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EUROPEAN STANDARD EN 61400-1
NORME EUROPÉENNE
EUROPÄISCHE NORM November 2005

ICS 27.180 Supersedes EN 61400-1:2004

English version
Wind turbines
Part 1: Design requirements
(IEC 61400-1:2005)
Eoliennes Windenergieanlagen
Partie 1: Exigences de conception Teil 1: Auslegungsanforderungen
(CEI 61400-1:2005) (IEC 61400-1:2005)

This European Standard was approved by CENELEC on 2005-10-01. 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 Central Secretariat 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 Central Secretariat has the same status as the official versions.

CENELEC members are the national electrotechnical committees of Austria, Belgium, Cyprus, Czech
Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, Netherlands, Norway, Poland, Portugal, Slovakia, Slovenia, Spain, Sweden,
Switzerland and United Kingdom.

CENELEC
European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung

Central Secretariat: rue de Stassart 35, B - 1050 Brussels

© 2005 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 61400-1:2005 E
Foreword
The text of document 88/228/FDIS, future edition 3 of IEC 61400-1, prepared by IEC TC 88, Wind
turbines, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as
EN 61400-1 on 2005-10-01.
This European Standard supersedes EN 61400-1:2004.
The main changes with respect to EN 61400-1:2004 are listed below:
– the title has been changed to “Design requirements” in order to reflect that the standard presents
safety requirements rather than requirements for safety or protection of personnel;
– wind turbine class designations have been adjusted and now refer to reference wind speed and
expected value of turbulence intensities only;
– turbulence models have been expanded and include an extreme turbulence model;
– gust models have been adjusted and simplified;
– design load cases have been rearranged and amended;
– the inclusion of turbulence simulations in the load calculations is emphasized and a scheme for
extreme load extrapolation has been specified;
– the partial safety factors for loads have been adjusted and simplified;
– the partial safety factors for materials have been amended and specified in terms of material
types and component classes;
– the requirements for the control and protection system have been amended and clarified in terms
of functional characteristics;
– a new clause on assessment of structural and electrical compatibility has been introduced with
detailed requirements for assessment, including information on complex terrain, earthquakes and
wind farm wake effects.
The following dates were fixed:
– latest date by which the EN has to be implemented
at national level by publication of an identical
national standard or by endorsement (dop) 2006-07-01
– latest date by which the national standards conflicting
with the EN have to be withdrawn (dow) 2006-11-01
Annex ZA has been added by CENELEC.
__________
- 3 - EN 61400-1:2005
Endorsement notice
The text of the International Standard IEC 61400-1:2005 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 60034 NOTE Harmonized in EN 60034 series (not modified).
IEC 60038 NOTE Harmonized as HD 472 S1:1989 (modified).
IEC 60146 NOTE Harmonized in EN 60146 series (not modified).
IEC 60173 NOTE Harmonized as HD 27 S1:1978 (not modified).
IEC 60227 NOTE The HD 21 series is related to, but not directly equivalent with the
IEC 60227 series.
IEC 60245 NOTE The HD 22 series is related to, but not directly equivalent with the
IEC 60245 series.
IEC 60269 NOTE Harmonized in EN/HD 60269 series (modified).
IEC 60439 NOTE Harmonized in EN 60439 series (not modified).
IEC 60446 NOTE Harmonized as EN 60446:1999 (not modified).
IEC 60529 NOTE Harmonized as EN 60529:1991 (not modified).
IEC 60898 NOTE Harmonized in EN 60898 series (modified).
IEC 61310-1 NOTE Harmonized as EN 61310-1:1995 (not modified).
IEC 61310-2 NOTE Harmonized as EN 61310-2:1995 (not modified).
__________
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following referenced documents are indispensable for the application 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.
NOTE Where an international publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
Publication Year Title EN/HD Year
IEC 60204-1 1997 Safety of machinery - Electrical EN 60204-1 1997
equipment of machines + corr. September 1998
Part 1: General requirements
IEC 60204-11 2000 Part 11: Requirements for HV equipment EN 60204-11 2000
for voltages above 1 000 V a.c. or
1 500 V d.c. and not exceeding 36 kV

