Wind energy generation systems - Part 50-2: Wind measurement - Application of ground-mounted remote sensing technology

IEC 61400-50-2:2022 is applicable specifically to the use of ground-mounted remote sensing wind measurement instruments, i.e. devices which measure the wind at some location generally above and distant from the location at which the instrument is mounted (e.g. sodars, vertical profiling lidars). This document specifically excludes other types of RSD such as forward facing or scanning lidars. This document specifies the following: a. the procedure and requirements for classifying ground-based RSDs in order to assess the uncertainty pertaining from sensitivity of the RSD response to meteorological conditions that can vary between the RSD calibration place and time and the use case (specific measurement campaign – SMC) place and time; b. the procedures and requirements for calibration of RSDs; c. the assessment of wind speed measurement uncertainty; d. additional checks of the RSD performance and measurement uncertainty during the SMC; e. application of the wind speed uncertainty derived from the RSD calibration and classification to the measurements taken during the SMC (e.g. interpolation of uncertainty or calibration results to different heights); f. requirements for reporting. This first edition of IEC 61400-50-2 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 50-2: Mesurage du vent - Application de la technologie de télédétection montée au sol

IEC 61400-50-2:2022 s'applique spécifiquement à l'utilisation d'instruments de mesure du vent par télédétection montés au sol, c'est-à-dire des dispositifs qui mesurent le vent à un endroit généralement situé au-dessus et éloigné de l'endroit dans lequel l'instrument est monté (par exemple, sodars, lidars à profil vertical). Le présent document exclut spécifiquement d'autres types de RSD tels que les lidars dirigés vers l'avant ou les lidars à balayage. Le présent document spécifie les points suivants:
a. la procédure et les exigences de classification des RSD au sol afin d'évaluer l'incertitude liée à la sensibilité de la réponse du RSD aux conditions météorologiques qui peuvent varier entre le lieu et le moment de l'étalonnage du RSD et le lieu et le moment du cas d'utilisation (SMC – specific measurement campaign, campagne de mesure spécifique).
b. les procédures et les exigences relatives à l'étalonnage des RSD.
c. l'évaluation de l'incertitude de mesure de la vitesse du vent.
d. les contrôles supplémentaires des performances du RSD et de l'incertitude de mesure pendant la SMC.
e. l'application de l'incertitude de la vitesse du vent dérivée de l'étalonnage et de la classification du RSD aux mesurages effectués pendant la SMC (par exemple, interpolation de l'incertitude ou des résultats de l'étalonnage à différentes hauteurs).
f. exigences relatives aux rapports.
La présente première édition de l’IEC 61400-50-2 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 61400-50-2
Edition 1.0 2022-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –
Part 50-2: Wind measurement – Application of ground-mounted remote sensing
technology
Systèmes de génération d'énergie éolienne –
Partie 50-2: Mesurage du vent – Application de la technologie de télédétection
montée au sol
IEC 61400-50-2:2022-08(en-fr)
---------------------- Page: 1 ----------------------
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---------------------- Page: 2 ----------------------
IEC 61400-50-2
Edition 1.0 2022-08
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –
Part 50-2: Wind measurement – Application of ground-mounted remote sensing
technology
Systèmes de génération d'énergie éolienne –
Partie 50-2: Mesurage du vent – Application de la technologie de télédétection
montée au sol
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.180 ISBN 978-2-8322-5602-2

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 61400-50-2:2022 © IEC 2022
CONTENTS

FOREWORD ........................................................................................................................... 4

INTRODUCTION ..................................................................................................................... 6

1 Scope .............................................................................................................................. 7

2 Normative references ...................................................................................................... 7

3 Terms and definitions ...................................................................................................... 7

4 Symbols, units and abbreviated terms ........................................................................... 10

5 General ......................................................................................................................... 11

6 Classification of RSDs ................................................................................................... 13

6.1 General ................................................................................................................. 13

6.2 Data acquisition .................................................................................................... 14

6.3 Data preparation ................................................................................................... 15

6.4 Principle and requirements of a sensitivity test ...................................................... 15

6.5 Assessment of environmental variable significance ............................................... 21

6.6 Assessment of interdependency between environmental variables ........................ 22

6.7 Calculation of accuracy class ................................................................................ 24

6.8 Acceptance criteria ............................................................................................... 26

