EN 61400-1:2004

SLOVENSKI SIST EN 61400-1:2004

STANDARD
september 2004
Sistemi generatorjev vetrne turbine – 1. del: Varnostne zahteve (IEC 61400-
1:1999, spremenjen)
Wind turbine generator systems - Part 1: Safety requirements
ICS 27.180 Referenčna številka
©  Standard je založil in izdal Slovenski inštitut za standardizacijo. Razmnoževanje ali kopiranje celote ali delov tega dokumenta ni dovoljeno

EUROPEAN STANDARD EN 61400-1
NORME EUROPÉENNE
EUROPÄISCHE NORM February 2004

ICS 27.180 Supersedes ENV 61400-1:1995

English version
Wind turbine generator systems
Part 1: Safety requirements
(IEC 61400-1:1999, modified)
Aérogénérateurs Windenergieanlagen
Partie 1: Spécifications de sécurité Teil 1: Sicherheitsanforderungen
(CEI 61400-1:1999, modifiée) (IEC 61400-1:1999, modifiziert)

This European Standard was approved by CENELEC on 2003-11-01. 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

© 2004 CENELEC - All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.

Ref. No. EN 61400-1:2004 E
Foreword
The text of the International Standard IEC 61400-1:1999, prepared by IEC TC 88, Wind turbines, together
with the common modifications prepared by the Technical Committee CENELEC TC 88, Wind turbine
systems, was submitted to the formal vote and was approved by CENELEC as EN 61400-1 on
2003-11-01.
This European Standard supersedes ENV 61400-1:1995.
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) 2004-11-01

- 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.
Formulae which are additional to those in IEC 61400-1 are prefixed Z.
__________
– 3 – EN 61400-1:2004
Endorsement notice
The text of the International Standard IEC 61400-1:1999 was approved by CENELEC as a European
Standard with agreed common modifications as given below.
COMMON MODIFICATIONS
Introduction
Replace the first existing paragraph by:
The standard contains some requirements for a safe operation of wind turbine generator systems falling
in the scope of Article 118a of the EC Treaty. Users of this Standard should, with the respect to these
requirements, be aware that standards have no formal legal relationship with Directives which may have
been made under Article 118a of the Treaty. In addition, national legislation in the Member states may
contain more stringent requirements than the minimum requirements of a Directive based on Article 118a.
Information on the relationship between the national legislation implementing Directives based on
Article 118a and this Standard may be given in a national foreword of the national standard implementing
this Standard.
1.1 Scope
Add the following fifth paragraph:
The standard contains requirements which directly address the operator of wind turbine generator
systems. These requirements for a safe operation, however, constitute recommendations for the
manufacturer, designed to support him in drafting the operation instruction handbook.

