EN IEC 61400-3-1:2019

Wind energy generation systems - Part 3-1: Design requirements for fixed offshore wind turbines

This part of IEC 61400 specifies additional requirements for assessment of the external conditions at an offshore wind turbine site and specifies essential design requirements to ensure the engineering integrity of fixed offshore wind turbines. Its purpose is to provide an appropriate level of protection against damage from all hazards during the planned lifetime. This document focuses on the engineering integrity of the structural components of an offshore wind turbine but is also concerned with subsystems such as control and protection mechanisms, internal electrical systems and mechanical systems. A wind turbine shall be considered as a fixed offshore wind turbine if the support structure is subject to hydrodynamic loading and it is founded on the seabed. The design requirements specified in this document are not sufficient to ensure the engineering integrity of floating offshore wind turbines. For floating installations, reference is made to IEC 61400-3-2. In the remainder of this document, the term "offshore wind turbine" is assumed to refer to those that are fixed to the seabed. This document should be used together with the appropriate IEC and ISO standards mentioned in Clause 2. In particular, this document is fully consistent with the requirements of IEC 61400-1. The safety level of the offshore wind turbine designed according to this document shall be at or exceed the level inherent in IEC 61400-1. In some clauses, where a comprehensive statement of requirements aids clarity, replication of text from IEC 61400-1 is included.

Windenergieanlagen - Teil 3-1: Auslegungsanforderungen für gegründete Offshore-Windenergieanlagen

Systèmes de génération d’énergie éolienne - Partie 3-1 : Exigences de conception des éoliennes fixes en pleine mer

l'IEC 61400-3-1:2019 spécifie des exigences complémentaires d'évaluation des conditions externes sur un site d'éoliennes en mer, ainsi que les exigences essentielles de conception, afin d'assurer l'intégrité technique des éoliennes en mer fixes. 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 se concentre sur l'intégrité technique des éléments de structure d'une éolienne en mer, mais concerne également les sous-systèmes, tels que les mécanismes de commande et de protection, les systèmes électriques internes et les systèmes mécaniques. Cette édition annule et remplace la première édition de l'IEC 61400-3 parue en 2009. Cette édition constitue une révision technique. Cette édition inclut les modifications techniques majeures suivantes par rapport à la première édition de l'IEC 61400-3: a) Le tableau des charges de conception a été révisé afin de simplifier l'approche par vagues, à la fois pour plusieurs cas de rafales avec l'état de mer normale et pour de nombreux cas avec l'état de mer extrême. Les recommandations concernant les calculs de charge ont été modifiées en conséquence; b) Pour les facteurs de sécurité de charge, il est désormais fait directement référence à l'IEC 61400-1; c) Le système de commande a été aligné sur les dernières mises à jour de l'IEC 61400-1; d) La première édition consacrée aux spectres d'ondes a été remplacée par une référence à l'ISO 19901-1; e) L'annexe consacrée aux surcharges de glace a été révisée et mise à jour f) Deux annexes informatives concernant les cyclones tropicaux ont été introduites: g) Les autres parties du texte ont été alignées sur l'IEC 61400-1.

Sistemi za proizvodnjo energije na veter - 3-1. del: Zahteve za načrtovanje fiksnih vetrnih turbin na morju (IEC 61400-3-1:2019)

