IEC 61400-1:2019

Wind energy generation systems - Part 1: Design requirements

IEC 61400-1:2019 specifies essential design requirements to ensure the structural integrity of wind turbines. Its purpose is to provide an appropriate level of protection against damage from all hazards during the planned lifetime. This document is concerned with all subsystems of wind turbines such as control and protection functions, internal electrical systems, mechanical systems and support structures. This document applies to wind turbines of all sizes. For small wind turbines, IEC 61400-2 can be applied. IEC 61400-3-1 provides additional requirements to offshore wind turbine installations. This document is intended to be used together with the appropriate IEC and ISO standards mentioned in Clause 2. This edition includes the following significant technical changes with respect to the previous edition:
a) general update and clarification of references and requirements;
b) extension of wind turbine classes to allow for tropical cyclones and high turbulence;
c) Weibull distribution of turbulence standard deviation for normal turbulence model (NTM);
d) updated design load cases (DLCs), in particular DLC 2.1 and 2.2;
e) revision of partial safety factor specifications
The contents of the corrigendum 1 (2019-09) and Interpretation sheet 1 (2025-02) have been included in this copy.

Systèmes de génération d'énergie éolienne - Partie 1: Exigences de conception

l'IEC 61400-1:2019 spécifie les exigences de conception essentielles pour assurer l’intégrité structurelle des éoliennes. Elle a pour objet de fournir un niveau de protection approprié contre les dommages causés par tous les dangers pendant la durée de vie prévue. Le présent document concerne tous les sous-systèmes des éoliennes tels que les fonctions de commande et de protection, les systèmes électriques internes, les systèmes mécaniques et les structures de support. Le présent document s'applique aux éoliennes de toutes dimensions. Pour les petites éoliennes, l'IEC 61400-2 peut s’appliquer. L'IEC 61400-3-1 donne les exigences supplémentaires relatives aux installations d'éoliennes en pleine mer. Le présent document est destiné à être utilisé avec les normes IEC et ISO appropriées mentionnées à l’Article  REF _Ref34379257 \r \h 2 08D0C9EA79F9BACE118C8200AA004BA90B02000000080000000D0000005F00520065006600330034003300370039003200350037000000 . Cette édition inclut les modifications techniques majeures suivantes par rapport à l'édition précédente:
a. mise à jour générale et clarification des références et des exigences;
b. extension des classes d'éoliennes pour les adapter aux cyclones tropicaux et aux fortes turbulences;
c. loi de Weibull de l'écart type de la turbulence pour le modèle de turbulence normale (NTM);
d. cas de charge pour la conception (DLC) mis à jour, en particulier les DLC 2.1 et 2.2;
e. révision des spécifications du facteur de sécurité partielle
Le contenu de la feuille d’interprétation 1 (2025-02) a été pris en considération dans cet exemplaire

General Information

• Status: Published
• Publication Date: 17-Dec-2025
• ICS: 27.180 - Wind turbine energy systems
• ICS: 31.220 - Electromechanical components for electronic and telecommunications equipment
• Technical Committee: TC 88 - Wind energy generation systems
• Drafting Committee: MT 1 - TC 88/MT 1
• Current Stage: PPUB - Publication issued
• Start Date: 08-Feb-2019
• Completion Date: 09-Nov-2018

Relations

• Amended By: IEC 61400-1:2019/AMD1:2025 - Amendment 1 - Wind energy generation systems - Part 1: Design requirements
• Effective Date: 05-Sep-2023
• Corrected By: IEC 61400-1:2019/COR1:2019 - Corrigendum 1 - Wind energy generation systems - Part 1: Design requirements
• Effective Date: 05-Sep-2023
• Revised: IEC 61400-1:2019/ISH1:2025 - Interpretation Sheet 1 - Wind energy generation systems - Part 1: Design requirements
• Effective Date: 27-Sep-2024
• Revises: IEC 61400-1:2005/AMD1:2010 - Amendment 1 - Wind turbines - Part 1: Design requirements
• Effective Date: 05-Sep-2023
• Revises: IEC 61400-1:2005 - Wind turbines - Part 1: Design requirements
• Effective Date: 05-Sep-2023

Overview - IEC 61400-1:2019 (Wind turbine design requirements)

IEC 61400-1:2019 is the 4th edition international standard that specifies essential design requirements to ensure the structural integrity and safe operation of wind turbines for their planned lifetime. It covers all turbine sizes and all major subsystems - control and protection functions, internal electrical systems, mechanical systems, and support structures. This edition incorporates Corrigendum 1 (2019-09) and Interpretation Sheet 1 (2025-02).

Key updates include:

• General clarifications and updated references
• Extension of wind turbine classes to address tropical cyclones and high turbulence
• Use of a Weibull distribution for turbulence standard deviation in the Normal Turbulence Model (NTM)
• Revised design load cases (DLCs) (notably DLC 2.1 and 2.2)
• Revision of partial safety factor specifications

Key Topics and Technical Requirements

• Design methodology and safety classes: Requirements for design methods, quality assurance, and marking.
• External conditions & wind classification: Defining site wind classes, normal and extreme wind conditions, and turbulence modeling (including Weibull-based NTM).
• Loads and load cases (DLCs): Prescribed load cases for power production, faults, start-up, shutdown, parked states, transport/erection and more - updated DLC definitions guide structural and dynamic load simulations.
• Ultimate limit state & fatigue: Procedures for ultimate strength, fatigue assessment, stability and critical deflection analyses.
• Control and protection systems: Requirements for control functions, protection logic, failure analysis, braking and restart procedures.
• Mechanical & electrical systems: Main gearbox, yaw/pitch systems, bearings, internal electrical protection, lightning protection, EMC and power electronic converter considerations.
• Site-specific assessment: Topography, turbulence measurement and evaluation, wake effects, soil and earthquake assessment, and verification of structural integrity against site data.
• Assembly, installation & documentation: Planning, erection, foundations and commissioning requirements.

Practical Applications - Who uses IEC 61400-1:2019

• Wind turbine designers and structural engineers for component sizing, load simulation and verification.
• Manufacturers and OEMs for product development and to meet certification requirements.
• Certification bodies and testing labs for conformity assessment and type certification.
• Project developers, asset owners and consultants for site assessment, specification of design class and procurement.
• Regulators and safety assessors evaluating compliance and safety of wind installations. Note: For small wind turbines, refer to IEC 61400-2; for offshore installations see IEC 61400-3-1.

Related standards

• IEC 61400-2 (Small wind turbines)
• IEC 61400-3-1 (Offshore wind turbine installations)
• Various IEC and ISO standards referenced in Clause 2 (used together with IEC 61400-1 for full compliance)

Keywords: IEC 61400-1, wind turbine design, design requirements, structural integrity, design load cases, turbulence model, Weibull distribution, partial safety factors, wind energy standards.

Standards Content (Sample)

IEC 61400-1 ®
Edition 4.0 2019-02
INTERNATIONAL
STANDARD
colour
inside
Wind energy generation systems –
Part 1: Design requirements
All rights reserved. Unless otherwise specified, no part of this publication may be reproduced or utilized in any form
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INTERNATIONAL
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Wind energy generation systems –

Part 1: Design requirements
INTERNATIONAL
ELECTROTECHNICAL
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ICS 27.180 ISBN 978-2-8322-6253-5

– 2 – IEC 61400-1:2019 © IEC 2019
CONTENTS
FOREWORD . 10
INTRODUCTION . 12
1 Scope . 13
2 Normative references . 13
3 Terms and definitions . 15
4 Symbols and abbreviated terms . 23
4.1 Symbols and units. 23
4.2 Abbreviated terms . 26
5 Principal elements . 27
5.1 General . 27
5.2 Design methods . 27
5.3 Safety classes . 27
5.4 Quality assurance . 27
5.5 Wind turbine markings . 27
6 External conditions . 28
6.1 General . 28
6.2 Wind turbine classes . 28
6.3 Wind conditions . 30
6.3.1 General . 30
6.3.2 Normal wind conditions . 31
6.3.3 Extreme wind conditions . 33
6.4 Other environmental conditions . 38
6.4.1 General . 38
6.4.2 Normal other environmental conditions . 39
6.4.3 Extreme other environmental conditions . 39
6.5 Electrical power network conditions . 39
7 Structural design . 40
7.1 General . 40
7.2 Design methodology . 40
7.3 Loads. 40
7.3.1 General . 40
7.3.2 Gravitational and inertial loads . 41
7.3.3 Aerodynamic loads . 41
7.3.4 Actuation loads . 41
7.3.5 Other loads . 41
7.4 Design situations and load cases . 41
7.4.1 General . 41
7.4.2 Power production (DLC 1.1 to 1.5) . 44
7.4.3 Power production plus occurrence of fault or loss of electrical network
connection (DLC 2.1 to 2.5) . 45
7.4.4 Start-up (DLC 3.1 to 3.3) . 47
7.4.5 Normal shutdown (DLC 4.1 to 4.2) . 47
7.4.6 Emergency stop (DLC 5.1) . 48
7.4.7 Parked (standstill or idling) (DLC 6.1 to 6.4) . 48
7.4.8 Parked plus fault conditions (DLC 7.1) . 49
7.4.9 Transport, assembly, maintenance and repair (DLC 8.1 and 8.2) . 49