6.9 Classification of RSD ............................................................................................ 27

7 Verification of the performance of RSDs ........................................................................ 27

8 Evaluation of uncertainty of measurements by RSDs ..................................................... 30

8.1 General ................................................................................................................. 30

8.2 Reference uncertainty ........................................................................................... 30

8.3 Uncertainty resulting from the RSD calibration test ............................................... 30

8.4 Uncertainty due to RSD classification ................................................................... 32

8.5 Uncertainty due to non-homogenous flow within the measurement volume ............ 33

8.6 Uncertainty due to mounting effects ...................................................................... 34

8.7 Combining uncertainties in the wind speed measurement from RSD (u ) ......... 34

VR,i

9 Additional checks .......................................................................................................... 34

9.1 Monitoring the performance of the RSD at the application site .............................. 34

9.2 Identification of malfunctioning of the RSD ............................................................ 34

9.3 Consistency check of the assessment of the RSD systematic uncertainties ........... 34

9.4 In-situ test of the RSD ........................................................................................... 35

10 Application to SMC ........................................................................................................ 36

11 Reporting....................................................................................................................... 36

11.1 Common reporting on classification test, calibration test, and monitoring of

the RSD during SMC ............................................................................................. 36

11.2 Additional reporting on classification test .............................................................. 37

11.3 Additional reporting on calibration test .................................................................. 37

11.4 Additional reporting on SMC ................................................................................. 38

Annex A (informative) Uncertainty due to non-homogenous flow within the

measurement volume ............................................................................................................ 39

Bibliography .......................................................................................................................... 40

Figure 1 – Tilt angular response V ∕V of a cup anemometer as a function of flow
α  α=0

angle α compared to cosine response (IEC 61400-50-1) ....................................................... 17

---------------------- Page: 4 ----------------------
IEC 61400-50-2:2022 © IEC 2022 – 3 –

Figure 2 – Deviation versus upflow angle determined for an RSD with respect to the

cup anemometer in Figure 1 ................................................................................................. 17

Figure 3 – Example of sensitivity analysis against wind shear ............................................... 19

Figure 4 – Example of wind shear versus turbulence intensity ............................................... 23

Figure 5 – Example of percentage deviation of RSD and reference sensor

measurements versus turbulence intensity ............................................................................ 23

Figure 6 – Comparison of 10 min averages of the horizontal wind speed component as

measured by an RSD and a cup anemometer ....................................................................... 29

Figure 7 – Bin-wise comparison of measurement of the horizontal wind speed

component of an RSD and a cup anemometer ...................................................................... 29

Table 1 – Interfaces from other standards to IEC 61400-50-2 ............................................... 12

Table 2 – Interfaces from IEC 61400-50-2 to other standards ............................................... 12

Table 3 – Bin width example for a list of environmental variables .......................................... 18

Table 4 – Parameters derived from a sensitivity analysis of an RSD ..................................... 20

Table 5 – Ranges of environmental parameters for sensitivity analysis ................................. 21

Table 6 – Example selection of environmental variables found to have a significant

influence ............................................................................................................................... 22

Table 7 – Sensitivity analysis parameters remaining after analysis of interdependency

of variables ........................................................................................................................... 24

Table 8 – Example scheme for calculating maximum influence of environmental

variables ............................................................................................................................... 25

Table 9 – Preliminary accuracy classes of an RSD considering both all and only the

most significant influential variables ...................................................................................... 26

Table 10 – Example final accuracy classes of an RSD .......................................................... 26

Table 11 – Example of uncertainty calculations arising from calibration of an RSD in

terms of systematic uncertainties .......................................................................................... 31

---------------------- Page: 5 ----------------------
– 4 – IEC 61400-50-2:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
WIND ENERGY GENERATION SYSTEMS –
Part 50-2: Wind measurement – Application of
ground-mounted remote sensing technology
FOREWORD

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

all national electrotechnical committees (IEC National Committees). The object of IEC is to promote international

co-operation on all questions concerning standardization in the electrical and electronic fields. To this end and

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with the IEC also participate in this preparation. IEC collaborates closely with the International Organization for

Standardization (ISO) in accordance with conditions determined by agreement between the two organizations.

