IEC 61400-12-1:2017
(Main)Wind energy generation systems - Part 12-1: Power performance measurements of electricity producing wind turbines
Wind energy generation systems - Part 12-1: Power performance measurements of electricity producing wind turbines
IEC 61400-12-1:2017 specifies a procedure for measuring the power performance characteristics of a single wind turbine and applies to the testing of wind turbines of all types and sizes connected to the electrical power network. In addition, this standard describes a procedure to be used to determine the power performance characteristics of small wind turbines (as defined in IEC 61400-2) when connected to either the electric power network or a battery bank. The procedure can be used for performance evaluation of specific wind turbines at specific locations, but equally the methodology can be used to make generic comparisons between different wind turbine models or different wind turbine settings when site-specific conditions and data filtering influences are taken into account. This new edition includes the following significant technical changes with respect to the previous edition: new definition of wind speed, inclusion of wind shear and wind veer, revision of air density correction, revision of site calibration, revision to definition of power curve, interpolation to bin centre method, revision of obstacle model, etc.
Key words: Wind turbines, Wind energy, renewable energy, performance, efficiency
The contents of the corrigendum 1 of September 2019, corrigendum 2 of March 2020 and corrigendum 3 of May 2021 have been included in this copy.
Systèmes de génération d'énergie éolienne – Partie 12-1: Mesures de performance de puissance des éoliennes de production d'électricité
L'IEC 61400-12-1:2017 spécifie une procédure de mesure des caractéristiques de performance de puissance d'une éolienne simple et s'applique aux essais d'éoliennes raccordées au réseau électrique de tous types et de toutes tailles. En outre, la présente norme décrit une procédure qui doit être utilisée pour déterminer les caractéristiques de performance de puissance des petites éoliennes (définies dans l'IEC 61400-2) raccordées soit au réseau électrique, soit à un banc de batteries. La procédure peut être utilisée pour évaluer la performance d'éoliennes spécifiques sur des sites spécifiques, mais la méthodologie peut également être utilisée pour procéder à des comparaisons génériques entre différents modèles d'éoliennes ou différents réglages d'éoliennes lorsque les influences des conditions spécifiques au site et du filtrage de données sont étudiées. Cette nouvelle édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente: nouvelle définition de la vitesse du vent; inclusion du cisaillement du vent et de la déviation de la trajectoire du vent; correction de la masse volumique de l'air; révision de l'étalonnage du site; révision de la définition de la courbe de puissance; interpolation de la méthode utilisant le centre de la tranche; révision du modèle d'obstacle; etc.
Mots clé: éoliennes, énergi renouvelable, performance, efficacité
Le contenu du corrigendum de septembre 2019, de mars 2020 et de mai 2021 a été pris en considération dans cet exemplaire.
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IEC 61400-12-1 ®
Edition 2.0 2017-03
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Wind turbines energy generation systems –
Part 12-1: Power performance measurements of electricity producing wind
turbines
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from
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IEC 61400-12-1 ®
Edition 2.0 2017-03
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Wind turbines energy generation systems –