IEC 60364 Series Electrical installations of buildings EN 60364 Series
(mod) HD 60364 Series
HD 384 Series
1)
IEC 60721-2-1 1982 Classification of environmental conditions HD 478.2.1 S1 1989
Part 2: Environmental conditions
appearing in nature - Temperature and
humidity
IEC 61000-6-1 1997 Electromagnetic compatibility (EMC) EN 61000-6-1 2001
(mod) Part 6-1: Generic standards - Immunity
for residential, commercial and light-
industrial environments
2)
IEC 61000-6-2 1999 Part 6-2: Generic standards - Immunity EN 61000-6-2 2001
(mod) for industrial environments

IEC 61000-6-4 1997 Part 6-4: Generic standards - Emission EN 61000-6-4 2001
(mod) standard for industrial environments

IEC 61024-1 1990 Protection of structures against lightning - -
Part 1: General principles
IEC 61312-1 1995 Protection against lightning - -
electromagnetic impulse
Part 1: General principles
IEC 61400-21 2001 Wind turbine generator systems EN 61400-21 2002
Part 21: Measurement and assessment of
power quality characteristics of grid
connected wind turbines
1)
HD 478.2.1 S1 includes A1:1987 to IEC 60721-2-1:1982.
2)
EN 61000-6-2:2001 is superseded by EN 61000-6-2:2005, which is based on IEC 61000-6-2:2005.

- 5 - EN 61400-1:2005
Publication Year Title EN/HD Year
IEC/TR 61400-24 2002 Part 24: Lightning protection - -

ISO 76 1987 Rolling bearings - Static load ratings - -

ISO 281 1990 Rolling bearings - Dynamic load ratings - -
and rating life
ISO 2394 1998 General principles on reliability for - -
structures
ISO 2533 1975 Standard atmosphere - -

ISO 4354 1997 Wind actions on structures - -

ISO 6336-1 1996 Calculation of load capacity of spur and - -
helical gears
Part 1: Basic principles, introduction and
general influence factors
ISO 9001 2000 Quality management systems - EN ISO 9001 2000
Requirements
INTERNATIONAL IEC
STANDARD 61400-1
Third edition
2005-08
Wind turbines –
Part 1:
Design requirements
 IEC 2005  Copyright - all rights reserved
No part of this publication may be reproduced or utilized in any form or by any means, electronic or
mechanical, including photocopying and microfilm, without permission in writing from the publisher.
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Telephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch Web: www.iec.ch
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For price, see current catalogue

– 2 – 61400-1  IEC:2005
CONTENTS
FOREWORD.5
INTRODUCTION.7

1 Scope.8
2 Normative references.8
3 Terms and definitions .9
4 Symbols and abbreviated terms .17
4.1 Symbols and units .17
4.2 Abbreviations.19
5 Principal elements .19
5.1 General .19
5.2 Design methods.19
5.3 Safety classes .20
5.4 Quality assurance.20
5.5 Wind turbine markings .20
6 External conditions .21
6.1 General .21
6.2 Wind turbine classes .21
6.3 Wind conditions .22
6.4 Other environmental conditions.31
6.5 Electrical power network conditions.32
7 Structural design.33
7.1 General .33
7.2 Design methodology .33
7.3 Loads .33
7.4 Design situations and load cases .34
7.5 Load calculations.39
7.6 Ultimate limit state analysis.39
8 Control and protection system.45
8.1 General .45
8.2 Control functions .45
8.3 Protection functions .46
8.4 Braking system .47
9 Mechanical systems.47
9.1 General .47
9.2 Errors of fitting.48
9.3 Hydraulic or pneumatic systems.48
9.4 Main gearbox.48
9.5 Yaw system .49
9.6 Pitch system .49
9.7 Protection function mechanical brakes .49
9.8 Rolling bearings.49

