IEC 61400-50-1:2022

Wind energy generation systems - Part 50-1: Wind measurement - Application of meteorological mast, nacelle and spinner mounted instruments

IEC 61400-50-1:2022 specifies methods and requirements for the application of instruments to measure wind speed (and related parameters, e.g. wind direction, 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 performance testing) described by other standards in the IEC 61400 series. This document is applicable specifically to the use of wind measurement instruments mounted on meteorological masts, turbine nacelles or turbine spinners which measure the wind at the location at which the instruments are mounted. This document excludes remote sensing devices which measure the wind at some location distant from the location at which the instrument is mounted (e.g. vertical profile or forward facing lidars).

Systèmes de génération d'énergie éolienne - Partie 50-1: Mesurages du vent - Application d'instruments météorologiques montés sur mât, nacelle et nez de rotor

IEC 61400-50-1:2022 spécifie les méthodes et les exigences pour l'application des instruments de mesure de la vitesse du vent (et des paramètres associés, par exemple la direction du vent et l'intensité des turbulences). Ces mesurages sont exigés pour certaines procédures d'évaluation et d'essai de l'énergie éolienne et de la technologie des éoliennes (par exemple, l'évaluation des ressources et les essais de performance des éoliennes) décrites dans d'autres normes de la série IEC 61400. Le présent document s'applique spécifiquement à l'utilisation d'instruments de mesure du vent montés sur des mâts météorologiques, des nacelles d’éolienne ou des nez de rotors d’éolienne qui mesurent le vent à un endroit dans lequel les instruments sont montés. Le présent document exclut les dispositifs de télédétection qui mesurent le vent à un endroit éloigné de celui dans lequel l'instrument est monté (par exemple, les lidars à profil vertical ou orientés vers l'avant)

General Information

• Status: Published
• Publication Date: 15-Nov-2022
• ICS: 27.180 - Wind turbine energy systems
• Technical Committee: TC 88 - Wind energy generation systems
• Drafting Committee: MT 12-1 - TC 88/MT 12-1
• Current Stage: PPUB - Publication issued
• Start Date: 16-Nov-2022
• Completion Date: 25-Nov-2022

Relations

• Replaces: IEC 61400-12-1:2017 - Wind energy generation systems - Part 12-1: Power performance measurements of electricity producing wind turbines
• Effective Date: 05-Sep-2023
• Replaces: IEC 61400-12-2:2013 - Wind turbines - Part 12-2: Power performance of electricity-producing wind turbines based on nacelle anemometry
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 61400-50-1 ®
Edition 1.0 2022-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –
Part 50-1: Wind measurement – Application of meteorological mast, nacelle and
spinner mounted instruments
Systèmes de génération d'énergie éolienne
Partie 50-1: Mesurages du vent – Application d'instruments météorologiques
montés sur mât, nacelle et nez de rotor

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IEC 61400-50-1 ®
Edition 1.0 2022-11
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –

