IEC 61400-12-1-2017

BS EN 61400‑12‑1:2017 BSI Standards Publication Wind power generation systems Part 12-1: Power performance measurement of electricity producing wind turbines (IEC 61400-12-1:2017) BS EN 61400‑12‑1:2017 BRITISH STANDARD National foreword This British Standard is the UK implementation of EN 61400‑12‑1:2017 It is identical to IEC 61400‑12‑1:2017 It supersedes BS EN 61400‑12‑1:2006, which is withdrawn The UK participation in its preparation was entrusted to Technical Committee PEL/88, Wind turbines A list of organizations represented on this committee can be obtained on request to its secretary This publication does not purport to include all the necessary provisions of a contract Users are responsible for its correct application © The British Standards Institution 2017 Published by BSI Standards Limited 2017 ISBN 978 580 79865 ICS 27.180 Compliance with a British Standard cannot confer immunity from legal obligations This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 July 2017 Amendments/corrigenda issued since publication Date Text affected EUROPEAN STANDARD BS EN 61400‑12‑1:2017 EN 61400-12-1 NORME EUROPÉENNE EUROPÄISCHE NORM June 2017 ICS 27.180 Supersedes EN 61400-12-1:2006 English Version Wind power generation systems - Part 12-1: Power performance measurement of electricity producing wind turbines (IEC 61400-12-1:2017) Systèmes de génération d'énergie éolienne - Partie 12-1: Mesures de performance de puissance des éoliennes de production d'électricité (IEC 61400-12-1:2017) Windenergieanlagen - Teil 12-1: Messung des Leistungsverhaltens einer Windenergieanlage (IEC 61400-12-1:2017) This European Standard was approved by CENELEC on 2017-04-07 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 CEN-CENELEC Management Centre 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 CEN-CENELEC Management Centre has the same status as the official versions CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic, Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden, Switzerland, Turkey and the United Kingdom European Committee for Electrotechnical Standardization Comité Européen de Normalisation Electrotechnique Europäisches Komitee für Elektrotechnische Normung CEN-CENELEC Management Centre: Avenue Marnix 17, B-1000 Brussels © 2017 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members Ref No EN 61400-12-1:2017 E BS EN 61400‑12‑1:2017 EN 61400-12-1:2017 European foreword The text of document 88/610/FDIS, future edition of IEC 61400-12-1, prepared by IEC TC 88 "Wind turbines" was submitted to the IEC-CENELEC parallel vote and approved by CENELEC as EN 61400-121:2017 The following dates are fixed: • latest date by which the document has to be implemented at national level by publication of an identical national standard or by endorsement (dop) 2018-01-07 • latest date by which the national standards conflicting with the document have to be withdrawn (dow) 2020-04-07 This document supersedes EN 61400-12-1:2006 Attention is drawn to the possibility that some of the elements of this document may be the subject of patent rights CENELEC shall not be held responsible for identifying any or all such patent rights Endorsement notice The text of the International Standard IEC 61400-12-1:2017 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 61400-1:2005 NOTE Harmonized as EN 61400-1:2005 IEC 61400-1:2005/AMD1:2010 NOTE Harmonized as EN 61400-1:2005/A1:2010 IEC 61400-2:2013 NOTE Harmonized as EN 61400-2:2013 IEC 61400-12-2 NOTE Harmonized as EN 61400-12-2 BS EN 61400‑12‑1:2017 EN 61400-12-1:2017 Annex ZA (normative) Normative references to international publications with their corresponding European publications The following documents, in whole or in part, are normatively referenced in this document and are indispensable for its application 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 NOTE Up-to-date information on the latest versions of the European Standards listed in this annex is available here: www.cenelec.eu Publication IEC 60688 Year 2012 IEC 61400-12-2 2013 IEC 61869-1 (mod) 2007 IEC 61869-2 2012 IEC 61869-3 2011 ISO 2533 ISO 3966 1975 2008 ISO/IEC 17025 2005 ISO/IEC 17043 2010 ISO/IEC Guide 98-3 2008 Title EN/HD Electrical measuring transducers for EN 60688 converting A.C and D.C electrical quantities to analogue or digital signals Wind turbines Part 12-2: Power EN 61400-12-2 performance of electricity producing wind turbines based on nacelle anemometry Instrument transformers Part 1: General EN 61869-1 requirements Instrument transformers Part 2: Additional EN 61869-2 requirements for current transformers Instrument transformers Part 3: Additional EN 61869-3 requirements for inductive voltage transformers Standard Atmosphere Measurement of fluid flow in closed conduits_- Velocity area method using Pitot static tubes General requirements for the competence of EN ISO/IEC 17025 testing and calibration laboratories Conformity assessment - General EN ISO/IEC 17043 requirements for proficiency testing