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Overview

The assessment of the design consists of the elements of evaluation on the basis of the respective standards to be applied for the assessment shown in the table below. It is generally carried out in two sequential steps. The first part covers all aspects of the safety and control concept as well as the load assumptions and load calculations. The load calculations for wind turbines are to be based on aeroelastic codes using stochastic wind fields and modal or finite element analysis techniques [3]. In the case of offshore wind turbines the loads have to contain both the aeroelastic and the fluid-structure interaction of the submerged part. The latter may have a considerable influence on the structural response for certain types of foundations and/or underwater structures [4].

During the second part of the Design Assessment all components (rotor blades, machinery, tower, foundation and electrical installations) of the system are being examined on the basis of the previously approved loads and the relevant standards and regulations. As no IEC standards are available for the design and assessment of the machinery components and the support structure GL's Wind Guideline is applied in most cases. In general all available national and international guidelines cam be applied.

At the end of the Design Assessment manuals and procedures for transport, erection, start-up, commissioning, operation and maintenance are checked for suitability, completeness and compliance with the assumptions in the design documentation. Rotor blade testing [5] forms an integral part of the design assessment of the blade. Lightning Protection will be assessed under the scope of the electrical installations. The Design Assessment can be carried out on three different levels: A-, B- and C-Design Assessment.

Report No.	Steps of evaluation	Codes or Standards to be applied
xxxxx-1	Load Assumptions	GL Wind Guideline [1], IEC 61400-1, Second [4] or Third [5] Edition, DIBt [13]
xxxxx-2	Safety System and Manuals	GL Wind Guideline [1], IEC 61400-1, Second [4] or Third [5] Edition, DIBt [13]
xxxxx-3	Rotor Blades Blade Tests	GL Wind Guideline [1] GL Wind Guideline [1] , IEC TS 61400-23 [6]
xxxxx-4	Machinery Components	GL Wind Guideline [1], (IEC 61400-1, Second [4] or Third [5] Edition)
xxxxx-5	Tower and Foundation	GL Wind Guideline [1]
xxxxx-6	Electrical Equipment and Lightning Protection	GL Wind Guideline [1], IEC TR 61400-24 [7], relevant IEC Standards
xxxxx-8	Commissioning Witnessing	GL Wind Guideline [1]
xxxxx-12	Nacelle Housing and Spinner	GL Wind Guideline [1]

Elements within Design Assessment

C-Design Assessment

Within the C-Design Assessment (for prototypes of wind turbines), a plausibility check of the prototype will be performed on the basis of the design documentation. This type of Design Assessment can be used to erect the prototype of a wind turbine. It is based on a load assessment and a complete plausibility check of the rotor blades, the machinery components as well as of the tower and foundation. Depending on national or local regulations the complete assessment of tower and foundation might be necessary. The final step will be the issue of a Statement of Compliance for the C-Design Assessment which is valid for test operation comprising a maximum of 2 years or 4000 equivalent hours at full load. After this period the B-Design Assessment shall be obtained at latest. 

A- and B-Design Assessment

A- or B-Design Assessment is the next step in certification. Both assessments consist of a complete examination of the design analyses with all required material and component tests and are completed with the commissioning witnessing of one of the first wind turbines of the assessed type. Following completion, the certification body will issue a Statement of Compliance for the A- or B-Design Assessment.

The B-Design Assessment may contain items that are outstanding, if these are not directly safety-relevant. Furthermore it has a validity period of one year. This period can be used to fulfil the missing requirements for the A-Design Assessment which may not contain any outstanding items and does not expire unless the design is modified.

The examination of a foundation is optional within the scope of the A- or B-Design Assessments. The submission of documents for the Implementation of design-related requirements in Production and Erection (IPE), which is part of Type Certification, is of advantage to be carried out within the Design Assessment to reduce the total time of Type Certification.

After a successful assessment the Statement of Compliance for the Design Assessment and the respective Certification Reports on load assumptions, safety system, rotor blades, machinery components, tower and foundation, electrical installations, commissioning witnessing, hub and nacelle cover will be issued.

References: 

• Germanischer Lloyd: Guideline for the Certification of Wind Turbines, Edition 2003 with Supplement 2004, [1]

• D. Quarton, F. Rasmussen, K. Argyriadis, C. Nath: Wind Turbine Design Calculations - the State of the Art, Proceedings, European Wind Energy Conference, Göteborg, 1996, [2]

• Kühn, M. et al: Structural and Economic Optimisation of Bottom-Mounted Offshore Wind Energy Converters, EU JOULE III, JOR3-CT95-0087, Final Report, August 1998, [3]

• IEC 61400-1: Wind Turbine Generator Systems – Part 1: Safety Requirements, Second Edition, 1999-02, [4]

• IEC 61400-1: Wind Turbines – Part 1: Design Requirements, Third Edition, 2005-08, [5]

• IEC TS 61400-23: Wind Turbine Generator Systems – Part 23: Full Scale Structural Testing of Rotor Blades, 2001-04, [6]

• IEC TR 61400-24: Wind Turbine Generator Systems – Part 24: Lightning Protection, 2002-07, [7]

• IEC 61400-12: Wind Turbine Generator Systems – Part 12: Wind Turbine Power Performance Testing, 1998-02, [8]

• IEC 61400-11: Wind Turbine Generator Systems – Part 11: Acoustic Noise Measurement Techniques, 2002-12, [9]

• IEC TS 61400-13: Wind Turbine Generator Systems – Part 13: Measurements of Mechanical Loads, 2001-06, [10]

• IEC 61400-21: Wind Turbine Generator Systems – Part 21: Power Quality Requirements for Grid Connected Wind Turbines, 2001-12, [11]

• Germanischer Lloyd: Guideline for the Certification of Offshore Wind Turbines, Edition 2005, [12]

• Deutsches Institut für Bautechnik (DIBt): Richtlinie für Windenergieanlagen, Einwirkungen und Standsicherheitsnachweise für Turm und Gründung, March 2004, [13]  

• NVN 11400-0: Wind Turbines – Part 0: Criteria for type-certification – Technical criteria, first edition April 1999, [14]

• FGW TR 3: Technische Richtlinien für Windenergieanlagen – Teil 3: Bestimmung der Elektrischen Eigenschaften, [15]

• M. Wöbbeking: Development Accompanying Assessment - A New and efficient Approach for Development and Certification, GL Wind, 2007, [16]

• Note on Engineering Details, DWM-Woeb-extern-001, D-Design Assessment, [17]

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