IEC 61400-3:2009

Wind turbines - Part 3: Design requirements for offshore wind turbines

IEC 61400-3:2009 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 offshore wind turbines. Its purpose is to provide an appropriate level of protection against damage from all hazards during the planned lifetime. 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. It should be used together with the appropriate IEC and ISO standards, in particular with IEC 61400-1.
This publication is to be read in conjunction with IEC 61400-1:2005.
This publication is of high relevance for Smart Grid.

Eoliennes - Partie 3: Exigences de conception des éoliennes en pleine mer

La CEI 61400-3:2009 spécifie des exigences complémentaires d'évaluation des conditions externes sur un site d'éoliennes en pleine mer ainsi que les exigences essentielles de conception, afin d'assurer l'intégrité technique de ces dernières. Elle a pour objet de fournir un niveau de protection approprié contre les dommages causés par tous les risques pendant la durée de vie prévue. Se focalise sur l'intégrité technique des composants structurels d'une éolienne en pleine mer, mais concerne également les sous-systèmes, tels que les mécanismes de commande et de protection, les systèmes électriques internes et les systèmes mécaniques. Il convient d'utiliser la présente norme avec les normes CEI et ISO appropriées, en particulier avec la CEI 61400-1.
Cette publication doit être lue conjointement avec la CE I 61400-1:2005.

General Information

• Status: Replaced
• Publication Date: 10-Feb-2009
• ICS: 27.180 - Wind turbine energy systems
• Technical Committee: TC 88 - Wind energy generation systems
• Drafting Committee: WG 3 - TC 88/WG 3
• Current Stage: DELPUB - Deleted Publication
• Completion Date: 05-Apr-2019

Relations

• Replaced By: IEC 61400-3-1:2019 - Wind energy generation systems - Part 3-1: Design requirements for fixed offshore wind turbines
• Effective Date: 05-Sep-2023

Standards Content (Sample)

IEC 61400-3


®

Edition 1.0 2009-02



INTERNATIONAL



STANDARD



NORME
INTERNATIONALE


Wind turbines –
Part 3: Design requirements for offshore wind turbines

Eoliennes –
Partie 3: Exigences de conception des éoliennes en pleine mer


IEC 61400-3:2009

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IEC 61400-3


®

Edition 1.0 2009-02



INTERNATIONAL



STANDARD



NORME
INTERNATIONALE


Wind turbines –
Part 3: Design requirements for offshore wind turbines

Eoliennes –
Partie 3: Exigences de conception des éoliennes en pleine mer


INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
PRICE CODE
INTERNATIONALE
XF
CODE PRIX
ICS 27.180 ISBN 978-2-88910-514-4
® Registered trademark of the International Electrotechnical Commission
Marque déposée de la Commission Electrotechnique Internationale

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CONTENTS

FOREWORD.5


INTRODUCTION.7

1 Scope.8

2 Normative references.8


3 Terms and definitions .9

4 Symbols and abbreviated terms .15

4.1 Symbols and units .15
4.2 Abbreviations.16
5 Principal elements .17
5.1 General .17
5.2 Design methods.17
5.3 Safety classes .19
5.4 Quality assurance.19
5.5 Rotor – nacelle assembly markings.20
6 External conditions .20
6.1 General .20
6.2 Wind turbine classes .21
6.3 Wind conditions .21
6.4 Marine conditions .22
6.5 Other environmental conditions.31
6.6 Electrical power network conditions.32
7 Structural design.33
7.1 General .33
7.2 Design methodology .33
7.3 Loads .33
7.4 Design situations and load cases .34
7.5 Load and load effect calculations .51
7.6 Ultimate limit state analysis.54
8 Control and protection system.57
9 Mechanical systems.57
10 Electrical system.58

11 Foundation design .58
12 Assessment of the external conditions at an offshore wind turbine site .59
12.1 General .59
12.2 The metocean database.59
12.3 Assessment of wind conditions.60
12.4 Assessment of waves .62
12.5 Assessment of currents.63
12.6 Assessment of water level, tides and storm surges.63
12.7 Assessment of sea ice .63
12.8 Assessment of marine growth .64
12.9 Assessment of seabed movement and scour.64
12.10 Assessment of wake effects from neighbouring wind turbines.65
12.11 Assessment of other environmental conditions .65