Uncertainty of measurement - Part 3: Guide to the expression of uncertainty in measurement (GUM:1995) Year 2013 2013 2009 2012 2011 2005 2010 - This page deliberately left blank –2– BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 CONTENTS FOREWORD 13 INTRODUCTION 15 Scope 16 Normative references 16 Terms and definitions 17 Symbols and units 20 Power performance method overview 23 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 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 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 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 BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 –3– 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 A.2 A.3 A.4 A.5 Annex B General 52 Requirements regarding neighbouring and operating wind turbines 52 Requirements regarding obstacles 53 Method for calculation of sectors to exclude 53 Special requirements for extended obstacles 57 (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– BS EN 61400‑12‑1:2017 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 BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 E.10.1 E.10.2 E.10.3 E.10.4 –5– General 118 Category B uncertainties: Air density – Temperature introduction 118 Category B uncertainties: Air density – Temperature – Calibration 119 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 121 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 P,i ) 133 E.13.3 Combining uncertainties in the wind speed measurement (u V,i ) 133 E.13.4 Combining uncertainties in the wind speed measurement from cup or sonic (u VS,i ) 133 E.13.5 Combining uncertainties in the wind speed measurement from RSD (u VR,i ) 134 E.13.6 Combining uncertainties in the wind speed measurement from REWS u REWS,i 134 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 139 E.13.10 Combining uncertainties in the wind speed measurement from REWS due to wind veer across the whole rotor u REWS,veer,i 141 E.13.11 Combining uncertainties in the wind speed measurement from flow distortion due to site calibration u VT,i 144 E.13.12 Combining uncertainties for the temperature measurement u T,i 145 BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 O.3 – 249 – Uncertainties Extended temperature range: Given by the class S O.4 Reporting In addition to the normal reporting requirements, the precautions that have been adopted to ensure that the instruments that are used to measure the wind speed are not affected by ice and that low temperature effects on the measurement of the wind speed are accounted for The filtering for ice conditions should be individually documented The results of the power performance test with and without the temperature extension taken into account shall be reported BS EN 61400‑12‑1:2017 – 250 – IEC 61400-12-1:2017 © IEC 2017 Annex P (informative) Wind shear normalisation procedure P.1 General For deriving a climate specific power curve, the influence of the wind shear and wind veer on the power curve shall be accounted for by normalising the hub height wind speed to a predefined reference wind shear and wind veer The reference wind shear and wind veer profile can have any shape and may be defined as function of the wind speed at hub height The reference wind shear and wind veer could for instance reflect the conditions expected at the power curve test site if the purpose of the power curve test is to verify a warranted power curve that is specified for the same reference conditions If not defined otherwise, a power law wind shear profile with shear exponent of 0,2 and a wind veer of 0° throughout the entire height range of the turbine rotor shall be applied The normalisation of the wind speed at hub height to the reference wind shear and wind veer shall be performed by means of the rotor equivalent wind speed concept The kinetic energy in the wind across the rotor height range is: Pkin = ∫A ρ (V cos(ϕ – ϕhub )) (P.1) dA and the rotor equivalent wind speed that corresponds to the kinetic energy is:  Veq =   A ∫i (Vi 13  cos(ϕ i – ϕhub ))3 dAi   (P.2) The ratio of the rotor equivalent wind and the hub height wind speed characterises the shape of the wind shear profile and wind veer profile that is relevant for the description of the available kinetic energy at a certain wind speed at hub height This ratio is called wind shear correction factor: fr = Veq (P.3) Vh The same rotor equivalent wind speed can be reached by different combinations of hub height wind speeds and wind shear/veer conditions, e.g by the wind shear/veer and hub height wind speed present within a 10-minute period at the power curve test as well as by the reference wind shear / veer and a corresponding hub height wind speed (here called normalised wind speed): Veq = f r ,measured ⋅ V h ,measured = f r ,reference ⋅ V h ,normalised (P.4) Consequently, the wind shear/veer normalised hub height wind speed shall be calculated for each 10-minute period as: V h ,normalised = Veq f r ,reference (P.5) BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 – 251 – or as Vh,normalised = f r,measured f r,reference ⋅ Vh,measured (P.6) For a reference wind shear correction factor of (f r,reference = 1), i.e in case of zero shear and veer, the normalised hub height wind speed equals the rotor equivalent wind speed The uncertainty of the measurement of the wind shear and wind veer normalised wind speed shall be assessed according to Clause E.8, E.11.2.2 and E.11.2.3 It is pointed out that the rotor equivalent wind speed may overestimate the wind energy effectively usable by large wind turbines in case of the presence of high wind shear Thus, a method uncertainty of one third of the correction of the hub height wind speed shall be applied as additional uncertainty to the uncertainty of the measurement of the wind shear and wind veer normalised wind speed Under certain conditions, the evaluation of the wind shear and wind veer over the height range of the turbine rotor may not be possible, because no measurements of the wind speed or wind direction over the height range of the turbine rotor are available or because a site calibration of the wind speed and wind direction at other heights than hub height is not possible In this case, the lack of the integration of the wind shear/veer in the power curve evaluation shall be accounted for according to E.11.2.2.2 and E.11.2.3.2 for the desired reference wind shear/veer conditions In addition, a method uncertainty of one third of a virtual wind speed correction from the assumed wind shear/veer conditions at the power curve test to the desired reference wind shear/veer conditions shall be taken into account – 252 – BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 Annex Q (informative) Definition of the rotor equivalent wind speed under consideration of wind veer Q.1 General The wind speed at hub height is not always representative of the wind over the whole rotor Large wind speed and direction variations may be present as a result of either the atmospheric stability and/or terrain influence Figure Q.1 shows LIDAR wind profiles over flat terrain as well as the cosine of wind direction changes relative to an assumed hub height It is seen that the wind speed component perpendicular to the wind turbine rotor at a specific height will occasionally be much less than the wind speed at the specific height IEC a) Lidar wind profiles IEC b) Cosine of wind direction variation angle relative to a height Figure Q.1 – Wind profiles measured with LIDAR over flat terrain BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 – 253 – Therefore, the energy yield through the wind turbine rotor will depend on both the wind shear and wind veer of the specific profile Using the power curve based on the wind speed at hub height ignores both wind shear and wind veer The power curve obtained with the rotor equivalent wind speed depends less on the wind shear and wind veer than the power curve obtained with the wind speed at hub height Q.2 Definition of rotor equivalent wind speed under consideration of wind veer The rotor equivalent wind speed is the wind speed corresponding to the kinetic energy flux through the swept rotor area, when accounting for the wind shear and wind veer For the case that at least three measurement heights are available (see 7.2.6) the rotor equivalent wind speed is defined as  νeq =   n ∑i =1(νi cos(ϕi ))3 13 Ai   A  (Q.1) where n is the number of available measurement heights (n ≥ 3); vi is the wind speed measured at height i; φi is the angle difference between the wind direction at hub height and segment i; A is the area swept by the rotor (i.e πR with radius R); Ai is the area of the i th segment, i.e the segment the wind speed v i represents (refer to 9.1.3.2, Equation (6) Q.3 Measurement of wind veer The rotor equivalent wind speed as defined in Equation (Q.1) is influenced by the difference of wind direction measurements at various heights relative to hub height In order to provide accurate measurements of the difference of wind directions, it is important to measure the wind directions at the different height levels with the same type of sensor, i.e one remote sensing device measuring all heights, or same sensors on the meteorological mast at all heights Q.4 Combined wind shear and wind veer normalisation The procedures described in Annex P may be extended to referencing back the measured power curve to reference wind veer conditions by considering also a reference wind veer profile in addition to a reference wind shear profile The integration of the reference profiles over the rotor area shall be done according to Equation (Q.1) – 254 – BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 Annex R (informative) Uncertainty considerations for tests on multiple turbines R.1 General Annex R addresses the uncertainty considerations that arise when compiling test results from multiple turbines When testing multiple turbines, the quantities of interest are typically the mean AEP of the sample and the uncertainty in that