61400-1  IEC:2005 − 3 −
10 Electrical system.50
10.1 General .50
10.2 General requirements for the electrical system .50
10.3 Protective devices.50
10.4 Disconnect devices .50
10.5 Earth system.50
10.6 Lightning protection.51
10.7 Electrical cables.51
10.8 Self-excitation.51
10.9 Protection against lightning electromagnetic impulse .51
10.10 Power quality .51
10.11 Electromagnetic compatibility.51
11 Assessment of a wind turbine for site-specific conditions.52
11.1 General .52
11.2 Assessment of the topographical complexity of the site .52
11.3 Wind conditions required for assessment .52
11.4 Assessment of wake effects from neighbouring wind turbines.53
11.5 Assessment of other environmental conditions .54
11.6 Assessment of earthquake conditions .54
11.7 Assessment of electrical network conditions.55
11.8 Assessment of soil conditions .55
11.9 Assessment of structural integrity by reference to wind data .56
11.10 Assessment of structural integrity by load calculations with reference to site
specific conditions .57
12 Assembly, installation and erection .57
12.1 General .57
12.2 Planning .58
12.3 Installation conditions.58
12.4 Site access .58
12.5 Environmental conditions .58
12.6 Documentation.59
12.7 Receiving, handling and storage.59
12.8 Foundation/anchor systems.59
12.9 Assembly of wind turbine .59
12.10 Erection of wind turbine.59
12.11 Fasteners and attachments .59
12.12 Cranes, hoists and lifting equipment.60
13 Commissioning, operation and maintenance .60
13.1 General .60
13.2 Design requirements for safe operation, inspection and maintenance .60
13.3 Instructions concerning commissioning .61
13.4 Operator’s instruction manual.62
13.5 Maintenance manual.63

– 4 – 61400-1  IEC:2005
Annex A (normative) Design parameters for describing wind turbine class S .65
Annex B (informative) Turbulence models .66
Annex C (informative) Assessment of earthquake loading.72
Annex D (informative) Wake and wind farm turbulence .73
Annex E (informative) Prediction of wind distribution for wind turbine sites by measure-
correlate-predict (MCP) methods.76
Annex F (informative) Statistical extrapolation of loads for ultimate strength analysis .78
Annex G (informative) Fatigue analysis using Miner’s rule with load extrapolation .81

Bibliography .85

Figure 1a –Turbulence standard deviation for the Normal Turbulence Model (NTM) .25
Figure 1b – Turbulence intensity for the Normal Turbulence Model (NTM).25
Figure 2 – Example of extreme operating gust.27
Figure 3 – Example of extreme direction change magnitude .28
Figure 4 – Example of extreme direction change .28
Figure 5 – Example of extreme coherent gust amplitude for ECD.29
Figure 6 –Direction change for ECD .30
Figure 7 – Example of direction change transient.30
Figure 8 – Examples of extreme positive and negative vertical wind shear, wind profile
before onset (t = 0, dashed line) and at maximum shear (t = 6 s, full line). .31
Figure 9 – Example of wind speeds at rotor top and bottom, respectively, illustrate the
transient positive wind shear .31
Figure D.1 – Configuration – Inside a wind farm with more than 2 rows.75
Figure F.1 – Exceedance probability for largest out-of-plane blade bending load in 10 min
(normalized by mean bending load at rated wind speed). .80

Table 1 – Basic parameters for wind turbine classes.22
Table 2 – Design load cases .35
Table 3 – Partial safety factors for loads γ .42
f
Table 4 – Terrain complexity indicators .52
Table B.1 – Turbulence spectral parameters for the Kaimal model.70