Part 50-1: Wind measurement – Application of meteorological mast, nacelle and

spinner mounted instruments
Systèmes de génération d'énergie éolienne

Partie 50-1: Mesurages du vent – Application d'instruments météorologiques

montés sur mât, nacelle et nez de rotor

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.180 ISBN 978-2-8322-5937-5

– 2 – IEC 61400-50-1:2022 © IEC 2022
CONTENTS
FOREWORD . 6
INTRODUCTION . 8
1 Scope . 9
2 Normative references . 9
3 Terms and definitions . 10
4 Symbols, units and abbreviated terms . 11
5 General . 16
6 Classification of cup and sonic anemometry . 16
6.1 General . 16
6.2 Classification classes . 17
6.3 Influence parameter ranges . 17
6.4 Classification of cup and sonic anemometers . 17
6.5 Reporting format . 19
7 Assessment of cup and sonic anemometry . 19
7.1 General . 19
7.2 Measurements of anemometer characteristics . 19
7.2.1 Measurements in a wind tunnel for tilt angular response characteristics
of cup anemometers . 19
7.2.2 Wind tunnel measurements of directional characteristics of cup
anemometers . 21
7.2.3 Wind tunnel measurements of cup anemometer rotor torque
characteristics . 21
7.2.4 Wind tunnel measurements of step responses of cup anemometers . 22
7.2.5 Measurement of temperature induced effects on anemometer
performance . 23
7.2.6 Wind tunnel measurements of directional characteristics of sonic
anemometers . 24
7.3 A cup anemometer classification method based on wind tunnel and
laboratory tests and cup anemometer modelling . 25
7.3.1 Method . 25
7.3.2 Example of a cup anemometer model . 25
7.4 A sonic anemometer classification method based on wind tunnel tests and
sonic anemometer modelling . 32
7.5 Free field comparison measurements . 32
8 Wind tunnel calibration procedure for anemometers . 32
8.1 General requirements . 32
8.2 Requirements for the wind tunnel . 33
8.3 Instrumentation and calibration setup requirements . 35
8.4 Calibration procedure . 35
8.4.1 General procedure for cup and sonic anemometers . 35
8.4.2 Procedure for the calibration of sonic anemometers . 36
8.4.3 Determination of the wind speed at the anemometer position . 36
8.5 Data analysis . 37
8.6 Uncertainty analysis . 37
8.7 Reporting format . 38
8.8 Example uncertainty calculation . 39

9 In-situ comparison of anemometers . 42
9.1 General . 42
9.2 Prerequisite . 42
9.3 Analysis method . 42
9.4 Evaluation criteria . 43
10 Mounting of instruments on the meteorological mast . 45
10.1 General . 45
10.2 Single top-mounted anemometer. 46
10.3 Side-by-side top-mounted anemometers . 47
10.4 Side-mounted instruments . 49
10.4.1 General . 49
10.4.2 Tubular meteorological masts . 49
10.4.3 Lattice meteorological masts . 51
10.4.4 Flow distortion correction of side-mounted anemometers . 56
10.5 Lightning protection . 56
10.6 Mounting of other meteorological instruments . 56
10.7 Data acquisition system . 57
11 Uncertainty of wind speed measurement . 57
11.1 Category B uncertainties: Wind speed – Introduction . 57
11.2 Category B uncertainties: Wind speed – Hardware . 57
11.3 Category B uncertainties: Wind speed – Meteorological mast mounted
sensors . 57
11.3.1 General . 57
11.3.2 Pre-calibration . 58
11.3.3 Post-calibration . 58
11.3.4 Classification . 58
11.3.5 Mounting . 59
11.3.6 Lightning finial . 60
11.3.7 Data acquisition . 60
11.4 Category B uncertainties: Method – Cold climate . 60
11.5 Combining uncertainties . 60
11.5.1 General . 60
11.5.2 Combining uncertainties in the wind speed measurement (u ) . 61
V,i
11.5.3 Combining uncertainties in the wind speed measurement from cup or
sonic anemometer (u ) . 61
VS,i
12 Reporting. 61
Annex A (informative) Wind tunnel calibration procedure for wind direction sensors . 63
A.1 General requirements . 63
A.2 Requirements of the wind tunnel . 63
A.3 Instrumentation and calibration setup requirements . 64
A.4 Calibration procedure . 65
A.5 Data analysis . 66
A.6 Uncertainty analysis . 66
A.7 Reporting format . 67
A.8 Example of uncertainty calculation . 68
A.8.1 General . 68
A.8.2 Measurement uncertainties generated by determination of the flow
direction in the wind tunnel . 68

– 4 – IEC 61400-50-1:2022 © IEC 2022
A.8.3 Uncertainty contribution by uncertainties in the determination of the
geometrical centreline α (wind tunnel centreline) . 68
CL
A.8.4 Contribution by uncertainties in the determination of flow direction α . 68
dir
Annex B (informative) Mast flow distortion correction for lattice masts . 73
Annex C (informative) Nacelle instrument mounting . 76
C.1 General . 76
C.2 Preferred method of anemometer's mounting . 76
C.3 Preferred position of anemometer . 76
Annex D (informative) Spinner anemometers . 78
Bibliography . 79

