Survey of Reliability of Large Offshore Wind Farms

1. Nicola Barberis Negra nibne@dongenergy.com Ole Holmstrøm oleho@dongenergy.com Survey of Reliability of Large Offshore Wind Farms

2. General information • UpWind Integrated Wind Turbine Design • FP6 Integrated project • From March 2006 to February 2011 • 40 partners • Work package 9 • Survey of present status • Power system requirements • Different electrical concepts • Extreme wind conditions

3. DAWE General information • Offshore wind power – Research-related bottlenecks • Mutual shadow effect between blocks of wind turbines • Extreme structural loading of offshore wind turbines • Interaction of large wind farms with waves and current • Grid connection and reliability • Environmental aspects • Optimized operation and maintenance for offshore wind farms

4. Outline • Introduction • Current state of offshore wind farm • How to assess wind farm reliability • Reference

5. Outline • Introduction • Current state of offshore wind farm • How to assess wind farm reliability • Reference

6. Introduction • How has reliability of wind farms been addressed? • Overall power system (Grid Codes) • System adequacy – Prediction/reserves • System security • Wind farm owner/operator • Adequacy – Cost effective wind farm design • Security – Grid Code compliance

7. Outline • Introduction • Current state of offshore wind farm • How to assess wind farm reliability • Reference

8. Current Installations

9. Typical Wind Farm Layout

10. Wind Turbine • Large size for better production (>2 MW) • Higher voltages • Transformers • Generators • Protection (depends of Grid Code) • Selectivity is applied individually • Individual protection for under-/overvoltage • Individual protection for under-/overfrequency • Standard IEC 61400 for wind turbine design

11. Wind Turbine • The first offshore wind turbines experienced several problems - “built-in” failures or design errors • Simple systems and equipment placed offshore may experience new impact of climate, vibrations and intermittent operations • Offshore wind farms include a large number of identical units • Repairs to even simple problems may take disproportionately long time

12. Wind Turbine • Power electronics and electronic equipment • The experience shows relatively significant failure rates • Active stall – Electronic reactive power control • DFIG – Rotor side converters • Full size converters • Simple, robust and well-tried solutions should be preferred

13. Internal Distribution and Transmission Grid • Typical industrial distribution system • First wind resource, then electrical parts • Cluster/string configuration (redundancy only for North Hoyle) • Voltages at 33-36 kV • Protection • Faults cause tripping of interested radial • Time to inspect and reestablish

14. Connection to Shore • Belong to the wind farm or the TSO (i.e. Denmark) • Small wind farm (below ~100 MW) • 1 connection/cluster at MW level • Large wind farm (above ~100 MW) • Offshore substation • 1 HV connection for the whole wind farm • All HVAC solutions, HVDC are under study

15. Protections • Depends of each national Grid Code (if available) • System neutral earthing • Different solutions for different parks • Horns Rev is impedance earthed • Nysted is with isolated neutral • Lightning protection • The number of lightning strokes experienced by offshore wind turbines is 3-4 times larger than land-based turbines • Increased risk of damages

16. UpWind First Conclusions • First offshore wind farms shows a need for increasing focus on design, procurement, quality, risk assessments and quality assurance • New standards or practices for risk assessments and quality assurance of offshore installations are needed; existing IEC standards may not be sufficient • Quantification of reliability parameters is still uncertain due to the few installations and the short operational experience (e.g. no cable failures)

17. Outline • Introduction • Current state of offshore wind farm • How to assess wind farm reliability • Reference • Questions

18. Why to Assess Reliability of Wind Farms? • Wind farm design must be optimize according to losses, reliability and economical aspects • Increase of wind installations • Energy penetration (Denmark) • Installed capacity (Germany) • Wind generation is part of large power systems and it must be controlled for power balance issues • Models and data are required

19. Available Assessment Techniques • Deterministic solutions • First used approaches • No uncertainties are included • Probabilistic methods (sequential or not) • Analytical models or Monte Carlo simulations • Uncertainties are included • Broader range of studies

20. Comparison of Techniques • Analytical methods • Mathematical models to represent the system • Simplifications are needed • Faster, but the model is almost a “black box” • Monte Carlo simulations • Easier to implement with less approximations • Longer computation time • All aspects can individually be analyzed

21. Aspects of Relevance • Simulation of wind speed • Wake effects of the park • Wind turbine technology • Power collection grid of the park • Grid connection system • Offshore environment • Different wind speeds in the site • Correlation of output power among different wind farms • Hub height variations

22. General Model • 1. Simulation of wind speed • 2. Wake effects of the park • 9. Hub height variations a. Wind speed data d. Output Results c. Wind Farm b. Component availability data • 3. Wind turbine technology • 4. Power collection grid in the park • 5. Grid connection system • 6. Offshore environment • 7. Different wind speed in the site • 8. Correlation of output power among different wind farms

23. Reliability Data • New technology  Difficulty in getting data • Available data are based on values of land-based installations “guessed” at offshore locations • Example of data

24. Outline • Introduction • Current state of offshore wind farm • How to assess wind farm reliability • Reference

25. Reference • O. Holmstrøm, N. Barberis Negra, ‘UPWIND Deliverable D9.1 - Survey of reliability of large offshore wind farms. Part 1: Reliability of state of the art wind farms’, Report, May 2007. • N. Barberis Negra, O. Holmstrøm, B. Bak-Jensen, and P. Sorensen, ‘Aspects of relavance in offshore wind farm reliability assessment’, IEEE Transaction on Energy Conversion, Vol. 22, No. 1, March 2007, pp.159-166. • N. Barberis Negra, O. Holmstrøm, B. Bak-Jensen, and P. Sorensen, ‘Comparison of Different Techniques for Offshore Wind Farm Reliability Assessment’, 6th International Workshop on Large-Scale Integration of Wind Power and Transmission Networks for Offshore Wind Farms, October 26-28, 2006, Delft, The Netherlands. • G.J.W. van Bussel and M.B. Zaarijer, ‘Reliability, Availability and Maintenance aspects of large-scale offshore wind farms, a concepts study’, Proceeding of MAREC 2001, Newcastle, England, 2001. • A. Sannino, H. Breder, and E. K. Nielsen, ‘Reliability of collection grids for large offshore wind parks’, 9th International Conference on Probabilistic Methods Applied to Power Systems, June 11-15, 2006, Stockholm, Sweden, . • DOWEC Team ‘Estimation of turbine reliability figure within the DOWEC project’, DOWEC project No. 10048, No. 3, October, 2003. • ...

26. Thank you for the attention Ole Holmstrøm oleho@dongenergy.com c/o Dong Energy A/S Kraftvaerksvej 53 7000 Fredericia Denmark Nicola Barberis Negra nibne@dongenergy.com c/o Dong Energy A/S Kraftvaerksvej 53 7000 Fredericia Denmark