Ta dokument določa dodatne zahteve za ocenjevanje zunanjih pogojev na območju vetrnih turbin na morju in temeljne zahteve za načrtovanje, s katerimi se zagotovi inženirska celovitost fiksnih vetrnih turbin na morju. Njegov namen je zagotoviti ustrezno raven zaščite pred poškodbami zaradi vseh nevarnosti v predvideni življenjski dobi. Ta dokument se osredotoča na inženirsko celovitost sestavnih delov konstrukcije vetrne turbine na morju, obravnava pa tudi podsisteme, kot so nadzorni in zaščitni mehanizmi, notranji električni sistemi ter mehanski sistemi. Vetrno turbino je treba obravnavati kot fiksno vetrno turbino na morju, če je podporna konstrukcija podvržena hidrodinamični obremenitvi in ima temelje na morskem dnu. Zahteve za načrtovanje, ki so določene v tem dokumentu, ne zadostujejo za zagotovitev inženirske celovitosti plavajočih vetrnih turbin na morju. Za plavajoče namestitve je omenjen standard IEC 61400-3-2. V nadaljevanju tega dokumenta se izraz »vetrna turbina na morju« navezuje na vetrne turbine, ki so pritrjene na morsko dno. Ta dokument naj se uporablja skupaj z ustreznimi standardi IEC in ISO, omenjenimi v točki 2. Ta dokument je v celoti skladen z zahtevami iz standarda IEC 61400-1. Varnostna stopnja vetrne turbine na morju, načrtovane v skladu s tem dokumentom, mora biti enaka stopnji iz standarda IEC 61400-1 ali jo presegati. V nekaterih točkah, pri katerih obsežen opis zahtev pripomore k jasnosti, se ponavlja besedilo iz standarda IEC 61400-1.

General Information

• Status: Published
• Publication Date: 19-Sep-2019
• Withdrawal Date: 19-Sep-2022
• ICS: 27.180 - Wind turbine energy systems
• Technical Committee: CLC/TC 88 - Wind turbines
• Drafting Committee: IEC/TC 88 - IEC_TC_88
• Current Stage: 6060 - Document made available - Publishing
• Start Date: 20-Sep-2019
• Completion Date: 20-Sep-2019
• Ref Project: SIST EN IEC 61400-3-1:2019 - Wind energy generation systems - Part 3-1: Design requirements for fixed offshore wind turbines (IEC 61400-3-1:2019)

Relations

• Replaces: EN 61400-3:2009 - Wind turbines - Part 3: Design requirements for offshore wind turbines
• Effective Date: 23-Jan-2023
• Amended By: EN IEC 61400-3-1:2019/A11:2020 - Wind energy generation systems - Part 3-1: Design requirements for fixed offshore wind turbines
• Effective Date: 12-May-2020

Overview

EN IEC 61400-3-1:2019 - "Wind energy generation systems - Part 3‑1: Design requirements for fixed offshore wind turbines" (CLC) sets additional, offshore‑specific design requirements to ensure the engineering integrity of fixed offshore wind turbines founded on the seabed. It complements IEC 61400‑1 and provides requirements for assessing external conditions (metocean, marine and wind), structural design, foundations, control and protection subsystems, electrical and mechanical systems, installation, commissioning and operation to achieve an appropriate level of protection over the planned lifetime. This standard does not apply to floating turbines (see IEC 61400‑3‑2).

Key topics and technical requirements

• External conditions assessment: Metocean database requirements, wind classification, marine conditions, electrical network and soil assessment at the offshore wind turbine site.
• Loads and load cases: Definition of hydrodynamic, aerodynamic, gravitational, inertial, ice and other loads and prescribed design load cases (DLCs) for power production, start/stop, faults, parked conditions, transport/installation and ice scenarios.
• Structural design and analysis: Design methodology, ultimate limit state and fatigue analysis, load and load‑effect calculations, damping assessment and simulation requirements for support structures and substructures.
• Foundations and substructures: Requirements for foundation design, geotechnical assessment and cyclic loading considerations specific to seabed‑founded support structures.
• Subsystem considerations: Design requirements for control systems, mechanical systems, internal electrical systems and protection mechanisms to maintain engineering integrity.
• Assembly, installation and commissioning: Planning, installation conditions, handling, lifting equipment, commissioning tests and documentation for safe erection and start‑up.
• Operation & maintenance: Requirements for safe operation, inspection, maintenance instructions and records to preserve integrity through the turbine’s operational lifetime.