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 . 21
Figure 2 – Wind tunnel torque measurements Q − Q as a function of angular speed
A F
ω of a cup anemometer rotor at 8 m/s . 22
Figure 3 – Example of bearing friction torque Q as function of temperature for a range
F
of angular speeds ω . 24
Figure 4 – Example of rotor torque coefficient C as a function of speed ratio λ
QA
derived from step responses with κ equal to −5,5 and κ equal to −6,5 . 27
low high
Figure 5 – Classification deviations of example cup anemometer showing a class
1,69A (upper) and a class 6,56B (lower) . 30
Figure 6 – Classification deviations of example cup anemometer showing a class
8,01C (upper) and a class 9,94D (lower) . 31
Figure 7 – Definition of volume for flow uniformity test . 34
Figure 8 – Example valid control anemometer direction sector for a single top-mounted
anemometer on a triangular lattice meteorological mast . 44
Figure 9 – Example valid control anemometer direction sector for a single top-mounted
anemometer on a tubular meteorological mast . 45
Figure 10 – Example of a top-mounted anemometer and requirements for mounting . 47
Figure 11 – Example of alternative top-mounted primary and control anemometers
positioned side-by-side and wind vane and other instruments on the boom . 48
Figure 12 – Iso-speed plot of local flow speed around a cylindrical meteorological mast . 50
Figure 13 – Centreline relative wind speed as a function of distance R from the
d
centre of a tubular meteorological mast and meteorological mast diameter d . 51
Figure 14 – Representation of a three-legged lattice meteorological mast . 51
Figure 15 – Iso-speed plot of local flow speed around a triangular lattice
meteorological mast with a C of 0,5 . 52
T
Figure 16 – Centreline relative wind speed as a function of distance R from the centre
d
of a triangular lattice meteorological mast of leg distance L for various C values . 53
m T
Figure 17 – 3D CFD derived flow distortion for two different wind directions around a
triangular lattice meteorological mast (C = 0,27) . 55
T
Figure A.1 – Example of calibration setup of a wind direction sensor in a wind tunnel . 65
Figure B.1 – Example of mast flow distortion . 73
Figure B.2 – Flow distortion residuals versus wind direction . 75
Figure C.1 – Mounting of anemometer on top of nacelle . 77

Table 1 – Influence parameter ranges (10 min averages) of classes A, B, C, D and S . 18
Table 2 – Tilt angle response of example cup anemometer . 28
Table 3 – Friction coefficients of example cup anemometer . 29
Table 4 – Miscellaneous data related to classification of example cup anemometer . 29
Table 5 – Example of evaluation of anemometer calibration uncertainty . 39
Table 6 – Estimation method for C for various types of lattice mast . 54
T
Table A.1 – Uncertainty contributions in wind directions sensor calibration . 71
Table A.2 – Uncertainty contributions and total standard uncertainty in wind direction
sensor calibration . 72

– 6 – IEC 61400-50-1:2022 © IEC 2022
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
WIND ENERGY GENERATION SYSTEMS –

Part 50-1: Wind measurement – Application of meteorological mast,
nacelle and spinner mounted instruments

FOREWORD
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rights. IEC shall not be held responsible for identifying any or all such patent rights.
IEC 61400-50-1 has been prepared by IEC technical committee 88: Wind energy generation
systems. It is an International Standard.
This first edition of IEC 61400-50-1 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.

