IEC 61400-26-1:2019

IEC 61400-26-1 ®
Edition 1.0 2019-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –
Part 26-1: Availability for wind energy generation systems

Systèmes de génération d'énergie éolienne –
Partie 26-1: Disponibilité des systèmes de génération d'énergie éolienne

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IEC 61400-26-1 ®
Edition 1.0 2019-05
INTERNATIONAL
STANDARD
NORME
INTERNATIONALE
colour
inside
Wind energy generation systems –

Part 26-1: Availability for wind energy generation systems

Systèmes de génération d'énergie éolienne –

Partie 26-1: Disponibilité des systèmes de génération d'énergie éolienne

INTERNATIONAL
ELECTROTECHNICAL
COMMISSION
COMMISSION
ELECTROTECHNIQUE
INTERNATIONALE
ICS 27.180 ISBN 978-2-8322-6797-4

– 2 – IEC 61400-26-1:2019 © IEC 2019
CONTENTS
FOREWORD . 8
INTRODUCTION . 10
1 Scope . 12
2 Normative references . 12
3 Terms, definitions and abbreviated terms . 13
3.1 Terms and definitions . 13
3.2 Abbreviated terms . 15
4 Information model . 18
4.1 Basic model . 18
4.2 Information categories . 18
4.3 Information category priority . 19
4.4 Services . 20
4.5 Service delivery layers . 21
4.5.1 General . 21
4.5.2 Time layer . 21
4.5.3 Actual service delivery layer . 21
4.5.4 Potential service delivery layer . 21
4.5.5 Lost service . 22
4.6 Modelling multiple services . 22
4.7 Determination of information categories for the WPS . 24
4.8 Application of the information model to components of the WEGS. 25
5 Information categories . 25
5.1 INFORMATION AVAILABLE . 25
5.2 OPERATIVE . 26
5.3 IN SERVICE . 26
5.3.1 General . 26
5.3.2 FULL PERFORMANCE . 26
5.3.3 PARTIAL PERFORMANCE . 27
5.3.4 READY STANDBY . 27
5.4 OUT OF SERVICE . 28
5.4.1 General . 28
5.4.2 TECHNICAL STANDBY . 28
5.4.3 OUT OF ENVIRONMENTAL SPECIFICATION . 28
5.4.4 REQUESTED SHUTDOWN . 29
5.4.5 OUT OF ELECTRICAL SPECIFICATION . 29
5.5 NON-OPERATIVE . 30
5.5.1 General . 30
5.5.2 SCHEDULED MAINTENANCE . 30
5.5.3 PLANNED CORRECTIVE ACTION . 30
5.5.4 FORCED OUTAGE . 31
5.5.5 SUSPENDED. 31
5.6 FORCE MAJEURE . 32
5.7 INFORMATION UNAVAILABLE . 32
Annex A (informative) Entry and exit conditions overview for WEGS . 33
Annex B (informative) Optional information categories for WEGS information model –
illustrative explanation and examples . 34