6.3.2.1 Extreme wind speed model (EWM)
Replace the whole subclause by the following:
The EWM shall be either a steady or a turbulent wind model. The wind models shall be based on the
reference wind speed, V , and a fixed turbulence standard deviation σ .
ref 1
For the steady extreme wind model, the 50 year extreme wind speed V and the one year extreme wind
e50
speed V shall be based on the reference wind speed V . For wind turbine designs in the standard wind
e1 ref
turbine classes, V and V shall be computed as a function of height z using the following equations:
e50 e1
0,11
V (z) = 1,4 V (z/z ) (10)
e50 ref hub
V (z) = 0,8 V (z) (11)
e1 e50
For the turbulent extreme wind speed model, the 10 min average wind speeds as functions of height z
with recurrence intervals of 50 and 1 year, respectively, shall be given by the following equations:
0,11
V (z) = V (z/z ) (Z1)
50 ref hub
V (z) = 0,8 × V (z) (Z2)
1 50
In the turbulent extreme wind model, the mean wind speed at hub height, V , shall be V or 0,8 V ,
hub ref ref
respectively, and shall be used in the Turbulence Model (NTM) together with a turbulence standard
deviation of σ = 0,11 V .
1 hub
Replace Table 2 by the following:
Table 2 – Design load cases
a
Design situation DLC Wind condition Other conditions Type of Partial
analysis safety
factors
1) Power production 1.1 U N
NTM V ≤ V ≤ V
in hub out
1.2 NTM Vin < Vhub < Vout F *
1.3 ECD V = V U N
hub r
1.4 NWP V = V or V External electrical fault U N
hub r out
1.5 EOG V = V or V Loss of electrical U N
1 hub r out
connection
1.6 EOG V = V or V U N
50 hub r out
1.7 EWS V = V or V U N
hub r out
1.8 EDC V = V or V U N
50 hub r out
1.9 ECG V = V U N
hub r
2) Power production plus 2.1 NWP V < V < V Control system fault U N
in hub out
occurrence of fault
2.2 NWP V < V < V Protection system or U A
in hub out
preceding internal
electrical fault
2.3 NTM V < V < V Control or protection F *
in hub out
system fault
3) Start up 3.1 NWP V < V < V F *
in hub out
3.2 EOG V = V , V or V U N
1 hub in r out
3.3 EDC V = V , V or V U N
1 hub in r out
4) Normal shut down 4.1 NWP V < V < V F *
in hub out
4.2 EOG V = V or V U N
1 hub r out
5) Emergency shut down 5.1 NWP V = V or V U N
hub r out
6) Parked (standing still 6.1 EWM 50 year recurrence U N
or idling) interval
6.2 EWM 50 year recurrence Loss of electrical power U A
interval network
6.3 EWM 1 year recurrence Extreme yaw U N
interval misalignment
6.4 NTM V < 0,7 V F *
hub ref
7) Parked and fault 7.1 EWM 1 year recurrence U A
conditions interval
8) Transport, assembly, 8.1 To be stated by the U T
maintenance and manufacturer
repair
a
If no cut-out wind speed V is defined, the value of V should be used.
out ref
For abbreviations see below.
– 5 – EN 61400-1:2004
− DLC Design load case
− ECD Extreme coherent gust with direction change (see 6.3.2.5)
− ECG Extreme coherent gust (see 6.3.2.4)
− EDC Extreme direction change (see 6.3.2.3)
− EOG Extreme operating gust (see 6.3.2.2)
− EWM Extreme wind speed model (see 6.3.2.1)
− EWS Extreme wind shear (see 6.3.2.6)
− Subscript Recurrence period in years
− NTM Normal turbulence model (see 6.3.1.3)
− NWP Normal wind profile model (see 6.3.1.2)
− F Fatigue
− U Ultimate
− N Normal and extreme
− A Abnormal
− T Transport and erection
* Partial safety factor for fatigue (see 7.6.3)