mean The mean AEP can most simply be determined by taking a simple average of the individual turbine AEPs The determination of the uncertainty in the average AEP is not as straightforward As this is a frequently encountered situations, this standard provides an informative approach as to how this uncertainty may be estimated The mathematical framework for this approach is exactly the same as explained in IEC 61400-12-2:2013 Annex I and J and will not be repeated here What is different for this standard is Table R.1 of estimated correlations between tests on different turbines and the results as represented in Figures J.1 and J.2 of IEC 61400-122:2013, which will be repeated here As an introduction, a short discussion of the problem at hand will be repeated One approach to combining uncertainties is a simple average of the individual test uncertainties However, the simple average fails to account for the chief benefit of multiple tests, i.e a reduction in the combined test uncertainty A second approach is to calculate the standard uncertainty of the mean of the uncertainties: u AEPAVG = L L ∑ u 2AEP ,i (R.1) i =1 where u AEPAVG u AEP , i L 43 is the uncertainty in the average AEP; is the uncertainty in AEP for turbine i; is the number of turbines tested Equation (R.1) assumes full independence among the individual turbine test results, meaning there is no correlation in the individual test results from one unit to the next As a consequence application of Equation (R.1) would lead to an underestimation of the uncertainty in the average AEP Therefore, in order to accurately assess the uncertainty in the average AEP, it is necessary to identify a practical method for handling correlated uncertainty components An approach is suggested based on the ISO information publication ‘Guide to the expression of uncertainty in measurement’ with minor adjustments in the handling of correlation _ 43 Please note that the equation here is slightly different from the equation in IEC 61400-12-2 As this is the uncertainty of an average and division by 1/L is a linear transformation, we get a 1/L under the square root or a 1/L in front of the square root BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 – 255 – Table R.1 – List of correlated uncertainty components Measured parameter Electric power Source Correlation coefficient Condition Current transformers ρup1,m,n Same instrument make 0,9 Different instrument make 0,1 Voltage transformers ρup2,m,n Same instrument make 0,9 Different instrument make 0,1 Power transducer or power measurement device ρup3,m,n Same instrument make 0,9 Different instrument make 0,1 Dynamic power measurement ρup4,m,n Same instrument make 0,9 Different instrument make 0,1 Data acquisition ρudp,m,n Same instrument make 0,9 Different instrument make 0,1 Anemometer calibration ρuv1,m,n Shared instrument (same met mast) 1,0 Different masts, same make/model, same calibration lab 0,9 Different masts, different make/model, same calibration lab 0,7 Different masts, same make/model, different calibration labs 0,4 Different masts, different make/model, different calibration labs 0,1 Shared instrument (same met mast) 1,0 PostCal / Insitu cal ρuv2,m,n Same instrument make Wind speed Value range Different instrument make Operational uncertainty ρuv3,m,n 0,9 0,7 Shared Instrument (same masts) 1,0 Same instrument make 0,9 Different instrument make 0,8 Notes C Ts of the same make tend to have similar cat B error values relative to the true value V Ts of the same make tend to have similar cat B error Direct measurement of voltage eliminates this uncertainty Power measurement devices of the same make tend to have similar cat B error Power measurement devices of the same make tend to have similar cat B error Data acquisition devices of the same make tend to have similar cat B errors relative to the true value Calibration reference and method produces similar cat B error Anemometers of the same make tend to have similar cat B errors relative to the true value Anemometers of the same make tend to have similar cat B errors relative to the true value Mounting effects ρuv4,m,n Per specification in this standard 0,9 Similar mounting required for use of a given transfer function drives a correlated uncertainty DAQ ρuv5,m,n Shared DAQ 1,0 Different DAQ of same make, same design 0,9 DAQ will be correlated the more similar the setup is Different DAQ of different make, same design 0,7 Different DAQ of same make, different design 0,5 Different DAQ of different make, different design 0,2 – 256 – Measured parameter Source Flow distortion due to terrain without site cal ρuv6,m,n Flow distortion due to terrain amongst test units with site cal, anemometer calibration ρuv7,m,n Flow distortion due to terrain amongst test units with site cal, operational uncertainty ρuv7,m,n Data acquisition for site calibration ρudv,m,n Temperature sensor Radiation shielding Temperature Correlation coefficient Mounting effects Data acquisition ρut1,m,n ρut2,m,n ρut3,m,n ρudt,m,n BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 Condition Value range Both turbines 2D to 3D (or 3D to 4D) from met mast 0,9 One turbine 2D to 3D and one turbine 3D to 4D 0,6 Shared instrument (same met mast) 1,0 Different masts, same make/model, same calibration lab 0,9 Different masts, different make/model, same calibration lab 0,7 Different masts, same make/model, different calibration labs 0,4 Different masts, different make/model, different calibration labs 0,1 Shared instruments (same masts) 1,0 Different masts, same make/model) 0,9 Different masts, different make/model 0,7 Shared DAQ 1,0 Different DAQ of same make, same design 0,9 Different DAQ of different make, same design 0,7 Different DAQ of same make, different design 0,5 Different DAQ of different make, different design 0,2 Shared instruments(same met mast) 1,0 Same instrument make 0,9 Different instrument make 0,1 Shared instruments(same met mast) 1,0 Same instrument make 0,9 Different instrument make 0,6 Shared instruments(same met mast) 1,0 Same location and mounting 0,9 Different location or mounting 0,1 Shared instruments(same met mast) 0,9 Same instrument make 0,1 Different instrument make Notes Increased terrain complexity and variation in terrain amongst test units will tend to have dis-similar cat B errors on the wind speed relative to the true value, distance plays an important role Data acquisition devices of the same make tend to have similar cat B error Temperature measurement devices of the same make tend to have similar cat B error Radiation shields tend to have the same method errors relative to the true value Data acquisition devices of the same make tend to have similar cat B error BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 Measured parameter Source Pressure sensor Pressure Mounting effects Data acquisition Method Statistical Correlation coefficient ρub1,m,n ρub2,m,n ρudb,m,n – 257 – Condition Value range Shared instrument (same met mast) 1,0 Same instrument make 0,9 Different instrument make 0,1 Shared instrument (same met mast) 1,0 Same instrument make 0,9 Different instrument make 0,1 Shared instrument (same met mast) 1,0 Same instrument make 0,9 Different instrument make 0,1 Air density correction ρum1,m,n Same correction methodology for all turbines 1,0 Wind Conditions ρum2,m,n Same conditions for different turbines 1,0 Seasonal variation ρum3,m,n Testing occurs during the same time of year 1,0 Testing occurs during different time of year 0,6 Variance in electrical power ρsp,m,n 0,0 Notes Pressure measurement devices of the same make tend to have similar cat B error If using multiple instruments, mounting will likely be similar Data acquisition devices of the same make tend to have similar cat B error Inherently random and independent – 258 – BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 Annex S (informative) Mast flow distortion correction for lattice masts Annex S gives guidance regarding a possible method to determine a correction for flow distortion of side mounted anemometers Such a correction is already discussed in 7.2.4 as well as 9.1.2 In this annex, a more detailed approach is presented for a lattice mast A similar method may work for other types of mast configuration but it is likely that specific changes need to be made to allow for the differences in the configuration Other methods to determine a correction may be applied but shall be documented in sufficient detail to allow the results to be reproduced by a third party based on the reported information The starting point is to a linear regression between two anemometers installed on different booms at the same measurement height The residuals of the regression can be determined and plotted against wind direction for the full 0° to 360° sector Other filters may be applied to ensure data quality This plot will normally show two things: a) for specific directions large flow distortions will be visible, indicated wakes operation from mast, guy wires or other sensors; b) a slowly changing sine wave is normally visible with a period of 360° An example is given in Figure S.1 below This example is for a goal-post design for the top of the mast but it illustrates the expected signal behaviour As shown in the graph, it may be beneficial to also plot the expected wakes as determined from the geometric set-up as this will help to correctly interpret the plot Care should be taken when there are too many and/or too strong wakes, from masts, guys and other sensors as the wakes may overshadow the sine-wave we are interested in and thereby make this method impractical or impossible to apply IEC Figure S.1 – Example of mast flow distortion The sine wave is the flow distortion from the mast and other hardware at the same measurement height that we aim at correcting This is done by finding suitable values for the parameters in this equation: = V1 m ⋅ V2 + B + Asin(WD + Centre) (S.1) BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 – 259 – where V1 is the wind speed from sensor one; V2 