1. of Large Offshore Wind Farms
Survey of Reliability
of Large Offshore Wind Farms
Nicola Barberis Negra
Ole Holmstrøm

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. 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
DAWE

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
Power system adequacy
wind treated like a ”variable negative load”
addressed in terms of prediction and secoadary reserves
Capacity credit = low if any
With large offshore wind farms and high penetration: controllability of wind farms have been i intruduced. Some system support.
BUT APART FROM THIS GRID CODES HAVEN’T MADE ANY SPECIFIC REQUIREMENTS. TSO have no concern about WF avaialbility, etc.
Operation on market conditions.
Power system security: fault ride through requirements was adressed quite early and have been introduced in most power systems. Winfd farms and wind turbines can meet requirements.
Wind farm owner
adequacy analyses of wind power has mainly been related to the cost effective wind farm design (i.e. optimisation of the installation costs and owners revenue) rather than the contribution (positive or negative) to the power system reliability.
Security: fullfil grid code.

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 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 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. Component availability data
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
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 , No. 3, October, 2003.
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26. Thank you for the attention
Nicola Barberis Negra
c/o Dong Energy A/S
Kraftvaerksvej 53
7000 Fredericia
Denmark
Ole Holmstrøm
c/o Dong Energy A/S
Kraftvaerksvej 53
7000 Fredericia
Denmark