B.1 General . 34
B.2 PARTIAL PERFORMANCE – optional categories . 34
B.2.1 Introduction of optional categories . 34
B.2.2 Derated . 34
B.2.3 Degraded. 35
B.3 OUT OF ENVIRONMENTAL SPECIFICATION – optional categories . 36
B.3.1 Introduction of optional categories . 36
B.3.2 Calm winds . 36
B.3.3 Other environmental . 36
B.4 PLANNED CORRECTIVE ACTION – optional categories . 37
B.4.1 Introduction of optional categories . 37
B.4.2 Retrofit . 37
B.4.3 Upgrade . 37
B.4.4 Other planned corrective action . 37
B.5 FORCED OUTAGE – optional category . 38
B.5.1 Introduction of optional categories . 38
B.5.2 Response . 38
B.5.3 Diagnostic . 39
B.5.4 Logistic . 39
B.5.5 Repair . 39
B.6 SUSPENDED – optional categories. 40
B.6.1 Introduction of optional categories . 40
B.6.2 Suspended scheduled maintenance . 40
B.6.3 Suspended planned corrective action . 40
B.6.4 Suspended forced outage . 40
B.7 Considerations of competing assignment of lost service . 41
Annex C (informative) Examples of availability indicators . 42
C.1 General . 42
C.1.1 Introduction to the scope of this annex . 42
C.1.2 Time-based availability . 42
C.1.3 Production-based availability . 42
C.1.4 Mapping of availability and unavailability . 43
C.2 Time-based availability . 43
C.2.1 General . 43
C.2.2 Time-based availability – "operational availability" . 43
C.2.3 Time based availability – "technical availability" . 45
C.3 Production-based availability . 46
C.3.1 General . 46
C.3.2 Production-based availability – "operational availability" . 46
C.3.3 Production-based availability – "technical availability". 47
C.4 Capacity factor and other performance indicators . 48
C.4.1 General . 48
C.4.2 Capacity factor . 49
C.4.3 Production ratio . 49
C.4.4 Mean-value based information . 49
Annex D (informative) Verification scenarios – examples . 50
D.1 General . 50
D.2 Time-based scenarios for a WTGS . 50
D.2.1 Introduction to verification scenarios . 50

– 4 – IEC 61400-26-1:2019 © IEC 2019
D.2.2 Scenario 1 – communication aspects . 51
D.2.3 Scenario 2 – partial operational aspects . 52
D.2.4 Scenario 3 – maintenance aspects . 53
D.2.5 Scenario 4 – operational aspects . 54
D.2.6 Scenario 5 – grid/electrical network aspects . 57
D.2.7 Scenario 6 – environmental aspects . 58
D.3 Production-based scenarios for a WTGS . 60
D.3.1 Introduction to verification scenarios . 60
D.3.2 Scenarios under FULL PERFORMANCE . 60
D.3.3 Scenarios under PARTIAL PERFORMANCE . 62
D.3.4 Scenarios under READY STANDBY . 64
D.3.5 Scenarios under TECHNICAL STANDBY . 65
D.3.6 Scenarios under OUT OF ENVIRONMENTAL SPECIFICATION . 66
D.3.7 Scenarios under REQUESTED SHUTDOWN . 67
D.3.8 Scenarios under OUT OF ELECTRICAL SPECIFICATION . 68
D.3.9 Scenarios under SCHEDULED MAINTENANCE . 69
D.3.10 Scenarios under PLANNED CORRECTIVE ACTION . 69
D.3.11 Scenarios under FORCED OUTAGE . 70
D.3.12 Scenarios under SUSPENDED . 71
D.3.13 Scenarios under FORCE MAJEURE . 72
D.4 Production-based scenarios for a WTGS – calculation of lost production . 72
D.4.1 Introduction to verification scenarios . 72
D.4.2 Production-based availability algorithm based on mandatory information

categories ("operational availability") . 72
D.4.3 Production-based availability algorithm – including optional categories
("technical availability") . 75
D.5 Production-based scenarios for a WPS . 76
D.5.1 Introduction to verification scenarios . 76
D.5.2 Example 1: Normal operation – all WPS . 76
D.5.3 Example 2: Normal operation – part of WPS . 77
D.5.4 Example 3: Contaminated WTGSs blades – all WPS . 78
D.5.5 Example 4: Contaminated WTGSs blades – part of WPS . 79
D.5.6 Example 5: BOP limitations – all WPS . 80
D.5.7 Example 6: BOP limitations – part of WPS . 81
D.5.8 Example 7: "Spinning reserve" – part of WPS . 82
D.5.9 Example 8: "Spinning reserve" – all WPS . 83
D.5.10 Example 9: Noise restrictions – warranty related . 84
D.5.11 Example 10: Noise restrictions – environmentally related . 86
D.5.12 Example 11: Ice storm on grid – all WPS . 87
Annex E (informative) Possible methods for determination of potential WEGS energy
production . 89
E.1 General . 89
E.2 Specific power curve and velocities methods . 89
E.2.1 General . 89
E.2.2 Nacelle anemometer wind measurement with power curve . 89
E.2.3 Upstream wind measurement with power curve . 90
E.2.4 Met mast wind measurement with correction factors and power curve. 90
E.3 Power-based methods . 91
E.3.1 General . 91

