Offshore Wind Farm Design: Operation and Maintenance

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  • 1. Module 11: Operation & Maintenance OPERATION & MAINTENANCE Gerard van Bussel section Wind EnergyModule 11: Operation & Maintenance Typical contribution to energy cost Investment & Decommissioning 3% O&M Decommissioning O&M Investment 25 - 30% 23% 74% ~ 75 % Opti-OWECS study (1998) CA-OWEE (2001) 1
  • 2. Module 11: Operation & Maintenance Maintenance Concepts maintenance corrective preventive maintenance repair maintenance service batch wise corrective periodic condition corrective maintenance preventive based maintenance on demand maintenance maintenance opportunity calendar condition condition based based judging monitoringModule 11: Operation & Maintenance Failure frequencies 500kW class Tacke TW600 Enercon 40 Vestas V39/500 number of turbines 25 26 59 events/year events/year events/year Lightning 0 0.03 0 Blade 0.76 0.42 0.32 Rotor Brake 0 0 0 Pitch Mechanism 0 0.30 0.03 Brake 0.08 0 0 Shaft/Bearing 0.04 0.03 0 Gearbox 0.16 0 0.03 Generator 0 0.03 0.33 Hydraulic 0.32 0 0.27 Yaw System 0.32 0.23 0.08 Anemometry 0 0 0.01 Electronics 0.04 0.42 0.33 Electric 0.20 0.69 0.30 Inverter 0 0 0 Sensors 0.08 0.07 0.18 Other 0.20 0.38 0.37 Overall Total 2.2 2.6 2.25 Failure frequencies 2.2 2.6 2.25 For larger machines (onshore) => 2.2 /year 2
  • 3. Module 11: Operation & Maintenance Failure frequencies multi MWW class Component Failure frequency (failures/year) Shaft & Bearings 0.02 Brake 0.05 Generator 0.05 Parking Brake 0.05 Electric 0.14 Blade 0.16 Yaw System 0.23 Blade tips 0.28 Pitch Mechanism 0.28 Gearbox 0.30 Inverter 0.32 Control 0.34 Total 2.20 Total of all components: 2.20 failures/yearModule 11: Operation & Maintenance Reliability, Availability, Maintainability, Serviceability reliability maintainability serviceability (failures/year) (MTTR) (PM demand) theoretical availability accessibility maintenance of the site strategy actual availability 3
  • 4. Module 11: Operation & Maintenance A measure for availability state running failed MTTR MTTF Mean Time To Repair Mean Time To Failure time MTTF Availability = MTTR + MTTFModule 11: Operation & Maintenance Experienced Availability T uno Knob availability T uno Knob availability Tuno Knob 100.00% 100.00% (inshore, Denmark) 98.00% 97% 98.00% 96.00% 96.00% 94.00% 94.00% 92.00% 92.00% 90.00% 90.00% 1996 1996 1997 1997 1998 1998 4
  • 5. Module 11: Operation & Maintenance Present maintenance demand 4 Visits 3 per turbine per 2 year 1 0 Unplanned PlannedModule 11: Operation & Maintenance Accessibility of site (Vessel) Vindeby DK inshore Oct Nov Dec Jan Feb Mar Apr May June July Total Nominal 23 21 20 22 20 22 19 19 21 23 210 Working Days Bad Weather 1 1 0 2 4 5 4 0 0 0 17 (Days) Bad Weather 5 2 2 4 1 3 1 0 0 0 18 (o.5 Day) Lack of 0 2 0 0 1.5 4 6 1 0 0 14.5 Transport Inaccessible 3.5 4 1 4 6 10.5 10.5 1 0 0 40.5 Days % Total Time 15.2 19 5 18.2 30 47.7 55.3 5.3 0 0 19.3 5
  • 6. Module 11: Operation & Maintenance Accessibility of site (Vessel) Horns Rev Vindeby (near shore, (inshore, North Sea) Denmark) H orns R ev versus V indeby Accessibility 120.00% 100.00% Fraction of time 80.00% 6 hours 12 hours 60.00% 24 hours 40.00% V indeby 20.00% 0.00% nov feb apr aug mar jan jun jul sep dec may octModule 11: Operation & Maintenance Means of crew transport • Helicopter • Tender vessel - fast - fairly slow - expensive - cheap - helipad - boat landing - large operational - medium window window 6
  • 7. Module 11: Operation & Maintenance Means of crew transport 2 A tender vessel For crew transport A “gol” boat Harbour pilotsModule 11: Operation & Maintenance Means of crew transport 3 A tender vessel For crew transport With a Zodiac for landing 7
  • 8. Module 11: Operation & Maintenance Means of crew transport 4 With a Zodiac With a Zodiac for landing ?? for landing ??Module 11: Operation & Maintenance Means of crew transport 5 Crew transport by helicopter 8
  • 9. Module 11: Operation & Maintenance Trends: Access methods Catamaran landing vessel SWATH@A&R / Abeking &RasmussenModule 11: Operation & Maintenance Trends: Access methods Flexible gangway: OAS: P&R systems / Reinout Prins 9