7.4.6 Parked (stand-still or idling) (DLC 6.1 - 6.2)
Replace the whole subclause and its title by the following:
7.4.6 Parked (stand-still or idling) (DLC 6.1 - 6.4)
In this design situation, the rotor of a parked wind turbine is either in a stand-still or idling condition. In
DLC 6.1, 6.2 and 6.3 this situation shall be considered with the extreme wind speed model (EWM).
In the case of a rigid or well-damped wind turbine with little dynamic action, the steady extreme wind
model may be used for the analysis. For more flexible wind turbine structures liable to resonant
amplification the turbulent extreme wind model shall be used for turbulence simulation analysis or quasi-
steady analysis with correction for gusts and dynamic response.
The characteristic load shall be calculated as the expected value of the largest extreme load during the
design load case, e.g. calculated from a sufficient number of simulations.
In DLC 6.1, a yaw misalignment of up to ± 15° using the steady extreme wind model or ± 8° using the
turbulent wind model shall be assumed, provided that no slippage in the yaw system can be assured. If
not, a yaw misalignment of up to ± 180° shall be assumed.
In DLC 6.2 a loss of the electrical power network at an early stage in the storm containing the extreme
wind situation, shall be assumed. Unless power back-up for the control and yaw system with a capacity of
6 h of operation is provided, the effect of a yaw misalignment of up to ± 180° shall be analysed.
In DLC 6.3, the extreme wind with a 1-year recurrence interval shall be combined with an extreme yaw
misalignment. An extreme yaw misalignment of up to ± 30° using the steady extreme wind model or ± 20°
using the turbulent wind model shall be assumed.
If significant fatigue damage can occur to some components (e.g. from weight of idling blades), the
expected number of hours of non-power production time at each appropriate wind speed shall be
considered in DLC 6.4.
If the wind turbine has a yaw system where the yaw braking capacity will be exceeded at the extreme
wind situations (e.g. free yaw or semi-free yaw) the turbulent wind model shall be used.
If the wind turbine is subject to large yaw movements or change of equilibrium during wind speed
increase from normal operation to the extreme situation this behaviour shall be included in the analysis.
7.4.7 Parked plus fault conditions (DLC 7.1)
Add a new second paragraph:
In DLC 7.1, a yaw misalignment of up to ± 15° using the steady extreme wind model or ± 8° using the
turbulent wind model shall be assumed, provided that no slippage in the yaw system can be assured.
If not, a yaw misalignment of up to ± 180° shall be assumed.
8.4 Functional requirements of the control and protection system
Add a new second paragraph:
The protection system shall include two or more braking systems (mechanical, electrical or aerodynamic)
capable of bringing the rotor to rest or to an idling state from any operating condition.
Replace the second sentence with:
It is recommended that at least one braking system operate on an aerodynamic principle, and as such
acts directly on the rotor. If this recommendation is not met at least one braking system shall act on the
low speed shaft or on the rotor of the wind turbine.

Delete Annex C.
Replace “Annex D (informative) Bibliography” by:
“Bibliography”
– 7 – EN 61400-1:2004
Add Annex ZA.
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 When 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 equipment of EN 60204-1 1997
machines + corr. September 1998
Part 1: General requirements
IEC 60364 (mod) Series Electrical installations of buildings HD 384 Series

1)
IEC 60721-2-1 1982 Classification of environmental conditions 1989
HD 478.2.1 S1
Part 2: Environmental conditions appearing in
nature - Temperature and humidity

IEC 61000-3-2 (mod) 2000 Electromagnetic compatibility (EMC) EN 61000-3-2 2000
Part 3-2: Limits - Limits for harmonic current
emissions (equipment input current up to and
including 16 A per phase)
IEC 61000-3-3 1994 Part 3: Limits - Limitation of voltage fluctuations EN 61000-3-3 1995
and flicker in low-voltage supply systems for + corr. July 1997
equipment with rated current ≤ 16 A

IEC 61000-4-2 1995 Part 4-2: Testing and measurement techniques - EN 61000-4-2 1995
Electrostatic discharge immunity test

2)
IEC 61000-4-3 1995 Part 4-3: Testing and measurement techniques - 1996
EN 61000-4-3
(mod) Radiated, radio-frequency, electromagnetic field
immunity test
IEC 61000-4-4 1995 Part 4-4: Testing and measurement techniques - EN 61000-4-4 1995
Electrical fast transient/burst immunity test

IEC 61000-4-5 1995 Part 4-5: Testing and measurement techniques - EN 61000-4-5 1995
Surge immunity test
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
ISO 2394 1986 General principles on reliability for structures - -

1)
HD 478.2.1 S1 includes A1:1987 to IEC 60721-2-1.
2)
EN 61000-4-3:1996 is superseded by EN 61000-4-3:2002, which is based on IEC 61000-4-3:2002.