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8) Attention is drawn to the Normative references cited in this publication. Use of the referenced publications is

indispensable for the correct application of this publication.

9) Attention is drawn to the possibility that some of the elements of this IEC Publication may be the subject of patent

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

IEC 61400-50-2 has been prepared by IEC technical committee 88: Wind energy generation

systems. It is an International Standard.

This first edition of IEC 61400-50-2 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: 6 ----------------------
IEC 61400-50-2:2022 © IEC 2022 – 5 –
The text of this International Standard is based on the following documents:
Draft Report on voting
88/829/CDV 88/865/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/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 publication 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: 7 ----------------------
– 6 – IEC 61400-50-2:2022 © IEC 2022
INTRODUCTION
This part of IEC 61400 specifies procedures and methods which ensure that wind

measurements using ground-mounted remote sensing devices are carried out and reported

consistently and in accordance with best practice. This document does not define the purpose

or use case of the wind measurements. However, as this document forms part of the IEC 61400

series of standards, it is anticipated that the wind measurements will be used in relation to some

form of wind energy testing or resource assessment.

The main clauses of this document are not mutually dependent. Therefore, it is possible that a

user will refer to only certain of the main clauses rather than all clauses to adapt this document

to their specific use case. However, the main clauses are presented in a logical sequence that

could be applied in practice.

The technical content of this document could previously be found in IEC 61400-12-1:2017 [1] .

Because of the increasing complexity of this source document, IEC TC 88 decided that a re-

structuring of the IEC 61400-12 series of standards into a number of more specific parts would

allow more efficient management and maintenance going forward. This document has been

created as part of that re-structuring process.
___________
Numbers in square brackets refer to the Bibliography.
---------------------- Page: 8 ----------------------
IEC 61400-50-2:2022 © IEC 2022 – 7 –
WIND ENERGY GENERATION SYSTEMS –
Part 50-2: Wind measurement – Application of
ground-mounted remote sensing technology
1 Scope

IEC 61400-50 specifies methods and requirements for the application of instruments to

measure wind speed (and related parameters, e.g. wind direction and turbulence intensity).

Such measurements are required as an input to some of the evaluation and testing procedures

for wind energy and wind turbine technology (e.g. resource evaluation and turbine testing)

described by other standards in the IEC 61400 series. This document is applicable specifically

to the use of ground-mounted remote sensing wind measurement instruments, i.e. devices

which measure the wind at some location generally above and distant from the location at which

the instrument is mounted (e.g. sodars, vertical profiling lidars). This document specifically

excludes other types of RSD such as forward facing or scanning lidars. This document specifies

the following:

a) the procedure and requirements for classifying ground-based RSDs in order to assess the

uncertainty pertaining from sensitivity of the RSD response to meteorological conditions that

can vary between the RSD calibration place and time and the use case (specific
measurement campaign – SMC) place and time;
b) the procedures and requirements for calibration of RSDs;
c) the assessment of wind speed measurement uncertainty;

d) additional checks of the RSD performance and measurement uncertainty during the SMC;

e) application of the wind speed uncertainty derived from the RSD calibration and classification

to the measurements taken during the SMC (e.g. interpolation of uncertainty or calibration

results to different heights);
f) requirements for reporting.
2 Normative references

The following documents are referred to in the text in such a way that some or all of their content

constitutes requirements of this document. For dated references, only the edition cited applies.

For undated references, the latest edition of the referenced document (including any

amendments) applies.
IEC 61400-50-1, Wind energy generation systems – Part 50-1: Wind measurement –
Application of meteorological mast, nacelle and spinner mounted instruments
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.

