Survey of Reliability

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Survey of Reliability of Large Offshore Wind
Farms
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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

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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

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Outline

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

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Outline

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

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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

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Outline

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

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Current Installations
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Typical Wind Farm Layout
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Wind Turbine

• Large size for better production (gt2 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

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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

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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

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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

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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

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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

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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)

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Outline

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

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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

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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

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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

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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

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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
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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

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Outline

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

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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.
• ...

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Thank you for the attention
Ole Holmstrøm oleho_at_dongenergy.com c/o Dong
Energy A/S Kraftvaerksvej 53 7000 Fredericia
Denmark
Nicola Barberis Negra nibne_at_dongenergy.com c/o
Dong Energy A/S Kraftvaerksvej 53 7000 Fredericia
Denmark