Part 12-1: Power performance measurements of electricity producing wind
turbines
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.180 ISBN 978-2-8322-4081-6
– 2 – IEC 61400-12-1:2017 RLV © IEC 2017
CONTENTS
FOREWORD . 14
INTRODUCTION . 17
1 Scope . 18
2 Normative references . 18
3 Terms and definitions . 19
4 Symbols and units . 23
5 Power performance method overview . 26
6 Preparation for performance test . 30
6.1 General . 30
6.2 Wind turbine and electrical connection . 30
6.3 Test site . 30
6.3.1 General . 30
6.3.2 Location of the meteorological mast wind measurement equipment . 30
6.3.3 Measurement sector . 31
6.3.4 Correction factors and uncertainty due to flow distortion originating from
topography . 31
7 Test equipment . 32
7.1 Electric power . 32
7.2 Wind speed . 32
7.2.1 General . 32
7.2.2 General requirements for meteorological mast mounted anemometers . 34
7.2.3 Top-mounted anemometers . 34
7.2.4 Side-mounted anemometers . 35
7.2.5 Remote sensing device (RSD) . 35
7.2.6 Rotor equivalent wind speed measurement . 35
7.2.7 Hub height wind speed measurement . 36
7.2.8 Wind shear measurements . 36
7.3 Wind direction . 38
7.4 Air density. 38
7.5 Rotational speed and pitch angle . 39
7.6 Blade condition . 39
7.7 Wind turbine control system . 39
7.8 Data acquisition system . 39
8 Measurement procedure . 39
8.1 General . 39
8.2 Wind turbine operation . 40
8.3 Data collection . 40
8.4 Data rejection . 40
8.5 Data correction .
8.5 Database . 41
9 Derived results . 42
9.1 Data normalisation . 42
9.1.1 General . 42
9.1.2 Correction for meteorological mast flow distortion of side-mounted
anemometer . 43
9.1.3 Wind shear correction (when REWS measurements available) . 43
9.1.4 Wind veer correction . 46
9.1.5 Air density normalisation. 46
9.1.6 Turbulence normalisation . 47
9.2 Determination of the measured power curve . 47
9.3 Annual energy production (AEP) . 48
9.4 Power coefficient . 50
10 Reporting format . 50
Annex A (normative) Assessment of influences caused by wind turbines and obstacles
at the test site . 66
A.1 General . 66
A.2 Requirements regarding neighbouring and operating wind turbines . 66
A.3 Requirements regarding obstacles . 67
A.4 Method for calculation of sectors to exclude . 68
A.5 Special requirements for extended obstacles . 71
Annex B (normative) Assessment of terrain at the test site . 72
Annex C (normative) Site calibration procedure . 75
C.1 General . 75
C.2 Overview of the procedure . 76
C.3 Test set-up . 78
C.3.1 Considerations for selection of the test wind turbine and location of the
meteorological mast. 78
C.3.2 Instrumentation . 80
C.4 Data acquisition and analysis rejection criteria . 81
C.5 Selection of final measurement sector.
C.5 Uncertainty Analysis . 82
C.5.1 Assessment of site shear conditions . 82
C.5.2 Method 1: Bins of wind direction and wind shear . 84
C.5.3 Method 2: Linear regression method where shear is not a significant
influence . 85
C.5.4 Additional calculations . 86
C.6 Report requirements Site calibration uncertainty . 87
C.6.1 Site calibration category A uncertainty . 87
C.6.2 Site calibration category B uncertainty . 88
C.6.3 Combined uncertainty . 89
C.7 Quality checks and additional uncertainties . 89
C.7.1 Convergence check . 89
C.7.2 Correlation check for linear regression (see C.5.3) . 89
C.7.3 Change in correction between adjacent wind direction bins . 89
C.7.4 Removal of the wind direction sensor between site calibration and
power performance test . 90
C.7.5 Site calibration and power performance measurements in different
seasons . 91
C.8 Verification of results . 91
C.9 Site calibration examples . 93
C.9.1 Example A . 93
C.9.2 Example B . 98
C.9.3 Example C . 105
Annex D (normative) Evaluation of uncertainty in measurement . 108
Annex E (informative) Theoretical basis for determining the uncertainty of
measurement using the method of bins . 111
– 4 – IEC 61400-12-1:2017 RLV © IEC 2017
E.1 General . 111
E.2 Combining uncertainties . 111
E.2.1 General . 111
E.2.2 Expanded uncertainty . 113
E.2.3 Example Basis for the uncertainty assessment . 114
E.3 Category A uncertainties . 119
E.3.1 General . 119
E.3.2 Category A uncertainty in electric power . 119
E.3.3 Category A uncertainties in climatic variations the site calibration. 119
E.4 Category B uncertainties: Introduction and data acquisition system . 120
E.4.1 Category B uncertainties: Introduction . 120
E.4.2 Category B uncertainties: data acquisition system . 120
E.5 Category B uncertainties in electric power: Power output . 121
E.5.1 General . 121
E.5.2 Category B uncertainties: Power output – Current transformers . 121
E.5.3 Category B uncertainties: Power output – Voltage transformers . 122
E.5.4 Category B uncertainties: Power Output – Power transducer or other
power measurement device . 122
E.5.5 Category B uncertainties: Power output – Data acquisition . 123
E.6 Category B uncertainties: Wind speed – Introduction and sensors . 123
E.6.1 Category B uncertainties: Wind speed – Introduction . 125
E.6.2 Category B uncertainties: Wind speed – Hardware . 125
E.6.3 Category B uncertainties: Wind speed – Meteorological mast mounted
sensors. 125
E.7 Category B uncertainties: Wind speed – RSD . 128
E.7.1 General . 128
E.7.2 Category B uncertainties: Wind speed – RSD – Calibration . 128
E.7.3 Category B uncertainties: Wind speed – RSD – in-situ check . 129
E.7.4 Category B uncertainties: Wind speed – RSD – Classification . 129
E.7.5 Category B uncertainties: Wind speed – RSD – Mounting . 130
E.7.6 Category B uncertainties: Wind speed – RSD – Flow variation . 131
E.7.7 Category B uncertainties: Wind speed – RSD – Monitoring test . 131
E.8 Category B uncertainties: Wind speed – REWS . 132
E.8.1 General . 132
E.8.2 Category B uncertainties: Wind speed – REWS – Wind speed
measurement over whole rotor . 132
E.8.3 Category B uncertainties: Wind speed – REWS – Wind veer . 134
E.9 Category B uncertainties: Wind speed – Terrain . 134