ISO and IEC maintain terminological databases for use in standardization at the following

addresses:
• IEC Electropedia: available at https://www.electropedia.org/
• ISO Online browsing platform: available at https://www.iso.org/obp
---------------------- Page: 9 ----------------------
– 8 – IEC 61400-50-2:2022 © IEC 2022
3.1
accuracy

closeness of the agreement between the result of a measurement and a true value of the

measurand
3.2
complex terrain

terrain surrounding the test site that features significant variations in topography and terrain

obstacles (3.10) that can cause flow distortion
3.3
data set
collection of data sampled over a continuous period
3.4
flow distortion

change in air flow caused by obstacles, topographical variations, or other wind turbines that

results in the wind speed at the measurement location being different from the wind speed at

the wind turbine location
3.5
hub height

height of the centre of the swept area of the wind turbine rotor above the

ground at the tower

Note 1 to entry: For a vertical axis wind turbine the hub height is defined as the height of the centroid of the swept

area of the rotor above the ground at the tower.
3.6
measurement period

period during which a statistically significant database has been collected for the use case

EXAMPLE power performance test
3.7
measurement uncertainty

parameter, associated with the result of a measurement, which characterizes the dispersion of

the values that could reasonably be attributed to the measurand
3.8
measurement volume

region within which wind flow characteristics can influence a wind speed

measurement and which is defined by the scan geometry, device configuration or arrangement

of the multiple beams penetrating the volume in order to acquire that measurement

3.9
method of bins

data reduction procedure that groups test data for a certain parameter into intervals (bins)

Note 1 to entry: For each bin, the number of data sets or samples and their sum are recorded, and the average

parameter value within each bin is calculated.
3.10
obstacle
obstruction that blocks the wind and creates distortion of the flow
Note 1 to entry: Buildings and trees are examples of obstacles.
---------------------- Page: 10 ----------------------
IEC 61400-50-2:2022 © IEC 2022 – 9 –
3.11
pitch and roll angles
levelling angles
3.12
power performance
measure of the capability of a wind turbine to produce electric power and energy
3.13
probe volume

region from which a single constituent physical measurement of, for example, Doppler

shift or radial velocity, is acquired, several of which are typically required to derive a wind speed

measurement

Note 1 to entry: The probe volume is a characteristic of the basic physical interaction of the remote sensing device

with the atmosphere, rather than the wind speed measurement derived from these interactions, which is determined

by the flow within the measurement volume.
3.14
radial velocity
line of sight velocity
projection of the wind speed vector onto the RSD line of sight
3.15
standard uncertainty
uncertainty of the result of a measurement expressed as a standard deviation
3.16
swept area

projected area of the moving rotor upon a plane normal to the

axis of rotation

Note 1 to entry: For teetering rotors, it is assumed that the rotor remains normal to the low-speed shaft. For a

vertical axis wind turbine, it is the projected area of the moving rotor upon a vertical plane.

3.17
test site
location and surroundings where an RSD is deployed for the purpose of providing

measurements as part of a test of, for example, a wind turbine or testing of the RSD

3.18
wind shear
change of wind speed with height
3.19
wind shear exponent
exponent of the power law defining the variation of wind speed with height

Note 1 to entry: This parameter is used as a measure of the magnitude of wind shear and can be otherwise useful.

The power law equation is:
(1)
vv=
zi h
H
where
v is the hub height wind speed;
H is the hub height (m);
v is the wind speed at height z ;
zi i
α is the wind shear exponent.
---------------------- Page: 11 ----------------------
– 10 – IEC 61400-50-2:2022 © IEC 2022
3.20
wind veer
change of wind direction with height
4 Symbols, units and abbreviated terms
Symbol Description Unit
avg 10 min average
c slope in linear regression m/s
data in bin i
number of environmental variables considered to have a relevant influence on the
accuracy of the remote sensing device according to the classification test
m slope in linear regression
slope describing the sensitivity of the wind speed measurement of the remote
sensing device on the environmental variable j as gained from the combination of
the results from a minimum of 3 classification tests
maximum slope
max
minimum slope a month
min
slope of the nth test
N total number of data points in dataset
number of classification tests
number of bins according to the ranges of variables given in Table 3
number of data points in bin i
REWS rotor equivalent wind speed
RSD remote sensing device
r coefficient of determination in linear regression
SMC specific measurement campaign
std standard deviation
added category B standard uncertainty at measurement height j (not covered by
added_systematic,j,i
the meteorological mast)
added category B uncertainty at the height of the top of the meteorological mast
added_systematic,1,i

cumulated other category B uncertainties of the remote sensing device at height j

systematic,j,i
cumulated other category B uncertainties of the remote sensing device at the
systematic,1,
...

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