7.5 Load calculations . 49
7.6 Ultimate limit state analysis. 50
7.6.1 Method . 50
7.6.2 Ultimate strength analysis . 53
7.6.3 Fatigue failure . 56
7.6.4 Stability . 57
7.6.5 Critical deflection analysis . 57
7.6.6 Special partial safety factors . 58
8 Control system . 58
8.1 General . 58
8.2 Control functions . 58
8.3 Protection functions . 59
8.4 Control system failure analysis . 59
8.4.1 General . 59
8.4.2 Independence and common-cause failures . 60
8.4.3 Fault exclusions . 60
8.4.4 Failure mode return periods . 60
8.4.5 Systematic failures . 60
8.5 Manual operation . 60
8.6 Emergency stop button function . 60
8.7 Manual, automatic, and remote restart . 61
8.8 Braking system . 62
9 Mechanical systems . 62
9.1 General . 62
9.2 Errors of fitting . 63
9.3 Hydraulic or pneumatic systems . 63
9.4 Main gearbox . 63
9.5 Yaw system . 63
9.6 Pitch system . 64
9.7 Protection function mechanical brakes . 64
9.8 Rolling element bearings . 64
9.8.1 General . 64
9.8.2 Main shaft bearings . 64
9.8.3 Generator bearings . 64
9.8.4 Pitch and yaw bearings . 65
10 Electrical system . 65
10.1 General . 65
10.2 General requirements for the electrical system . 65
10.3 Internal environmental conditions . 65
10.4 Protective devices . 67
10.5 Disconnection from supply sources . 67
10.6 Earth system . 67
10.7 Lightning protection . 67
10.8 Electrical cables . 68
10.9 Self-excitation . 68
10.10 Protection against lightning electromagnetic impulse . 68
10.11 Power quality . 68
10.12 Electromagnetic compatibility . 69
10.13 Power electronic converter systems and equipment . 69

– 4 – IEC 61400-1:2019 © IEC 2019
10.14 Twist/drip loop . 69
10.15 Slip rings . 69
10.16 Vertical power transmission conductors and components . 70
10.17 Motor drives and converters . 70
10.18 Electrical machines . 71
10.19 Power transformers . 71
10.20 Low voltage switchgear and controlgear . 71
10.21 High voltage switchgear . 71
10.22 Hubs . 72
11 Assessment of a wind turbine for site-specific conditions . 72
11.1 General . 72
11.2 Assessment of the topographical complexity of the site and its effect on
turbulence . 72
11.2.1 Assessment of the topographical complexity . 72
11.2.2 Assessment of turbulence structure at the site . 75
11.3 Wind conditions required for assessment . 76
11.3.1 General . 76
11.3.2 Wind condition parameters . 76
11.3.3 Measurement setup . 77
11.3.4 Data evaluation . 78
11.4 Assessment of wake effects from neighbouring wind turbines . 78
11.5 Assessment of other environmental conditions . 78
11.6 Assessment of earthquake conditions . 79
11.7 Assessment of electrical network conditions . 80
11.8 Assessment of soil conditions . 80
11.9 Assessment of structural integrity by reference to wind data . 80
11.9.1 General . 80
11.9.2 Assessment of the fatigue load suitability by reference to wind data . 80
11.9.3 Assessment of the ultimate load suitability by reference to wind data . 82
11.10 Assessment of structural integrity by load calculations with reference to site-
specific conditions . 82
12 Assembly, installation and erection . 83
12.1 General . 83
12.2 Planning . 84
12.3 Installation conditions . 84
12.4 Site access . 84
12.5 Environmental conditions . 84
12.6 Documentation . 84
12.7 Receiving, handling and storage . 85
12.8 Foundation/anchor systems . 85
12.9 Assembly of wind turbine . 85
12.10 Erection of wind turbine . 85
12.11 Fasteners and attachments . 85
12.12 Cranes, hoists and lifting equipment . 85
13 Commissioning, operation and maintenance . 86
13.1 General . 86
13.2 Design requirements for safe operation, inspection and maintenance . 86
13.3 Instructions concerning commissioning . 87
13.3.1 General . 87

13.3.2 Energization . 87
13.3.3 Commissioning tests . 87
13.3.4 Records . 87
13.3.5 Post commissioning activities . 87
13.4 Operator’s instruction manual . 87
13.4.1 General . 87
13.4.2 Instructions for operations and maintenance records . 88
13.4.3 Instructions for unscheduled automatic shutdown . 88
13.4.4 Instructions for diminished reliability . 88
13.4.5 Work procedures plan . 88
13.4.6 Emergency procedures plan . 89
13.5 Maintenance manual . 89
14 Cold climate . 90
14.1 General . 90
14.2 Low temperature and icing climate . 90
14.3 External conditions for cold climate . 90
14.3.1 General . 90
14.3.2 Wind turbine class for cold climate. 90
14.4 Structural design . 91
14.5 Design situations and load cases . 91
14.5.1 General . 91
14.5.2 Load calculations . 91
14.5.3 Selection of suitable materials . 91
14.6 Control systems . 92
14.7 Mechanical systems . 92
14.8 Electrical systems . 92
Annex A (normative) Design parameters for external conditions . 93
A.1 Design parameters for describing wind turbine class S. 93
A.1.1 General . 93
A.1.2 Machine parameters . 93
A.1.3 Wind conditions . 93
A.1.4 Electrical network conditions . 93
A.1.5 Other environmental conditions (where taken into account) . 94
A.2 Additional design parameters for describing cold climate wind turbine class
S (CC-S) . 94
Annex B (informative) Design load cases for special class S wind turbine design or
site suitability assessment . 96
B.1 General . 96
B.2 Power production (DLC 1.1 to 1.9) . 96
Annex C (informative) Turbulence models . 100
C.1 General . 100
C.2 Mann [3] uniform shear turbulence model . 100
C.3 Kaimal [1] spectrum and exponential coherence model . 103
C.4 Reference documents . 105
Annex D (informative) Assessment of earthquake loading . 106
D.1 General . 106
D.2 Design response spectrum . 106
D.3 Structure model . 107
D.4 Seismic load evaluation . 108

– 6 – IEC 61400-1:2019 © IEC 2019
D.5 Additional load . 109
D.6 Reference documents . 110
Annex E (informative) Wake and wind farm turbulence . 111
E.1 Added wake turbulence method . 111
E.2 Dynamic wake meandering model . 113
E.2.1 General . 113
E.2.2 Wake deficit . 114
E.2.3 Meandering . 115
E.2.4 Wake induced turbulence. 116
E.2.5 Wake superposition . 116
E.2.6 Model synthesis . 117
E.3 Reference documents . 117
Annex F (informative) Prediction of wind distribution for wind turbine sites by
measure-correlate-predict (MCP) methods . 118
F.1 General . 118
F.2 Measure-correlate-predict (MCP) . 118
F.3 Application to annual mean wind speed and distribution . 118
F.4 Application to extreme wind speed . 118
F.5 Reference documents . 119
Annex G (informative) Statistical extrapolation of loads for ultimate strength analysis . 120
G.1 General . 120
G.2 Data extraction for extrapolation . 120
G.3 Load extrapolation methods . 121
G.3.1 General . 121
G.3.2 Global extremes . 121
G.3.3 Local extremes . 123
G.3.4 Long-term empirical distributions . 123
G.4 Convergence criteria . 124
G.4.1 General . 124
G.4.2 Load fractile estimate . 124
G.4.3 Confidence bounds . 125
G.4.4 Confidence intervals based on bootstrapping . 125
G.4.5 Confidence intervals based on the binomial distribution . 125
G.5 Inverse first-order reliability method (IFORM) . 126
G.6 Reference documents . 128
Annex H (informative) Fatigue analysis using Miner’s rule with load extrapolation . 130
H.1 Fatigue analysis . 130
H.2 Reference documents . 133
Annex I (informative) Contemporaneous loads . 135
I.1 General . 135
I.2 Scaling . 136
I.3 Averaging . 136
Annex J (informative) Prediction of the extreme wind speed of tropical cyclones by

using Monte Carlo simulation method . 137
J.1 General . 137
J.2 Prediction of tropical cyclone induced extreme wind speeds . 137
J.2.1 General . 137
J.2.2 Evaluation of tropical cyclone parameters . 137
J.2.3 Generation of synthetic tropical cyclones . 138