E.9.1 General . 134
E.9.2 Category B uncertainties: Wind speed – Terrain – Pre-calibration . 135
E.9.3 Category B uncertainties: Wind speed – Terrain – Post-calibration . 135
E.9.4 Category B uncertainties: Wind speed – Terrain – Classification . 136
E.9.5 Category B uncertainties: Wind speed – Terrain – Mounting . 136
E.9.6 Category B uncertainties: Wind speed – Terrain – Lightning finial . 137
E.9.7 Category B uncertainties: Wind speed – Terrain – Data acquisition . 137
E.9.8 Category B uncertainties: Wind speed – Terrain – Change in correction
between adjacent bins . 137
E.9.9 Category B uncertainties: Wind speed – Terrain – Removal of WD
sensor . 138
E.9.10 Category B uncertainties: Wind speed – Terrain – Seasonal variation . 138
E.10 Category B uncertainties: Air density . 138
E.10.1 General . 138
E.10.2 Category B uncertainties: Air density – Temperature introduction . 140
E.10.3 Category B uncertainties: Air density – Temperature – Calibration . 141
E.10.4 Category B uncertainties: Air density – Temperature – Radiation
shielding . 141
E.10.5 Category B uncertainties: Air density – Temperature – Mounting . 141
E.10.6 Category B uncertainties: Air density – Temperature – Data acquisition. 141
E.10.7 Category B uncertainties: Air density – Pressure introduction . 141
E.10.8 Category B uncertainties: Air density – Pressure – Calibration . 142
E.10.9 Category B uncertainties: Air density – Pressure – Mounting . 142
E.10.10 Category B uncertainties: Air density – Pressure – Data acquisition . 142
E.10.11 Category B uncertainties: Air density – Relative humidity introduction . 143
E.10.12 Category B uncertainties: Air density – Relative humidity – Calibration . 144
E.10.13 Category B uncertainties: Air density – Relative humidity – Mounting . 144
E.10.14 Category B uncertainties: Air Density – Relative humidity – Data
acquisition . 144
E.10.15 Category B uncertainties: Air density – Correction . 144
E.11 Category B uncertainties: Method . 145
E.11.1 General . 145
E.11.2 Category B uncertainties: Method – Wind conditions . 145
E.11.3 Category B uncertainties: Method – Seasonal effects . 150
E.11.4 Category B uncertainties: Method – Turbulence normalisation (or the
lack thereof) . 151
E.11.5 Category B uncertainties: Method – Cold climate . 151
E.12 Category B uncertainties: Wind direction . 152
E.12.1 General . 152
E.12.2 Category B uncertainties: Wind direction – Vane or sonic . 152
E.12.3 Category B uncertainties: Wind direction – RSD . 154
E.13 Combining uncertainties . 155
E.13.1 General . 155
E.13.2 Combining Category B uncertainties in electric power (u ) . 155
P,i
E.13.3 Combining uncertainties in the wind speed measurement (u ) . 155
V,i
E.13.4 Combining uncertainties in the wind speed measurement from cup or
sonic (u ) . 155
VS,i
E.13.5 Combining uncertainties in the wind speed measurement from RSD
(u ) . 156
VR,i
E.13.6 Combining uncertainties in the wind speed measurement from REWS
u . 156
REWS,i
E.13.7 Combining uncertainties in the wind speed measurement for REWS for
either a meteorological mast significantly above hub height or an RSD
with a lower-than-hub-height meteorological mast . 157
E.13.8 Combining uncertainties in the wind speed measurement for REWS for
a hub height meteorological mast + RSD for shear using an absolute
wind speed . 160
E.13.9 Combining uncertainties in the wind speed measurement for REWS for
a hub height meteorological mast and RSD for shear using a relative
wind speed . 161
E.13.10 Combining uncertainties in the wind speed measurement from REWS
due to wind veer across the whole rotor u . 163
REWS,veer,i
E.13.11 Combining uncertainties in the wind speed measurement from flow
distortion due to site calibration u . 166
VT,i
– 6 – IEC 61400-12-1:2017 RLV © IEC 2017
E.13.12 Combining uncertainties for the temperature measurement u . 167
T,i
E.13.13 Combining uncertainties for the pressure measurement u . 168
B,i
E.13.14 Combining uncertainties for the humidity measurement u . 168
RH,i
E.13.15 Combining uncertainties for the method related components u . 169
M,i
E.13.16 Combining uncertainties for the wind direction measurement with wind
vane or sonic anemometer u . 169
WV,i
E.13.17 Combining uncertainties for the wind direction measurement with RSD
u . 169
WR,i
E.13.18 Combined category B uncertainties. 170
E.13.19 Combined standard uncertainty – Power curve . 170
E.13.20 Combined standard uncertainty – Energy production . 170
E.14 Relevance of uncertainty components under specified conditions . 171
E.15 Reference tables . 172
Annex F (normative) Cup anemometer Wind tunnel calibration procedure
for anemometers . 181
F.1 General requirements . 181
F.2 Requirements to the wind tunnel . 181
F.3 Instrumentation and calibration set-up requirements . 183
F.4 Calibration procedure . 184
F.4.1 General procedure cup and sonic anemometers . 184
F.4.2 Procedure for the calibration of sonic anemometers . 184
F.4.3 Determination of the wind speed at the anemometer position . 185
F.5 Data analysis . 186
F.6 Uncertainty analysis . 186
F.7 Reporting format . 187
F.8 Example uncertainty calculation . 188
Annex G (normative) Mounting of instruments on the meteorological mast . 193
G.1 General . 193
G.2 Preferred method of top mounting of Single top-mounted anemometer. 193
G.3 Alternative method of top-mounting of Side-by-side top-mounted
anemometers . 196
G.4 Boom mounting of cup anemometers Side-mounted instruments . 198
G.4.1 General . 198
G.4.2 Tubular meteorological masts . 198
G.4.3 Lattice meteorological masts . 200
G.5 Lightning protection . 205
G.6 Mounting of other meteorological instruments . 205
Annex H (normative) Power performance testing of small wind turbines . 207
H.1 General . 207
H.2 Definitions. 207
H.3 Wind turbine system definition and installation . 207
H.4 Meteorological mast location . 208
H.5 Test equipment . 209
H.6 Measurement procedure . 210
H.7 Derived results . 210
H.8 Reporting . 211