Applications and users

This standard is essential for:

• Offshore wind turbine designers and structural engineers preparing certified designs for seabed‑fixed turbines.
• Project developers and asset owners specifying performance, safety and procurement requirements.
• Certification bodies and regulatory authorities assessing compliance and safety levels.
• Installation contractors, O&M teams and consultants responsible for site assessment, foundation design, erection planning and lifecycle maintenance.
  Practical uses include site suitability assessment, structural analysis, foundation specification, design verification, risk management and documentation for certification.

Related standards

• IEC 61400‑1 (design requirements) - this document is consistent with and supplements IEC 61400‑1.
• IEC 61400‑3‑2 (floating offshore turbines) - for floating systems.
• ISO 19900 / ISO 19901 / ISO 19902 / ISO 19903 (offshore structure and metocean guidance)
• IEC series referenced for electrical, environmental and testing requirements (e.g., IEC 60721, IEC 61400‑13, IEC 61400‑24).

Keywords: EN IEC 61400‑3‑1:2019, offshore wind turbines, fixed offshore wind turbines, design requirements, metocean, hydrodynamic loads, foundation design, structural integrity, IEC 61400.

Standards Content (Sample)

SLOVENSKI STANDARD
01-december-2019
Sistemi za proizvodnjo energije na veter - 3-1. del: Zahteve za načrtovanje fiksnih
vetrnih turbin na morju (IEC 61400-3-1:2019)
Wind energy generation systems - Part 3-1: Design requirements for fixed offshore wind
turbines (IEC 61400-3-1:2019)
Windenergieanlagen - Teil 3-1: Auslegungsanforderungen für Windenergieanlagen auf
offener See (IEC 61400-3-1:2019)
Systèmes de génération d’énergie éolienne - Partie 3-1 : Exigences de conception des
éoliennes fixes en pleine mer (IEC 61400-3-1:2019)
Ta slovenski standard je istoveten z: EN IEC 61400-3-1:2019
ICS:
27.180 Vetrne elektrarne Wind turbine energy systems
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

EUROPEAN STANDARD EN IEC 61400-3-1

NORME EUROPÉENNE
EUROPÄISCHE NORM
September 2019
ICS 27.180
English Version
Wind energy generation systems - Part 3-1: Design
requirements for fixed offshore wind turbines
(IEC 61400-3-1:2019)
Systèmes de génération d’énergie éolienne – Partie 3-1 : Windenergieanlagen - Teil 3-1: Auslegungsanforderungen
Exigences de conception des éoliennes fixes en pleine mer für Windenergieanlagen auf offener See
(IEC 61400-3-1:2019) (IEC 61400-3-1:2019)
This European Standard was approved by CENELEC on 2019-05-10. 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 CEN-CENELEC
Management Centre 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 CEN-CENELEC Management Centre has the
same status as the official versions.
CENELEC members are the national electrotechnical committees of Austria, Belgium, Bulgaria, Croatia, Cyprus, the Czech Republic,
Denmark, Estonia, Finland, Former Yugoslav Republic of Macedonia, France, Germany, Greece, Hungary, Iceland, Ireland, Italy, Latvia,
Lithuania, Luxembourg, Malta, the Netherlands, Norway, Poland, Portugal, Romania, Serbia, Slovakia, Slovenia, Spain, Sweden,
Switzerland, Turkey and the United Kingdom.

European Committee for Electrotechnical Standardization
Comité Européen de Normalisation Electrotechnique
Europäisches Komitee für Elektrotechnische Normung
CEN-CENELEC Management Centre: Rue de la Science 23, B-1040 Brussels
© 2019 CENELEC All rights of exploitation in any form and by any means reserved worldwide for CENELEC Members.
Ref. No. EN IEC 61400-3-1:2019 E