J.2.4 Prediction of wind speeds in the tropical cyclone boundary . 138
J.3 Prediction of extreme wind speed in mixed climate regions . 139
J.3.1 General . 139
J.3.2 Extreme wind distributions of extratropical cyclones by the MCP method . 139
J.3.3 Extreme wind distributions of tropical cyclones by the MCS method. 140
J.3.4 Determination of extreme wind speed in a mixed climate region . 140
J.4 Reference documents . 140
Annex K (informative) Calibration of structural material safety factors and structural
design assisted by testing . 142
K.1 Overview and field of application. 142
K.2 Target reliability level . 142
K.3 Safety formats . 142
K.4 Reliability-based calibration . 144
K.5 Calibration using the design value format . 145
K.6 Partial safety factors for fatigue for welded details in steel structures. 145
K.7 Types of tests for materials . 147
K.8 Planning of tests . 147
K.8.1 General . 147
K.8.2 Objectives and scope . 147
K.8.3 Prediction of test results . 147
K.8.4 Specification of test specimen and sampling . 148
K.8.5 Loading specifications . 148
K.8.6 Testing arrangement . 148
K.8.7 Measurements . 149
K.8.8 Evaluation and reporting the test . 149
K.9 General principles for statistical evaluations . 149
K.10 Derivation of characteristic values. 150
K.11 Statistical determination of characteristic value for a single property . 150
K.12 Statistical determination of characteristic value for resistance models. 151
K.12.1 General . 151
K.12.2 Step 1: Develop a design model . 152
K.12.3 Step 2: Compare experimental and theoretical values . 152
K.12.4 Step 3: Estimate the mean value correction factor (bias) b . 153
K.12.5 Step 4: Estimate the coefficient of variation of the errors . 153
K.12.6 Step 5: Analyse compatibility . 154
K.12.7 Step 6: Determine the coefficients of variation V of the basic variables . 154
Xi
K.12.8 Step 7: Determine the characteristic value r of the resistance . 154
k
K.13 Reference documents . 156
Annex L (informative) Cold climate: assessment and effects of icing climate . 157
L.1 Assessment of icing climate conditions . 157
L.1.1 General . 157
L.1.2 Icing climate . 157
L.1.3 Rotor icing . 158
L.1.4 Measurement methods . 159
L.1.5 Profile coefficients modification for ice . 159
L.2 Ice mass effects on wind turbine blades . 160
L.3 Cold climate design situations and load case . 161
L.3.1 General . 161
L.3.2 Power production (DLC 1.1 to 1.6) . 161

– 8 – IEC 61400-1:2019 © IEC 2019
L.3.3 Parked (standstill or idling) (DLC 6.1 to 6.5) . 161
L.3.4 Parked and fault conditions (DLC 7.1) . 161
L.4 Cold climate load calculations . 161
L.5 Reference documents and bibliography . 162
Annex M (informative) Medium wind turbines . 163
M.1 Overview. 163
M.2 External conditions . 163
M.2.1 General . 163
M.2.2 Wind shear . 163
M.3 Assembly, installation and erection . 163
M.4 Commissioning, operation and maintenance . 164
M.5 Documentation . 165
Bibliography . 167

Figure 1 – Turbulence standard deviation and turbulence intensity for the normal
turbulence model (NTM) . 32
Figure 2 – Example of extreme operating gust . 34
Figure 3 – Example of extreme direction change magnitude . 35
Figure 4 – Example of extreme direction change transient . 35
Figure 5 – Example of extreme coherent gust amplitude for ECD . 36
Figure 6 – Direction change for ECD . 37
Figure 7 – Example of direction change transient . 37
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) . 38
Figure 9 – Example of wind speeds at rotor top and bottom, respectively, which

illustrate the transient positive wind shear . 38
Figure 10 – Examples of 30° sectors for fitting the terrain data . 73
Figure 11 – Terrain variation (∆z) and terrain slope (θ ) . 74
Figure 12 – Possible combinations of normalized mean wind speed and Weibull shape
parameter k (shaded area) . 81
Figure D.1 – Structure model for response spectrum method . 108
Figure E.1 – Configuration – Inside a wind farm with more than 2 rows . 113
Figure E.2 – The three fundamental parts of the DWM model . 114
Figure K.1 – r -r diagram . 153

e t
Figure L.1 – Definition of meteorological icing and rotor icing . 158
Figure L.2 – Representative ice affected rotor area as defined by rotor icing height . 159
Figure L.3 – Iced airfoil lift and drag penalty factors . 160

Table 1 – Basic parameters for wind turbine classes . 29
Table 2 – Design load cases (DLC) . 43
Table 3 – Partial safety factors for loads γ
........................................................................... 54
f
Table 4 – Minimum safety factor S and S for the yaw gear system . 63
H,min F,min
Table 5 – Threshold values of the terrain complexity categories L, M and H. 75
Table 6 – Values of lateral and vertical turbulence standard deviations relative to the
longitudinal component depending on terrain complexity category L, M and H . 75

Table 7 – Values of turbulence structure correction parameter depending on terrain
complexity category L, M and H . 76
Table A.1 – Design parameters for describing cold climate wind turbine class S (CC-S) . 94
Table B.1 – Design load cases . 97
Table C.1 – Turbulence spectral parameters for the Kaimal model . 104
Table E.1 – Number (N) of neighbouring wind turbines . 112
Table G.1 – Parameters needed to establish binomial-based confidence intervals . 126
Table G.2 – Short-term load exceedance probabilities as a function of hub-height wind
speed for different wind turbine classes for use with the IFORM procedure . 128
Table I.1 – Extreme loading matrix . 135
Table K.1 – Partial safety factor for model uncertainty, γ . . 145
δ
Table K.2 – Recommended values for partial safety factor for fatigue strength, γ . 146
Mf
Table K.3 – Recommended partial safety factor for fatigue stresses, γ . 147
Ff
Table K.4 – Values of k for the 5 % characteristic value . 151

n
Table L.1 – Cold climate design load cases . 161
Table L.2 – Blade ice mass and airfoil penalty factors used in different analysis types . 162
...

IEC 61400-1 ®
Edition 4.0 2019-02
REDLINE VERSION
INTERNATIONAL
STANDARD
colour
inside
Wind turbines energy generation systems –
Part 1: Design requirements
All rights reserved. Unless otherwise specified, 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
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copyright or have an enquiry about obtaining additional rights to this publication, please contact the address below or
your local IEC member National Committee for further information.

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About the IEC
The International Electrotechnical Commission (IEC) is the leading global organization that prepares and publishes
International Standards for all electrical, electronic and related technologies.

About IEC publications
The technical content of IEC publications is kept under constant review by the IEC. Please make sure that you have the
latest edition, a corrigendum or an amendment might have been published.

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committee,…). It also gives information on projects, replaced and French, with equivalent terms in 16 additional languages.
and withdrawn publications. Also known as the International Electrotechnical Vocabulary

(IEV) online.
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Edition 4.0 2019-02
REDLINE VERSION
INTERNATIONAL
STANDARD
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inside
Wind turbines energy generation systems –

Part 1: Design requirements
INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.180 ISBN 978-2-8322-6571-0

– 2 – IEC 61400-1:2019 RLV © IEC 2019
CONTENTS
FOREWORD . 10
INTRODUCTION . 13
1 Scope . 14
2 Normative references . 14
3 Terms and definitions . 16
4 Symbols and abbreviated terms . 25
4.1 Symbols and units. 25
4.2 Abbreviated terms . 28
5 Principal elements . 29
5.1 General . 29
5.2 Design methods . 29
5.3 Safety classes . 29
5.4 Quality assurance . 29
5.5 Wind turbine markings . 29
6 External conditions . 30
6.1 General . 30
6.2 Wind turbine classes . 30
6.3 Wind conditions . 32
6.3.1 General . 32
6.3.2 Normal wind conditions . 34
6.3.3 Extreme wind conditions . 36
6.4 Other environmental conditions . 41
6.4.1 General . 41
6.4.2 Normal other environmental conditions . 42
6.4.3 Extreme other environmental conditions . 42
6.5 Electrical power network conditions . 42
7 Structural design . 43
7.1 General . 43
7.2 Design methodology . 43
7.3 Loads. 43
7.3.1 General . 43
7.3.2 Gravitational and inertial loads . 44
7.3.3 Aerodynamic loads . 44
7.3.4 Actuation loads . 44
7.3.5 Other loads . 44
7.4 Design situations and load cases . 44
7.4.1 General . 44
7.4.2 Power production (DLC 1.1 to 1.5) . 47
7.4.3 Power production plus occurrence of fault or loss of electrical network
connection (DLC 2.1 to 2.4 2.5) . 48
7.4.4 Start-up (DLC 3.1 to 3.3) . 50
7.4.5 Normal shutdown (DLC 4.1 to 4.2) . 50
7.4.6 Emergency shutdown stop (DLC 5.1) . 51
7.4.7 Parked (standstill or idling) (DLC 6.1 to 6.4) . 51
7.4.8 Parked plus fault conditions (DLC 7.1) . 52
7.4.9 Transport, assembly, maintenance and repair (DLC 8.1 and 8.2) . 52