H.9 Annex A – Assessment of influence cause by wind turbines and obstacles at
the test site . 211
H.10 Annex B – Assessment of terrain at test site . 211
H.11 Annex C – Site calibration procedure . 211
Annex I (normative) Classification of cup and sonic anemometry . 212
I.1 General . 212
I.2 Classification classes . 213
I.3 Influence parameter ranges and classes . 213
I.4 Classification of cup and sonic anemometers . 213
I.5 Reporting format . 216
Annex J (informative normative) Assessment of cup and sonic anemometry . 217
J.1 General . 217
J.2 Measurements of cup anemometer characteristics . 217
J.2.1 Measurements in a wind tunnel for tilt angular response characteristics
of cup anemometers . 225
J.2.2 Wind tunnel measurements of directional characteristics of cup
anemometers . 227
J.2.3 Wind tunnel measurements of cup anemometer rotor torque
characteristics . 227
J.2.4 Wind tunnel measurements of step responses of cup anemometers . 228
J.2.5 Measurement of temperature induced effects on anemometer
performance . 229
J.2.6 Wind tunnel measurements of directional characteristics of sonic
anemometers . 230
J.3 A cup anemometer classification method based on wind tunnel and
laboratory tests and cup anemometer modelling . 231
J.3.1 Method . 231
J.3.2 Example of a cup anemometer model . 231
J.4 A sonic anemometer classification method based on wind tunnel tests and
sonic anemometer modelling . 237
J.5 Free field comparison measurements . 238
Annex K (informative normative) In-situ comparison of anemometers . 239
K.1 General . 239
K.2 Prerequisite . 239
K.3 Realisation Analysis method . 239
K.4 Evaluation criteria . 241
Annex L (normative) The application of remote sensing technology . 243
L.1 General . 243
L.2 Classification of remote sensing devices . 244
L.2.1 General . 244
L.2.2 Data acquisition . 244
L.2.3 Data preparation . 245
L.2.4 Principle and requirements of a sensitivity test . 246
L.2.5 Assessment of environmental variable significance. 252
L.2.6 Assessment of interdependency between environmental variables . 253
L.2.7 Calculation of accuracy class . 255
L.2.8 Acceptance criteria . 257
L.2.9 Classification of RSD . 258
L.3 Verification of the performance of remote sensing devices . 258
L.4 Evaluation of uncertainty of measurements of remote sensing devices . 261
L.4.1 General . 261
L.4.2 Reference uncertainty . 261
L.4.3 Uncertainty resulting from the RSD calibration test . 261
L.4.4 Uncertainty due to remote sensing device classification . 263
– 8 – IEC 61400-12-1:2017 RLV © IEC 2017
L.4.5 Uncertainty due to non-homogenous flow within the measurement
volume. 264
L.4.6 Uncertainty due to mounting effects . 264
L.4.7 Uncertainty due to variation in flow across the site . 264
L.5 Additional checks . 265
L.5.1 Monitoring the performance of the remote sensing device at the
application site . 265
L.5.2 Identification of malfunctioning of the remote sensing device . 265
L.5.3 Consistency check of the assessment of the remote sensing device
systematic uncertainties . 265
L.5.4 In-situ test of the remote sensing device . 266
L.6 Other requirements specific to power curve testing . 266
L.7 Reporting . 268
L.7.1 Common reporting on classification test, calibration test, and monitoring
of the remote sensing device during application . 268
L.7.2 Additional reporting on classification test . 268
L.7.3 Additional reporting on calibration test . 269
L.7.4 Additional reporting on application . 269
Annex M (informative) Normalisation of power curve data according to the turbulence
intensity . 270
M.1 General . 270
M.2 Turbulence normalisation procedure . 270
M.3 Determination of the zero turbulence power curve . 272
M.4 Order of wind shear correction (normalisation) and turbulence normalisation . 277
M.5 Uncertainty of turbulence normalisation or of power curves due to turbulence
effects . 277
Annex N (informative) Wind tunnel calibration procedure for wind direction sensors . 279
N.1 General . 279
N.2 General requirements . 279
N.3 Requirements of the wind tunnel . 279
N.4 Instrumentation and calibration set-up requirements . 280
N.5 Calibration procedure . 281
N.6 Data analysis . 282
N.7 Uncertainty analysis . 282
N.8 Reporting format . 282
N.9 Example of uncertainty calculation . 284
N.9.1 General . 284
N.9.2 Measurement uncertainties generated by determination of the flow
direction in the wind tunnel . 284
N.9.3 Contribution to measurement uncertainty by the wind direction sensor . 285
N.9.4 Result of the uncertainty calculation . 286
Annex O (informative) Power performance testing in cold climate . 289
O.1 General . 289
O.2 Recommendations . 289
O.2.1 General . 289
O.2.2 Sonic anemometers . 289
O.2.3 Cup anemometers . 289
O.3 Uncertainties. 290
O.4 Reporting . 290
Annex P (informative) Wind shear normalisation procedure . 291
P.1 General . 291
Annex Q (informative) Definition of the rotor equivalent wind speed under
consideration of wind veer . 293
Q.1 General . 293
Q.2 Definition of rotor equivalent wind speed under consideration of wind veer . 294
Q.3 Measurement of wind veer . 294
Q.4 Combined wind shear and wind veer normalisation . 294
Annex R (informative) Uncertainty considerations for tests on multiple turbines . 295
R.1 General . 295
Annex S (informative) Mast flow distortion correction for lattice masts . 299
Bibliography . 302
Figure 1 – Requirements as to distance of the the meteorological mast wind
measurement equipment and maximum allowed measurement sectors . 31
Figure 2 – Wind shear measurement heights appropriate to measurement of rotor
equivalent wind speed . 37
Figure 3 – Wind shear measurement heights when no wind speed measurements
above hub height are available (for wind shear exponent determination only) . 38
Figure 4 – Process of application of the various normalisations . 43
Figure 5 – Presentation of example site calibration (only the sectors 20° to 30°, 40° to
60°, 160° to 210° and 330° to 350° are valid sectors) .