European foreword
The text of document 88/708/FDIS, future edition 1 of IEC 61400-3-1, prepared by IEC/TC 88 "Wind
energy generation systems" was submitted to the IEC-CENELEC parallel vote and approved by
CENELEC as EN IEC 61400-3-1:2019.
The following dates are fixed:
• latest date by which the document has to be implemented at national (dop) 2020-03-20
level by publication of an identical national standard or by endorsement
• latest date by which the national standards conflicting with the (dow) 2022-09-20
document have to be withdrawn
Attention is drawn to the possibility that some of the elements of this document may be the subject of
patent rights. CENELEC shall not be held responsible for identifying any or all such patent rights.
Endorsement notice
The text of the International Standard IEC 61400-3-1:2019 was approved by CENELEC as a
European Standard without any modification.
In the official version, for Bibliography, the following notes have to be added for the standards
indicated:
IEC 60034 (series) NOTE Harmonized as EN 60034-9:2005/A1 (series)
IEC 60038 NOTE Harmonized as EN 60038
IEC 60146 (series) NOTE Harmonized as EN 60146 (series)
IEC 60204-1 NOTE Harmonized as EN 60204-1
IEC 60204-11:2000 NOTE Harmonized as EN 60204-11:2000 (not modified)
IEC 60269 (series) NOTE Harmonized as EN 60269 (series)
IEC 60364 (series) NOTE Harmonized as HD 60364 (series) (modified)
IEC 60439 (series) NOTE Harmonized as EN 60439 (not modified)
IEC 60446:2007 NOTE Harmonized as EN 60446:2007 (not modified)
IEC 60529:1989 NOTE Harmonized as EN 60529:1991 (not modified)
IEC 60755:2008 NOTE Harmonized as EN 60755:—
IEC 60898 NOTE Harmonized as EN IEC 60898 (not modified)
IEC 61000-6-1 NOTE Harmonized as EN IEC 61000-6-1
IEC 61000-6-4 NOTE Harmonized as EN 61000-6-4
IEC 61310-1:2007 NOTE Harmonized as EN 61310-1:2008 (not modified)
IEC 61310-2:2007 NOTE Harmonized as EN 61310-2:2008 (not modified)
IEC 61400-13 NOTE Harmonized as EN 61400-13
IEC 61400-21 NOTE Harmonized as EN 61400-21
IEC 61400-24 NOTE Harmonized as EN 61400-24

Under preparation. Stage at the time of publication: prEN 60755:2016.
Annex ZA
(normative)
Normative references to international publications
with their corresponding European publications
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments)
applies.
NOTE 1  Where an International Publication has been modified by common modifications, indicated by (mod), the relevant
EN/HD applies.
NOTE 2  Up-to-date information on the latest versions of the European Standards listed in this annex is available here:
www.cenelec.eu.
Publication Year Title EN/HD Year
IEC 60721 series Classification of environmental conditions EN IEC 60721 series
IEC 61400-1 2019 Wind energy generation systems - Part 1: EN IEC 61400-1 2019
Design requirements
ISO 2394 1998 General principles on reliability for structures - -
ISO 2533 1975 Standard Atmosphere - -
ISO 19900 2002 Petroleum and natural gas industries - General - -
requirements for offshore structures
ISO 19901-1 2015 Petroleum and natural gas industries - Specific EN ISO 19901-1 2015
requirements for offshore structures - Part 1:
Metocean design and operating conditions
ISO 19901-4 2003 Petroleum and natural gas industries - Specific - -
requirements for offshore structures - Part 4:
Geotechnical and foundation design
considerations
ISO 19902 2007 Petroleum and natural gas industries - Fixed EN ISO 19902 2007
steel offshore structures
ISO 19903 2006 Petroleum and natural gas industries - Fixed EN ISO 19903 2006
concrete offshore structures
IEC 61400-3-1 ®
Edition 1.0 2019-04
INTERNATIONAL
STANDARD
colour
inside
Wind energy generation systems –

Part 3-1: Design requirements for fixed offshore wind turbines

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
ICS 27.180 ISBN 978-2-8322-6600-7