7.5 Load calculations . 53
7.6 Ultimate limit state analysis. 54
7.6.1 Method . 54
7.6.2 Ultimate strength analysis . 56
7.6.3 Fatigue failure . 60
7.6.4 Stability . 61
7.6.5 Critical deflection analysis . 61
7.6.6 Special partial safety factors . 62
8 Control and protection system . 63
8.1 General . 63
8.2 Control functions . 63
8.3 Protection functions . 64
8.4 Control system failure analysis . 65
8.4.1 General . 65
8.4.2 Independence and common-cause failures . 65
8.4.3 Fault exclusions . 66
8.4.4 Failure mode return periods . 66
8.4.5 Systematic failures . 66
8.5 Manual operation . 66
8.6 Emergency stop button function . 66
8.7 Manual, automatic, and remote restart . 67
8.8 Braking system . 68
9 Mechanical systems . 68
9.1 General . 68
9.2 Errors of fitting . 69
9.3 Hydraulic or pneumatic systems . 69
9.4 Main gearbox . 69
9.5 Yaw system . 69
9.6 Pitch system . 70
9.7 Protection function mechanical brakes . 70
9.8 Rolling element bearings . 71
9.8.1 General . 71
9.8.2 Main shaft bearings . 71
9.8.3 Generator bearings . 71
9.8.4 Pitch and yaw bearings . 71
10 Electrical system . 72
10.1 General . 72
10.2 General requirements for the electrical system . 72
10.3 Internal environmental conditions . 72
10.4 Protective devices . 74
10.5 Disconnection devices from supply sources . 74
10.6 Earth system . 74
10.7 Lightning protection . 75
10.8 Electrical cables . 75
10.9 Self-excitation . 75
10.10 Protection against lightning electromagnetic impulse . 76
10.11 Power quality . 76
10.12 Electromagnetic compatibility . 76
10.13 Power electronic converter systems and equipment . 76

– 4 – IEC 61400-1:2019 RLV © IEC 2019
10.14 Twist/drip loop . 76
10.15 Slip rings . 77
10.16 Vertical power transmission conductors and components . 77
10.17 Motor drives and converters . 78
10.18 Electrical machines . 78
10.19 Power transformers . 78
10.20 Low voltage switchgear and controlgear . 78
10.21 High voltage switchgear . 79
10.22 Hubs . 79
11 Assessment of a wind turbine for site-specific conditions . 79
11.1 General . 79
11.2 Assessment of the topographical complexity of the site and its effect on
turbulence . 80
11.2.1 Assessment of the topographical complexity . 80
11.2.2 Assessment of turbulence structure at the site . 83
11.3 Wind conditions required for assessment . 84
11.3.1 General . 84
11.3.2 Wind condition parameters . 84
11.3.3 Measurement setup . 85
11.3.4 Data evaluation . 86
11.4 Assessment of wake effects from neighbouring wind turbines . 87
11.5 Assessment of other environmental conditions . 87
11.6 Assessment of earthquake conditions . 87
11.7 Assessment of electrical network conditions . 88
11.8 Assessment of soil conditions . 89
11.9 Assessment of structural integrity by reference to wind data . 89
11.9.1 General . 89
11.9.2 Assessment of the fatigue load suitability by reference to wind data . 90
11.9.3 Assessment of the ultimate load suitability by reference to wind data . 91
11.10 Assessment of structural integrity by load calculations with reference to site-
specific conditions . 92
12 Assembly, installation and erection . 93
12.1 General . 93
12.2 Planning . 94
12.3 Installation conditions . 94
12.4 Site access . 94
12.5 Environmental conditions . 94
12.6 Documentation . 95
12.7 Receiving, handling and storage . 95
12.8 Foundation/anchor systems . 95
12.9 Assembly of wind turbine . 95
12.10 Erection of wind turbine . 95
12.11 Fasteners and attachments . 95
12.12 Cranes, hoists and lifting equipment . 96
13 Commissioning, operation and maintenance . 96
13.1 General . 96
13.2 Design requirements for safe operation, inspection and maintenance . 96
13.3 Instructions concerning commissioning . 97
13.3.1 General . 97

13.3.2 Energization . 97
13.3.3 Commissioning tests . 97
13.3.4 Records . 97
13.3.5 Post commissioning activities . 97
13.4 Operator’s instruction manual . 98
13.4.1 General . 98
13.4.2 Instructions for operations and maintenance records . 98
13.4.3 Instructions for unscheduled automatic shutdown . 98
13.4.4 Instructions for diminished reliability . 98
13.4.5 Work procedures plan . 98
13.4.6 Emergency procedures plan . 99
13.5 Maintenance manual . 99
14 Cold climate . 100
14.1 General . 100
14.2 Low temperature and icing climate . 100
14.3 External conditions for cold climate . 100
14.3.1 General . 100
14.3.2 Wind turbine class for cold climate. 100
14.4 Structural design . 101
14.5 Design situations and load cases . 101
14.5.1 General . 101
14.5.2 Load calculations . 101
14.5.3 Selection of suitable materials . 102
14.6 Control systems . 102
14.7 Mechanical systems . 102
14.8 Electrical systems . 102
Annex A (normative) Design parameters for external conditions . 103
A.1 Design parameters for describing wind turbine class S. 103
A.1.1 General . 103
A.1.2 Machine parameters . 103
A.1.3 Wind conditions . 103
A.1.4 Electrical network conditions . 103
A.1.5 Other environmental conditions (where taken into account) . 104
A.2 Additional design parameters for describing cold climate wind turbine class
S (CC-S) . 104
Annex B (informative) Design load cases for special class S wind turbine design or
site suitability assessment . 106
B.1 General . 106
B.2 Power production (DLC 1.1 to 1.9) . 106
Annex C (informative) Turbulence models . 110
C.1 General . 110
C.2 Mann [3] uniform shear turbulence model . 110
C.3 Kaimal [1] spectrum and exponential coherence model . 113
C.4 Reference documents . 115
Annex D (informative) Assessment of earthquake loading . 116
D.1 General . 116
D.2 Design response spectrum . 116
D.3 Structure model . 118
D.4 Seismic load evaluation . 118

– 6 – IEC 61400-1:2019 RLV © IEC 2019
D.5 Additional load . 119
D.6 Reference documents . 120
Annex E (informative) Wake and wind farm turbulence . 121
E.1 Wake effects Added wake turbulence method . 121
E.2 Dynamic wake meandering model . 123
E.2.1 General . 123
E.2.2 Wake deficit . 124
E.2.3 Meandering . 125
E.2.4 Wake induced turbulence. 126
E.2.5 Wake superposition . 126
E.2.6 Model synthesis . 127
E.3 Reference documents . 127
Annex F (informative) Prediction of wind distribution for wind turbine sites by measure-
correlate-predict (MCP) methods . 128
F.1 General . 128
F.2 Measure-correlate-predict (MCP) . 128
F.3 Application to annual mean wind speed and distribution . 128
F.4 Application to extreme wind speed . 128
F.5 Reference documents . 129
Annex G (informative)  Statistical extrapolation of loads for ultimate strength analysis . 130
G.1 General . 132
G.2 Data extraction for extrapolation . 133
G.3 Load extrapolation methods . 133
G.3.1 General . 133
G.3.2 Global extremes . 134
G.3.3 Local extremes . 135
G.3.4 Long-term empirical distributions . 136
G.4 Convergence criteria . 136
G.4.1 General . 136
G.4.2 Load fractile estimate . 137
G.4.3 Confidence bounds . 137
G.4.4 Confidence intervals based on bootstrapping . 138
G.4.5 Confidence intervals based on the binomial distribution . 138
G.5 Inverse first-order reliability method (IFORM) . 139
G.6 Reference documents . 141
Annex H (informative) Fatigue analysis using Miner’s rule with load extrapolation . 143
H.1 Fatigue analysis . 143
H.2 Reference documents . 146
Annex I (informative) Contemporaneous loads . 148
I.1 General . 148
I.2 Scaling . 149
I.3 Averaging . 149
Annex J (informative) Prediction of the extreme wind speed of tropical cyclones by

using Monte Carlo simulation method . 150
J.1 General . 150
J.2 Prediction of tropical cyclone induced extreme wind speeds . 150
J.2.1 General . 150
J.2.2 Evaluation of tropical cyclone parameters . 150
J.2.3 Generation of synthetic tropical cyclones . 151

J.2.4 Prediction of wind speeds in the tropical cyclone boundary . 151
J.3 Prediction of extreme wind speed in mixed climate regions . 152
J.3.1 General . 152
J.3.2 Extreme wind distributions of extratropical cyclones by the MCP method . 152
J.3.3 Extreme wind distributions of tropical cyclones by the MCS method. 153
J.3.4 Determination of extreme wind speed in a mixed climate region . 153
J.4 Reference documents . 153
Annex K (informative) Calibration of structural material safety factors and structural
design assisted by testing . 155
K.1 Overview and field of application. 155
K.2 Target reliability level . 155
K.3 Safety formats . 155
K.4 Reliability-based calibration . 157
K.5 Calibration using the design value format . 158
K.6 Partial safety factors for fatigue for welded details in steel structures. 158
K.7 Types of tests for materials . 160
K.8 Planning of tests . 160
K.8.1 General . 160
K.8.2 Objectives and scope . 160
K.8.3 Prediction of test results . 160
K.8.4 Specification of test specimen and sampling . 161
K.8.5 Loading specifications . 161
K.8.6 Testing arrangement . 161
K.8.7 Measurements . 162
K.8.8 Evaluation and reporting the test . 162
K.9 General principles for statistical evaluations . 162
K.10 Derivation of characteristic values. 163
K.11 Statistical determination of characteristic value for a single property . 163
K.12 Statistical determination of characteristic value for resistance models. 164
K.12.1 General . 164
K.12.2 Step 1: Develop a design model . 165
K.12.3 Step 2: Compare experimental and theoretical values . 165
K.12.4 Step 3: Estimate the mean value correction factor (bias) b . 166
K.12.5 Step 4: Estimate the coefficient of variation of the errors . 166
K.12.6 Step 5: Analyse compatibility . 167
K.12.7 Step 6: Determine the coefficients of variation V of the basic variables . 167
Xi
K.12.8 Step 7: Determine the characteristic value r of the resistance . 167
k
K.13 Reference documents . 169
Annex L (informative) Cold climate: assessment and effects of icing climate . 170
L.1 Assessment of icing climate conditions . 170
L.1.1 General . 170
L.1.2 Icing climate . 170
L.1.3 Rotor icing . 171
L.1.4 Measurement methods . 172
L.1.5 Profile coefficients modification for ice . 172
L.2 Ice mass effects on wind turbine blades . 173
L.3 Cold climate design situations and load case . 174
L.3.1 General . 174
L.3.2 Power production (DLC 1.1 to 1.6) . 174