Figure 5 – Presentation of example database A and B: power performance test scatter
plot sampled at 1 Hz (mean values averaged over 10 min) . 56
Figure 6 – Presentation of example measured power curve for databases A and B . 58
Figure 7 – Presentation of example C curve for databases A and B . 60
P
Figure A.1 – Sectors to exclude due to wakes of neighbouring and operating wind
turbines and significant obstacles . 69
Figure A.2 – An example of sectors to exclude due to wakes of the wind tur
...
IEC 61400-12-1 ®
Edition 2.0 2017-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –
Part 12-1: Power performance measurements of electricity producing wind
turbines
Systèmes de génération d'énergie éolienne –
Partie 12-1: Mesures de performance de puissance des éoliennes de production
d'électricité
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
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About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.
About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigenda or an amendment might have been published.
IEC Catalogue - webstore.iec.ch/catalogue Electropedia - www.electropedia.org
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bibliographical information on IEC International Standards, electrical terms containing 20 000 terms and definitions in
Technical Specifications, Technical Reports and other English and French, with equivalent terms in 16 additional
documents. Available for PC, Mac OS, Android Tablets and languages. Also known as the International Electrotechnical
iPad. Vocabulary (IEV) online.
IEC publications search - www.iec.ch/searchpub IEC Glossary - std.iec.ch/glossary
The advanced search enables to find IEC publications by a 65 000 electrotechnical terminology entries in English and
variety of criteria (reference number, text, technical French extracted from the Terms and Definitions clause of
committee,…). It also gives information on projects, replaced IEC publications issued since 2002. Some entries have been
and withdrawn publications. collected from earlier publications of IEC TC 37, 77, 86 and
CISPR.
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IEC 61400-12-1 ®
Edition 2.0 2017-03
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –
Part 12-1: Power performance measurements of electricity producing wind
turbines
Systèmes de génération d'énergie éolienne –
Partie 12-1: Mesures de performance de puissance des éoliennes de production
d'électricité
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.180 ISBN 978-2-8322-3823-3
– 2 – IEC 61400-12-1:2017 © IEC 2017
CONTENTS
FOREWORD . 13
INTRODUCTION . 15
1 Scope . 16
2 Normative references . 16
3 Terms and definitions . 17
4 Symbols and units . 20
5 Power performance method overview . 23
6 Preparation for performance test . 27
6.1 General . 27
6.2 Wind turbine and electrical connection . 27
6.3 Test site . 27
6.3.1 General . 27
6.3.2 Location of the wind measurement equipment . 27
6.3.3 Measurement sector . 28
6.3.4 Correction factors and uncertainty due to flow distortion originating from
topography . 28
7 Test equipment . 29
7.1 Electric power . 29
7.2 Wind speed . 29
7.2.1 General . 29
7.2.2 General requirements for meteorological mast mounted anemometers . 30
7.2.3 Top-mounted anemometers . 31
7.2.4 Side-mounted anemometers . 31
7.2.5 Remote sensing device (RSD) . 31
7.2.6 Rotor equivalent wind speed measurement . 32
7.2.7 Hub height wind speed measurement . 32
7.2.8 Wind shear measurements . 32
7.3 Wind direction . 34
7.4 Air density. 34
7.5 Rotational speed and pitch angle . 35
7.6 Blade condition . 35
7.7 Wind turbine control system . 35
7.8 Data acquisition system . 35
8 Measurement procedure . 35
8.1 General . 35
8.2 Wind turbine operation . 35
8.3 Data collection . 36
8.4 Data rejection . 36
8.5 Database . 37
9 Derived results . 37
9.1 Data normalisation . 37
9.1.1 General . 37
9.1.2 Correction for meteorological mast flow distortion of side-mounted
anemometer . 38
9.1.3 Wind shear correction (when REWS measurements available) . 38
9.1.4 Wind veer correction . 41
9.1.5 Air density normalisation. 41
9.1.6 Turbulence normalisation . 42
9.2 Determination of the measured power curve . 42
9.3 Annual energy production (AEP) . 43
9.4 Power coefficient . 45
10 Reporting format . 45
Annex A (normative) Assessment of influences caused by wind turbines and obstacles
at the test site . 52
A.1 General . 52
A.2 Requirements regarding neighbouring and operating wind turbines . 52
A.3 Requirements regarding obstacles . 53
A.4 Method for calculation of sectors to exclude . 53
A.5 Special requirements for extended obstacles . 57
Annex B (normative) Assessment of terrain at the test site . 58