– 2 – IEC 61400-3-1:2019 © IEC 2019
CONTENTS
FOREWORD . 7
INTRODUCTION . 9
1 Scope . 10
2 Normative references . 10
3 Terms and definitions . 11
4 Symbols and abbreviated terms . 19
4.1 Symbols and units. 19
4.2 Abbreviations . 20
5 Principal elements . 21
5.1 General . 21
5.2 Design methods . 21
5.3 Safety classes . 22
5.4 Quality assurance . 22
5.5 Rotor–nacelle assembly markings . 23
6 External conditions – definition and assessment . 23
6.1 General . 23
6.2 Wind turbine classes . 24
6.3 Definition of external conditions at an offshore wind turbine site . 24
6.3.1 General . 24
6.3.2 Wind conditions . 25
6.3.3 Marine conditions . 25
6.3.4 Electrical power network conditions . 32
6.3.5 Other environmental conditions . 32
6.4 Assessment of external conditions at an offshore wind turbine site . 33
6.4.1 General . 33
6.4.2 The metocean database . 33
6.4.3 Assessment of wind conditions . 34
6.4.4 Assessment of marine conditions . 36
6.4.5 Assessment of other environmental conditions . 40
6.4.6 Assessment of electrical network conditions . 41
6.4.7 Assessment of soil 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 . 42
7.3.3 Aerodynamic loads . 43
7.3.4 Actuation loads . 43
7.3.5 Hydrodynamic loads . 43
7.3.6 Sea/lake ice loads . 43
7.3.7 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 1.6) . 50

IEC 61400-3-1:2019 © IEC 2019 − 3 −
7.4.3 Power production plus occurrence of fault or loss of electrical network
connection (DLC 2.1 – 2.5) . 51
7.4.4 Start up (DLC 3.1 to 3.3). 53
7.4.5 Normal shutdown (DLC 4.1 to 4.2) . 54
7.4.6 Emergency stop (DLC 5.1) . 54
7.4.7 Parked (standstill or idling) (DLC 6.1 to 6.4) . 55
7.4.8 Parked plus fault conditions (DLC 7.1 to 7.2) . 56
7.4.9 Transport, assembly, maintenance and repair (DLC 8.1 to 8.4) . 57
7.4.10 Sea/lake ice design load cases . 60
7.5 Load and load effect calculations . 61
7.5.1 General . 61
7.5.2 Relevance of hydrodynamic loads . 61
7.5.3 Calculation of hydrodynamic loads . 62
7.5.4 Calculation of sea/lake ice loads . 62
7.5.5 Overall damping assessment for support structure response evaluations . 62
7.5.6 Simulation requirements . 64
7.5.7 Other requirements . 65
7.6 Ultimate limit state analysis. 66
7.6.1 Method . 66
7.6.2 Ultimate strength analysis . 68
7.6.3 Fatigue failure . 68
7.6.4 Special partial safety factors . 69
7.6.5 Assessment of cyclic loading for foundation assessment . 69
8 Control system . 69
9 Mechanical systems . 70
10 Electrical system . 70
11 Foundation and substructure design . 70
12 Assembly, installation and erection . 71
12.1 General . 71
12.2 Planning . 72
12.3 Installation conditions . 72
12.4 Site access . 72
12.5 Environmental conditions . 73
12.6 Documentation . 73
12.7 Receiving, handling and storage . 73
12.8 Support structure systems . 73
12.9 Assembly of offshore wind turbine . 73
12.10 Erection of offshore wind turbine . 74
12.11 Fasteners and attachments . 74
12.12 Cranes, hoists and lifting equipment . 74
13 Commissioning, operation and maintenance . 74
13.1 General . 74
13.2 Design requirements for safe operation, inspection and maintenance . 75
13.3 Instructions concerning commissioning . 76
13.3.1 General . 76
13.3.2 Energization . 76
13.3.3 Commissioning tests . 76
13.3.4 Records . 76

