National Wind Technology Center

1. Wind Turbine Design According to IEC 61400-1 (Onshore) and -3 (Offshore) Standards Overview for NWTC November 8, 2005 Sandy Butterfield NREL National Wind Technology Center

2. Outline • Overview of design process • IEC standards organization • Load cases • Determination of design load • Fatigue • Extreme • Special cases, e.g. faults • History and origin of design load cases

3. Where does Certification & Standards Fit Into Design Process & Product Development Phases? Design and Analysis Phase Test and Verification Phase Certification Documentation Type Testing Power Performance Dynamic Behavior Noise Safety Test Power Quality Maintenance Manual Installation Manual Operating Manual Personal Safety Manufacturing Quality Design Refinements Type Certification Reliability Tests Load Verification Dynamic Behavior Final Design Performance and Prototype Loads Tests Structural Detailed Design Mech. & Electrical Design Certification Loads Test Final Loads Document Control & Protection System Detailed Design and Analysis Component Qualification Tests Even More Load Case Analysis Control & Protection System Preliminary Design and Analysis More Load Case Analysis Control & Protection System Define Certification Requirements Preliminary Load Case Analysis Control & Protection System Conceptual Design PRODUCT VALIDATION DESIGN REFINEMENT • Standards are seamless(?) woven into design process • Load estimations are continually refined

4. IEC Standards for Wind • TC88 responsibility • Working Groups and Maintenance Teams do the work • WT01 sets certification requirements and Conformity Assessment Board (CAB) has final authority (not TC88)

5. WT01 References Technical Standards Offshore Support Structures • 61400-12 (Performance) • 61400-13 (loads) • 61400-21 (Power Quality) • 61400-23 (Blades) • 61400-24 (Lightning) • 61400-1 ed 3 (Onshore) • 61400-2 ed 2 (Small) • 61400-3 (Offshore) • 61400-4 (Gearboxes) • 61400-11 (Noise) • 61400-14 (Sound Power) • ISO 9002 DesignEvaluation TypeTesting Manufacturing Evaluation Foundation Design Evaluation(Optional) Type Characteristic Measurements(Optional) Final EvaluationReport WT01 Type Certificate Project Certificate Boundaries of design evaluation:

6. -1 Primary Table of Contents • 6 External conditions 25 • 6.1 General 25 • 6.2 Wind turbine classes 25 • 6.3 Wind conditions 26 • 6.4 Other environmental conditions 35 • 6.5 Electrical power network conditions 37 • 7 Structural design 38 • 7.1 General 38 • 7.2 Design methodology 38 • 7.3 Loads 38 • 7.4 Design situations and load cases 39 • 7.5 Load calculations 46 • 7.6 Ultimate limit state analysis 48 • 8 Control and protection system 55 • 9 Mechanical systems 57 • 10 Electrical system 60 • 11 Assessment of structural and electrical compatibility of a wind turbine for site-specific conditions 62 • 12 Assembly, installation and erection 68 • 13 Commissioning, operation and maintenance 71

7. Annexes • Annex A (Normative) Design parameters for describing wind turbine class S 76 • Annex B (Informative) Turbulence models 77 • Annex C (informative) Assessment of Earthquake Loading 82 • Annex D (Informative) Wake and Wind Farm Turbulence 83 • Annex E (Informative) Prediction of Wind Distribution for Wind Turbine Sites by Measure-Correlate-Predict (MCP) Methods 85 • Annex F (Informative) Characteristic Wind Turbine Loads for Ultimate Strength Analysis 88 • Annex G (Informative) Fatigue Analysis Using Miner’s Rule with Load Extrapolation 91 • Annex H (Informative) Bibliography 95

8. Clause 6 - Design Classes

9. Normal Turbulence Model Bonnie’s Version

10. Extreme Turbulence Model

11. Extreme Coherent Gust w/ Direction Change 15 m/s gust profile

12. ECD Direction Change

13. Clause 7 – Design Power Production Clause 7 includes detailed explanations on how to implement each load case.

14. Faults While Operating

15. Non-operating extreme load cases Must sweep yaw angle

16. In Practice Loads Cases are Expanded Multiple wind speeds, seeds, operating states, etc.

17. Synthesizing Simulation Time Series into Design Loads Normal Operating (fatigue) Loads Extreme Operating, Faulted & Parked Loads Multiple time series for one wind speed Multiple time series for one wind speed Sweep wind speed range Sweep wind speed, operating & fault conditions Scale distribution according to wind distribution Fit maximum load statistics to extreme value model Sum all loads into Rainflow (fatigue) matrix Extrapolation to 1 & 50 year loads

18. Max Design Load Analysis Loads Summary

19. Max/Min Loads Chosen from all Cases Load Case 1.3b = ECD (11.2 m/s, 15 m/s gust, 64o direction change, causes shut down on yaw error trigger)

20. Load Case 2.1c • Two defining load cases involving emergency shut downs. • Peak loads could be reduced by nearly 50% if loads were contained through 1.3b and 2.1c events.

21. Offshore : 61400-3 • Addresses all marine related design considerations • Refers to 61400-1 for all turbine issues • Add waves to the equation

22. Two stochastic load sources • Turbulence spectra • Broad band • Wave spectra • Narrower band • Approaching system resonances • Floating system dynamics? • Foundation design included

23. Merging Two Design Paths

24. Load Case Table Includes Sea State

25. Need Joint Wind/Wave Probability Distributions Turbulence Waves

26. 50 year Environmental Contours

27. Two Excitation Sources • Controls could play a very important role in detecting damaging operating conditions and controlling floating platform stability • Many more load cases • Floating dynamics more complicated -Floating- -Fixed-

28. Summary • Standards are intimately connected to design process • Load reduction depends on details of load cases (“whack a mole” or “rat killing”) • Fatigue and extreme loads could be reduced through non-traditional controls • Floating platforms could present great controls opportunities • COE?