The text of this International Standard is based on the following documents:
Draft Report on voting
88/902/FDIS 88/916/RVD
Full information on the voting for its approval can be found in the report on voting indicated in
the above table.
The language used for the development of this International Standard is English.
This document was drafted in accordance with ISO/IEC Directives, Part 2, and developed in
accordance with ISO/IEC Directives, Part 1 and ISO/IEC Directives, IEC Supplement, available
at www.iec.ch/members_experts/refdocs. The main document types developed by IEC are
described in greater detail at www.iec.ch/standardsdev/publications.
A list of all parts in the IEC 61400 series, published under the general title Wind energy
generation systems, can be found on the IEC website.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under webstore.iec.ch in the data related to the
specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
IMPORTANT – The "colour inside" logo on the cover page of this document indicates
that it contains colours which are considered to be useful for the correct understanding
of its contents. Users should therefore print this document using a colour printer.

– 8 – IEC 61400-50-1:2022 © IEC 2022
INTRODUCTION
This part of IEC 61400 specifies procedures and methods which ensure that wind
measurements using cup or sonic anemometers mounted on meteorological masts or wind
turbine nacelles/spinners 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 carried out in accordance with this standard 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 and
IEC 61400-12-2:2013.
NOTE A technical correction to the value of the tolerance of the anemometer mounting tube has been made in 10.2.
Due to the increasing complexity of these source documents, 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. The requirements on wind measurement
specific to the use cases described in IEC 61400-12-1:2017 and IEC 61400-12-2:2013 (for
example, the required location of the meteorological mast relative to the test turbine and the
height of wind measurement relative to hub height) remain within the new editions of
IEC 61400-12-1 and IEC 61400-12-2.

WIND ENERGY GENERATION SYSTEMS –

Part 50-1: Wind measurement – Application of meteorological mast,
nacelle and spinner mounted instruments

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, 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 performance
testing) described by other standards in the IEC 61400 series. This document is applicable
specifically to the use of wind measurement instruments mounted on meteorological masts,
turbine nacelles or turbine spinners which measure the wind at the location at which the
instruments are mounted. This document excludes remote sensing devices which measure the
wind at some location distant from the location at which the instrument is mounted (e.g. vertical
profile or forward facing lidars). This document specifies the following:
a) the classification parameters for cup and sonic anemometers such that the uncertainty in
wind speed measurement for a specific type and model of anemometer exposed to a certain
class of environmental conditions can be assessed;
b) the procedure and requirements for classifying cup and sonic anemometers as, for example,
part of the type testing of a specific anemometer model and type;
c) the procedures and requirements for wind tunnel calibration of anemometers;
d) an additional or alternative method of checking the consistency of the calibration of an
anemometer in the field by carrying out an in-situ comparison with another anemometer;
e) the requirements for the mounting of anemometers and other instruments on meteorological
masts;
f) the assessment of wind speed measurement uncertainty;
g) reporting requirements.
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.
ISO 2533:1975, Standard atmosphere
ISO 3966, Measurement of fluid flow in closed conduits – Velocity area method using Pitot static
tubes
ISO/IEC Guide 98-3:2008, Uncertainty of measurement – Part 3: Guide to the expression of
uncertainty in measurement (GUM:1995)

– 10 – IEC 61400-50-1:2022 © IEC 2022
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
3.1
accuracy
closeness of the agreement between the result of a measurement and a true value of the
measurand
3.2
data set
collection of data sampled over a continuous period
3.3
distance constant
indication of the response time of an anemometer, defined as the length of air that shall pass
the instrument for it to indicate 63 % of the final value for a step input in wind speed
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
Note 1 to entry: A power performance test is an example of a use case.
3.7
measurement sector
sector of wind directions from which data are selected for the use case
Note 1 to entry: A measured power curve is an example of a use case.
3.8
obstacle
obstruction that blocks the wind and creates distortion of the flow
Note 1 to entry: Buildings and trees are examples of obstacles.
3.9
power performance
measure of the capability of a wind turbine to produce electric power and energy