  • 10. Module 11: Operation & Maintenance Trends: Access methods Flexible gangway Flexible gangway OAS: P&R systems / Reinout PrinsModule 11: Operation & Maintenance Trends: Access methods Ampelmann Ampelmann 10
  • 11. Module 11: Operation & Maintenance Cost comparison transport Vessel/Helicopter 2 MW Wind turbine farm 8000 7000 6000 Costs [euro] 5000 4000 3000 Vessel 2000 Helicopter 1000 Vessel+Downtime Heli+Downtime 0 0 10 20 30 40 50 60 70 80 Distance Mantenance base to offshore wind farm [km]Module 11: Operation & Maintenance Experiences in the real world Maintaining Horns Rev: – Access by boat: Winter 02/03: 5/7 days » Winter 03/04: 1/7 days – Helicopter: 6/7 days – Vestas responsible for crew (60 people) Elsam for transport (6 people) – 75.000 transfers in 1.5 years (2 x /day/turbine) 11
  • 12. Module 11: Operation & Maintenance Experiences in the real world Maintaining Horns Rev: Reasons: – Design not well adapted for offshore – Strategy not optimal – Onshore crew – Sophisticated alarms, but what does it mean?Module 11: Operation & Maintenance Lifting equipment • Jack-up barge • Crane vessels • Helicopter • Jack up vessel assisted with built-in facility (in wind turbine) 12
  • 13. Module 11: Operation & Maintenance Installation & O&M lifting facilities Jack up vessels A2Sea Ocean Hanne at Horns Rev Denmark Utgrunden Wind farm, SwedenModule 11: Operation & Maintenance Installation and O&M lifting facilities Jack up vessels A2Sea Ocean Hanne at Horns Rev and at Nysted Denmark 13
  • 14. Module 11: Operation & Maintenance Trends: Lifting at wind turbine Hoisting outside Picture: Enron (Utgrunden, Sweden) Picture: Nordex N80 Offshore Internal cranesModule 11: Operation & Maintenance Trends: Installation Ballast-Nedam NEG-Micon Dowec project 14
  • 15. Module 11: Operation & Maintenance Maintenance strategies • PM and CM on demand (onshore practice) • Opportunity based maintenance (PM when CM is demanded) • Condition based maintenance (PM and CM only when demanded) • No maintenance/ batch maintenanceModule 11: Operation & Maintenance Maintenance strategies • PM and CM on demand (reduced PM demand, increased reliability) • Opportunity based maintenance (flexible PM interval, increased reliability) • Condition based maintenance (extensive condition monitoring) • No maintenance/ batch maintenance (only feasible when failure freq. < 0.2 /year) 15
  • 16. Module 11: Operation & Maintenance Importance of Reliability and Accessibility 100% 90% Reliability Availability 80% highly improved 70% improved 60% onshore design 50% 100 % 80 % 60 % 40 % (remote (onshore) (nearshore) (offshore) offshore) AccessibilityModule 11: Operation & Maintenance Importance of (improved) Reliability 100% Availability 90% Offshore 80% designed 70% Offshore adapted 60% 50% 100 % 80 % 60 % 40 % (remote (onshore) (near shore) (offshore) offshore) Vessel accessibility Tuno & Vindeby Horns Rev (DK inshore) (North Sea) 16
  • 17. Module 11: Operation & Maintenance Assessing reliability, availability and O&M in the design process RAMS targets Waiting time on system Design evaluation level analysis Feasibility study RAMS targets Expert system sub-system level approach Conceptual design RAMS targets on Monte Carlo component level Simulations Final design RAMS targets Full FMECA sub-component level analysis Systems specificationModule 11: Operation & Maintenance Probabilistic Waiting time analysis Time To Repair IJmuiden Munitie Stortplaats 100% 90% 80% Chance 70% 60% [%] T_mission: 24 h CDF 50% 40% T_mission: 72 h 30% 20% T_mission: 168 h 10% 0% 0 100 200 300 400 500 600 700 800 900 1000 time [hrs] Time [hrs] ECN/ Luc Rademakers 17
  • 18. Module 11: Operation & Maintenance Trend lines in expert system Availability as Function of Maximum (onshore) Availability and Storm Percentage 120 Availability [%] 100 Max.availability 80 99.0 % 98.0 % 60 97.0 % 40 Symbols: simulations 20 0 0 50 100 150 No access percentageModule 11: Operation & Maintenance Monte Carlo simulations • Analysis of complex stochastic processes • Failure simulation of wind turbines • Storm simulation for OWECS accessibility • Availability estimates for OWECS • O&M costs estimates for OWECS 18