– 8 – IEC 61400-1:2019 RLV © IEC 2019
L.3.3 Parked (standstill or idling) (DLC 6.1 to 6.5) . 174
L.3.4 Parked and fault conditions (DLC 7.1) . 174
L.4 Cold climate load calculations . 174
L.5 Reference documents and bibliography . 175
Annex M (informative) Medium wind turbines . 176
M.1 Overview. 176
M.2 External conditions . 176
M.2.1 General . 176
M.2.2 Wind shear . 176
M.3 Assembly, installation and erection . 176
M.4 Commissioning, operation and maintenance . 177
M.5 Documentation . 178
Bibliography . 180

Figure – Exceedance probability for largest out-of-plane blade bending load in 10 min
(normalized by mean bending load at rated wind speed). .
Figure 1 – Turbulence standard deviation and turbulence intensity for the normal
turbulence model (NTM) . 35
Figure 2 – Example of extreme operating gust . 37
Figure 3 – Example of extreme direction change magnitude . 38
Figure 4 – Example of extreme direction change transient . 38
Figure 5 – Example of extreme coherent gust amplitude for ECD . 39
Figure 6 – Direction change for ECD . 40
Figure 7 – Example of direction change transient . 40
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) . 41
Figure 9 – Example of wind speeds at rotor top and bottom, respectively, which
illustrate the transient positive wind shear . 41
Figure 10 – Examples of 30° sectors for fitting the terrain data . 81
Figure 11 – Terrain variation (∆z) and terrain slope (θ ) . 81
Figure 12 – Possible combinations of normalized mean wind speed and Weibull shape
parameter k (shaded area) . 91
Figure D.1 – Structure model for response spectrum method . 118
Figure E.1 – Configuration – Inside a wind farm with more than 2 rows . 123
Figure E.2 – The three fundamental parts of the DWM model . 124
Figure K.1 – r -r diagram . 166

e t
Figure L.1 – Definition of meteorological icing and rotor icing . 171
Figure L.2 – Representative ice affected rotor area as defined by rotor icing height . 172
Figure L.3 – Iced airfoil lift and drag penalty factors . 173

Table – Terrain complexity indicators .
Table 1 – Basic parameters for wind turbine class . 31
Table 2 – Design load cases (DLC) . 46
Table 3 – Partial safety factors for loads γ . 58
f
Table 4 – Minimum safety factor S and S for the yaw gear system . 70
H,min F,min
Table 5 – Threshold values of the terrain complexity categories L, M and H. 83

Table 6 – Values of lateral and vertical turbulence standard deviations relative to the
longitudinal component depending on terrain complexity category L, M and H . 83
Table 7 – Values of turbulence structure correction parameter depending on terrain

complexity category L, M and H . 84
Table A.1 – Design parameters for describing cold climate wind turbine class S (CC-S) . 105
Table B.1 – Design load cases . 107
Table C.1 – Turbulence spectral parameters for the Kaimal model . 114
Table E.1 – Number (N) of neighbouring wind turbines . 122
Table G.1 – Parameters needed to establish binomial-based confidence intervals . 139
Table G.2 – Short-term load exceedance probabilities as a function of hub-height wind
speed for different wind turbine classes for use with the IFORM procedure . 141
Table I.1 – Extreme loading matrix . 148
Table K.1 – Partial safety factor for model uncertainty, γ . 158
δ
Table K.2 – Recommended values for partial safety factor for fatigue strength, γ . 159
Mf
Table K.3 – Recommended partial safety factor for fatigue stresses, γ . 160
Ff
Table K.4 – Values of k for the 5 % characteristic value . 164

n
Table L.1 – Cold climate design load cases . 174
Table L.2 – Blade ice mass and airfoi
...

IEC 61400-1 ®
Edition 4.1 2025-12
INTERNATIONAL
STANDARD
CONSOLIDATED VERSION
Wind energy generation systems -
Part 1: Design requirements
ICS 27.180 ISBN 978-2-8327-0966-5
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INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
IEC 61400-1
Edition 4.0  2019-02
WIND ENERGY GENERATION SYSTEMS –

Part 1: Design requirements
INTERPRETATION SHEET 1
This interpretation sheet has been prepared by IEC technical committee 88: Wind energy
generation systems.
The text of this interpretation sheet is based on the following documents:
DISH Report on voting
88/1065/DISH 88/1078/RVDISH
Full information on the voting for the approval of this interpretation sheet can be found in the
report on voting indicated in the above table.

___________
Question 1:
Subclause 6.4.2 mentions normal other environmental conditions that shall be taken into
account and, specifically speaking, an ambient temperature range of –10 °C to +40 °C. Does
this mean that the wind turbines shall be designed to operate at rated power up to 40 °C on the
maximum limit, or does it mean that the wind turbine can be designed to operate at any
maximum temperature limit below 40 °C, let's assume 35 °C or 32 °C, etc. ?

Answer 1:
The standard requires that turbines designed to one of the design classes stated in Table 1 in
Subclause 6.2 be capable of operating and generating at temperatures up to +40 °C. There is
no requirement that the turbine shall generate maximum rated power at +40 °C.