Annex C (normative) Site calibration procedure . 61
C.1 General . 61
C.2 Overview of the procedure . 61
C.3 Test set-up . 63
C.3.1 Considerations for selection of the test wind turbine and location of the
meteorological mast. 63
C.3.2 Instrumentation . 65
C.4 Data acquisition and rejection criteria . 65
C.5 Analysis . 66
C.5.1 Assessment of site shear conditions . 66
C.5.2 Method 1: Bins of wind direction and wind shear . 68
C.5.3 Method 2: Linear regression method where shear is not a significant
influence . 69
C.5.4 Additional calculations . 69
C.6 Site calibration uncertainty . 70
C.6.1 Site calibration category A uncertainty . 70
C.6.2 Site calibration category B uncertainty . 72
C.6.3 Combined uncertainty . 72
C.7 Quality checks and additional uncertainties . 72
C.7.1 Convergence check . 72
C.7.2 Correlation check for linear regression (see C.5.3) . 73
C.7.3 Change in correction between adjacent wind direction bins . 73
C.7.4 Removal of the wind direction sensor between site calibration and
power performance test . 73
C.7.5 Site calibration and power performance measurements in different
seasons . 74
C.8 Verification of results . 75
C.9 Site calibration examples . 76
C.9.1 Example A . 76
C.9.2 Example B . 81
C.9.3 Example C . 88
Annex D (normative) Evaluation of uncertainty in measurement . 91
Annex E (informative) Theoretical basis for determining the uncertainty of
measurement using the method of bins . 94
E.1 General . 94
– 4 – IEC 61400-12-1:2017 © IEC 2017
E.2 Combining uncertainties . 94
E.2.1 General . 94
E.2.2 Expanded uncertainty . 96
E.2.3 Basis for the uncertainty assessment . 97
E.3 Category A uncertainties . 100
E.3.1 General . 100
E.3.2 Category A uncertainty in electric power . 100
E.3.3 Category A uncertainties in the site calibration . 101
E.4 Category B uncertainties: Introduction and data acquisition system . 101
E.4.1 Category B uncertainties: Introduction . 101
E.4.2 Category B uncertainties: data acquisition system . 102
E.5 Category B uncertainties: Power output . 102
E.5.1 General . 102
E.5.2 Category B uncertainties: Power output – Current transformers . 102
E.5.3 Category B uncertainties: Power output – Voltage transformers . 103
E.5.4 Category B uncertainties: Power Output – Power transducer or other
power measurement device . 104
E.5.5 Category B uncertainties: Power output – Data acquisition . 104
E.6 Category B uncertainties: Wind speed – Introduction and sensors . 104
E.6.1 Category B uncertainties: Wind speed – Introduction . 104
E.6.2 Category B uncertainties: Wind speed – Hardware . 104
E.6.3 Category B uncertainties: Wind speed – Meteorological mast mounted
sensors. 105
E.7 Category B uncertainties: Wind speed – RSD . 108
E.7.1 General . 108
E.7.2 Category B uncertainties: Wind speed – RSD – Calibration . 108
E.7.3 Category B uncertainties: Wind speed – RSD – in-situ check . 108
E.7.4 Category B uncertainties: Wind speed – RSD – Classification . 108
E.7.5 Category B uncertainties: Wind speed – RSD – Mounting . 110
E.7.6 Category B uncertainties: Wind speed – RSD – Flow variation . 110
E.7.7 Category B uncertainties: Wind speed – RSD – Monitoring test . 111
E.8 Category B uncertainties: Wind speed – REWS . 112
E.8.1 General . 112
E.8.2 Category B uncertainties: Wind speed – REWS – Wind speed
measurement over whole rotor . 112
E.8.3 Category B uncertainties: Wind speed – REWS – Wind veer . 113
E.9 Category B uncertainties: Wind speed – Terrain . 113
E.9.1 General . 113
E.9.2 Category B uncertainties: Wind speed – Terrain – Pre-calibration . 114
E.9.3 Category B uncertainties: Wind speed – Terrain – Post-calibration . 114
E.9.4 Category B uncertainties: Wind speed – Terrain – Classification . 115
E.9.5 Category B uncertainties: Wind speed – Terrain – Mounting . 116
E.9.6 Category B uncertainties: Wind speed – Terrain – Lightning finial . 116
E.9.7 Category B uncertainties: Wind speed – Terrain – Data acquisition . 117
E.9.8 Category B uncertainties: Wind speed – Terrain – Change in correction
between adjacent bins . 117
E.9.9 Category B uncertainties: Wind speed – Terrain – Removal of WD
sensor . 117
E.9.10 Category B uncertainties: Wind speed – Terrain – Seasonal variation . 117
E.10 Category B uncertainties: Air density . 118
E.10.1 General . 118
E.10.2 Category B uncertainties: Air density – Temperature introduction . 118
E.10.3 Category B uncertainties: Air density – Temperature – Calibration . 119
E.10.4 Category B uncertainties: Air density – Temperature – Radiation
shielding . 119
E.10.5 Category B uncertainties: Air density – Temperature – Mounting . 119
E.10.6 Category B uncertainties: Air density – Temperature – Data acquisition. 119
E.10.7 Category B uncertainties: Air density – Pressure introduction . 120
