EN 61400-2:2006

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EUROPEAN STANDARD EN 61400-2 NORME EUROPÉENNE
EUROPÄISCHE NORM July 2006
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
© 2006 CENELEC -
All rights of exploitation in any form and by any means reserved worldwide for CENELEC members.
Ref. No. EN 61400-2:2006 E
ICS 27.180 Supersedes EN 61400-2:1996
English version
Wind turbines
Part 2: Design requirements for small wind turbines (IEC 61400-2:2006)
Aérogénérateurs
Partie 2: Exigences en matière de conception des petits aérogénérateurs (CEI 61400-2:2006)
Windenergieanlagen
Teil 2: Sicherheit kleiner Windenergieanlagen (IEC 61400-2:2006)
This European Standard was approved by CENELEC on 2006-05-01. 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, the Czech Republic, Denmark, Estonia, Finland, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia, Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Slovakia, Slovenia, Spain, Sweden, Switzerland and the United Kingdom.

- 2 -
Foreword The text of document 88/254/FDIS, future edition 2 of IEC 61400-2, prepared by IEC TC 88, Wind turbines, was submitted to the IEC-CENELEC parallel vote and was approved by CENELEC as EN 61400-2 on 2006-05-01. This European Standard supersedes EN 61400-2:1996. The most significant changes with respect to EN 61400-2:1996 are: – revised simplified equations based upon recent test and research results; – several parameters in the simplified equations shall now be based upon test results; – added option for use of aeroelastic models instead of simplified equations; – expanded testing requirements. 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)
2007-02-01 – latest date by which the national standards conflicting
with the EN have to be withdrawn
(dow)
2009-05-01 Annex ZA has been added by CENELEC. __________ Endorsement notice The text of the International Standard IEC 61400-2:2006 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: ISO/IEC 17020 NOTE
Harmonized as EN ISO/IEC 17020:2004 (not modified). ISO 9001 NOTE
Harmonized as EN ISO 9001:2000 (not modified). ISO 9002 NOTE
Harmonized as EN ISO 9002:1994 (not modified). ISO 9003 NOTE
Harmonized as EN ISO 9003:1994 (not modified). __________

- 3 - EN 61400-2:2006
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 60034-1 -1) Rotating electrical machines
Part 1: Rating and performance EN 60034-1 20042)
IEC 60034-2 -1) Rotating electrical machines
Part 2: Methods for determining losses and efficiency of rotating electrical machinery from tests (excluding machines for traction vehicles) EN 60034-2
19962)
IEC 60034-5
-1)
Rotating electrical machines
Part 5: Degrees of protection provided by the integral design of rotating electrical machines (IP code) - Classification EN 60034-5 20012)
IEC 60034-8
-1) Rotating electrical machines
Part 8: Terminal markings and direction of rotation EN 60034-8 20022)
IEC 60038 (mod) + A1 + A2 1983 1994 1997 IEC standard voltages3) HD 472 S1 + corr. February
+ A1 1989 2002 1995
IEC 60204-1 (mod) -1) Safety of machinery - Electrical equipment of machines
Part 1: General requirements EN 60204-1 20062)
IEC 60364-5-54 (mod) -1) Electrical installations of buildings
Part 5-54: Selection and erection of electrical equipment - Earthing arrangements, protective conductors and protective bonding conductors HD 60364-5-54 20062)
IEC 60721-2-1 -1) Classification of environmental conditions Part 2-1: Environmental conditions appearing in nature - Temperature and humidity HD 478.2.1 S1
19892)
IEC 61400-1 -1) Wind turbines
Part 1: Design requirements EN 61400-1 20052)
IEC 61400-12-1 -1) Wind turbines
Part 12-1: Power performance measurements of electricity producing wind turbines EN 61400-12-1 20062)
1) Undated reference. 2) Valid edition at date of issue. 3) The title of HD 472 S1 is: Nominal voltages for low voltage public electricity supply systems.