is the wind speed from the second sensor; m B is the slope of the regression between V and V ; is the offset of the regression between V and V ; A is a scaling parameter; WD is the wind direction Centre is the wind direction where the residuals are expected to be zero; In the above examples where the boom angles are 92° and 272°, Centre = 182° Figure G.3, Figure G.6 and Figure G.8 may be useful in assessing the directions where flow distortion is equal at both sensor locations Solutions within the measurement sector (or closest to) are most useful A is a scaling parameter that we need to solve for A can be found by iteration; by first setting A to zero and picking another point in the data (keeping away from the wakes data), we can determine the current value for the residuals In the graph above we see a residual value of 0,03 at 150° and a residual value of at 182° Now we define Centre = 182° and require a value of zero for V at 150° This determines value for A of 0,06 (note the negative sign for the sine at an angle of 150°+180° = 330°) Further checking of other points is recommended to make sure we have the right value for A and that this is not based on accidental outlier data A reflects the magnitude of the sum effect of the flow distortion on both anemometers Therefore, each anemometer wind speed must be corrected by half of amplitude A according to Equations (S.2) and (S.3) below: V1corr = V1 + A sin(WD + Centre) (S.2) V2= corr V2 − A sin(WD + Centre) (S.3) The flow distortion correction shown here does not correct to zero flow distortion but only normalizes to the direction where the flow distortion effect is the same at both anemometers The direction at which the flow distortion is zero may be estimated from the flow speed graphs in Clause G.4, and the final flow correction can be adjusted accordingly The corrected wind speeds can now be used to recalculate residuals, which can be plotted in the same graph to show the improvement The residuals of the corrected signal (in red) are clearly less depending on wind direction than the original (in blue), as shown in Figure S.2 – 260 – BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 IEC Figure S.2 – Flow distortion residuals versus direction BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 – 261 – Bibliography [1] IEC 61400-1:2005, Wind turbines – Part 1: Design requirements IEC 61400-1:2005/AMD1:2010 IEC 61400-1:2005/AMD1:2010 [2] IEC 61400-2:2013, Wind turbines – Part 2: Small wind turbines [3] IEC 61400-12-2, Wind turbines – Part 12-2: Power performance of electricity-producing wind turbines based on nacelle anemometry [4] ISO 16622, Meteorology – Sonic anemometers/thermometers – Acceptance test methods for mean wind measurements [5] VDI/VDE 2648, Transducers and measuring systems for measurement of angle [6] JCGM 200:2012, International vocabulary of metrology – Basic and general concepts and associated terms (VIM), 3rd edition [7] ACCUWIND – Methods for classification of cup anemometers, J-Å DAHLBERG, T.F PEDERSEN, P BUSCHE, Risø-R-1555 (EN), May 2006 [8] ACCUWIND – Classification of five cup anemometers according to IEC61400-12-1, T.F PEDERSEN, J-Å DAHLBERG, P BUSCHE, Risø-R-1556 (EN), May 2006 [9] Quantification of linear torque characteristics of cup anemometers with step responses, T.F PEDERSEN, Risø-I-3131 (EN), February 2011 [10] Wind shear proportional errors in the horizontal wind speed send by focused range gated lidars, LINDELOW et al., IOP conf Series: Earth and Env Sc., Vol 1, 2008 [11] Modelling conically scanning lidar error in complex terrain with WAsP engineering, BINGÖL, F., MANN, J., and FOUSSEKIS, D., Riso-R-1664(EN), 2008 [12] How to Gain Acceptance for Lidar Measurements, ALBERS, A., JANSSEN, A.W., Mander, J., Proceedings of German Wind Energy Conference, 2010 [13] Turbulence and Shear Normalisation of Wind Turbine Power Curve, ALBERS, A, Proceedings of European Wind Energy Conference, 2010 [14] Turbulence Normalisation of Wind Turbine Power Curve Measurements, ALBERS, A., Report PP09037, Deutsche WindGuard This page deliberately left blank NO COPYING WITHOUT BSI PERMISSION EXCEPT AS PERMITTED BY COPYRIGHT LAW British Standards Institution (BSI) BSI is the national body responsible for preparing British Standards and other standards-related publications, information and services BSI is incorporated by Royal 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Publication IEC 60688 Year 2012 IEC 61400-12-2 2013 IEC 61869-1 (mod) 2007 IEC 61869-2 2012 IEC 61869-3 2011 ISO 2533 ISO 3966 1975 2008 ISO /IEC 17025 2005 ISO /IEC 17043 2010 ISO /IEC Guide 98-3... indicated: IEC 61400-1:2005 NOTE Harmonized as EN 61400-1:2005 IEC 61400-1:2005/AMD1:2010 NOTE Harmonized as EN 61400-1:2005/A1:2010 IEC 61400-2:2013 NOTE Harmonized as EN 61400-2:2013 IEC 61400-12-2... ISO /IEC GUIDE 98-3:2008, Uncertainty of measurement – Part 3: Guide to the expression of uncertainty in measurement (GUM:1995) BS EN 61400‑12‑1:2017 IEC 61400-12-1:2017 © IEC 2017 – 17 – ISO/IEC