E.3.2 Average production of WPS . 91
E.3.3 Average production of representative comparison WTGSs . 92
E.3.4 Data acquisition with comparison chart/database . 93
E.3.5 Average wind speed of WPS . 93
E.4 Determination of potential production for a WPS – examples . 94
E.4.1 Overview . 94
E.4.2 Primary service . 94
E.4.3 Secondary services . 94
Annex F (informative) Balance of plant integration . 96
F.1 WPS functions and services . 96
F.2 Externally required functions and services . 96
F.3 Internally required functions and services . 96
F.4 Expansion of the information model for BOP functions and services . 97
Bibliography . 98

Figure 1 – Data stakeholders for a wind energy generation system . 10
Figure 2 – Information category overview . 19
Figure 3 – Information category priority . 20
Figure 4 – Three-layer information model . 21
Figure 5 – Information categories, definitions for layer 2 and layer 3, mandatory
categories . 23
Figure 6 – Examples of an information model representing active energy, reactive
energy, high and low frequency response services . 24
Figure A.1 – Overview of the entry and exit conditions of all mandatory information
categories described in this document . 33
Figure B.1 – Information category overview – mandatory and optional . 35
Figure B.2 – Workflow breakdown structure . 38
Figure B.3 – Example of simultaneous degrading and derating . 41
Figure E.1 – Step 1: Calculation of wind speed based on working WEGS 1 to n . 93
Figure E.2 – Step 2: Estimation of lost production for WEGS not in FULL
PERFORMANCE . 94

Table C.1 – Example of mapping of available and unavailable information categories . 43
Table D.1 – Verification scenarios – time allocation to information categories . 50
Table D.2 – Verification scenarios – communication aspects . 51
Table D.3 – Verification scenarios – partial operational aspects . 52
Table D.4 – Verification scenarios – maintenance aspects . 53
Table D.5 – Verification scenarios – operational aspects . 54
Table D.6 – Verification scenarios – grid / electrical network aspects . 57
Table D.7 – Verification scenarios – environmental aspects . 58
Table D.8 – FULL PERFORMANCE: By definition, actual energy production is equal to

the potential energy production . 60
Table D.9 – FULL PERFORMANCE: Actual energy production is less than potential
energy production but within agreed uncertainty . 61
Table D.10 – FULL PERFORMANCE: Actual energy production greater than potential
energy production . 61
Table D.11 – PARTIAL PERFORMANCE – derated: Grid constraint . 62

– 6 – IEC 61400-26-1:2019 © IEC 2019
Table D.12 – PARTIAL PERFORMANCE – derated: Grid constraint, actual energy
production less than requested . 62
Table D.13 – Partial performance – derated: Output constraint due to excessive noise