- 4 -
Publication Year Title EN/HD Year IEC/TS 61400-13 -1) Wind turbine generator systems
Part 13: Measurement of mechanical loads - -
IEC/TS 61400-23 -1) Wind turbine generator systems
Part 23: Full-scale structural testing of rotor blades - -
IEC 61643-1 (mod) -1) Low-voltage surge protective devices
Part 1: Surge protective devices connected to low-voltage power distribution systems - Requirements and tests EN 61643-11 20022)
ISO/IEC 17025 2005 General requirements for the competence of testing and calibration laboratories EN ISO/IEC 17025 2005
ISO 2394 -1) General principles on reliability for structures - -

NORME INTERNATIONALECEIIEC INTERNATIONAL STANDARD 61400-2Deuxième éditionSecond edition2006-03 Aérogénérateurs – Partie 2: Exigences en matière de conception des petits aérogénérateurs
Wind turbines – Part 2: Design requirements for small
wind turbines
Pour prix, voir catalogue en vigueur For price, see current catalogue IEC 2006
Droits de reproduction réservés

Copyright - all rights reserved Aucune partie de cette publication ne peut être reproduite ni utilisée sous quelque forme que ce soit et par aucun procédé, électronique ou mécanique, y compris la photocopie et les microfilms, sans l'accord écrit de l'éditeur. 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, PO Box 131, CH-1211 Geneva 20, SwitzerlandTelephone: +41 22 919 02 11 Telefax: +41 22 919 03 00 E-mail: inmail@iec.ch
Web: www.iec.ch CODE PRIX PRICE CODE XC Commission Electrotechnique InternationaleInternational Electrotechnical Commission

61400-2  IEC:2006 – 3 – CONTENTS FOREWORD.9
1 Scope.13 2 Normative references.13 3 Terms and definitions.15 4 Symbols and abbreviated terms.29 4.1 Symbols.29 4.2 Coordinate system.37 5 Principal elements.39 5.1 General.39 5.2 Design methods.39 5.3 Quality assurance.39 6 External conditions.43 6.1 General.43 6.2 SWT classes.43 6.3 Wind conditions.45 6.4 Other environmental conditions.57 6.5 Electrical load conditions.61 7 Structural design.63 7.1 General.63 7.2 Design methodology.63 7.3 Loads and load cases.63 7.4 Simplified load model.67 7.5 Aeroelastic modelling.79 7.6 Load measurements.87 7.7 Stress calculation.87 7.8 Safety factors.89 7.9 Limit state analysis.91 8 Protection and shutdown system.93 8.1 General.93 8.2 Functional requirements of the protection system.93 8.3 Manual shutdown.93 8.4 Shutdown for maintenance.93 9 Testing.95 9.1 General.95 9.2 Tests to verify design data.95 9.3 Mechanical load testing.97 9.4 Duration testing.99 9.5 Mechanical component testing.105 9.6 Safety and function.107 9.7 Environmental testing.109 9.8 Electrical.109

61400-2  IEC:2006 – 5 – 10 Electrical system.109 10.1 General.109 10.2 Protective devices.109 10.3 Disconnect device.109 10.4 Earthing systems.111 10.5 Lightning protection.111 10.6 Electrical conductors and cables.111 10.7 Electrical loads.111 11 Support structure.115 11.1 General.115 11.2 Dynamic requirements.115 11.3 Environmental factors.115 11.4 Earthing.115 11.5 Foundation.115 11.6 Turbine access design loads.115 12 Documentation requirements.115 12.1 General.115 12.2 Installation.117 12.3 Operation.117 12.4 Maintenance and routine inspection.119 13 Wind turbine markings.121
Annex A (informative)
Type certification of small wind turbines.123 Annex B (normative)
Design parameters for describing SWT class S.129 Annex C (informative)
Stochastic turbulence models.131 Annex D (informative)
Deterministic turbulence description.135 Annex E (informative)
Partial safety factors for materials.139 Annex F (informative)
Development of the simple design equations.159
Bibliography.179
Figure 1 – Definition of the system of axes for HAWT.37 Figure 2 – IEC 61400-2 decision path.41 Figure 3 – Characteristic wind turbulence.49 Figure 4 – example of extreme operating gust (N = 1, Vhub = 25 m/s).51 Figure 5 – Example of extreme direction change magnitude (N = 50, D = 5 m, zhub = 20 m).53 Figure 6 – Example of extreme direction change
(N = 50, Vhub = 25 m/s).53 Figure 7 – Extreme coherent gust (Vhub = 25 m/s) (ECG).55 Figure 8 – The direction change for ECD.57 Figure 9 – Time development of direction change for Vhub = 25 m/s.57 Figure A.1 – Modules of type certification (per IEC WT01 and IEC 61400-2).123 Figure A.2 – Elements of design evaluation (recommended per IEC 61400-2).125 Figure A.3 – Elements of type testing (per IEC WT01 and IEC 61400-2).127

