Offshore Farms failures, maintenance plan and constraints Offshore Wind farms (OWF) • The OWF is expected to be the major source of energy [Reh 2014] • European countries are leader (117GW) • OWF negative and positive aspects are presented in [Synder 2009] • higher wind speeds; smoother, less turbulent airflows; larger amounts of open space; and the outside ability to build larger, more cost-effective turbines of Copenhagen, Denmark. Image (6MW) obtained with thanks from Kim Hansen on Wikipedia • Cost of installation of offshore turbines is more important than onshore • Cost of maintenance is very important in OWF

3

Offshore Wind farms (OWF) “Example” • DOWEC wind farm • 80 turbines, 6MW each => 480MW • North sea at the location “NL7”, 50 Km offshore [Lindenburg 2003] • Equipped with 50MT mobile crane • In each there is 1MT crane • A supplier with an Offshore Access System is used to transport personal and small components [Radermarkrs]

[DOWEC 2003]

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Development of OWF

Energy (GW) Energy

[Reh 2014]

5 Development of OWF

Annual onshore and offshore installation [EWEA 2014]

EUROPEAN WIND ENERGY ASSOCIATION

6 Development of OWF

Onshore historical growth 1994–2004 compared to EWEA'S offshore projection 2010–2020 [Reh 2014]

7 Failure of OWF

• 60% of the failures are contained in the following ones: [chun 2012]

•Electrical equipment • Yaw system • Gearbox • Rotor • Hydraulic system

Primary Components and Dimensions of One of the 2-MW Turbines in Denmark’s Offshore Wind Park [USA 20006]

8 Failure of OWF • Failure rate l is the frequency with which an engineered system or component fails

• It is dynamic (not determinative) because it depending of the maintenance actions

• Different consequences of the failures

• The failure mode determine what Failure rate of Danish type of actions is required and thus components [chun 2012] [Hyers 2006] define the cost.

9 Failure of OWF country Sweden Finland Germany Average number of failures 0.402 times/year 1,38 times/year 2,38 times/year per turbine Average downtime per 170 h/year 172 H/year 62,2 h/year failure Longest downtime per drive train Gears Generators failure [Kawady 2008] • Variation of failure nature by country ( position, policy; …) • Each wind farm has its own failure behavior

10 Failure mode and failure cause Resonances within Poor component Production Icing problem Frequent Improper resistor-capacitor quality and defects in extreme stoppage and installation (60%) (RC) circuits system abuse weather starting Turbulent High/Low Poor electrical wind Poor High Particle temperature installation system level during contaminations design Technical overload Corrosion Out-of-control High loaded defects Lightning rotation operation conditions Vibration

Electrical Yaw Blade Gearbox Hydraulic Control Failures System

●Generator windings, •Damages •Cracking of shafts, •Wearing, Leakages ●Short-circuit • Cracks • Fracture of gear teeth, • Backlash, ●Over voltage of • Breakups • Pitting of the race • Tooth breakage electronics components • Bends • Failure of the bearing mounting ●Transformers bolts Weather ●Wiring damages Human Technical

11 Maintenance cost and availability Generator Downtime Cost of maintenance gearbox Generator Blade gearbox Electrical system Blade Electrical system Control Control Shaft & bearing Shaft & bearing Yaw system Yaw system pitch mechanism pitch mechanism invertor invertor parking parking brake brake brake Relative contribution of the components to the costs and downtime (Netherlands)[Radermarks ]

sensors Cost of maintenance Downtime gear sensors mechanical breakes gear hydrolics mechanical breakes hydrolics yew system yew system structure structure Entire unit Entire unit Hub Hub Blades/pitch Blades/pitch generator generator electric system electric system Control system Control system Drive train Drive train Distribution of failures in the Swedish plants (1997-2005) [Kawady 2008]