61400-1  IEC:2005 − 5 −
INTERNATIONAL ELECTROTECHNICAL COMMISSION
___________
WIND TURBINES –
Part 1: Design requirements
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 in addition to other activities, IEC publishes International Standards, Technical Specifications,
Technical Reports, Publicly Available Specifications (PAS) and Guides (hereafter referred to as “IEC
Publication(s)”). Their preparation is entrusted to technical committees; any IEC National Committee interested
in the subject dealt with may participate in this preparatory work. International, governmental and non-
governmental organizations liaising 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.
2) The formal decisions or agreements of IEC on technical matters express, as nearly as possible, an international
consensus of opinion on the relevant subjects since each technical committee has representation from all
interested IEC National Committees.
3) IEC Publications have the form of recommendations for international use and are accepted by IEC National
Committees in that sense. While all reasonable efforts are made to ensure that the technical content of IEC
Publications is accurate, IEC cannot be held responsible for the way in which they are used or for any
misinterpretation by any end user.
4) In order to promote international uniformity, IEC National Committees undertake to apply IEC Publications
transparently to the maximum extent possible in their national and regional publications. Any divergence
between any IEC Publication and the corresponding national or regional publication shall be clearly indicated in
the latter.
5) IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with an IEC Publication.
6) All users should ensure that they have the latest edition of this publication.
7) No liability shall attach to IEC or its directors, employees, servants or agents including individual experts and
members of its technical committees and IEC National Committees for any personal injury, property damage or
other damage of any nature whatsoever, whether direct or indirect, or for costs (including legal fees) and
expenses arising out of the publication, use of, or reliance upon, this IEC Publication or any other IEC
Publications.
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.
International Standard IEC 61400-1 has been prepared by IEC technical committee 88: Wind
turbines.
This third edition cancels and replaces the second edition published in 1999. It constitutes a
technical revision.
The main changes with respect to the previous edition are listed below:
– the title has been changed to “Design requirements” in order to reflect that the standard
presents safety requirements rather than requirements for safety or protection of personnel;
– wind turbine class designations have been adjusted and now refer to reference wind speed
and expected value of turbulence intensities only;
– turbulence models have been expanded and include an extreme turbulence model;
– gust models have been adjusted and simplified;

– 6 – 61400-1  IEC:2005
– design load cases have been rearranged and amended;
– the inclusion of turbulence simulations in the load calculations is emphasised and a scheme
for extreme load extrapolation has been specified;
– the partial safety factors for loads have been adjusted and simplified;
– the partial safety factors for materials have been amended and specified in terms of
material types and component classes;
– the requirements for the control and protection system have been amended and clarified in
terms of functional characteristics;
– a new clause on assessment of structural and electrical compatibility has been introduced
with detailed requirements for assessment, including information on complex terrain,
earthquakes and wind farm wake effects.
The text of this standard is based on the following documents:
FDIS Report on voting
88/228/FDIS 88/232/RVD
Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.
This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.
IEC 61400 consists of the following parts under the general title Wind turbine generator
systems:
Part 1: Design requirements
Part 2: Design requirements for small wind turbines
Part 11: Acoustic noise measurement techniques
Part 12: Wind turbine power performance testing
Part 13: Measurement of mechanical loads
Part 14: Declaration of apparent sound power level and tonality values
Part 21: Measurement and assessment of power quality characteristics of grid connected
wind turbines
Part 23: Full-scale structural testing of rotor blades
Part 24: Lightning protection
The committee has decided that the contents of this publication will remain unchanged until the
maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in the data
related to the specific publication. At this date, the publication will be
• reconfirmed;
• withdrawn;
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