61400-2  IEC:2006 – 7 – Figure E.1 – Normal and Weibull distribution.141 Figure E.2 – Typical S-N diagram for fatigue of glass fibre composites
.............................145 Figure E.3 – Typical environmental effects on glass fibre composites
...............................145 Figure E.4 – Fatigue strain diagram for large tow unidirectional 0° carbon fibre/vinyl ester composites, R = 0,1 and 10
......................................................................................147 Figure E.5 – S-N curves for fatigue of typical metals...........................................................147 Figure E.6 – Fatigue life data for jointed softwood .............................................................149 Figure E.7 – Typical S-N curve for wood.............................................................................151 Figure E.8 – Effect of moisture content on compressive strength
of lumber parallel to grain.151 Figure E.9 – Effect of moisture content on wood strength properties.153 Figure E.10 – Effect of grain angle on mechanical property of clear wood
according to Hankinson-type formula.153
Table 1 – Basic parameters for SWT classes.45 Table 2 – Design load cases for the simplified load calculation method.69 Table 3 – Force coefficients, Cf.79 Table 4 – Minimum set of design load cases for aeroelastic models.81 Table 5 – Equivalent stresses.87 Table 6 – Partial safety factors for materials.89 Table 7 – Partial safety factors for loads.91 Table C.1 – Turbulence spectral parameters for Kaimal model.131 Table E.1 – Factors for different survival probabilities and variabilities.141 Table E.2 – Geometric discontinuities.155

61400-2  IEC:2006 – 9 – INTERNATIONAL ELECTROTECHNICAL COMMISSION ____________
WIND TURBINES –
Part 2: Design requirements for small wind turbines
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 61400-2 has been prepared by IEC technical committee 88: Wind turbines. This second edition cancels and replaces the first edition published in 1996. This edition constitutes a technical revision. Numerous substantive changes have been made. The most significant of these are: – revised simplified equations based upon recent test and research results; – several parameters in the simplified equations shall now be based upon test results; – added option for use of aeroelastic models instead of simplified equations; – expanded testing requirements.

61400-2  IEC:2006 – 11 – The text of this standard is based on the following documents: FDIS Report on voting 88/254/FDIS 88/259/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 turbines: Part 1:
Design requirements
Part 2:
Design requirements for small wind turbines
Part 3:
Design requirements for offshore wind turbines1 Part 11:
Acoustic noise measurement techniques Part 12:
Wind turbine power performance testing
Part 12-1: Power performance measurements of electricity producing wind turbines
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 Part 25-1:
Communications for monitoring and control of wind power plants – Overall description of principles and models1 Part 25-2:
Communications for monitoring and control of wind power plants – Information models1 Part 25-3:
Communications for monitoring and control of wind power plants – Information exchange models1 Part 25-4:
Communications for monitoring and control of wind power plants – Mapping to XML based communication profile1 Part 25-5:
Communications for monitoring and control of wind power plants – Conformance testing1 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.
——————— 1
Under consideration.
61400-2  IEC:2006 – 13 – WIND TURBINES –
Part 2: Design requirements for small wind turbines
1 Scope This part of IEC 61400 deals with safety philosophy, quality assurance, and engineering integrity and specifies requirements for the safety of Small Wind Turbines (SWTs) including design, installation, maintenance and operation under specified external conditions. Its purpose is to provide the appropriate level of protection against damage from hazards from these systems during their planned lifetime. This part of IEC 61400 is concerned with all subsystems of SWT such as protection mechanisms, internal electrical systems, mechanical systems, support structures, foundations and the electrical interconnection with the load. While this part of IEC 61400 is similar to IEC 61400-1, it does simplify and make significant changes in order to be applicable to small turbines. This part of IEC 61400 applies to wind turbines with a rotor swept area smaller than 200 m2, generating at a voltage below 1 000 V a.c. or 1 500 V d.c. This part of IEC 61400 should be used together with the appropriate IEC and ISO standards (see 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 60034-1, Rotating electrical machines – Part 1: Rating and performance IEC 60034-2, Rotating electrical machines – Part 2: Methods for determining losses and efficiency of rotating electrical machinery from tests (excluding machines for traction vehicles) IEC 60034-5, Rotating electrical machines – Part 5: Degrees of protection provided by the integral design of rotating electrical machines (IP code) – Classification IEC 60034-8, Rotating electrical machines – Part 8: Terminal markings and direction of rotation IEC 60038:1983, IEC standard voltages
Amendment 1 (1994)
Amendment 2 (1997)
61400-2  IEC:2006 – 15 – IEC 60204-1, Safety of machinery – Electrical equipment of machines – Part 1: General requirements IEC 60364-5-54, Electrical installations of buildings – Part 5-54: Selection and erection of electrical equipment – Earthing arrangements, protective conductors and protective bonding conductors IEC 60721-2-1, Classification of environmental conditions – Part 2-1: Environmental conditions appearing in nature – Temperature and humidity IEC 61400-1, Wind turbines
– Part 1: Design requirements
IEC 61400-12-1, Wind turbines – Part 12-1: Power performance measurements of electricity producing wind turbines IEC 61400-13, Wind turbine generator systems – Part 13: Measurement of mechanical loads IEC 61400-23, Wind turbine generator systems – Part 23: Full-scale structural testing of rotor blades IEC 61643-1, Low-voltage surge protective devices – Part 1: Surge protective devices connected to low-voltage power distribution systems – Requirements and tests ISO/IEC 17025:2005, General requirements for the competence of testing and calibration laboratories ISO 2394, General principles on reliability for structures 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 NOTE The averaging time interval shall be an integer 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 cycles
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
brake (for wind turbines) device capable of reducing the rotor speed or stopping rotation