12 Maintenance cost

• Preventive Maintenance (PM) 0.003 to 0.006(€/kWh) • Corrective Maintenance (CM) 0.005 to 0.01 (€/kWh) • The contribution of maintenance cost in the price is 25 to 30% [Europ 2001]. Size and Maintenance Weather reliability of the OWF position concept Conditions turbine

Maintenance plan/ cost

[Radermakrs]

13 Maintenance cost Size and Maintenan OWF Weather reliability of ce position conditions • Size and reliability of the turbine the turbine concept • Large turbines optimized for offshore applications Maintenance • Adapted storage equipment cost • Maintenance concept • Maintenance strategy • Maintenance actions management • Types of maintenance • OWF position • Water depth • Size of wind farm • The travel duration

14 Maintenance cost [Radermkers]

Size and Maintenan OWF Weather reliability of ce position conditions • The weather Conditions the turbine concept • Each repair equipment has its own maximum condition Maintenance of use : cost • Example : The OAS (Offshore Access System) is assumed to operate up to waves_high_max (Hs_Max)=2m and wind_speed_max(Vs_max)= 12 m/s for transporting personals and 1.5 m and 8m/s for spare parts. • The time series of wave and wind data to define : • The waiting time as a function of the duration of the repair, Hs_max and Vs_max; • The damages caused by lightning • Visibility

15 Required data (input) • Location and characteristics of wind farms • Failure rates • Expected time-to-failures • Preventive maintenance (historical data or model) • Repair strategies • Wind and wave statistics • Costs • Lead time of vessels and spare parts • …

16 Actions for optimization • Improvement of maintenance strategy • Reduction of failure rate including redundancy • Fault tolerance operation • Improvement of collaboration mode (ICT, MAS, …) • Improvement of accessibility • Improve the design of turbine to be more robust with less maintenance requirement and actions • …

17 References • [BOEM2013] http://www.boem.gov/Renewable-Energy-Program/Renewable-Energy-Guide/Offshore-Wind-Energy.aspx • [Pieterman 2011] Braam, H. & Obdam, T.S., 2011. Optimisation of maintenance strategies for offshore wind farms. , (December), pp.1–12. • [Radermakrs] Braam, H., Zaaijer, M.B. & Energy, S.W., ASSESSMENT AND OPTIMISATION OF OPERATION AND MAINTENANCE OF OFFSHORE WIND TURBINES. • [Lindenburg 2003] Lindenburg, C., Winkelaar, D. & Hooft, E.L. Van Der, 2003. Dowec 6 mw pre-design. , (September), pp.1– 46. • [Péres 2010] Morant, F., Correcher, A. & Quiles, E., 2010. Optimal maintenance system for offshore wind turbines -. , (Table I). • [Chun 2012] Pecht, M., 2012. Review of offshore wind turbine failures and fault prognostic methods. Proceedings of the IEEE 2012 Prognostics and System Health Management Conference (PHM-2012 Beijing), pp.1–5. Available at: http://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=6228954. • [Reh 2014] Perveen, R., Kishor, N. & Mohanty, S.R., 2014. Off-shore wind farm development: Present status and challenges. Renewable and Sustainable Energy Reviews, 29, pp.780–792. Available at: http://linkinghub.elsevier.com/retrieve/pii/S1364032113006849 [Accessed February 20, 2014]. • [Europ 2001] G.Hassan, 2001. Concerted Action on Offshore Wind Energy in Europe • [Snyder 2009] Snyder, B. & Kaiser, M.J., 2009. Ecological and economic cost-benefit analysis of offshore wind energy. , 34(6), pp.1567–1578. Available at: http://linkinghub.elsevier.com/retrieve/pii/S0960148108004217 [Accessed February 19, 2014] • [EWEA 2014]Anon, 2014. Wind in power 2013. , (February), pp.1–12. • [Kawady 2008] Kawady, T.A. et al., 2008. Wind Farm Protection Systems: State of the Art and Challenges. , 2008. • [USA 2006] Anon, 2006. Wind Energy Potential on the U.S. Outer Continental Shelf. , (May).

18 Questions

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