61400-1  IEC:2005 − 7 −
INTRODUCTION
This part of IEC 61400 outlines minimum design requirements for wind turbines and is not
intended for use as a complete design specification or instruction manual.
Any of the requirements of this standard may be altered if it can be suitably demonstrated that
the safety of the system is not compromised. This provision, however, does not apply to the
classification and the associated definitions of external conditions in Clause 6.Compliance with
this standard does not relieve any person, organization, or corporation from the responsibility
of observing other applicable regulations.
The standard is not intended to give requirements for wind turbines installed offshore, in
particular for the support structure. A future document dealing with offshore installations is
under consideration.
– 8 – 61400-1  IEC:2005
WIND TURBINES –
Part 1: Design requirements
1 Scope
This part of IEC 61400 specifies essential design requirements to ensure the engineering
integrity of wind turbines. Its purpose is to provide an appropriate level of protection against
damage from all hazards during the planned lifetime.
This standard is concerned with all subsystems of wind turbines such as control and protection
mechanisms, internal electrical systems, mechanical systems and support structures.
This standard applies to wind turbines of all sizes. For small wind turbines IEC 61400-2 may be
applied.
This standard should be used together with the appropriate IEC and ISO standards mentioned
in Clause 2.
2 Normative references
The following referenced documents are indispensable for the application 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 60204-1:1997, Safety of machinery – Electrical equipment of machines – Part 1: General
requirements
IEC 60204-11:2000, Safety of machinery – Electrical equipment of machines – Part 11:
Requirements for HV equipment for voltages above 1 000 V a.c. or 1 500 V d.c. and not
exceeding 36 kV
IEC 60364 (all parts), Electrical installations of buildings
IEC 60721-2-1:1982, Classification of environmental conditions – Part 2: Environmental
conditions appearing in nature. Temperature and humidity
IEC 61000-6-1:1997, Electromagnetic compatibility (EMC) – Part 6: Generic standards –
Section 1: Immunity for residential, commercial and light-industrial environments
IEC 61000-6-2:1999, Electromagnetic compatibility (EMC) – Part 6: Generic standards –
Section 2: Immunity for industrial environments 15
IEC 61000-6-4:1997, Electromagnetic compatibility (EMC) – Part 6: Generic standards –
Section 4: Emission standard for industrial environments
IEC 61024-1:1990, Protection of structures against lightning – Part 1: General principles
IEC 61312-1:1995, Protection against lightning electromagnetic impulse – Part 1: General
principle
IEC 61400-21:2001, Wind turbine generator systems – Part 21: Measurement and assessment
of power quality characteristics of grid connected wind turbines

61400-1  IEC:2005 − 9 −
IEC 61400-24: 2002, Wind turbine generator systems – Part 24: Lightning protection
ISO 76:1987, Rolling bearings – Static load ratings
ISO 281:1990, Rolling bearings – Dynamic load ratings and rating life
ISO 2394:1998, General principles on reliability for structures
ISO 2533:1975, Standard Atmosphere
ISO 4354:1997, Wind actions on structures
ISO 6336 (all parts), Calculation of load capacity of spur and helical gears
ISO 9001:2000, Quality management systems – Requirements
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1
annual average
mean value of a set of measured data of sufficient size and duration to serve as an estimate of
the expected value of the quantity. The averaging time interval should be a whole number of
years to average out non-stationary effects such as seasonality
3.2
annual average wind speed
V
ave
wind speed averaged according to the definition of annual average
3.3
auto-reclosing cycle
event with a time period, varying from approximately 0,01 s to a few seconds, during which a
breaker released after a grid fault is automatically reclosed and the line is reconnected to the
network
3.4
blocking (wind turbines)
use of a mechanical pin or other device (other than the ordinary mechanical brake) that cannot
be released accidentally to prevent movement, for instance of the rotor shaft or yaw
mechanism
3.5
brake (wind turbines)
device capable of reducing the rotor speed or stopping rotation
NOTE The brake may operate on, for example, aerodynamic, mechanical or electrical principles.
3.6
characteristic value
value having a prescribed probability of not being attained (i.e. an exceedance probability of
less than or equal to a prescribed amount)

– 10 – 61400-1  IEC:2005
3.7
complex terrain
surrounding terrain that features significant variations in topography and terrain obstacles that
may cause flow distortion
3.8
control functions (wind turbines)
functions of the control and protection system that based on information about the condition of
the wind turbine and/or its environment, adjust the turbine in order to maintain it within its
operating limits
3.9
cut-in wind speed
V
in
lowest wind speed at hub height at which the wind turbine starts to produce power in the case
of steady wind without turbulence
3.10
cut-out wind speed
V
out
highest wind speed at hub height at which the wind turbine is designed to produce power in the
case of steady wind without turbulence
3.11
design limits
maximum or minimum values used in a design
3.12
dormant failure
failure of a component or system which remains undetected during normal operation
3.13
downwind
in the direction of the main wind vector
3.14
electrical power network
particular installations, substations, lines or cables for the transmission and distribution of
electricity
NOTE The boundaries of the different parts of this network are defined by appropriate criteria, such as
geographical situation, ownership, voltage, etc.
3.15
emergency shutdown (wind turbines)
rapid shutdown of the wind turbine triggered by a protection function or by manual intervention
3.16
environmental conditions
characteristics of the environment (wind, altitude, temperature, humidity, etc.) which may affect
the wind turbine behaviour
3.17
external conditions (wind turbines)
factors affecting operation of a wind turbine, including the environmental conditions
(temperature, snow, ice, etc.) and the electrical network conditions