– 4 – IEC 61400-3-1:2019 © IEC 2019
13.3.5 Post commissioning activities . 76
13.4 Operator’s instruction manual . 76
13.4.1 General . 76
13.4.2 Instructions for operations and maintenance record . 77
13.4.3 Instructions for unscheduled automatic shutdown . 77
13.4.4 Instructions for diminished reliability . 77
13.4.5 Work procedures plan . 77
13.4.6 Emergency procedures plan . 78
13.5 Maintenance manual . 78
Annex A (informative) Key design parameters for an offshore wind turbine . 80
A.1 Offshore wind turbine identifiers . 80
A.1.1 General . 80
A.1.2 Rotor-nacelle assembly (machine) parameters . 80
A.1.3 Support structure parameters . 80
A.1.4 Wind conditions (based on a 10-min reference period and including
wind farm wake effects where relevant) . 80
A.1.5 Marine conditions (based on a 3-hour reference period where relevant) . 81
A.1.6 Electrical network conditions at turbine . 81
A.2 Other environmental conditions . 82
A.3 Limiting conditions for transport, erection and maintenance . 82
Annex B (informative) Shallow water hydrodynamics and breaking waves . 83
B.1 Selection of suitable wave theories . 83
B.2 Modelling of irregular wave trains. 84
B.3 Wave height distributions . 84
B.3.1 General . 84
B.3.2 The Goda model for maximum wave height . 84
B.3.3 The Battjes and Groenendijk wave height distribution . 87
B.3.4 The Forristall wave and crest height distributions . 90
B.4 Breaking waves . 92
B.5 Reference documents . 95
Annex C (informative) Guidance on calculation of hydrodynamic loads . 96
C.1 General . 96
C.2 Morison’s equation . 97
C.3 Diffraction . 98
C.4 Slap and slam loading . 99
C.5 Vortex-induced vibrations. 102
C.5.1 General . 102
C.5.2 Critical velocities for cross-flow motion . 103
C.5.3 Critical velocities for in-line motion . 104
C.6 Appurtenances . 105
C.6.1 General . 105
C.6.2 Alternative method for estimating hydrodynamic coefficients accounting
for appurtenances and marine growth . 105
C.7 Calculation methods . 112
C.7.1 General . 112
C.7.2 Explicit approach . 113
C.7.3 Constrained wave approach. 113
C.8 Reference documents . 113

IEC 61400-3-1:2019 © IEC 2019 − 5 −
Annex D (informative) Recommendations for design of offshore wind turbine support
structures with respect to ice loads . 115
D.1 Introductory remarks . 115
D.2 General . 115
D.3 Choice of ice thickness . 116
D.4 Load cases . 117
D.4.1 General . 117
D.4.2 Horizontal load from fast ice cover originating from temperature
fluctuations (DLC D1) . 117
D.4.3 Horizontal load from fast ice cover originating from water level
fluctuations and arch effect (DLC D2) . 118
D.4.4 Horizontal load from moving ice (DLC D3, D4, D7 and D8) . 118
D.4.5 Vertical load from fast ice cover (DLC D5) . 122
D.4.6 Pressure from ice ridges (DLC D6) . 123
D.4.7 Dynamic loading (DLC D3, D4, D7, and D8). 123
D.5 Requirements on stochastic simulation . 126
D.6 Requirements on model testing . 126
D.7 Reference documents . 127
D.8 Databases for ice conditions . 129
Annex E (informative) Offshore wind turbine foundation and substructure design . 130
Annex F (informative) Statistical extrapolation of operational metocean parameters
for ultimate strength analysis . 131
F.1 General . 131
F.2 Use of IFORM to determine 50-yr significant wave height conditional on
mean wind speed . 131
F.3 Examples of joint distributions of V and H and approximations to the
s
environmental contour . 133
F.4 Choice of sea state duration . 135
F.5 Determination of the extreme individual wave height to be embedded in SSS . 135
F.6 Reference documents . 136
Annex G (informative) Corrosion protection . 137
G.1 General . 137
G.2 The marine environment . 137
G.3 Corrosion protection considerations . 138
G.4 Corrosion protection systems – Support structures . 138
G.5 Corrosion protection in the rotor–nacelle assembly . 139
G.6 Reference documents . 140
Annex H (informative) Prediction of extreme wave heights during tropical cyclones . 141
H.1 General . 141
H.2 Wind field estimation for tropical cyclones . 141
H.3 Wave estimation for tropical cyclones . 142
H.4 Reference documents . 142
H.5 Databases for tropical storms conditions . 143
Annex I (informative) Recommendations for alignment of safety levels in tropical
cyclone regions . 144
I.1 General . 144
I.2 Global robustness level criteria . 144
I.3 Design load cases. 145
Bibliography . 147