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61400-3 © IEC:2009 − 3 −


12.12 Assessment of earthquake conditions .65

12.13 Assessment of weather windows and weather downtime.65

12.14 Assessment of electrical network conditions.65

12.15 Assessment of soil conditions .66

13 Assembly, installation and erection .67

13.1 General .67

13.2 Planning .68

13.3 Installation conditions.68

13.4 Site access .68

13.5 Environmental conditions .68
13.6 Documentation.69
13.7 Receiving, handling and storage.69
13.8 Foundation/anchor systems.69
13.9 Assembly of offshore wind turbine.69
13.10 Erection of offshore wind turbine .69
13.11 Fasteners and attachments .69
13.12 Cranes, hoists and lifting equipment.70
14 Commissioning, operation and maintenance .70
14.1 General .70
14.2 Design requirements for safe operation, inspection and maintenance .70
14.3 Instructions concerning commissioning .71
14.4 Operator’s instruction manual .72
14.5 Maintenance manual.74
Annex A (informative) Key design parameters for an offshore wind turbine.76
Annex B (informative) Wave spectrum formulations.79
Annex C (informative) Shallow water hydrodynamics and breaking waves .84
Annex D (informative) Guidance on calculation of hydrodynamic loads.92
Annex E (informative) Recommendations for design of offshore wind turbine support
structures with respect to ice loads. 105
Annex F (informative) Offshore wind turbine foundation design. 116
Annex G (informative) Statistical extrapolation of operational metocean parameters for
ultimate strength analysis. 117
Annex H (informative) Corrosion protection . 123

Bibliography . 127

Figure 1 – Parts of an offshore wind turbine.10
Figure 2 – Design process for an offshore wind turbine.19
Figure 3 – Definition of water levels.29
Figure 4 – The two approaches to calculate the design load effect.55
Figure B.1 – PM spectrum .80
Figure B.2 – Jonswap and PM spectrums for typical North Sea storm sea state .81
Figure C.1 – Regular wave theory selection diagram.84
Figure D.1 – Breaking wave and cylinder parameters.96
Figure D.2 – Oblique inflow parameters .96
Figure D.3 – Distribution over height of the maximum impact line force (γ = 0°) .98

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Figure D.4 – Response of model and full-scale cylinder in-line and cross-flow (from

reference document 4) .100

Figure E.1 – Ice force coefficients for plastic limit analysis (from reference document 6) . 110


Figure E.2 – Serrated load profile (T = 1/f or 1/f ) . 113
0,1 N b

Figure G.1 – Example of the construction of the 50-year environmental contour for a 3-hour

sea state duration. . 118




Table 1 – Design load cases .36

Table 2 – Design load cases for sea ice .50

Table 3 – Partial safety factors for loads γ .56
f
Table 4 – Conversion between extreme wind speeds of different averaging periods .61
Table C.1 – Constants h and h and normalised wave heights h as a function of H .87
1 2 x% tr
Table C.2 – Breaking wave type .90

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61400-3 © IEC:2009 − 5 −


INTERNATIONAL ELECTROTECHNICAL COMMISSION

____________



WIND TURBINES –



Part 3: Design requirements for offshore wind turbines





FOREWORD


1) The International Electrotechnical Commission (IEC) is a worldwide organization for standardization comprising
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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 has been prepared by IEC technical committee 88: Wind
turbines.
This part is to be read in conjunction with IEC 61400-1:2005, Wind turbines – Part 1: Design
requirements.
The text of this standard is based on the following documents:
FDIS Report on voting
88/329/FDIS 88/338/RVD

Full information on the voting for the approval of this standard can be found in the report on
voting indicated in the above table.

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This publication has been drafted in accordance with the ISO/IEC Directives, Part 2.


A list of all parts of IEC 61400 series, published under the general title Wind turbines, can be

found on the IEC website.


The committee has decided that the contents of this publication will remain unchanged until the

maintenance result date indicated on the IEC web site under "http://webstore.iec.ch" in the data

related to the specific publication. At this date, the publication will be


• reconfirmed,

• withdrawn,

• replaced by a revised edition, or
• amended.

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61400-3 © IEC:2009 − 7 −


INTRODUCTION


This part of IEC 61400 outlines minimum design requirements for 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

standard are met. The division of responsibility between these parties is a contractual matter

and is outside the scope of this standard.


Any of the requirements of this standard may be altered if it can be suitably demonstrated that
the safety of the system is not compromised. Compliance with this standard does not relieve
any person, organization, or corporation from the responsibility of observing other applicable
regulations.