61400-1  IEC:2005 − 11 −
3.18
extreme wind speed
value of the highest wind speed, averaged over t s, with an annual probability of exceedance of
1/N ("recurrence period": N years)
NOTE In this standard recurrence periods of N = 50 years and N = 1 year and averaging time intervals of t = 3 s
and t = 10 min are used. In popular language, the less precise term survival wind speed is often used. In this
standard, however, the turbine is designed using extreme wind speeds for design load cases.
3.19
fail-safe
design property of an item which prevents its failures from resulting in critical faults
3.20
gust
temporary change in the wind speed
NOTE A gust may be characterised by its rise-time, its magnitude and its duration.
3.21
horizontal axis wind turbine
wind turbine whose rotor axis is substantially horizontal
3.22
hub (wind turbines)
fixture for attaching the blades or blade assembly to the rotor shaft
3.23
hub height (wind turbines)
z
hub
height of the centre of the swept area of the wind turbine rotor above the terrain surface. (see
3.51, swept area)
3.24
idling (wind turbines)
condition of a wind turbine that is rotating slowly and not producing power
3.25
inertial sub-range
frequency interval of the turbulence spectrum, where eddies – after attaining isotropy –
undergo successive break-up with negligible energy dissipation
NOTE At a typical 10 m/s wind speed, the inertial sub-range is roughly from 0, 2 Hz to 1 kHz.
3.26
limit state
state of a structure and the loads acting upon it, beyond which the structure no longer satisfies
the design requirement
[ISO 2394, modified]
NOTE The purpose of design calculations (i.e. the design requirement for the limit state) is to keep the probability
of a limit state being reached below a certain value prescribed for the type of structure in question (see ISO 2394).
3.27
logarithmic wind shear law
see 3.62
– 12 – 61400-1  IEC:2005
3.28
mean wind speed
statistical mean of the instantaneous value of the wind speed averaged over a given time
period which can vary from a few seconds to many years
3.29
nacelle
housing which contains the drive-train and other elements on top of a horizontal axis wind
turbine tower
3.30
network connection point (wind turbines)
cable terminals of a single wind turbine or, for a wind power station, the connection point to the
electrical bus of the site power collection system
3.31
network loss
loss of network for period exceeding any ride through provision in the turbine control system
3.32
normal shutdown (wind turbines)
shutdown in which all stages are under the control of the control system
3.33
operating limits
set of conditions defined by the wind turbine designer that govern the activation of the control
and protection system
3.34
parked wind turbine
depending on the design of the wind turbine, parked refers to the turbine being either in a
standstill or an idling condition
3.35
power collection system (wind turbines)
electric system that collects the power from one or more wind turbines. It includes all electrical
equipment connected between the wind turbine terminals and the network connection point
3.36
power law for wind shear
see 3.62
3.37
power output
power delivered by a device in a specific form and for a specific purpose
NOTE (wind turbines) The electric power delivered by a wind turbine
3.38
protection functions (wind turbine)
functions of the control and protection system which ensure that a wind turbine remains within
the design limits
61400-1  IEC:2005 − 13 −
3.39
rated power
quantity of power assigned, generally by a manufacturer, for a specified operating condition of
a component, device or equipment
NOTE (wind turbines) Maximum continuous electrical power output which a wind turbine is designed to achieve
under normal operating and external conditions.
3.40
rated wind speed
V
r
minimum wind speed at hub height at which a wind turbine's rated power is achieved in the
case of steady wind without turbulence
3.41
Rayleigh distribution
P
R
probability distribution function, see 3.63
3.42
reference wind speed
V
ref
basic parameter for wind speed used for defining wind turbine classes. Other design related
climatic parameters are derived from the reference wind speed and other basic wind turbine
class parameters (see Clause 6)
NOTE A turbine designed for a wind turbine class with a reference wind speed V , is designed to withstand
ref
climates for which the extreme 10 min average wind speed with a recurrence period of 50 years at turbine hub
height is lower than or equal to V .
ref
3.43
rotationally sampled wind velocity
wind velocity experienced at a fixed point of the rotating wind turbine rotor
NOTE The turbulence spectrum of a rotationally sampled wind velocity is distinctly different from the normal
turbulence spectrum. While rotating, the blade cuts through a wind flow that varies in space. Therefore, the
resulting turbulence spectrum will contain sizeable amounts of variance at the frequency of rotation and harmonics
of the same.
3.44
rotor speed (wind turbines)
rotational speed of a wind turbine rotor about its axis
3.45
roughness length
z
extrapolated height at which the mean wind speed becomes zero if the vertical wind profile is
assumed to have a logarithmic variation with height
3.46
scheduled maintenance
preventive maintenance carried out in accordance with an established time schedule
3.47
site data
environmental, seismic, soil and electrical network data for the wind turbine site. Wind data
shall be the statistics of 10 min samples unless otherwise stated