INTERNATIONAL
IEC
STANDARD
61400-1
Second edition
1999-02
Wind turbine generator systems –
Part 1:
Safety requirements
Aérogénérateurs –
Partie 1:
Spécifications de sécurité
 IEC 1999  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.
International Electrotechnical Commission 3, rue de Varembé Geneva, Switzerland
Telefax: +41 22 919 0300 e-mail: inmail@iec.ch IEC web site http://www.iec.ch
Commission Electrotechnique Internationale
PRICE CODE
XA
International Electrotechnical Commission
For price, see current catalogue

– 2 – 61400-1 © IEC:1999(E)
CONTENTS
Page
FOREWORD . 5
INTRODUCTION . 6
Clause
1 Scope and object . 7
2 Normative references . 7
3 Terms and definitions. 8
4 Symbols and abbreviated terms. 16
4.1 Symbols and units. 16
4.2 Abbreviations . 17
5 Principal elements. 18
5.1 General. 18
5.2 Design methods . 18
5.3 Safety classes. 18
5.4 Quality assurance . 18
5.5 Wind turbine markings . 19
6 External conditions. 19
6.1 General. 19
6.2 WTGS classes . 19
6.3 Wind conditions . 20
6.4 Other environmental conditions . 28
6.5 Electrical power network conditions . 29
7 Structural design . 29
7.1 General. 29
7.2 Design methodology. 30
7.3 Loads. 30
7.4 Design situations and load cases . 31
7.5 Load calculations . 34
7.6 Ultimate limit state analysis . 34
8 Control and protection system . 39
8.1 General. 39
8.2 Wind turbine control . 40
8.3 Wind turbine protection . 40
8.4 Functional requirements of the control and protection system . 41
9 Mechanical systems . 41
9.1 General. 41
9.2 Errors of fitting . 41
9.3 Hydraulic or pneumatic systems . 41
10 Electrical system . 42
10.1 General. 42
10.2 General requirements for the WTGS electrical system . 42
10.3 Protective devices. 42
10.4 Disconnect devices . 42
10.5 Earth system. 42
10.6 Lightning protection. 43

61400-1  IEC:1999(E) − 3 −
Clause Page
10.7 Electrical cables. 43
10.8 Self-excitation . 43
10.9 Over-voltage protection . 43
10.10 Harmonics and power conditioning equipment . 43
11 Assessment of external conditions. 43
11.1 General. 43
11.2 Assessment of wind conditions. 44
11.3 Assessment of other environmental conditions . 44
11.4 Assessment of electrical network conditions . 45
11.5 Assessment of soil conditions . 45
12 Assembly, installation and erection. 45
12.1 General. 45
12.2 Planning. 46
12.3 Installation conditions. 46
12.4 Site access . 46
12.5 Environmental conditions . 46
12.6 Documentation. 46
12.7 Receiving, handling and storage. 47
12.8 Foundation/anchor systems. 47
12.9 Assembly of WTGS. 47
12.10 Erection of WTGS . 47
12.11 Fasteners and attachments . 47
12.12 Cranes, hoists and lifting equipment . 47
13 Commissioning, operation and maintenance . 48
13.1 General. 48
13.2 Commissioning . 48
13.3 Operations . 49
13.4 Inspection and maintenance. 50
Annex A (normative) Design parameters for describing WTGS class S. 52
Annex B (normative) Stochastic turbulence models . 53
Annex C (normative) Deterministic turbulence description . 55
Annex D (informative) Bibliography . 57
Tables
Table 1 – Basic parameters for WTGS classes . 20
Table 2 – Design load cases. 32
Table 3 – Partial safety factors for loads γ . 37
f
Table 4 – General partial safety factors for materials for inherent variability. 37
Table B.1 – Turbulence spectral parameters for Kaimal model . 53

– 4 – 61400-1 © IEC:1999(E)
Figures
Figure 1 – Characteristic wind turbulence. 22
Figure 2 – Example of extreme operating gust . 24
Figure 3 – Example of extreme direction change magnitude . 25
Figure 4 – Example of extreme direction change. 25
Figure 5 – Extreme coherent gust (ECG) . 25
Figure 6 – The direction change for ECD . 26
Figure 7 – Time development of direction change for V = 25 m/s . 26
hub
Figure 8 – Extreme vertical wind shear, wind profile before onset and at maximum shear. 27
Figure 9 – Wind speeds at rotor top and bottom respectively illustrate the
time development of wind shear. 27