3.10
standard uncertainty
uncertainty of the result of a measurement expressed as a standard deviation
3.11
wind measurement equipment
meteorological mast-mounted instruments or remote sensing device
3.12
wind shear
change of wind speed with height
3.13
wind shear exponent
α
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:
α
z

i
vv= (1)
zi h 
H
where
v is the hub height wind speed;
h
H is the hub height (m);
v is the wind speed at height z ;
zi i
α is the wind shear exponent.
4 Symbols, units and abbreviated terms
Symbol Description Unit
A swept area of the wind turbine rotor
m
B barometric pressure Pa
B measured air pressure averaged over 10 min Pa
10min
C pitot tube head coefficient
h
C generalized aerodynamic torque coefficient
QA
C thrust coefficient
T
c sensitivity factor of a parameter (the partial differential)
c sensitivity factor of air pressure in bin i W/Pa
B,i
c sensitivity factor of data acquisition system in bin i
d,i
c sensitivity factor of index parameter
index
c sensitivity factor of component k in bin i
k,i
c sensitivity factor of air temperature in bin i W/K
T,i
c sensitivity factor of wind speed in bin i Ws/m
V,i
c sensitivity factor of air density correction in bin i
Wm /kg
ρ,i
– 12 – IEC 61400-50-1:2022 © IEC 2022
Symbol Description Unit
d meteorological mast diameter m
e eccentricity
F(V) Rayleigh cumulative probability distribution function for wind
speed

tilt and yaw response function for the sonic anemometer
F (αγ,,U )
α,γ
correction function due to interference between the anemometer
f k , kk, , v ,.
( )
b ip p
including its mounting tube and the wind tunnel flow
H hub height of wind turbine m
h height of obstacle m
I inertia of cup anemometer rotor
kg·m
K barometer sensitivity
N/m V
B,t
K barometer gain
B,s
K barometer sampling conversion
B,d
K temperature transducer sensitivity K/A
T,t
K temperature transducer gain A/V
T,s
K temperature transducer sampling conversion
T,d
K pressure transducer sensitivity
p,t
K pressure transducer gain
p,s
K pressure transducer sampling conversion
p,d
k class number
k blockage correction factor
b
k wind tunnel calibration factor
c
k wind tunnel correction factor to other tunnels (only used in
f
uncertainty estimate)
k correction factor due to interference between the anemometer
i
(including mounting tube) and test section enclosure, also
including flow effects due to mounting tubes extending through
the enclosure
k class number of anemometer sample number n (n = 1, …, 5 or
n
more)
k correction factor due to interference caused by the anemometer
p
(including mounting tube) on the velocity measured by the pitot
tube
k humidity correction to density
ρ
L distance between adjacent legs of lattice meteorological mast m
m
L distance between the wind turbine and the wind measurement m
equipment
M number of uncertainty components in each bin

M number of category A uncertainty components
A
M number of category B uncertainty components
B
m slope of the regression relating V to V
control primary_est
Symbol Description Unit
m slope of the regression between V and V
1 2
N number of bins
N h
number of hours in one year ≈ 8 760
h
N number of 10 min data sets in wind speed bin i
i
N number of 10 min data sets in wind direction bin j
j
n number of samples within sampling interval

n number of available measurement heights
h
P vapour pressure Pa
w
p axial run-out deviation
Q aerodynamic torque N·m
A
Q friction torque N·m
F
R rotor radius m
r effective radius of angle measurement
a
R gas constant of dry air (287,05) J/kg·K
R distance to meteorological mast centre m
d
R gas constant of water vapour (461,5) J/kg·K
w
REWS rotor equivalent wind speed

RSD remote sensing device
r correlation coefficient
s category A standard uncertainty component

s category A standard uncertainty of tunnel wind speed time series
A
s category A standard uncertainty of component k in bin i
k,i
s combined category A uncertainties in bin i
i
S meteorological mast solidity
T absolute temperature K
TI turbulence intensity
T measured absolute air temperature averaged over 10 min K
10min
t time s
U wind speed m/s
U centreline wind speed deficit m/s
d
U equivalent horizontal wind speed m/s
eq
U wind speed in bin i m/s
i
U wind speed in bin j
j
U sonic anemometer
sonic
U threshold wind speed m/s
t

