------------------- Page: 3 ----------------------
– 2 – IEC 61400-12-6:2022 © IEC 2022
CONTENTS

FOREWORD ........................................................................................................................... 5

INTRODUCTION ..................................................................................................................... 7

1 Scope .............................................................................................................................. 8

2 Normative references ...................................................................................................... 8

3 Terms and definitions ...................................................................................................... 9

4 Symbols, units and abbreviated terms ........................................................................... 11

5 Overview of test method ................................................................................................ 15

6 Preparation for measurement of nacelle transfer function .............................................. 15

6.1 General ................................................................................................................. 15

6.2 Wind turbine ......................................................................................................... 15

6.3 Test site ................................................................................................................ 16

6.3.1 General ......................................................................................................... 16

6.3.2 Terrain classification ...................................................................................... 17

6.4 Test plan ............................................................................................................... 17

7 Test equipment .............................................................................................................. 17

7.1 General ................................................................................................................. 17

7.2 Data acquisition .................................................................................................... 18

8 Measurement procedure ................................................................................................ 19

8.1 General ................................................................................................................. 19

8.2 Data system(s) synchronisation ............................................................................ 19

8.3 Data collection ...................................................................................................... 20

8.4 Data quality check ................................................................................................ 20

8.4.1 General ......................................................................................................... 20

8.4.2 Measured signals are in range and available ................................................. 20

8.4.3 Sensors are operating properly ...................................................................... 20

8.4.4 Ensure data acquisition system(s) is(are) operating properly ......................... 21

8.4.5 Sector self-consistency check ........................................................................ 21

8.5 Data rejection ....................................................................................................... 21

8.6 Data correction ..................................................................................................... 21

8.7 Database .............................................................................................................. 22

9 Derived results .............................................................................................................. 22

9.1 Overview of derived results ................................................................................... 22

9.2 Determination of measured nacelle transfer function ............................................. 23

9.3 Data quality check ................................................................................................ 24

9.3.1 General ......................................................................................................... 24

9.3.2 Directional stability check .............................................................................. 24

9.3.3 Self-consistency check for NTF, using the NPC ............................................. 25

9.4 Uncertainty analysis .............................................................................................. 25

10 Reporting format ............................................................................................................ 25

Annex A (informative) Nacelle instrument mounting ............................................................. 29

A.1 General ................................................................................................................. 29

A.2 Preferred method of anemometer's mounting ........................................................ 29

A.3 Preferred position of anemometer ......................................................................... 29

Annex B (normative) Evaluation of uncertainty in measurement ........................................... 31

B.1 General ................................................................................................................. 31

---------------------- Page: 4 ----------------------
IEC 61400-12-6:2022 © IEC 2022 – 3 –

B.2 The measurands ................................................................................................... 31

B.3 Uncertainty components........................................................................................ 31

B.4 Wind direction uncertainty ..................................................................................... 33

Annex C (normative) Theoretical basis for determining the uncertainty of

measurement using the method of bins ................................................................................. 34

C.1 General ................................................................................................................. 34

C.2 Propagation of uncertainty through the stages of NTF/NPC measurement ............ 35

C.3 Category A uncertainties ....................................................................................... 38

C.3.1 General ......................................................................................................... 38

C.3.2 Category A uncertainty in electric power ........................................................ 38

C.4 Category B uncertainties ....................................................................................... 39

C.4.1 General ......................................................................................................... 39

C.4.2 Category B uncertainties in climatic variations ............................................... 40

C.5 Expanded uncertainty ........................................................................................... 40

Annex D (normative) NTF uncertainty estimates and calculation .......................................... 41

D.1 Methods and assumptions..................................................................................... 41

D.1.1 General ......................................................................................................... 41

D.1.2 Site calibration ............................................................................................... 41

D.1.3 Nacelle transfer function uncertainty component estimates ............................ 43

D.1.4 Nacelle power curve uncertainty component estimates .................................. 45

D.1.5 Wind direction uncertainty ............................................................................. 45

D.1.6 Contribution factors ....................................................................................... 47

D.2 Uncertainty example calculations .......................................................................... 48

D.2.1 Example description ...................................................................................... 48

D.2.2 Example case – NTF uncertainty ................................................................... 49

D.2.3 Example case – NPC uncertainty ................................................................... 49

Annex E (normative) Allowable anemometry instrument types.............................................. 51

E.1 General ................................................................................................................. 51

E.2 Recalibration of sonic anemometers ..................................................................... 51

E.3 Uncertainty of sonic and propeller anemometers ................................................... 51

Annex F (informative) Organisation of test, safety and communication ................................. 52

F.1 General ................................................................................................................. 52

F.2 Responsibility for test ........................................................................................... 52

F.3 Safety during test .................................................................................................. 52

F.4 Communication ..................................................................................................... 52

F.5 Prior to test ........................................................................................................... 52

F.6 During test ............................................................................................................ 52