E.10.8 Category B uncertainties: Air density – Pressure – Calibration . 120
E.10.9 Category B uncertainties: Air density – Pressure – Mounting . 120
E.10.10 Category B uncertainties: Air density – Pressure – Data acquisition . 121
E.10.11 Category B uncertainties: Air density – Relative humidity introduction . 121
E.10.12 Category B uncertainties: Air density – Relative humidity – Calibration . 122
E.10.13 Category B uncertainties: Air density – Relative humidity – Mounting . 122
E.10.14 Category B uncertainties: Air Density – Relative humidity – Data
acquisition . 122
E.10.15 Category B uncertainties: Air density – Correction . 122
E.11 Category B uncertainties: Method . 123
E.11.1 General . 123
E.11.2 Category B uncertainties: Method – Wind conditions . 123
E.11.3 Category B uncertainties: Method – Seasonal effects . 128
E.11.4 Category B uncertainties: Method – Turbulence normalisation (or the
lack thereof) . 129
E.11.5 Category B uncertainties: Method – Cold climate . 129
E.12 Category B uncertainties: Wind direction . 130
E.12.1 General . 130
E.12.2 Category B uncertainties: Wind direction – Vane or sonic . 130
E.12.3 Category B uncertainties: Wind direction – RSD . 132
E.13 Combining uncertainties . 133
E.13.1 General . 133
E.13.2 Combining Category B uncertainties in electric power (u ) . 133
P,i
E.13.3 Combining uncertainties in the wind speed measurement (u ) . 133
V,i
E.13.4 Combining uncertainties in the wind speed measurement from cup or
sonic (u ) . 133
VS,i
E.13.5 Combining uncertainties in the wind speed measurement from RSD
(u ) . 134
VR,i
E.13.6 Combining uncertainties in the wind speed measurement from REWS
u . 134
REWS,i
E.13.7 Combining uncertainties in the wind speed measurement for REWS for
either a meteorological mast significantly above hub height or an RSD
with a lower-than-hub-height meteorological mast . 135
E.13.8 Combining uncertainties in the wind speed measurement for REWS for
a hub height meteorological mast + RSD for shear using an absolute
wind speed . 138
E.13.9 Combining uncertainties in the wind speed measurement for REWS for
a hub height meteorological mast and RSD for shear using a relative
wind speed . 140
E.13.10 Combining uncertainties in the wind speed measurement from REWS
due to wind veer across the whole rotor u . 141
REWS,veer,i
E.13.11 Combining uncertainties in the wind speed measurement from flow
distortion due to site calibration u . 144
VT,i
E.13.12 Combining uncertainties for the temperature measurement u . 145
T,i
– 6 – IEC 61400-12-1:2017 © IEC 2017
E.13.13 Combining uncertainties for the pressure measurement u . 146
B,i
E.13.14 Combining uncertainties for the humidity measurement u . 146
RH,i
E.13.15 Combining uncertainties for the method related components u . 147
M,i
E.13.16 Combining uncertainties for the wind direction measurement with wind
vane or sonic anemometer u . 147
WV,i
E.13.17 Combining uncertainties for the wind direction measurement with RSD
u . 147
WR,i
E.13.18 Combined category B uncertainties. 148
E.13.19 Combined standard uncertainty – Power curve . 148
E.13.20 Combined standard uncertainty – Energy production . 148
E.14 Relevance of uncertainty components under specified conditions . 148
E.15 Reference tables . 149
Annex F (normative) Wind tunnel calibration procedure for anemometers . 153
F.1 General requirements . 153
F.2 Requirements to the wind tunnel . 153
F.3 Instrumentation and calibration set-up requirements . 155
F.4 Calibration procedure . 155
F.4.1 General procedure cup and sonic anemometers . 155
F.4.2 Procedure for the calibration of sonic anemometers . 156
F.4.3 Determination of the wind speed at the anemometer position . 156
F.5 Data analysis . 157
F.6 Uncertainty analysis . 157
F.7 Reporting format . 158
F.8 Example uncertainty calculation . 159
Annex G (normative) Mounting of instruments on the meteorological mast . 162
G.1 General . 162
G.2 Single top-mounted anemometer. 162
G.3 Side-by-side top-mounted anemometers . 164
G.4 Side-mounted instruments . 166
G.4.1 General . 166
G.4.2 Tubular meteorological masts . 167
G.4.3 Lattice meteorological masts . 169
G.5 Lightning protection . 174
G.6 Mounting of other meteorological instruments . 174
Annex H (normative) Power performance testing of small wind turbines . 175
H.1 General . 175
H.2 Definitions. 175
H.3 Wind turbine system definition and installation . 175
H.4 Meteorological mast location . 176
H.5 Test equipment . 177
H.6 Measurement procedure . 177
H.7 Derived results . 178
H.8 Reporting . 179
H.9 Annex A – Assessment of influence cause by wind turbines and obstacles at
the test site . 179
H.10 Annex B – Assessment of terrain at test site . 179
H.11 Annex C – Site calibration procedure . 179