– 6 – IEC 61400-3-1:2019 © IEC 2019

Figure 1 – Parts of a fixed offshore wind turbine . 13
Figure 2 – Design process for an offshore wind turbine . 22
Figure 3 – Definition of water levels . 30
Figure 4 – The two approaches to calculate the design load effect . 67
Figure B.1 – Regular wave theory selection diagram . 83
Figure B.2 – Comparison of wave height distribution results . 92
Figure C.1 – Breaking wave and cylinder parameters . 100
Figure C.2 – Oblique inflow parameters . 101
Figure C.3 – Distribution over height of the maximum impact line force (γ = 0°) . 102
Figure C.4 – Response of model and full-scale cylinder in-line and cross-flow . 104
Figure C.5 – Geometrical definition of blocking and shielding . 109
Figure C.6 – Influence of a fixed boundary on the drag coefficient on a circular cylinder
5 6
in oscillatory supercritical flow KC > 20, R = 10 – 2 x 10 . 110
e
Figure C.7 – Shielding factors . 111
Figure C.8 – Recommended value for the added mass coefficient C of a circular
m
cylinder; influence of a fixed boundary . 112
Figure D.1 – Ice force coefficients for plastic limit analysis . 121
Figure D.2 – Ice load history for frequency lock-in conditions . 125
Figure D.3 – Time history of horizontal force component of ice load acting on a conical
structure . 125
Figure F.1 – Example of the construction of the 50-year environmental contour for a 3-
hour sea state duration. . 132

Table 1 – Conversion between extreme wind speeds of different averaging periods . 34
Table 2 – Design load cases . 46
Table 3 – Design load cases for sea/lake ice . 61
Table B.1 – Constants h and h and normalised wave heights h as a function of H . 88
1 2 x % tr
Table B.2 – Breaking wave type . 94
Table I.1 – Additional load cases for tropical cyclone affected regions . 146

IEC 61400-3-1:2019 © IEC 2019 − 7 −
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
WIND ENERGY GENERATION SYSTEMS –

Part 3-1: Design requirements for fixed offshore wind turbines

FOREWORD
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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 61400-3-1 has been prepared by IEC technical committee 88:
Wind energy generation systems.
This edition cancels and replaces the first edition of IEC 61400-3 published in 2009. This
edition constitutes a technical revision.
This edition includes the following significant technical changes with respect to the first
edition of IEC 61400-3:
a) Clause 12 has been merged with Clause 6 in order to acknowledge that the design of the
wind turbine support structure is generally site specific for offshore projects;
b) The design load table has been revised to simplify the approach to waves, both for several
gust cases with the Normal Sea State, and for a number of cases with the Extreme Sea
State. The guidance for load calculations has been altered accordingly;
c) For load safety factors reference is now made directly to IEC 61400-1;
d) Clause 8 on the control system has been aligned with the latest updates in IEC 61400-1;

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e) Annex B to edition one on wave spectra has been replaced by a reference to ISO 19901-1;
f) The annex on ice loading has been revised and updated (now Annex D);
g) Two informative annexes concerning tropical cyclones have been introduced: Annex H on
wave height assessment and Annex I on safety level;
h) Other parts of the text have been aligned with IEC 61400-1.
This part is to be read in conjunction with IEC 61400-1, Wind turbines – Part 1: Design
requirements .
The text of this International Standard is based on the following documents:
FDIS Report on voting
88/708/FDIS 88/712/RVD
Full information on the voting for the approval of this International 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.
A list of all parts of the IEC 61400 series, published under the general title Wind energy
generation systems, can be found on the IEC website.
Future standards in this series will carry the new general title as cited above. Titles of existing
standards in this series will be updated at the time of the next edition.
This document has been drafted in accordance with the ISO/IEC Directives, Part 2.
The committee has decided that the contents of this document will remain unchanged until the
stability date indicated on the IEC website under "http://webstore.iec.ch" in the data related to
the specific document. At this date, the document will be
• reconfirmed,
• withdrawn,
• replaced by a revised edition, or
• amended.
A bilingual version of this publication may be issued at a later date.