61400-1  IEC:1999(E) − 5 −
INTERNATIONAL ELECTROTECHNICAL COMMISSION
––––––––––
WIND TURBINE GENERATOR SYSTEMS –
Part 1: Safety requirements
FOREWORD
1) The IEC (International Electrotechnical Commission) is a worldwide organization for standardization comprising
all national electrotechnical committees (IEC National Committees). The object of the 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, the IEC publishes International Standards. 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. The 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 the 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 National Committees.
3) The documents produced have the form of recommendations for international use and are published in the form
of standards, technical reports or guides and they are accepted by the National Committees in that sense.
4) In order to promote international unification, IEC National Committees undertake to apply IEC International
Standards transparently to the maximum extent possible in their national and regional standards. Any
divergence between the IEC Standard and the corresponding national or regional standard shall be clearly
indicated in the latter.
5) The IEC provides no marking procedure to indicate its approval and cannot be rendered responsible for any
equipment declared to be in conformity with one of its standards.
6) Attention is drawn to the possibility that some of the elements of this International Standard may be the subject
of patent rights. The 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
turbine systems.
This second edition of IEC 61400-1 cancels and replaces the first edition published in 1994.
The text of this standard is based on the following documents:
FDIS Report on voting
88/98/FDIS 88/103/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.
Annexes A, B and C form an integral part of this standard.
Annex D is for information only.
A bilingual version of this standard may be issued at a later date.

– 6 – 61400-1 © IEC:1999(E)
INTRODUCTION
This International Standard outlines minimum safety requirements for wind turbine generator
systems and is not intended for use as a complete design specification or instruction manual.
Any of the requirements of this standard may be waived if it can be suitably demonstrated that
the safety of the system is not compromised. Nevertheless this waiver does not apply to
clause 6.
Compliance with this standard does not relieve any person, organization, or corporation from
the responsibility of observing other applicable regulations.

61400-1  IEC:1999(E) − 7 −
WIND TURBINE GENERATOR SYSTEMS –
Part 1: Safety requirements
1 Scope and object
This part of IEC 61400 deals with safety philosophy, quality assurance and engineering
integrity, and specifies requirements for the safety of Wind Turbine Generator Systems
(WTGS), including design, installation, maintenance, and operation under specified
environmental conditions. Its purpose is to provide the appropriate level of protection against
damage from all hazards from these systems during their planned lifetime.
This standard is concerned with all subsystems of WTGS such as control and protection
mechanisms, internal electrical systems, mechanical systems, support structures and the
electrical interconnection equipment.
This standard applies to WTGS with a swept area equal to or larger than 40 m .
This standard should be used together with the appropriate IEC/ISO standards identified in
clause 2.
2 Normative references
The following normative documents contain provisions which, through reference in this text,
constitute provisions of this part of IEC 61400. At the time of publication, the editions indicated
were valid. All normative documents are subject to revision, and parties to agreements based
on this part of IEC 61400 are encouraged to investigate the possibility of applying the most
recent editions of the normative documents indicated below. Members of IEC and ISO maintain
registers of currently valid International Standards.
IEC 60204-1:1997, Safety of machinery – Electrical equipment of machines – Part 1: General
requirements
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 61000-3-2:1998, Electromagnetic compatibility (EMC) – Part 3-2: Limits – Limits for
harmonic current emissions (equipment input current ≤16 A per phase)
IEC 61000-3-3:1994, Electromagnetic compatibility (EMC) – Part 3-3: Limits – Limitation of
voltage fluctuations and flicker in low-voltage supply systems for equipment with rated current
≤16 A
IEC 61000-4-2:1995, Electromagnetic compatibility (EMC) – Part 4-2: Testing and
measurement techniques – Electrostatic discharge immunity test. Basic EMC publication
IEC 61000-4-3:1995, Electromagnetic compatibility (EMC) – Part 4-3: Testing and
measurement techniques – Radiated, radio-frequency, electromagnetic field immunity test