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WIND TURBINES –



Part 3: Design requirements for 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 it specifies essential design requirements to
ensure the engineering integrity of offshore wind turbines. Its purpose is to provide an
appropriate level of protection against damage from all hazards during the planned lifetime.
This standard 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 an offshore wind turbine if the support structure is
subject to hydrodynamic loading. The design requirements specified in this standard are not
necessarily sufficient to ensure the engineering integrity of floating offshore wind turbines.
This standard should be used together with the appropriate IEC and ISO standards mentioned
in Clause 2. In particular, this standard is fully consistent with the requirements of IEC 61400-
1. The safety level of the offshore wind turbine designed according to this standard 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 referenced documents are indispensable for the application of this document. For
dated references, only the edition cited applies. For undated references, the latest edition of
the referenced document (including any amendments) applies.
IEC 60721-2-1:1982, Classification of environmental conditions – Part 2-1: Environmental
conditions appearing in nature. Temperature and humidity
Amendment 1:1987
IEC 61400-1:2005, Wind turbines – Part 1: Design requirements

IEC 62305-3:2006, Protection against lightning – Part 3: Physical damage to structures and life
hazard
IEC 62305-4:2006, Protection against lightning – Part 4: Electrical and electronic systems
within structures
ISO 2394:1998, General principles on reliability for structures
ISO 2533:1975, Standard Atmosphere
ISO 9001:2000, Quality management systems – Requirements
ISO 19900:2002, Petroleum and natural gas industries – General requirements for offshore
structures

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61400-3 © IEC:2009 − 9 −


ISO 19901-1:2005, Petroleum and natural gas industries – Specific 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, 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 following terms and definitions apply in addition to
those stated in IEC 61400-1.
3.1
co-directional (wind and waves)
acting in the same direction
3.2
current
flow of water past a fixed location usually described in terms of a current speed and direction
3.3
design wave
deterministic wave with a defined height, period and direction, used for the design of an
offshore structure. A design wave may be accompanied by a requirement for the use of a
particular periodic wave theory
3.4
designer
party or parties responsible for the design of an offshore wind turbine
3.5
environmental conditions
characteristics of the environment (wind, waves, sea currents, water level, sea ice, marine
growth, scour and overall seabed movement, etc.) which may affect the wind turbine behaviour
3.6

external conditions (wind turbines)
factors affecting operation of an offshore wind turbine, including the environmental conditions,
the electrical network conditions, and other climatic factors (temperature, snow, ice, etc.)
3.7
extreme significant wave height
expected value of the highest significant wave height, averaged over 3 h, with an annual
probability of exceedance of 1/N (“recurrence period”: N years)
3.8
extreme wave height
expected value of the highest individual wave height (generally the zero up-crossing wave
height) with an annual probability of exceedance of 1/N (“recurrence period”: N years)

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3.9

fast ice cover

rigid continuous cover of ice not in motion


3.10

fetch

distance over which the wind blows constantly over the sea with approximately constant wind

speed and direction


3.11

foundation

part of an offshore wind turbine support structure which transfers the loads acting on the
structure into the seabed. Different foundation concepts are shown in Figure 1 together with
the other parts of an offshore wind turbine
Rotor-nacelle assembly
Tower
Tower
Support
Platform
structure
Water level
Sub-structure
Sub-structure
Pile
Sea floor
Pile
Seabed

Foundation
IEC  001/09

Figure 1 – Parts of an offshore wind turbine
3.12
highest astronomical tide
highest still water level that can be expected to occur under any combination of astronomical
conditions and under average meteorological conditions. Storm surges, which are
meteorologically generated and essentially irregular, are superimposed on the tidal variations,
so that a total still water level above highest astronomical tide may occur

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61400-3 © IEC:2009 − 11 −


3.13

hindcasting

method of simulating historical (metocean) data for a region through numerical modelling


3.14

hub height (wind turbines)

height of the centre of the swept area of the wind turbine rotor above the mean sea level


3.15

hummocked ice

crushed ice and ice floes piled up into ridges when large ice floes meet with each other or with

a rigid obstacle, for example an offshore wind turbine support structure
3.16
ice floe
sheet of ice in size from metres to several kilometres, not rigidly frozen to a shore, still or in
motion
3.17
icing
build-up of a cover of ice or frost on parts of an offshore wind turbine that can result in added
loads and/or changed properties
3.18
land-locked waters
waters almost or entirely surrounded by land
3.19
load effect
effect of a single load or combination of loads on a structural component or system, for
example internal force, stress, strain, motion, etc.
3.20
lowest astronomical tide
low
...