ICS 27.180
CONTENTS
FOREWORD. 9
INTRODUCTION . 11
1 Scope . 12
2 Normative references . 12
3 Terms and definitions . 14
4 Symbols and abbreviated terms . 23
4.1 Symbols and units . 23
4.2 Abbreviated terms . 26
5 Principal elements . 27
5.1 General . 27
5.2 Design methods . 27
5.3 Safety classes . 27
5.4 Quality assurance . 28
5.5 Wind turbine markings . 28
6 External conditions . 28
6.1 General . 28
6.2 Wind turbine classes . 29
6.3 Wind conditions. 30
6.3.1 General . 30
6.3.2 Normal wind conditions . 32
6.3.3 Extreme wind conditions. 34
6.4 Other environmental conditions . 40
6.4.1 General . 40
6.4.2 Normal other environmental conditions . 41
6.4.3 Extreme other environmental conditions . 41
6.5 Electrical power network conditions . 41
7 Structural design . 42
7.1 General . 42
7.2 Design methodology . 42
7.3 Loads . 42
7.3.1 General . 42
7.3.2 Gravitational and inertial loads . 43
7.3.3 Aerodynamic loads . 43
7.3.4 Actuation loads . 43
7.3.5 Other loads . 43
7.4 Design situations and load cases . 43
7.4.1 General . 43
7.4.2 Power production (DLC 1.1 to 1.5) . 46
7.4.3 Power production plus occurrence of fault or loss of electrical network
connection (DLC 2.1 to 2.5) . 47
7.4.4 Start-up (DLC 3.1 to 3.3) . 49
7.4.5 Normal shutdown (DLC 4.1 to 4.2) . 49
7.4.6 Emergency stop (DLC 5.1) . 50
7.4.7 Parked (standstill or idling) (DLC 6.1 to 6.4) . 50
7.4.8 Parked plus fault conditions (DLC 7.1) . 51
7.4.9 Transport, assembly, maintenance and repair (DLC 8.1 and 8.2) . 51
7.5 Load calculations . 51
7.6 Ultimate limit state analysis . 52
7.6.1 Method . 52
7.6.2 Ultimate strength analysis . 55
7.6.3 Fatigue failure . 59
7.6.4 Stability . 60
7.6.5 Critical deflection analysis . 60
7.6.6 Special partial safety factors . 61
7.6.7 Evaluation of limit state through load comparison . 61
8 Control system . 63
8.1 General . 63
8.2 Control functions . 63
8.3 Protection functions . 63
8.4 Control system failure analysis . 64
8.4.1 General . 64
8.4.2 Independence and common-cause failures . 64
8.4.3 Fault exclusions . 64
8.4.4 Failure mode return periods . 65
8.4.5 Systematic failures . 65
8.5 Manual operation . 65
8.6 Emergency stop button function . 65
8.7 Manual, automatic, and remote restart . 66
8.8 Braking system . 66
9 Mechanical systems . 67
9.1 General . 67
9.2 Errors of fitting . 67
9.3 Hydraulic or pneumatic systems . 67
9.4 Main gearbox . 68
9.5 Yaw system . 68
9.6 Pitch system . 68
9.7 Protection function mechanical brakes . 69
9.8 Rolling element bearings . 69
9.8.1 General . 69
9.8.2 Main shaft bearings . 69
9.8.3 Generator bearings . 69
9.8.4 Pitch and yaw bearings . 69
10 Electrical system . 69
10.1 General . 69
10.2 General requirements for the electrical system. 70
10.3 Internal environmental conditions . 70
10.4 Protective devices . 71
10.5 Disconnection from supply sources . 71
10.6 Earth system . 72
10.7 Lightning protection . 72
10.8 Electrical cables . 73
10.9 Self-excitation . 73
10.10 Protection against lightning electromagnetic impulse . 73
10.11 Power quality . 73
10.12 Electromagnetic compatibility (EMC) . 73
10.12.1 General . 73
10.12.2 EMC design requirements . 73
10.13 Power electronic converter systems and equipment . 74
10.14 Twist/drip loop . 74
10.15 Slip rings . 74
10.16 Vertical power transmission conductors and components . 75
10.17 Motor drives and converters . 76
10.18 Electrical machines . 76
10.19 Power transformers . 76
10.20 Low voltage switchgear and controlgear . 76
10.21 High voltage switchgear . 77
10.22 Hubs . 77
11 Assessment of a wind turbine for site-specific conditions . 77
11.1 General . 77
11.2 Assessment of the topographical complexity of the site and its effect on
turbulence . 78
11.2.1 Assessment of the topographical complexity . 78
11.2.2 Assessment of turbulence structure at the site . 81
11.3 Wind conditions required for assessment . 82
11.3.1 General . 82
11.3.2 Wind condition parameters . 82
11.3.3 Measurement setup . 84
11.3.4 Data evaluation . 84
11.4 Assessment of wake effects from neighbouring wind turbines . 85
11.5 Assessment of other environmental conditions . 85
11.6 Assessment of earthquake conditions . 85
11.7 Assessment of electrical network conditions . 87
11.8 Assessment of soil conditions . 88
11.9 Assessment of structural integrity by reference to wind data . 88
11.9.1 General . 88
11.9.2 Assessment of the fatigue load suitability by reference to wind data . 88
11.9.3 Assessment of the ultimate load suitability by reference to wind data . 90
11.10 Assessment of structural integrity by load calculations with reference to site-
specific conditions . 91
12 Assembly, installation and erection . 92
12.1 General . 92
12.2 Planning . 93
12.3 Installation conditions . 93
12.4 Site access . 93
12.5 Environmental conditions . 93
12.6 Documentation . 94
12.7 Receiving, handling and storage . 94
12.8 Foundation/anchor systems . 94
12.9 Assembly of wind turbine . 94
12.10 Erection of wind turbine . 94
12.11 Fasteners and attachments . 94
12.12 Cranes, hoists and lifting equipment . 95
13 Commissioning, operation and maintenance . 95
13.1 General . 95
13.2 Design requirements for safe operation, inspection and maintenance . 95
13.3 Instructions concerning commissioning . 96
13.3.1 General . 96
13.3.2 Energization . 96
13.3.3 Commissioning tests . 96
13.3.4 Records . 96
13.3.5 Post commissioning activities . 96
13.4 Operator’s instruction manual . 97
13.4.1 General . 97
13.4.2 Instructions for operations and maintenance records. 97
13.4.3 Instructions for unscheduled automatic shutdown . 97
13.4.4 Instructions for diminished reliability . 97
13.4.5 Work procedures plan . 97
13.4.6 Emergency procedures plan . 98
13.5 Maintenance manual . 98
14 Cold climate . 99
14.1 General . 99
14.2 Low temperature and icing climate . 99
14.3 External conditions for cold climate . 99
14.3.1 General . 99
14.3.2 Wind turbine class for cold climate . 99
14.4 Structural design . 100
14.5 Design situations and load cases . 100
14.5.1 General . 100
14.5.2 Load calculations . 100
14.5.3 Selection of suitable materials . 101
14.6 Control systems . 101
14.7 Mechanical systems . 101
14.8 Electrical systems . 101
Annex A (normative) Design parameters for external conditions . 102
A.1 Design parameters for describing wind turbine class S . 102
A.1.1 General . 102
A.1.2 Machine parameters . 102
A.1.3 Wind conditions . 102
A.1.4 Electrical network conditions . 102
A.1.5 Other environmental conditions (where taken into account) . 103
A.2 Additional design parameters for describing cold climate wind turbine class
S (CC-S) . 103
Annex B (informative) Design load cases for special class S wind turbine design or
site suitability assessment . 105
B.1 General . 105
B.2 Power production (DLC 1.1 to 1.9) . 105
Annex C (informative) Turbulence models . 109
C.1 General . 109
C.2 Mann [3] uniform shear turbulence model . 109
C.3 Kaimal [1] spectrum and exponential coherence model . 112
C.4 Reference documents . 114
Annex D (informative) Assessment of earthquake loading . 115
D.1 General . 115
D.2 Design response spectrum . 115
D.3 Structure model. 116
D.4 Seismic load evaluation . 117
D.5 Additional load . 118
D.6 Reference documents . 119
Annex E (informative) Wake and wind farm turbulence . 120
E.1 Added wake turbulence method . 120
E.2 Dynamic wake meandering model . 123
E.2.1 General . 123
E.2.2 Wake deficit . 124
E.2.3 Meandering . 125
E.2.4 Wake induced turbulence . 126
E.2.5 Wake superposition . 126
E.2.6 Model synthesis . 127
E.3 Reference documents . 127
Annex F (informative) Prediction of wind distribution for wind turbine sites by
measure-correlate-predict (MCP) methods . 128
F.1 General . 128
F.2 Measure-correlate-predict (MCP) . 128
F.3 Application to annual mean wind speed and distribution . 128
F.4 Application to extreme wind speed . 128
F.5 Reference documents . 129
Annex G (informative) Statistical extrapolation of loads for ultimate strength analysis . 130
G.1 General . 130
G.2 Data extraction for extrapolation . 130
G.3 Load extrapolation methods. 131
G.3.1 General . 131
G.3.2 Global extremes . 131
G.3.3 Local extremes . 133
G.3.4 Long-term empirical distributions . 133
G.4 Convergence criteria . 134
G.4.1 General . 134
G.4.2 Load fractile estimate . 134
G.4.3 Confidence bounds . 135
G.4.4 Confidence intervals based on bootstrapping . 135
G.4.5 Confidence intervals based on the binomial distribution . 135
G.5 Inverse first-order reliability method (IFORM) . 136
G.6 Reference documents . 138
Annex H (informative) Fatigue analysis using Miner’s rule with load extrapolation . 140
H.1 Fatigue analysis . 140
H.2 Reference documents . 143
Annex I (informative) Contemporaneous loads . 145
I.1 General . 145
I.2 Scaling . 146
I.3 Averaging . 146
Annex J (informative) Prediction of the extreme wind speed of tropical cyclones by
using Monte Carlo simulation method . 147
J.1 General . 147
J.2 Prediction of tropical cyclone induced extreme wind speeds . 147
J.2.1 General . 147
J.2.2 Evaluation of tropical cyclone parameters . 147
J.2.3 Generation of synthetic tropical cyclones . 148
J.2.4 Prediction of wind speeds in the tropical cyclone boundary . 148
J.3 Prediction of extreme wind speed in mixed climate regions . 149
J.3.1 General . 149
J.3.2 Extreme wind distributions of extratropical cyclones by the MCP method . 149
J.3.3 Extreme wind distributions of tropical cyclones by the MCS method . 150
J.3.4 Determination of extreme wind speed in a mixed climate region . 150
J.4 Reference documents . 150
Annex K (informative) Calibration of structural material safety factors and structural
design assisted by testing . 152
K.1 Overview and field of application . 152
K.2 Target reliability level . 152
K.3 Safety formats . 152
K.4 Reliability-based calibration . 154
K.5 Calibration using the design value format . 155
K.6 Partial safety factors for fatigue for welded details in steel structures . 155
K.7 Types of tests for materials . 157
K.8 Planning of tests . 157
K.8.1 General . 157
K.8.2 Objectives and scope . 157
K.8.3 Prediction of test results . 158
K.8.4 Specification of test specimen and sampling . 158
K.8.5 Loading specifications . 158
K.8.6 Testing arrangement . 159
K.8.7 Measurements . 159
K.8.8 Evaluation and reporting the test . 159
K.9 General principles for statistical evaluations . 159
K.10 Derivation of characteristic values . 160
K.11 Statistical determination of characteristic value for a single property . 160
K.12 Statistical determination of characteristic value for resistance models . 161
K.12.1 General . 161
K.12.2 Step 1: Develop a design model . 162
K.12.3 Step 2: Compare experimental and theoretical values . 162
K.12.4 Step 3: Estimate the mean value correction factor (bias) b . 163
K.12.5 Step 4: Estimate the coefficient of variation of the errors . 163
K.12.6 Step 5: Analyse compatibility . 164
K.12.7 Step 6: Determine the coefficients of variation V of the basic variables . 164
Xi
K.12.8 Step 7: Determine the characteristic value r of the resistance . 165
k
K.13 Reference documents . 166
Annex L (informative) Cold climate: assessment and effects of icing climate . 167
L.1 Assessment of icing climate conditions . 167
L.1.1 General . 167
L.1.2 Icing climate . 167
L.1.3 Rotor icing . 168
L.1.4 Measurement methods . 169
L.1.5 Profile coefficients modification for ice . 169
L.2 Ice mass effects on wind turbine blades . 170
L.3 Cold climate design situations and load case . 171
L.3.1 General . 171
L.3.2 Power production (DLC 1.1 to 1.7) . 171
L.3.3 Parked (standstill or idling) (DLC 6.1 to 6.5) . 172
L.3.4 Parked and fault conditions (DLC 7.1) . 172
L.4 Cold climate load calculations . 172
L.5 Reference documents and bibliography . 173
Annex M (informative) Medium wind turbines . 174
M.1 Overview . 174
M.2 External conditions . 174
M.2.1 General . 174
M.2.2 Wind shear . 174
M.3 Assembly, installation and erection . 174
12.6Documentation . 174
M.4 Commissioning, operation and maintenance . 175
13.1 General . 175
13.2Design requirements for safe operation, inspection and maintenance . 176
M.5 Documentation . 176
Bibliography .178
Figure 1 – Turbulence standard deviation and turbulence intensity for the normal
turbulence model (NTM) . 33
Figure 2 – Example of extreme operating gust . 36
Figure 3 – Example of extreme direction change magnitude . 37
Figure 4 – Example of extreme direction change transient . 37
Figure 5 – Example of extreme coherent gust amplitude for ECD . 38
Figure 6 – Direction change for ECD . 38
Figure 7 – Example of direction change transient. 38
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) . 40
Figure 9 – Example of wind speeds at rotor top and bottom, respectively, which
illustrate the transient positive wind shear . 40
Figure 10 – Examples of 30° sectors for fitting the terrain data . 79
Figure 11 – Terrain variation (∆z) and terrain slope (θ ) . 79
Figure 12 – Possible combinations of normalized mean wind speed and Weibull shape
parameter k (shaded area) . 89
Figure D.1 – Structure model for response spectrum method . 117
Figure E.1 – Configuration – Inside a wind farm with more than 2 rows . 123
Figure E.2 – The three fundamental parts of the DWM model . 123
Figure K.1 – r -r diagram . 163

