from national approval scheme to international certification scheme

FROM NATIONAL APPROVAL SCHEME TO INTERNATIONAL
CERTIFICATION SCHEME
Erik R. Jørgensen, erik.r.joergensen@risoe.dk
Jørgen Lemming, joergen.lemming@risoe.dk
Risø National Laboratory
Summary
In Denmark approval of wind turbines has been performed since 1979. In January 2005 a certification scheme was
introduced based on IEC WT01. The purpose of the new certification scheme was to have a Danish certification
system based on international standards and to include both type certification and project certification. Special Danish
requirements has been identified and added to rules as described in WT01. The new scheme as well as the Danish
addenda to the international certification scheme is presented.
Certification in Denmark
In 1979 a System Approval of wind turbines were introduced as a requirement for receiving subsidy for a wind
turbine project.
In the beginning the approvals were carried out by wind turbine experts from Risø and based on an evaluation on the
overall safety and power performance of the wind turbine. In 1991 a formal Type Approval system [1] including
certification of QA systems was established a legal requirement for installation of wind turbines and from 2000 other
institutions like “Det Norske Veritas (DNV)” and “Germanisher Lloyd (GL)” also were recognized by the Danish
Energy Authority as approving and certification bodies.
Until 2005 approval and certification of wind turbines has been carried out according to “Technical Criteria for the
Danish Approval Scheme for Wind Turbines” [2] and the loads and safety according to Danish standard “DS472” [3].
The new certification scheme is legally described in the new executive order no. 1268 [4] and based on the
international certification standard “IEC WT 01” [5] and the load and safety standard “IEC 61400-1” [6] and “IEC
61400-2” [7].
Background for new certification scheme
Certification of a wind turbine is now done in many countries and the need of common set of rules is increasing. In
Denmark offshore projects were also not addressed in the old certification scheme and some procedures for
specifying loads and load cases were not up to date.
Arguments for a new scheme:
• Certification is no longer a national business. A certification scheme based on international standards gives
worldwide acceptance
• An international procedures for certification of Wind Turbines has been developed (IEC WT01)
• Some procedures and requirements in the old system did not meet the challenges from the new MW
turbines
• Offshore installations were not included in the old system
• Project certification was not part of the old scheme
Therefore the new certification scheme was set up and based on the international scheme as described in IEC WT 01
[5].
Internationalization of the Danish certification scheme
Working groups under Danish Energy Authority compared the old Danish certification scheme [2] with the “IEC WT
01” [5] and the standards connected to two like standards for loads and safety [3], [6] and [7] to ensure same safety
level and quality as previously.

This work pointed out some important differences to be taken into account as special Danish supplements to the
international standards.
Some of the supplements which have been included:
• Three categories of type approval (A, B and C)
• Danish external conditions
• Aerodynamic acting braking system
• Normal safety class. Main components as component class 2 as minimum
• Blade reflection should be specified according to DS/ISO 2813
• CE marking
• Lightning protection specified according to DS/IEC/TR 61400-24
• Electrical installations according to executive order on “High Voltage” 204-1/EN60204-1
• Electrical impact on power network according to TF3.2.5 or TF 3.2.6
• Power curve according to DS/EN61400/12
• Blade test (static and fatigue). DS/IEC/TS 61400-23
• Manufacturing Evaluation. Certified quality system for construction / manufacturing of WTGs
• Foundation design evaluation
• Power quality measurements
• Acoustic noise measurements
• User manual in Danish
• Installation manual in Danish
The three categories of certification A, B and C is seen as necessary in a new scheme, covering fully developed
wind turbines as well as wind turbines under development (prototypes).
The Danish external conditions are of course essential. As an example a comparison of the roughness classes [3],
which normally are used to classify wind in Denmark showed a relationship between these classes and the IEC
wind turbine classes (I to IV) and IEC turbulence intensity classes (A and B) as specified in Table 1.
Table 1. Relationship between roughness classes and the IEC wind turbine classes (I to IV) and IEC turbulence
intensity classes (A and B). Example: A wind turbine located less than 25 km from the North Sea, with a hub height of
100m, at a site classified as roughness class 0, requires an IEC wind turbine class 1 with turbulence class B.
Local installation
at
Hub Height h
(m)
< 25 km from the
North Sea
> 25 km from the
North Sea
DS roughness class versus IEC wind turbine class and turbulence class
DS roughness class 0 DS roughness class I DS roughness class II
h50 h80 h130
IEC 2B IEC 1B IEC 2B IEC 1B IEC 2A IEC 2B
IEC 2B IEC 2B IEC 3B IEC 2B IEC 3A IEC 2B
Ocean IEC 1B IEC 1B
Aerodynamically acting brakes has always been mandatory in Denmark and this principle is also transferred to
the new scheme as an essential principle in the safety system of the wind turbine.
Evaluation of the foundation design for a “standard foundation” was a mandatory element previously and so also
in the new scheme.