– 8 – 61400-1 © IEC:1999(E)
IEC 61000-4-4:1995, Electromagnetic compatibility (EMC) – Part 4-4: Testing and measurement
techniques – Electrical fast transient/burst immunity test. Basic EMC publication
IEC 61000-4-5:1995, Electromagnetic compatibility (EMC) – Part 4-5: Testing and measurement
techniques – Surge immunity test
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
ISO 2394:1986, General principles on reliability for structures
3 Terms and definitions
For the purpose of this International Standard, the following 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 shall be a whole number of
years to average out non-stationary effects such as seasonality
3.2
annual average wind speed
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) 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
3.6
catastrophic failure (wind turbines)
disintegration or collapse of a component or structure, that results in loss of vital function which
impairs safety
3.7
characteristic value (of a material property)
value having a prescribed probability of not being attained in a hypothetical unlimited test
series
61400-1  IEC:1999(E) − 9 −
3.8
complex terrain
surrounding terrain that features significant variations in topography and terrain obstacles that
may cause flow distortion
3.9
control system (wind turbines)
subsystem that receives information about the condition of the wind turbine and/or its
environment and adjusts the turbine in order to maintain it within its operating limits
3.10
cut-in wind speed (V )
in
lowest mean wind speed at hub-height at which the wind turbine starts to produce power (see
3.24, hub-height)
3.11
cut-out wind speed (V )
out
highest mean wind speed at hub-height at which the wind turbine is designed to produce power
(see 3.24, hub-height)
3.12
design limits
maximum or minimum values used in a design
3.13
dormant failure (also known as latent fault)
failure of a component or system which remains undetected during normal operation
3.14
downwind
in the direction of the main wind vector
3.15
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.
3.16
emergency shutdown (wind turbines)
rapid shutdown of the wind turbine triggered by a protection system or by manual intervention
3.17
environmental conditions
characteristics of the environment (altitude, temperature, humidity, etc.) which may affect the
WTGS behaviour
3.18
external conditions (wind turbines)
factors affecting operation of a wind turbine, including the wind regime, the electrical network
conditions, and other climatic factors (temperature, snow, ice, etc.)

– 10 – 61400-1 © IEC:1999(E)
3.19
extreme wind speed
highest average wind speed, averaged over t s, that is likely to be experienced within a
specified time period of N years ("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.
3.20
fail-safe
design property of an item which prevents its failures from resulting in critical faults
3.21
gust
temporary change in the wind speed
NOTE – A gust may be characterized by its rise-time, its magnitude and its duration.
3.22
horizontal axis wind turbine
wind turbine whose rotor axis is substantially parallel to the wind flow
3.23
hub (wind turbines)
fixture for attaching the blades or blade assembly to the rotor shaft
3.24
hub-height (wind turbines)
height of the centre of the swept area of the wind turbine rotor above the terrain surface (see
3.55, swept area)
3.25
idling (wind turbines)
condition of a wind turbine that is rotating slowly and not producing power
3.26
inertial subrange
frequency interval of the wind 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 subrange is roughly from 0,02 Hz to 2 kHz.
3.27
isolated operation
stable and temporary operation of a discrete part of a power system after network splitting
3.28
limit state
state of a structure and the loads acting upon it, beyond which the structure no longer satisfies
the design requirement (ISO 2394)
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 (ISO 2394).
3.29
logarithmic wind shear law
see wind profile
61400-1  IEC:1999(E) − 11 −
3.30
maximum power (wind turbines)
highest level of net electrical power delivered by a wind turbine in normal operation
3.31
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
3.32
nacelle
housing which contains the drive-train and other elements on top of a horizontal axis wind
turbine tower
3.33
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
3.34
normal shutdown (wind turbines)
shutdown in which all stages are under the control of the control system
3.35
operating limits
set of conditions defined by the WTGS designer that govern the activation of the control and
protection system
3.36
parked wind turbine
depending on the construction of the wind turbine, parked refers to the turbine being either in a
stand-still or an idling condition
3.37
power collection system (wind turbines)
electric connection system that collects the power from one or more wind turbines. It includes
all electrical equipment connected between the WTGS terminals and the network connection
point
3.38
power law for wind shear
see wind profile
3.39
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 WTGS.
3.40
protection system (wind turbine)
system which ensures that a WTGS remains within the design limits