of the WTGS . 63
Table D.14 – PARTIAL PERFORMANCE – derated: Dirt on blades constrained
performance . 63
Table D.15 – PARTIAL PERFORMANCE – derated: Ice accumulated on blades has
been detected, WTGS is allowed to operate although the power performance is
‘derated’ . 64
Table D.16 – PARTIAL PERFORMANCE – degraded: WTGS deterioration known to the
WTGS user . 64
Table D.17 – READY STANDBY: Avian detection system . 64
Table D.18 – READY STANDBY: Automatic generation control – Var support . 65
Table D.19 – TECHNICAL STANDBY: WTGS is cable unwinding . 65
Table D.20 – OUT OF ENVIRONMENTAL SPECIFICATION – calm winds . 66
Table D.21 – OUT OF ENVIRONMENTAL SPECIFICATION – high winds . 66
Table D.22 – OUT OF ENVIRONMENTAL SPECIFICATION – temperature too high . 66
Table D.23 – REQUESTED SHUTDOWN: ice on blades is detected and WTGS user
requests shutdown of the WTGS . 67
Table D.24 – REQUESTED SHUTDOWN: Sector management . 67
Table D.25 – REQUESTED SHUTDOWN: Noise nuisance – warranty claim . 68
Table D.26 – OUT OF ELECTRICAL SPECIFICATION: Low voltage . 68
Table D.27 – SCHEDULED MAINTENANCE: WTGS is under scheduled maintenance
work by the WTGS manufacturer or maintenance provider within the time allowance
agreed by the maintenance contract . 69
Table D.28 – PLANNED CORRECTIVE ACTION: WTGS manufacturer or maintenance
provider performs corrective action to the WTGS at his discretion outside the time

allowance of scheduled maintenance . 69
Table D.29 – FORCED OUTAGE: Short circuit . 70
Table D.30 – FORCED OUTAGE: Corrosion . 70
Table D.31 – FORCED OUTAGE: Overheating . 71
Table D.32 – SUSPENDED: Suspended repair work due to storm with lightning . 71
Table D.33 – FORCE MAJEURE: No access to the WTGS due to flooding impacting
infrastructure . 72
Table D.34 – Production-based availability algorithm based on mandatory information
categories only ,‘operational availability’ . 73
Table D.35 – Production-based availability algorithm – including optional categories,

‘technical availability’ . 75
Table D.36 – Scenario, Example 1: Normal operation – all WPS . 77
Table D.37 – Scenario, Example 2: Normal operation – part of WPS . 78
Table D.38 – Scenario, Example 3: Contaminated WTGSs blades – all WPS . 79
Table D.39 – Scenario, Example 4: Contaminated WTGSs blades – part of WPS . 80
Table D.40 – Scenario, Example 5: BOP limitations – all WPS . 81
Table D.41 – Scenario, Example 6: BOP limitations – part of WPS . 82
Table D.42 – Scenario, Example 8: ‘Spinning reserve’ – part of WPS . 83
Table D.43 – Scenario, Example 7: ‘Spinning reserve’ – all WPS . 84
Table D.44 – Scenario, Example 9: Noise restrictions – all WPS . 85

Table D.45 – Scenario, Example 10: Noise restrictions – all WPS . 86
Table D.46 – Scenario, Example 11: Ice storm on grid – all WPS . 87
Table E.1 – Examples on how to determine potential production . 95

– 8 – IEC 61400-26-1:2019 © IEC 2019
INTERNATIONAL ELECTROTECHNICAL COMMISSION
____________
WIND ENERGY GENERATION SYSTEMS –

Part 26-1: Availability for wind energy generation systems

FOREWORD
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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 61400-26-1 has been prepared by IEC technical committee 88:
Wind energy generation systems.
This first edition cancels and replaces IEC TS 61400-26-1:2011, IEC TS 61400-26-2:2014 and
IEC TS 61400-26-3:2016.
The text of this International Standard is based on the following documents:
CDV Report on voting
88/665/CDV 88/705/RVC
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, 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.
Mandatory information categories defined in this document are written in capital letters;
optional information categories are written in bold letters.
The committee has decided that the contents of this publication will remain unchanged until
the stability date indicated on the IEC website 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.
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.
– 10 – IEC 61400-26-1:2019 © IEC 2019
INTRODUCTION
The intention of this International Standard is to define a common basis for exchange of
information on availability metrics between stakeholders in the wind power generation
business such as owners, utilities, lenders, operators, manufacturers, maintenance providers,
consultants, regulatory bodies, certification bodies and insurance companies. From this
diverse group of stakeholders, a number of external and internal interfaces arise in the
operation and delivery of power. Some of these are energy related and many are
informational. Since the intention is for a common basis of informational exchange, many of
these interfaces are illustrated in Figure 1, which identifies external and internal elements
related to energy production and asset management and which also benefit from a defined set
of terms. This is achieved by providing an information model specifying how time designations
shall be split into information categories.

