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

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

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 Design Evaluation Type Testing Manufacturing Evaluation Foundation Design Evaluation (Optional) Type Characteristic Measurements (Optional) Final Evaluation Report Type Certificate Boundaries of design evaluation: Project Certificate ed 3 (Onshore) ed 2 (Small) (Offshore) (Gearboxes) (Performance) (loads) (Power Quality) (Blades) (Lightning) (Noise) (Sound Power) ISO 9002 WT01 Offshore Support Structures

6 -1 Primary Table of Contents 6External conditions25 –6.1General25 –6.2Wind turbine classes25 –6.3Wind conditions26 –6.4Other environmental conditions35 –6.5Electrical power network conditions37 7Structural design38 –7.1General38 –7.2Design methodology38 –7.3Loads38 –7.4Design situations and load cases39 –7.5Load calculations46 –7.6Ultimate limit state analysis48 8Control and protection system55 9Mechanical systems57 10Electrical system60 11Assessment of structural and electrical compatibility of a wind turbine for site- specific conditions62 12Assembly, installation and erection68 13Commissioning, operation and maintenance71

7 Annexes Annex A (Normative) Design parameters for describing wind turbine class S76 Annex B (Informative) Turbulence models77 Annex C (informative) Assessment of Earthquake Loading82 Annex D (Informative) Wake and Wind Farm Turbulence83 Annex E (Informative) Prediction of Wind Distribution for Wind Turbine Sites by Measure- Correlate-Predict (MCP) Methods85 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) Bibliography95

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 Figure 6 –Direction change for ECDFigure 7 - Example of direction change transient

13 Power Production Clause 7 – Design 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 Multiple time series for one wind speed Sum all loads into Rainflow (fatigue) matrix Scale distribution according to wind distribution Sweep wind speed range Normal Operating (fatigue) Loads Multiple time series for one wind speed Extrapolation to 1 & 50 year loads Fit maximum load statistics to extreme value model Sweep wind speed, operating & fault conditions Extreme Operating, Faulted & Parked 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, 64 o 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 : Addresses all marine related design considerations Refers to 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 Waves Turbulence

26 50 year Environmental Contours

27 Two Excitation Sources -Fixed- -Floating- 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

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?