instantaneous wind vector
U
u category B standard uncertainty component

– 14 – IEC 61400-50-1:2022 © IEC 2022
Symbol Description Unit
u category B standard uncertainty of air pressure in bin i Pa
B,i
u combined standard uncertainty of the power in bin i W
c,i
u uncertainty component of data acquisition of the wind speed
dVS,i
signal
u combined category B uncertainties in bin i
i
u category B standard uncertainty of index parameter
index
u category B standard uncertainty of component k in bin i
k,i
u influence of measurement in cold climate on the classification of
M,cc,i
the anemometers
u category B standard uncertainty of wind speed in bin i m/s
V,i
u uncertainty on the hardware used and is one of u , u or
VHW,i VS,i VR,i
u
REWS,i
u uncertainty related to the method applied
VM,i
u uncertainty related to the classification of the sensors
VS,class,i
u uncertainty related to the flow distortion from lightning finial
VS,lgt,i
u uncertainty related to the mounting of the sensors
VS,mnt,i
u uncertainty relating to the pre-calibration
VS,precal,i
u uncertainty related to the post-calibration
VS,postcal,i
u wind speed uncertainty assessment
v2,i
u(t) measured wind speed by the cup anemometer at time t using the
ordinary calibration function
u tunnel wind speed
t
difference between wind tunnel wind speed and the indicated
Δu
wind speed of the cup anemometer, at the beginning of the step
response measurement, at time t
V wind speed m/s
V annual average wind speed at hub height m/s
ave
V wind speed of the control anemometer
control
V wind speed of the control anemometer in bin i
control,i
V normalized and averaged wind speed in bin i m/s
i
V normalized wind speed m/s
n
V normalized wind speed of data set j in bin i m/s
n,i,j
V wind speed of the primary anemometer in bin i
primary,i
V estimated primary anemometer wind speed
primary_est
V measured wind speed averaged over 10 min m/s
10min
V wind speed from sensor one
V wind speed from the second sensor
v transversal wind speed component m/s

Symbol Description Unit
average wind speed at the anemometer position m/s
v
v
average wind speed at the reference position
p
v measured equivalent wind speed m/s
eq
WD wind direction
WME wind measurement equipment
w vertical wind speed component m/s

w weighting function to define deviation envelope
i
α wind shear exponent from power law
°
α pitot static tube head coefficient
α angle to be measured (calibration value)
α wind tunnel centreline
CL
α uncertainty by digital output signal
Digital
α uncertainties in the determination of flow direction
dir
α influence of the angle between the axes of rotation
incl.1
α uncertainty by mounting the wind direction sensor
item
α uncertainty by possible malposition of the wind direction sensor
incl.2
α uncertainties in the calibration of the reference yawing sensor
sensor
α aligning the centreline with the north marking of the wind
set
direction sensor
α uncertainty by the determination of the ohmic resistance of a
Ω
wind direction sensor
ε deviation in m/s for influence parameter combination i
i
ε maximum deviation for any wind speed bin i in the wind speed m/s
max,i
range
θ disturbed sector °
κ von Karman constant 0,4
λ speed ratio
λ speed ratio for C = 0
0 QA
ρ air density
kg/m
τ the time constant to be determined for the step response (τ for
low
step response from below and τ for step response from
high
above)
ρ reference air density
kg/m
ρ derived air density averaged over 10 min
kg/m
10min
σ standard deviation of the normalized power data in bin i W
P,i
σ standard deviation of parameter averaged over 10 min
10min
σ /σ /σ standard deviations of longitudinal/transversal/vertical wind
u v w
speeds
Φ relative humidity (range 0 % to 100 %)

– 16 – IEC 61400-50-1:2022 © IEC 2022
Symbol Description Unit
−1
ω angular speed
s
Δp mean differential pressure
ref
5 General
This document defines methods and requirements for carrying out wind measurements using
instruments such as anemometers (cup and ultrasonic) mounted on meteorological masts, wind
turbine nacelles (Annex C) and wind turbine spinners (Annex D). Requirements for calibration,
classification and mounting are described. Wind measurements carried out in accordance with
this document are useable for many
...