F.7 After test ............................................................................................................... 53

Annex G (informative) NTF flowchart ................................................................................... 54

Bibliography .......................................................................................................................... 55

Figure 1 – Presentation of example data: measured transfer function ................................... 27

Figure A.1 – Mounting of anemometer on top of nacelle ........................................................ 30

Figure G.1 – NTF flowchart ................................................................................................... 54

Table 1 – Example of presentation of a measured power curve based on data from the

meteorological mast, for consistency check .......................................................................... 28

Table B.1 – Uncertainty components in nacelle transfer function evaluation .......................... 32

---------------------- Page: 5 ----------------------
– 4 – IEC 61400-12-6:2022 © IEC 2022

Table B.2 – Uncertainty components in nacelle based absolute wind direction ...................... 33

Table C.1 – Example cancellation sources ............................................................................ 36

Table C.2 – List of category A and B uncertainties for NTF ................................................... 39

Table C.3 – Expanded uncertainties...................................................................................... 40

Table D.1 – Estimates for uncertainty components from site calibration ................................ 42

Table D.2 – Estimates for uncertainty components from NTF measurement .......................... 44

Table D.3 – Estimates for uncertainty components for wind direction .................................... 46

Table D.4 – Estimates for contribution factors for site calibration .......................................... 47

Table D.5 – Estimates for contribution factors for NTF .......................................................... 48

---------------------- Page: 6 ----------------------
IEC 61400-12-6:2022 © IEC 2022 – 5 –
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
WIND ENERGY GENERATION SYSTEMS –
Part 12-6: Measurement based nacelle transfer
function of electricity producing wind turbines
FOREWORD

1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising

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rights. IEC shall not be held responsible for identifying any or all such patent rights.

IEC 61400-12-6 has been prepared by IEC technical committee 88: Wind energy generation

systems. It is an International Standard.

This first edition of IEC 61400-12-6 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.
---------------------- Page: 7 ----------------------
– 6 – IEC 61400-12-6:2022 © IEC 2022
The text of this International Standard is based on the following documents:
Draft Report on voting
88/826/CDV 88/871/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.

---------------------- Page: 8 ----------------------
IEC 61400-12-6:2022 © IEC 2022 – 7 –
INTRODUCTION

The IEC 61400-12 series consists of the following parts, under the general title Wind energy

generation systems:
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 wind turbines based on

nacelle anemometry
IEC 61400-12-3: Power performance – Measurement based site calibration
IEC 61400-12-4: Numerical 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

The purpose of this document is to provide a uniform methodology of measurement, analysis,

and reporting for the determination of a nacelle transfer function of 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 herein be utilised when applying the methodology described in IEC 61400-12-2 to

determine the power performance of individual wind turbines. 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 procedure describes how to characterise a wind turbine's nacelle transfer function in terms

of wind speeds measured on a meteorological mast as well as a wind speed measured on the

hub or nacelle of a wind turbine. The anemometer that is placed on the turbine is measuring a

wind speed that is strongly affected by the test turbine's rotor. This procedure includes methods

for determining and applying appropriate corrections for this interference. Such a correction is

termed a nacelle transfer function which relates the wind speed measured on the turbine to a

free-stream wind speed as measured on a meteorological mast. The procedure also provides

guidance on determination of measurement uncertainty including assessment of uncertainty

sources and recommendations for combining them into uncertainties.

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 interested in power performance testing of wind

turbines using IEC 61400-12-2 as well as parties involved in the installation, planning and

execution of such tests. When and where 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.

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 engaging in nacelle transfer function

measurements.
---------------------- Page: 9 ----------------------
– 8 – IEC 61400-12-6:2022 © IEC 2022
WIND ENERGY GENERATION SYSTEMS –
Part 12-6: Measurement based nacelle transfer
function of electricity producing wind turbines
1 Scope

This part of IEC 61400-12 specifies a procedure for measuring the nacelle transfer function of

a single electricity-producing, horizontal axis wind turbine, which is not considered to be a small

wind turbine in accordance with IEC 61400-2. It is expected that this document be used when

a valid nacelle transfer function is needed to execute a power performance measurement

according to IEC 61400-12-2.

A wind speed measured on the nacelle or hub of a wind turbine is affected by the turbine rotor

(i.e. speeded up or slowed down wind speed). In IEC 61400-12-1, an anemometer is located on

a meteorological tower that is located between two and four rotor diameters upwind of the test

turbine. This location allows direct measurement of the "free" wind with minimum interference

from the test turbine's rotor. In the procedure of this document, the anemometer is located on

or near the test turbine's nacelle. In this location, the anemometer is measuring a wind speed

that is strongly affected by the test turbine's rotor and the nacelle. The procedure in this

document includes methods for determining and applying appropriate corrections for this

interference. However, note that these corrections inherently increase the measurement

uncertainty compared to a properly configured test co
...

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