– 12 – 61400-1 © IEC:1999(E)
3.41
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 WTGS is designed to achieve under
normal operating conditions.
3.42
rated wind speed (V )
r
specified wind speed at which a wind turbine's rated power is achieved
3.43
Rayleigh distribution
probability distribution function, see 3.66 (wind speed distribution)
3.44
reference wind speed (V )
ref
basic parameter for wind speed used for defining WTGS classes. Other design related climatic
parameters are derived from the reference wind speed and other basic WTGS class
parameters (see clause 6)
NOTE – A turbine designed for a WTGS class with a reference wind speed V , is designed to withstand climates
ref
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
3.45
resonance
phenomenon appearing in an oscillating system, in which the period of a forced oscillation is
very close to that of free oscillation
3.46
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.
3.47
rotor speed (wind turbines)
rotational speed of a wind turbine rotor about its axis
3.48
roughness length
extrapolated height at which the mean wind speed becomes zero if the vertical wind profile is
assumed to have a logarithmic variation with height
3.49
safe life
prescribed service life with a declared probability of catastrophic failure
3.50
scheduled maintenance
preventive maintenance carried out in accordance with an established time schedule
3.51
serviceability limit state
limit state which corresponds with criteria governing function related normal use (ISO 2394)

61400-1  IEC:1999(E) − 13 −
3.52
standstill
condition of a WTGS that is stopped
3.53
support structure (wind turbines)
part of a wind turbine comprising the tower and foundation
3.54
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 3.19).
3.55
swept area
projected area perpendicular to the wind direction that a rotor will describe during one complete
rotation
3.56
turbulence intensity
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
3.57
turbulence scale parameter
wave length where the non-dimensional, longitudinal power spectral density is equal to 0,05
NOTE – The wave length is thus defined as Λ = V /f , where f S (f )/σ = 0,05
1 hub 0 0 1 0 1
3.58
ultimate limit state
limit states which generally correspond to maximum load carrying capacity (ISO 2394)
3.59
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
3.60
upwind
in the direction opposite to the main wind vector
3.61
vertical axis wind turbine
wind turbine whose rotor axis is vertical
3.62
Weibull distribution
probability distribution function, see 3.66 (wind speed distribution)
3.63
wind farm
see 3.64 (wind power station)
3.64
wind power station
group or groups of wind turbine generators, commonly called a wind farm

– 14 – 61400-1 © IEC:1999(E)
3.65
wind profile – wind shear law
mathematical expression for assumed wind speed variation with height above ground
NOTE – Commonly used profiles are the logarithmic profile (1) or the power law profile (2).
ln (z/z )
V(z)=V(z ) × (1)
r
ln (z /z )
r 0
α
 
z
V((z) =V(z ) ×   2)
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
3.66
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
( ) = 1 − exp [− π ( /2 ]
)
P V V V
R 0 0 ave
(3)
k
( ) = 1 − exp [− ( /C ) ]
P V V
w 0 0
 
 1 
CΓ 1 +
 
 
k
 
 
with V = (4)
ave  
 π 
C , if  k = 2
 
 2 
where
P(V ) is the cumulative probability function, i.e. the probability that V < V
0 0
V is the wind speed (limit)
V is the average value of V
ave
C is the scale parameter of the Weibull function
k is the shape parameter of the Weibull function
Γ is the gamma function
Both C and k can be evaluated from real data. The Rayleigh function is identical to the Weibull
function if k = 2 is chosen and C and V satisfy the condition stated in equation (4) for k = 2.
ave
The distribution functions express the cumulative probability that the wind speed is lower than
V . Thus (P(V ) – P(V )), if evaluated between the specified limits V and V , will indicate the
0 1 2 1 2
fraction of time that the wind speed is within these limits. Differentiating the distribution
functions yields the corresponding probability density functions.
...