61400-2  IEC:2006 – 17 – 3.5
catastrophic failure (for wind turbines) disintegration or collapse of a component or structure, that results in loss of vital function which impairs safety 3.6
characteristic value (of a material property) value having a prescribed probability of not being attained in a hypothetical unlimited test series 3.7
control system (for wind turbines) sub-system 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 3.8
cut-in wind speed
Vin lowest mean wind speed at hub height at which the wind turbine produces power 3.9
cut-out wind speed
Vout highest mean wind speed at hub height at which the wind turbine is designed to produce power
3.10
design limits maximum or minimum values used in a design 3.11
design situation possible mode of wind turbine operation, for example power production, parking, etc. 3.12
design wind speed wind speed used as input for the simple design equations (equal to 1,4 Vave) 3.13
downwind in the main wind direction 3.14
emergency shutdown (for wind turbines) rapid shutdown of the wind turbine triggered by a protection system or by manual intervention 3.15
environmental conditions characteristics of the environment (altitude, temperature, humidity, etc.) which may affect the turbine system behaviour

61400-2  IEC:2006 – 19 – 3.16
external conditions (for wind turbines) factors affecting the operation of a wind turbine including the wind regime, other climatic factors (snow, ice, etc.), earthquake and power network conditions 3.17
extreme wind speed highest average wind speed, averaged over t seconds, that is likely to be experienced within a specified time period (recurrence period) of T years NOTE Recurrence periods of T = 50 years and T = 1 year and averaging time interval of t = 3 s and t = 10 min are used in a number of standards. In popular language, the less precise term "survival wind speed" is often used. In practice, however, the wind turbine generator system is designed using the extreme wind speed for design load cases. 3.18
fail-safe design property of an item which prevents its failures from resulting in critical faults 3.19
furling a passive overspeed control mechanism by means of reducing the projected swept area 3.20
gust sudden and brief increase of the wind speed over its mean value. NOTE A gust can be characterized by its rise-time, its amplitude and its duration.
3.21
horizontal axis wind turbine wind turbine whose rotor axis is substantially parallel to the wind flow 3.22
hub (for wind turbines) fixture for attaching the blades or blade assembly to the rotor shaft 3.23
hub height (for wind turbines) height of the centre of the wind turbine rotor above the terrain surface. For a vertical axis wind turbine, the hub height is the height of the equator plane 3.24
idling (for wind turbines) condition of a wind turbine that is rotating slowly and not producing power 3.25
limit state state of a structure and the loads acting upon it beyond which the structure no longer satisfies the design requirement
[ISO 2394, 2.2.9, 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 (ISO 2394).