e t
Figure L.1 – Definition of meteorological icing and rotor icing . 168
Figure L.2 – Representative ice affected rotor area as defined by rotor icing height . 169
Figure L.3 – Iced airfoil lift and drag penalty factors . 170
Table 1 – Basic parameters for wind turbine classes . 29
Table 2 – Design load cases (DLC) . 45
Table 3 – Partial safety factors for loads γ . 57
f
Table 4 – Minimum safety factor S and S for the yaw gear system . 68
H,min F,min
Table 5 – Threshold values of the terrain complexity categories L, M and H . 81
Table 6 – Values of lateral and vertical turbulence standard deviations relative to the
longitudinal component depending on terrain complexity category L, M and H . 81
Table 7 – Values of turbulence structure correction parameter depending on terrain
complexity category L, M and H . 82
Table A.1 – Design parameters for describing cold climate wind turbine class S (CC-S) . 103
Table B.1 – Design load cases . 106
Table C.1 – Turbulence spectral parameters for the Kaimal model . 113
Table E.1 – Number (N) of neighbouring wind turbines .
...

IEC 61400-1 ®
Edition 4.0 2019-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –
Part 1: Design requirements
Systèmes de génération d'énergie éolienne –
Partie 1: Exigences de conception

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IEC 61400-1 ®
Edition 4.0 2019-02
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –

Part 1: Design requirements
Systèmes de génération d'énergie éolienne –

Partie 1: Exigences de conception

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.180 ISBN 978-2-8322-7972-4

– 2 – IEC 61400-1:2019 © IEC 2019
CONTENTS
FOREWORD . 10
INTRODUCTION . 12
1 Scope . 13
2 Normative references . 13
3 Terms and definitions . 15
4 Symbols and abbreviated terms . 23
4.1 Symbols and units. 23
4.2 Abbreviated terms . 26
5 Principal elements . 27
5.1 General . 27
5.2 Design methods . 27
5.3 Safety classes . 27
5.4 Quality assurance . 27
5.5 Wind turbine markings . 28
6 External conditions . 28
6.1 General . 28
6.2 Wind turbine classes . 29
6.3 Wind conditions . 30
6.3.1 General . 30
6.3.2 Normal wind conditions . 31
6.3.3 Extreme wind conditions . 33
6.4 Other environmental conditions . 38
6.4.1 General . 38
6.4.2 Normal other environmental conditions . 39
6.4.3 Extreme other environmental conditions . 39
6.5 Electrical power network conditions . 40
7 Structural design . 40
7.1 General . 40
7.2 Design methodology . 41
7.3 Loads. 41
7.3.1 General . 41
7.3.2 Gravitational and inertial loads . 41
7.3.3 Aerodynamic loads . 41
7.3.4 Actuation loads . 41
7.3.5 Other loads . 42
7.4 Design situations and load cases . 42
7.4.1 General . 42
7.4.2 Power production (DLC 1.1 to 1.5) . 44
7.4.3 Power production plus occurrence of fault or loss of electrical network
connection (DLC 2.1 to 2.5) . 45
7.4.4 Start-up (DLC 3.1 to 3.3) . 47
7.4.5 Normal shutdown (DLC 4.1 to 4.2) . 47
7.4.6 Emergency stop (DLC 5.1) . 48
7.4.7 Parked (standstill or idling) (DLC 6.1 to 6.4) . 48
7.4.8 Parked plus fault conditions (DLC 7.1) . 49
7.4.9 Transport, assembly, maintenance and repair (DLC 8.1 and 8.2) . 49

7.5 Load calculations . 49
7.6 Ultimate limit state analysis. 50
7.6.1 Method . 50
7.6.2 Ultimate strength analysis . 53
7.6.3 Fatigue failure . 56
7.6.4 Stability . 57
7.6.5 Critical deflection analysis . 57
7.6.6 Special partial safety factors . 58
8 Control system . 58
8.1 General . 58
8.2 Control functions . 58
8.3 Protection functions . 59
8.4 Control system failure analysis . 59
8.4.1 General . 59
8.4.2 Independence and common-cause failures . 60
8.4.3 Fault exclusions . 60
8.4.4 Failure mode return periods . 60
8.4.5 Systematic failures . 60
8.5 Manual operation . 60
8.6 Emergency stop button function . 60
8.7 Manual, automatic, and remote restart . 61
8.8 Braking system . 62
9 Mechanical systems . 62
9.1 General . 62
9.2 Errors of fitting . 63
9.3 Hydraulic or pneumatic systems . 63
9.4 Main gearbox . 63
9.5 Yaw system . 63
9.6 Pitch system . 64
9.7 Protection function mechanical brakes . 64
9.8 Rolling element bearings . 64
9.8.1 General . 64
9.8.2 Main shaft bearings . 64
9.8.3 Generator bearings . 64
9.8.4 Pitch and yaw bearings . 65
10 Electrical system . 65
10.1 General . 65
10.2 General requirements for the electrical system . 65
10.3 Internal environmental conditions . 65
10.4 Protective devices . 67
10.5 Disconnection from supply sources . 67
10.6 Earth system . 67
10.7 Lightning protection . 67
10.8 Electrical cables . 68
10.9 Self-excitation . 68
10.10 Protection against lightning electromagnetic impulse . 68
10.11 Power quality . 68
10.12 Electromagnetic compatibility . 69
10.13 Power electronic converter systems and equipment . 69

– 4 – IEC 61400-1:2019 © IEC 2019
10.14 Twist/drip loop . 69
10.15 Slip rings . 69
10.16 Vertical power transmission conductors and components . 70
10.17 Motor drives and converters . 70
10.18 Electrical machines . 71
10.19 Power transformers . 71
10.20 Low voltage switchgear and controlgear . 71
10.21 High voltage switchgear . 71
10.22 Hubs . 72
11 Assessment of a wind turbine for site-specific conditions . 72
11.1 General . 72
11.2 Assessment of the topographical complexity of the site and its effect on
turbulence . 72
11.2.1 Assessment of the topographical complexity . 72
11.2.2 Assessment of turbulence structure at the site . 75
11.3 Wind conditions required for assessment . 76
11.3.1 General . 76
11.3.2 Wind condition parameters . 76
11.3.3 Measurement setup . 77
11.3.4 Data evaluation . 78
11.4 Assessment of wake effects from neighbouring wind turbines . 78
11.5 Assessment of other environmental conditions . 78
11.6 Assessment of earthquake conditions . 79
11.7 Assessment of electrical network conditions . 80
11.8 Assessment of soil conditions . 80
11.9 Assessment of structural integrity by reference to wind data . 80
11.9.1 General . 80
11.9.2 Assessment of the fatigue load suitability by reference to wind data . 80
11.9.3 Assessment of the ultimate load suitability by reference to wind data . 82
11.10 Assessment of structural integrity by load calculations with reference to site-
specific conditions . 82
12 Assembly, installation and erection . 83
12.1 General . 83
12.2 Planning . 84
12.3 Installation conditions . 84
12.4 Site access . 84
12.5 Environmental conditions . 84
12.6 Documentation . 84
12.7 Receiving, handling and storage . 85
12.8 Foundation/anchor systems . 85
12.9 Assembly of wind turbine . 85
12.10 Erection of wind turbine . 85
12.11 Fasteners and attachments . 85
12.12 Cranes, hoists and lifting equipment . 85
13 Commissioning, operation and maintenance . 86
13.1 General . 86
13.2 Design requirements for safe operation, inspection and maintenance . 86
13.3 Instructions concerning commissioning . 87
13.3.1 General . 87