Figure 1 – Data stakeholders for a wind energy generation system
Throughout the document, reference is made to wind energy generation systems (WEGS);
however, the document may be used for a single wind turbine (WTGS), as well as for any
number of WTGSs combined with additional components to represent a complete wind power
station (WPS). The designation WEGS used throughout the document thus shall be
understood as the specifications being applicable to individual wind turbines as well as for
wind power stations.
The information model specifies the terminology for reporting availability indicators.
Availability indicators include time-based and production-based availability. A WEGS includes
all equipment up to the point of interconnection , or in case of a single WTGS in a WPS, the
interconnection point defined by the user. Availability indicators are based upon fractions of
time and the amount a service is providing or capable of providing within the time fractions,
taking internal and external aspects into account. Internal aspects will include the WEGS’
components and their condition. External aspects are wind and other weather conditions, as
well as grid and substation conditions.

___________
Defined in IEC 60050-415:1999, Definition 415-04-01.

– 12 – IEC 61400-26-1:2019 © IEC 2019
WIND ENERGY GENERATION SYSTEMS –

Part 26-1: Availability for wind energy generation systems

1 Scope
This part of IEC 61400 defines an information model from which time-based, and production-
based availability indicators for services can be derived and reported.
The purpose is to provide standardised metrics that can be used to create and organise
methods for availability calculation and reporting according to the user’s needs.
The document provides information categories, which unambiguously describe how data is
used to characterise and categorise the operation. The information model specifies category
priority for discrimination between possible concurrent categories. Further, the model defines
entry and exit criteria to allocate fractions of time and production values to the proper
information category. A full overview of all information categories, exit and entry criteria is
given in Annex A, see Figure A.1.
The document can be applied to any number of WTGSs, whether represented by an individual
turbine, a fleet of wind turbines, a wind power station or a portfolio of wind power stations. A
wind power station is typically made up of all WTGSs, functional services and balance of plant
elements as seen from the point of common coupling.
Examples are provided in informative annexes which provide guidelines for calculation of
availability indicators:
• examples of optional information categories, Annex B;
• examples of application of the information categories for determination of availability,
Annex C;
• examples of application scenarios, Annex D;
• examples on methods for determination of potential production, Annex E;
• examples of how to expand the model to balance of plant elements, Annex F.
This document does not prescribe how availability indicators shall be calculated. The standard
does not specify the method of information acquisition, how to estimate the production terms
or to form the basis for power curve performance measurements – which is the objective of
IEC 61400-12.
A degree of uncertainty is inherent in both the measurement of a power curve and the
calculation of potential energy production. The stakeholders should agree upon acceptable
uncertainty parameters.
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 60050-415, International Electrotechnical Vocabulary – Part 415: Wind turbine generator
systems
IEC 61400-1, Wind energy generation systems – Part 1: Design requirements
3 Terms, definitions and abbreviated terms
3.1 Terms and definitions
For the purposes of this document, the terms and definitions given in IEC 60050-415 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 platform: available at http://www.iso.org/obp
3.1.1
actual service delivery
quantified level of a service provided by the WEGS as measured
Note 1 to entry: Actual service delivery can only be assigned to measurable services.
3.1.2
balance of plant
BOP
infrastructural components of the WPS except for the WTGS(s) and its internal components
and subsystems
Note 1 to entry: The infrastructure normally consists of site electrical facilities, monitoring and control (often
called SCADA) as well as civil plant (such as foundations and roads) supporting the operation and maintenance of
the WTGS(s).
3.1.3
constrained potential service delivery
calculated level of a service that could have been provided by the WEGS based on operating
specifications such as external set-points or contractually imposed constraints combined with
design criteria, technical specifications and site conditions
3.1.4
design specifications
the collection of precise and expli
...