– 14 – 61400-1  IEC:2005
3.48
standstill
condition of a wind turbine that is stopped
3.49
support structure (wind turbines)
part of a wind turbine comprising the tower and foundation
3.50
survival wind speed
popular name for the maximum wind speed that a construction is designed to withstand
NOTE In this standard, the expression is not used. Design conditions instead refer to extreme wind speed
(see 3.18).
3.51
swept area
projected area perpendicular to the wind direction that a rotor will describe during one complete
rotation
3.52
turbulence intensity
I
ratio of the wind speed standard deviation to the mean wind speed, determined from the same
set of measured data samples of wind speed, and taken over a specified period of time
3.53
turbulence scale parameter
Λ
wavelength where the non-dimensional, longitudinal power spectral density is equal to 0,05
NOTE The wavelength is thus defined as Λ =V /f , where f S (f )/σ = 0,05
1 hub 0 0 1 0 1
3.54
turbulence standard deviation
σ
standard deviation of the longitudinal component of the turbulent wind velocity at hub height
3.55
ultimate limit state
limit states which generally correspond to maximum load carrying capacity
[ISO 2394, modified]
3.56
unscheduled maintenance
maintenance carried out, not in accordance with an established time schedule, but after
reception of an indication regarding the state of an item
3.57
upwind
in the direction opposite to the main wind vector
3.58
vertical axis wind turbine
wind turbine whose rotor axis is vertical

61400-1  IEC:2005 − 15 −
3.59
Weibull distribution
P
W
probability distribution function, see 3.63
3.60
wind farm
see 3.61
3.61
wind power station
group or groups of wind turbines, commonly called a wind farm
3.62
wind profile – wind shear law
mathematical expression for assumed wind speed variation with height above ground
NOTE Commonly used profiles are the logarithmic profile (equation 1) or the power law profile (equation 2).
ln(z/ )
z 0
V(z) = V(z ). (1)
r
ln(/ )
z z
r0
z
α
V(z)= V( ).( ) (2)
z
r
z
r
where
V(z) is the wind speed at height z;
z is the height above ground;
z is a reference height above ground used for fitting the profile;
r
z is the roughness length;
α is the wind shear (or power law) exponent
3.63
wind speed distribution
probability distribution function, used to describe the distribution of wind speeds over an
extended period of time
NOTE Often used distribution functions are the Rayleigh, P (V ), and the Weibull, P (V ), functions.
R o W o

PV()=−1 exp −π V/2V
()
R0 0 ave

(3)
k

PV()1=−exp −()V/C
W0 0

 1 
C Γ(1+ )
 
with  = k (4)
V  
ave
 
C π /2, if k = 2
 
where
P(V ) is the cumulative probability function, i.e. the probability that V 0 o
V is the wind speed (limit);
V is the average value of V;
ave
...