13.3.2 Energization . 87
13.3.3 Commissioning tests . 87
13.3.4 Records . 87
13.3.5 Post commissioning activities . 87
13.4 Operator’s instruction manual . 87
13.4.1 General . 87
13.4.2 Instructions for operations and maintenance records . 88
13.4.3 Instructions for unscheduled automatic shutdown . 88
13.4.4 Instructions for diminished reliability . 88
13.4.5 Work procedures plan . 88
13.4.6 Emergency procedures plan . 89
13.5 Maintenance manual . 89
14 Cold climate . 90
14.1 General . 90
14.2 Low temperature and icing climate . 90
14.3 External conditions for cold climate . 90
14.3.1 General . 90
14.3.2 Wind turbine class for cold climate. 90
14.4 Structural design . 91
14.5 Design situations and load cases . 91
14.5.1 General . 91
14.5.2 Load calculations . 91
14.5.3 Selection of suitable materials . 91
14.6 Control systems . 92
14.7 Mechanical systems . 92
14.8 Electrical systems . 92
Annex A (normative) Design parameters for external conditions . 93
A.1 Design parameters for describing wind turbine class S. 93
A.1.1 General . 93
A.1.2 Machine parameters . 93
A.1.3 Wind conditions . 93
A.1.4 Electrical network conditions . 93
A.1.5 Other environmental conditions (where taken into account) . 94
A.2 Additional design parameters for describing cold climate wind turbine class
S (CC-S) . 94
Annex B (informative) Design load cases for special class S wind turbine design or
site suitability assessment . 96
B.1 General . 96
B.2 Power production (DLC 1.1 to 1.9) . 96
Annex C (informative) Turbulence models . 100
C.1 General . 100
C.2 Mann [3] uniform shear turbulence model . 100
C.3 Kaimal [1] spectrum and exponential coherence model . 103
C.4 Reference documents . 105
Annex D (informative) Assessment of earthquake loading . 106
D.1 General . 106
D.2 Design response spectrum . 106
D.3 Structure model . 107
D.4 Seismic load evaluation . 108

– 6 – IEC 61400-1:2019 © IEC 2019
D.5 Additional load . 109
D.6 Reference documents . 110
Annex E (informative) Wake and wind farm turbulence . 111
E.1 Added wake turbulence method . 111
E.2 Dynamic wake meandering model . 113
E.2.1 General . 113
E.2.2 Wake deficit . 114
E.2.3 Meandering . 115
E.2.4 Wake induced turbulence. 116
E.2.5 Wake superposition . 116
E.2.6 Model synthesis . 117
E.3 Reference documents . 117
Annex F (informative) Prediction of wind distribution for wind turbine sites by
measure-correlate-predict (MCP) methods . 118
F.1 General . 118
F.2 Measure-correlate-predict (MCP) . 118
F.3 Application to annual mean wind speed and distribution . 118
F.4 Application to extreme wind speed . 118
F.5 Reference documents . 119
Annex G (informative) Statistical extrapolation of loads for ultimate strength analysis . 120
G.1 General . 120
G.2 Data extraction for extrapolation . 120
G.3 Load extrapolation methods . 121
G.3.1 General . 121
G.3.2 Global extremes . 121
G.3.3 Local extremes . 123
G.3.4 Long-term empirical distributions . 123
G.4 Convergence criteria . 124
G.4.1 General . 124
G.4.2 Load fractile estimate . 124
G.4.3 Confidence bounds . 125
G.4.4 Confidence intervals based on bootstrapping . 125
G.4.5 Confidence intervals based on the binomial distribution . 125
G.5 Inverse first-order reliability method (IFORM) . 126
G.6 Reference documents . 128
Annex H (informative) Fatigue analysis using Miner’s rule with load extrapolation . 130
H.1 Fatigue analysis . 130
H.2 Reference documents . 133
Annex I (informative) Contemporaneous loads . 135
I.1 General . 135
I.2 Scaling . 136
I.3 Averaging . 136
Annex J (informative) Prediction of the extreme wind speed of tropical cyclones by

using Monte Carlo simulation method . 137
J.1 General . 137
J.2 Prediction of tropical cyclone induced extreme wind speeds . 137
J.2.1 General . 137
J.2.2 Evaluation of tropical cyclone parameters . 137
J.2.3 Generation of synthetic tropical cyclones . 138

J.2.4 Prediction of wind speeds in the tropical cyclone boundary . 138
J.3 Prediction of extreme wind speed in mixed climate regions . 139
J.3.1 General . 139
J.3.2 Extreme wind distributions of extratropical cyclones by the MCP method . 139
J.3.3 Extreme wind distributions of tropical cyclones by the MCS method. 140
J.3.4 Determination of extreme wind speed in a mixed climate region . 140
J.4 Reference documents . 140
Annex K (informative) Calibration of structural material safety factors and structural
design assisted by testing . 142
K.1 Overview and field of application. 142
K.2 Target reliability level . 142
K.3 Safety formats . 142
K.4 Reliability-based calibration . 144
K.5 Calibration using the design value format . 145
K.6 Partial safety factors for fatigue for welded details in steel structures. 145
K.7 Types of tests for materials . 147
K.8 Planning of tests . 147
K.8.1 General . 147
K.8.2 Objectives and scope . 147
K.8.3 Prediction of test results . 147
K.8.4 Specification of test specimen and sampling . 148
K.8.5 Loading specifications . 148
K.8.6 Testing arrangement . 148
K.8.7 Measurements . 149
K.8.8 Evaluation and reporting the test . 149
K.9 General principles for statistical evaluations . 149
K.10 Derivation of characteristic values. 150
K.11 Statistical determination of characteristic value for a single property . 150
K.12 Statistical determination of characteristic value for resistance models. 151
K.12.1 General . 151
K.12.2 Step 1: Develop a design model . 152
K.12.3 Step 2: Compare experimental and theoretical values . 152
K.12.4 Step 3: Estimate the mean value correction factor (bias) b . 153
K.12.5 Step 4: Estimate the coefficient of variation of the errors . 153
K.12.6 Step 5: Analyse compatibility . 154
K.12.7 Step 6: Determine the coefficients of variation V of the basic variables . 154
Xi
K.12.8 Step 7: Determine the characteristic value r of the resistance . 154
k
K.13 Reference documents . 156
Annex L (informative) Cold climate: assessment and effects of icing climate . 157
L.1 Assessment of icing climate conditions . 157
L.1.1 General . 157
L.1.2 Icing climate . 157
L.1.3 Rotor icing . 158
L.1.4 Measurement methods . 159
L.1.5 Profile coefficients modification for ice . 159
L.2 Ice mass effects on wind turbine blades . 160
L.3 Cold climate design situations and load case . 161
L.3.1 General . 161
L.3.2 Power production (DLC 1.1 to 1.6) . 161

– 8 – IEC 61400-1:2019 © IEC 2019
L.3.3 Parked (standstill or idling) (DLC 6.1 to 6.5) . 161
L.3.4 Parked and fault conditions (DLC 7.1) . 161
L.4 Cold climate load calculations . 161
L.5 Reference documents and bibliography . 162
Annex M (informative) Medium wind turbines . 163
M.1 Overview. 163
M.2 External conditions . 163
M.2.1 General . 163
M.2.2 Wind shear . 163
M.3 Assembly, installation and erection . 163
M.4 Commissioning, operation and maintenance . 164
M.5 Documentation . 165
Bibliography . 167

Figure 1 – Turbulence standard deviation and turbulence intensity for the normal
turbulence model (NTM) . 32
Figure 2 – Example of extreme operating gust . 34
Figure 3 – Example of extreme direction change magnitude . 36
Figure 4 – Example of extreme direction change transient . 36
Figure 5 – Example of extreme coherent gust amplitude for ECD . 36
Figure 6 – Direction change for ECD . 37
Figure 7 – Example of direction change transient . 37
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) . 38
Figure 9 – Example of wind speeds at rotor top and bottom, respectively, which

illustrate the transient positive wind shear . 38
Figure 10 – Examples of 30° sectors for fitting the terrain data . 73
Figure 11 – Terrain variation (∆z) and terrain slope (θ ) . 74
Figure 12 – Possible combinations of normalized mean wind speed and Weibull shape
parameter k (shaded area) . 81
Figure D.1 – Structure model for response spectrum method . 108
Figure E.1 – Configuration – Inside a wind farm with more than 2 rows . 113
Figure E.2 – The three fundamental parts of the DWM model . 114
Figure K.1 – r -r diagram . 153

e t
Figure L.1 – Definition of meteorological icing and rotor icing . 158
Figure L.2 – Representative ice affected rotor area as defined by rotor icing height . 159
Figure L.3 – Iced airfoil lift and drag penalty factors . 160

Table 1 – Basic parameters for wind turbine classes . 29
Table 2 – Design load cases (DLC) .
...