Annex I (normative) Classification of cup and sonic anemometry . 180
I.1 General . 180
I.2 Classification classes . 180
I.3 Influence parameter ranges . 181
I.4 Classification of cup and sonic anemometers . 181
I.5 Reporting format . 183
Annex J (normative) Assessment of cup and sonic anemometry . 184
J.1 General . 184
J.2 Measurements of anemometer characteristics . 184
J.2.1 Measurements in a wind tunnel for tilt angular response characteristics
of cup anemometers . 184
J.2.2 Wind tunnel measurements of directional characteristics of cup
anemometers . 185
J.2.3 Wind tunnel measurements of cup anemometer rotor torque
characteristics . 186
J.2.4 Wind tunnel measurements of step responses of cup anemometers . 186
J.2.5 Measurement of temperature induced effects on anemometer
performance . 187
J.2.6 Wind tunnel measurements of directional characteristics of sonic
anemometers . 189
J.3 A cup anemometer classification method based on wind tunnel and
laboratory tests and cup anemometer modelling . 189
J.3.1 Method . 189
J.3.2 Example of a cup anemometer model . 189
J.4 A sonic anemometer classification method based on wind tunnel tests and
sonic anemometer modelling . 196
J.5 Free field comparison measurements . 197
Annex K (normative) In-situ comparison of anemometers . 198
K.1 General . 198
K.2 Prerequisite . 198
K.3 Analysis method . 198
K.4 Evaluation criteria . 199
Annex L (normative) The application of remote sensing technology . 202
L.1 General . 202
L.2 Classification of remote sensing devices . 203
L.2.1 General . 203
L.2.2 Data acquisition . 203
L.2.3 Data preparation . 204
L.2.4 Principle and requirements of a sensitivity test . 205
L.2.5 Assessment of environmental variable significance. 211
L.2.6 Assessment of interdependency between environmental variables . 212
L.2.7 Calculation of accuracy class . 214
L.2.8 Acceptance criteria . 216
L.2.9 Classification of RSD . 217
L.3 Verification of the performance of remote sensing devices . 217
L.4 Evaluation of uncertainty of measurements of remote sensing devices . 220
L.4.1 General . 220
L.4.2 Reference uncertainty . 220
L.4.3 Uncertainty resulting from the RSD calibration test . 220
L.4.4 Uncertainty due to remote sensing device classification . 222
L.4.5 Uncertainty due to non-homogenous flow within the measurement
volume. 223
– 8 – IEC 61400-12-1:2017 © IEC 2017
L.4.6 Uncertainty due to mounting effects . 223
L.4.7 Uncertainty due to variation in flow across the site . 223
L.5 Additional checks . 224
L.5.1 Monitoring the performance of the remote sensing device at the
application site . 224
L.5.2 Identification of malfunctioning of the remote sensing device . 224
L.5.3 Consistency check of the assessment of the remote sensing device
systematic uncertainties . 224
L.5.4 In-situ test of the remote sensing device . 225
L.6 Other requirements specific to power curve testing . 225
L.7 Reporting . 227
L.7.1 Common reporting on classification test, calibration test, and monitoring
of the remote sensing device during application . 227
L.7.2 Additional reporting on classification test . 227
L.7.3 Additional reporting on calibration test . 228
L.7.4 Additional reporting on application . 228
Annex M (informative) Normalisation of power curve data according to the turbulence
intensity . 229
M.1 General . 229
M.2 Turbulence normalisation procedure . 229
M.3 Determination of the zero turbulence power curve . 231
M.4 Order of wind shear correction (normalisation) and turbulence normalisation . 236
M.5 Uncertainty of turbulence normalisation or of power curves due to turbulence
effects . 236
Annex N (informative) Wind tunnel calibration procedure for wind direction sensors . 238
N.1 General . 238
N.2 General requirements . 238
N.3 Requirements of the wind tunnel . 238
N.4 Instrumentation and calibration set-up requirements . 239
N.5 Calibration procedure . 240
N.6 Data analysis . 241
N.7 Uncertainty analysis . 241
N.8 Reporting format . 241
N.9 Example of uncertainty calculation . 243
N.9.1 General . 243
N.9.2 Measurement uncertainties generated by determination of the flow
direction in the wind tunnel . 243
N.9.3 Contribution to measurement uncertainty by the wind direction sensor . 244
N.9.4 Result of the uncertainty calculation . 245
Annex O (informative) Power performance testing in cold climate . 248
O.1 General . 248
O.2 Recommendations . 248
O.2.1 General . 248
O.2.2 Sonic anemometers . 248
O.2.3 Cup anemometers . 248
O.3 Uncertainties. 249
O.4 Reporting . 249
Annex P (informative) Wind shear normalisation procedure . 250
P.1 General . 250
Annex Q (informative) Definition of the rotor equivalent wind speed under
consideration of wind veer .
...
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