IMPORTANT – The 'colour inside' logo on the cover page of this publication indicates
that it contains colours which are considered to be useful for the correct
understanding of its contents. Users should therefore print this document using a
colour printer.
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IEC 61400-3-1:2019 © IEC 2019 − 9 −
INTRODUCTION
This part of IEC 61400 outlines the minimum design requirements for fixed offshore wind
turbines and is not intended for use as a complete design specification or instruction manual.
Several different parties may be responsible for undertaking the various elements of the
design, manufacture, assembly, installation, erection, commissioning, operation and
maintenance of an offshore wind turbine and for ensuring that the requirements of this
document are met. The division of responsibility between these parties is a contractual matter
and is outside the scope of this document.
Any of the requirements of this document may be altered if it can be suitably demonstrated
that the safety of the system is not compromised. Compliance with this document does not
relieve any person, organization, or corporation from the responsibility of observing other
applicable regulations.
The document is not intended to give requirements for floating offshore wind turbines. For
floating installations, reference is made to IEC 61400-3-2.

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WIND ENERGY GENERATION SYSTEMS –

Part 3-1: Design requirements for fixed offshore wind turbines

1 Scope
This part of IEC 61400 specifies additional requirements for assessment of the external
conditions at an offshore wind turbine site and specifies essential design requirements to
ensure the engineering integrity of fixed offshore wind turbines. Its purpose is to provide an
appropriate level of protection against damage from all hazards during the planned lifetime.
This document focuses on the engineering integrity of the structural components of an
offshore wind turbine but is also concerned with subsystems such as control and protection
mechanisms, internal electrical systems and mechanical systems.
A wind turbine shall be considered as a fixed offshore wind turbine if the support structure is
subject to hydrodynamic loading and it is founded on the seabed. The design requirements
specified in this document are not sufficient to ensure the engineering integrity of floating
offshore wind turbines. For floating installations, reference is made to IEC 61400-3-2. In the
remainder of this document, the term “offshore wind turbine” is assumed to refer to those that
are fixed to the seabed.
This document should be used together with the appropriate IEC and ISO standards
mentioned in Clause 2. In particular, this document is fully consistent with the requirements of
IEC 61400-1. The safety level of the offshore wind turbine designed according to this
document shall be at or exceed the level inherent in IEC 61400-1. In some clauses, where a
comprehensive statement of requirements aids clarity, replication of text from IEC 61400-1 is
included.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their
content constitutes requirements of this document. For dated references, only the edition
cited applies. For undated references, the latest edition of the referenced document (including
any amendments) applies.
IEC 60721 (all parts), Classification of environmental conditions
IEC 61400-1:2018, Wind energy generation systems – Part 1: Design requirements
ISO 2394:1998, General principles on reliability for structures
ISO 2533:1975, Standard Atmosphere
ISO 19900:2002, Petroleum and natural gas industries – General requirements for offshore
structures
ISO 19901-1:2015, Petroleum and natural gas industries – Specific requirements for offshore
structures – Part 1: Metocean design and operating conditions
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IEC 61400-3-1:2019 © IEC 2019 − 11 −
ISO 19901-4:2003, Petroleum and natural gas industries – Specific requirements for offshore
structures – Part 4: Geotechnical and foundation design considerations
ISO 19902:2007, Petroleum and natural gas industries – Fixed steel offshore structures
ISO 19903:2006, Petroleum and natural gas industries – Fixed concrete offshore structures
3 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 61400-1 and the
following apply.
ISO and IEC maintain terminological databases for use in standardization at the following
addresses:
• IEC Electropedia: available at http://www.electropedia.org/
• ISO Online browsing
...