Type certification according to the new scheme is based on the requirements in WT 01, chapter 12 and the safety
standards DS/EN 61400-1 and DS/EN 61400-2.
The three certification classes are defined. A type certification class C is a certification of the safety related issues
only and is meant for prototype wind turbines, The validity is up to three years where after is has to be taken down or
re-certified. Quality and energy conditions are not verified. Certification class A and B is for a type certification
according to IEC WT01 with the Danish addenda, but for a type B it is allowed that some minor issues, not related to
the safety of the wind turbine, is not documented at the date of issue of the certificate, but has to be documented in a
given period there after. The validity of a class A is up to five years and for class B is up to one year. It is the
intention that a class B certification passes into a class A certification, when the validity expires.
The Danish certification scheme based on IEC WT01 and the Danish addenda, gives a scheme shown in the figure
below.
The Danish Technical Certification
Scheme for Design, Manufacture
and Installation of Wind Turbines
(valid from January 2005)
Class A
IEC WT 01
Valid up to 5 years
Class B
IEC WT 01
Non safety related issues may be
documented after issue of certificate
Valid up to 1 year
Class C
( IEC WT 01 )
Safety related issues only
Valid up to 3 years
Special requirements
• Danish climate/soil conditions
• Aerodynamic acting brake
system
• Normal safety class. Main components
as component class 2
minimum
• Blade reflection specified
• CE marking
• Lightning protection specified
• Electrical installations
• Electrical impact on grid
• Power curve according to
DS/EN61400/12
• Blade test (static and fatigue)
• Manufacturing Evaluation.
Certified quality system for
construction / manufacturing of
WTGs
• Foundation design evaluation
• Power quality measurements
• Acoustic noise measurements
• User manual in Danish
• Installation manual in Danish
Special requirements
• Danish environmental conditions
• Aerodynamic acting brake
system
• Normal safety class. Main components
as component class 2
minimum
• Blade reflection specified
• CE marking
• Lightning protection specified
• Electrical installations
• Electrical impact on grid
• Power curve according to
DS/EN61400/12
• Blade test (static and fatigue)
• Manufacturing Evaluation.
Certified quality system for
construction / manufacturing of
WTGs
• Foundation design evaluation
• Power quality measurements
• Acoustic noise measurements
• User manual in Danish
• Installation manual in Danish
Special requirements
• Danish environmental conditions
• Aerodynamic acting brake
system
• Normal safety class. Main components
as component class 2
minimum
• Blade test (static)
• Foundation design evaluation
• User manual
Figure 1 Danish certification scheme for type approval of wind turbines. The scheme is based on WT 01 and the
Danish addenda to this.
The IEC WT01 elements and the elements which are mandatory in the Danish scheme are shown in the figure below.
Design Evaluation
Mandatory
Type Testing
Mandatory
Manufacturing
Evaluation
Mandatory
Foundation Design
Evaluation
Mandatory
Type Characteristic
Measurements
Some parts
mandatory
Final Evaluation Report
Mandatory
Type Certificate
Mandatory
Figure 2 IEC WT 01 elements. In the Danish scheme Foundation design evaluation and some type characteristic
measurements are mandatory.

Project certification is also a part of the new scheme and ensures that a wind turbine with a valid type certificate
with a foundation design matches the external conditions at a specific site.
A Danish project certification is shown in the figure below. With a project certificate the local building authority may
judge the technical design requirements of the regulations as being fulfilled.
Type Certificate
Mandatory
Site Assessment
Mandatory
Foundation design
Evaluation
Mandatory
Installation
Evaluation
Some Parts
mandatory
Project Certificate
Mandatory
O&M surveillance
Not mandatory
The new scheme has now been implemented for more than a year.
The certification bodies now issues Danish “International” type certificates based on IEC WT01, with the Danish
addenda.
References
1. Executive order no. 270 of 2 May 1991 on type certification and certification of wind turbines, Danish
Energy Authority.
2. Technical Criteria for the Danish Approval Scheme for Wind Turbines, April 2000
3. Loads and Safety for Wind Turbines, DS472
4. Executive order no. 1268 of 10 December 2005 on type certification and certification of wind turbines,
Danish Energy Authority.
5. IEC WT 01, IEC system for conformity testing and certification of wind turbine generator systems – Rules
and procedures
6. IEC61400-1, Wind turbines, Design requirements
7. IEC61400-2, Wind turbines, Design requirements for small wind turbines