61400-2  IEC:2006 – 21 – 3.26
load case combination of a design situation and an external condition which results in structural loading 3.27
logarithmic wind shear law a mathematical law which expresses wind speed variations as a logarithmic function of height above ground 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
normal shutdown (for wind turbines) shutdown in which all stages are under the control of the control system 3.31
operating limits set of conditions defined by the SWT designer that govern the activation of the control and protection system 3.32
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 3.33
parking situation to which a wind turbine returns after a normal shutdown 3.34
power law for wind shear a mathematical law which expresses wind speed variations as a power law function of height above ground 3.35
power output power delivered by a device in a specific form and for a specific purpose NOTE For wind turbines, this is the electric power delivered by a wind turbine. 3.36
protection system (wind turbine) system which ensures that a wind turbine generator system remains within the design limits

61400-2  IEC:2006 – 23 – 3.37
Rayleigh distribution a probability distribution function often used for wind speeds. The distribution depends on one adjustable parameter – the scale parameter, which controls the average wind speed NOTE The Rayleigh distribution is identical to a Weibull distribution (see 3.55) with shape parameter 2. 3.38
reference wind speed
Vref basic parameter for wind speed used for defining SWT classes. Other design related climatic parameters are derived from the reference wind speed and other basic SWT class parameters NOTE A turbine designed for a SWT class with a reference wind speed, Vref, is designed to withstand 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 Vref (see 3.17). 3.39
resonance phenomenon appearing in an oscillating system, in which the period of a forced oscillation is very close to that of free oscillation 3.40
rotor speed (for wind turbines) rotational speed of a wind turbine rotor about its axis 3.41
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 3.42
safe life prescribed service life with a declared probability of catastrophic failure 3.43
scheduled maintenance preventive maintenance carried out in accordance with an established time schedule 3.44
shutdown (for wind turbines) transitional state of a wind turbine between power production and standstill or idling 3.45
standstill condition of a wind turbine generator system that is stopped 3.46
support structure (for wind turbines) part of a wind turbine comprising the tower and foundation 3.47
survival wind speed (deprecated) a popular name for the maximum wind speed that a construction is designed to withstand NOTE This term is not used in the IEC 61400 series; the design conditions instead refer to extreme wind speed (see 3.17).

61400-2  IEC:2006 – 25 – 3.48
Small Wind Turbine
SWT a system of 200 m2 rotor swept area or less that converts kinetic energy in the wind into electrical energy 3.49
swept area projected area perpendicular to the wind direction that a rotor will describe during one complete rotation 3.50
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 3.51
ultimate limit state limit states which generally correspond to maximum load carrying capacity
3.52
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 3.53
upwind in the direction opposite to the main wind direction 3.54
vertical axis wind turbine wind turbine whose rotor axis is vertical 3.55
Weibull distribution probability distribution function often used for wind speeds. This distribution function depends on two parameters, the shape parameter, which controls the width of the distribution and the scale parameter, which in turn controls the average wind speed NOTE See 3.60, wind speed distribution. 3.56
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)(ln)()(0r0rz/zzz/zV=zV (1)
))(()(rrαzzzV=zV (2)
61400-2  IEC:2006 – 27 – where V(z) is the wind speed at height z; z is the height above ground; zr is a reference height above ground used for fitting the profile; zo is the roughness length; α is the wind shear (or power law) exponent. 3.57
wind shear variation of wind speed across a plane perpendicular to the wind direction 3.58
wind shear exponent also commonly known as power law exponent (see 3.56, wind profile – wind shear law) 3.59
wind speed at a specified point in space, the wind speed is the speed of motion of a minute amount of air surrounding the specified point NOTE The wind speed is also the magnitude of the local wind velocity (vector) (see 3.61). 3.60
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, PR(Vo), and the Weibull, PW(Vo), functions.
{}[]{}[]kCVVVPVVVVP)/(exp1)2/(exp100W2ave00R−−=<π−−=< (3)
πΓ
=k
C k+ C
=
V
2if/2,)1(1avecave (4) where P(V0)
is the cumulative probability function, i.e. the probability that V < V0; V0
is the wind speed (limit); Vave
is the average value of V; 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 Vave satisfy the condition stated in equation (4) for k = 2. The distribution functions express the cumulative probability that the wind speed is lower than V0. Thus (P(V1) – P(V2)), if evaluated between the specified limits V1 and V2, will indicate the fraction of time that the wind speed is within these limits. Differentiating the distribution functions yields the corresponding probability density functions.

61400-2  IEC:2006 – 29 – 3.61
wind velocity vector pointing in the direction of motion of a minute amount of air surrounding the point of consideration, the magnitude of the vector being equal to the speed of motion of this air "parcel" (i.e. the local wind speed) NOTE The vector at any point is thus the time derivative of the position vector of the air "parcel" moving through the point. 3.62
yawing rotation of the rotor axis about a vertical axis (for horizontal axis wind turbines only) 3.63
yaw rate the time rate of change of yaw angle, the rate of yawing 3.64
yaw misalignment horizontal deviation of the wind turbine rotor axis from the wind direction 4 Symbols and abbreviated terms 4.1 Symbols A cross section area [m2] Aproj the component area projected on to a plane perpendicular or
parallel to the wind direction
[m2] a slope parameter for turbulence standard deviation model [-] B number of blades
[-] C scale parameter of the Weibull distribution function [m/s] Cd drag coefficient [-] Cf force coefficient [-] Cl lift coefficient [-] CT thrust coefficient [-] Coh coherency function [-] D rotor diameter
[m] er distance from the centre of gravity of the rotor to the rotation axis [m] F force [N] FzB force on the blade at the blade root in the spanwise direction [N] Fx-shaft axial shaft load [N] f frequency
[s–1] fk characteristic value for material strength [-] G ratio between rated torque and short circuit torque for a generator [-] g acceleration due to gravity: 9,81
[m/s2]
61400-2  IEC:2006 – 31 – IB mass moment of inertia of the blade about the blade root flap axis [kgm2] I15 characteristic value of hub-height turbulence intensity at a
10 min average wind speed of 15 m/s
[-] K modified Bessel function [-] k shape parameter of the Weibull distribution function [-] L isotropic turbulence integral scale parameter [m] Llt distance between the lifting point and the top of the tower
[m] Lrt distance between the rotor centre and the yaw axis [m] Lrb distance between rotor centre and first bearing
[m] Lc coherency scale parameter [m] Lk velocity component integral scale parameter [m] MxB, MyB blade root bending moments [Nm] Mbrake torque on the low speed shaft caused by the brake [Nm] Mx-shaft torsion moment on the rotor shaft at the first bearing [Nm] Mshaft combined bending moment for the shaft at the first bearing (nearest to rotor) [Nm] Mtower the bending moment in the tower at the lifting point attachment [Nm] mB blade mass
[kg] moverhang the mass of the tower between the lifting point and the top of the tower [kg] mr rotor mass being the mass of the blades plus the mass of the hub
[kg] mtowertop the mass of the nacelle and rotor combined [kg] N(.) is the number of cycles to failure as a function of the stress (or strain)
indicated by the argument (i.e. the characteristic S-N curve) [-] N recurrence period for extreme situations [yr] n rotor speed [r.p.m.] ni counted number of fatigue cycles in load bin i [-] O operational time fraction [%] P electrical power [W] PR(V0) Rayleigh cumulative probability distribution, i.e. the probability that V in bin i [-]
61400-2  IEC:2006 – 33 – T gust characteristic time [s] t time [s] Td design life [s] TE excluded time [h] TN time during which the turbine was not operational [h] TT total time elapsed in the duration test [h] TU unknown time [h] V wind speed
[m/s] V(z) wind speed at height z
[m/s] Vave annual average wind speed at hub height
[m/s] Vcg extreme coherent gust magnitude over the whole rotor swept area [m/s] Vdesign design wind speed [m/s] VeN
expected extreme wind speed (averaged over 3 s),
with a recurrence time interval of N years. Ve1 and Ve50 for
1 year and 50 years, respectively [m/s] VgustN largest gust magnitude with an expected recurrence period of N years.
[m/s] Vhub wind speed at hub height averaged over 10 min [m/s] Vin cut-in wind speed
[m/s] Vmax,shutdown the maximum wind speed at which the manufacturer allows a normal
shutdown [m/s] V0 limit wind speed in wind speed distribution model [m/s] Vout cut-out wind speed
[m/s] Vref
reference wind speed averaged over 10 min [m/s] Vtip speed of the blade tip
[m/s] V(z, t,) longitudinal wind velocity component to describe transient variation
for extreme gust and shear conditions [m/s] W
section modulus used in stress calculations [m3] x, y, z co-ordinate system used for the wind field description; along wind
(longitudinal), across wind (lateral) and height respectively [m] zhub hub height of the wind turbine
[m] zr reference height above ground [m] z0 roughness length for the logarithmic wind profile [m] α wind shear power law exponent [-] β parameter for extreme direction change model and extreme operating
gust model [-] Γ gamma function [-] γf
partial safety factor for loads [-] γm
partial safety factor f
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