  • 19. Module 11: Operation & Maintenance FMECA: Failure Mode Effect and Criticality Analysis • systematic brake down of: - functional components - hardware component • analysis of: - effects of all kinds of failures upon functioning - criticality of failure (how does failure affect costs/environment)Module 11: Operation & Maintenance Reliability vs. turbine design • Turbine design gets more complex: – Three bladed, variable speed pitch control – Doubly fed generators, Inverters BUT • Offshore environment demands a robust, lean design: – Two blades !? – Stall control !?? – Low speed or Direct drive generator !? 19
  • 20. Module 11: Operation & Maintenance Recent wind turbine failures NEG Micon Yttre Stengrunden V 80 at Tjaereborg Nordex N 80 Blyth offshoreModule 11: Operation & Maintenance Context of the project • Consortium of industries and institutes • Project: ~ 500 MW offshore wind farm • Location: North Sea > 12 mile zone • Concepts of 5 MW wind turbines • Turbine design for large scale wind farm Assess wind turbine RAMS aspects in the context of the whole wind farm 20
  • 21. Module 11: Operation & Maintenance Wind turbine’s reliability Yearly failure freq. 2 1 0 Present Assumed DOWEC 500 kW 1.5 - 2 MW target (5 MW)Module 11: Operation & Maintenance Reduction of failure frequencies Components factor events/year • Electric system 0.7 0.10 • Blades 0.7 0.07 / 0.11 • Yaw System 0.65 0.15 • blade tips 0.5 0.14 • Pitch Mechanism 0.5 0.13 / 0.14 • Gearbox 0.5 0.13 / 0.15 • Inverter 0.5 0.16 • Control system 0.5 0.15 / 0.19 21
  • 22. Module 11: Operation & Maintenance DOWEC concepts Base line Advanced Robust Stall-teeter Smart stall Direct drive Active Stall Pitch Stall Stall Stall pitch 3 blades 3 blades 2 blades 2 blades 3 blades 3 blades 2 speed Var. speed Fixed speed Var. speed Var. speed Var. speed (30%) (full) (full) (full) Tubular Tubular Tubular Truss Tubular Tubular tower tower tower tower tower tower Piled Piled Monopile Gravity Piled Piled (tripod) (tripod) (tripod) (tripod) Up wind Up wind Up wind Down wind Up wind Up wind (teetered hub)Module 11: Operation & Maintenance DOWEC concepts: reliability basic control concepts: yearly failure frequencies 1.40 Cumulative failure frequency 1.20 target 1.00 Control Inverter 0.80 Gearbox Pitch Mechanism blade tips 0.60 Yaw System Blade 0.40 Electric Brakes 0.20 Generator Shaft & Bearings 0.00 Base Line Advanced Robust Stall- Smart- Direct teeter stall drive 22
  • 23. Module 11: Operation & Maintenance DOWEC concepts: failure classes basic control concepts: yearly failure frequencies 1.40 Cat. 4: Small or no parts, 24 hrs Cum ulative failure frequency 1.20 target 1.00 Cat. 3: Small parts, 48 hrs 0.80 Cat. 2: Large 0.60 components internal crane 0.40 Cat. 1: Heavy components, 0.20 external crane 0.00 Base Line Advanced Robust Stall- Smart- Direct teeter stall driveModule 11: Operation & Maintenance Numerical Monte Carlo Simulation Quantity of Spare Parts in Stock • Site conditions 25 20 Spare Part 1 quantity 15 Spare Part 2 (wind and waves) 10 5 0 Spare Part 3 Spare Part 4 11071 12301 13531 14761 15991 17221 1231 2461 3691 4921 6151 7381 8611 9841 • Failures 1 time [hours] components of turbine, Accumulative Availability of Wind Farm against Time and wind farm 101.00% 100.00% 99.00% • Maintenance strategy 98.00% 97.00% 96.00% - ships and crew 10341 11281 12221 13161 14101 15041 15981 16921 941 1881 2821 3761 4701 5641 6581 7521 8461 9401 1 time [hours] - immediate/batch repair Availability of Turbines turbine 1 turbine 2 - overhaul 101.00% 100.00% turbine 3 turbine 4 turbine 5 - stock keeping 99.00% turbine 6 98.00% turbine 7 97.00% turbine 8 96.00% turbine 9 95.00% turbine 10 94.00% turbine 11 93.00% turbine 12 23
  • 24. Module 11: Operation & Maintenance DOWEC 500 MW wind farm 100.00% Accessibility 80 % 2.10E+09 2.00E+09target 95.00% Yearly yield [kWh] 1.90E+09 90.00% 1.80E+09 85.00% 1.70E+09 80.00% t 1.60E+09 ll er e d e us ta n iv ce et Li t-s ob dr n e e l-t va ar R ct as al Ad Sm ire B St DModule 11: Operation & Maintenance DOWEC 500 MW wind farm 100.00% Accessibility 60 % 2.10E+09 2.00E+09target 95.00% Yearly yield [kWh] 1.90E+09 90.00% 1.80E+09 85.00% 1.70E+09 80.00% 1.60E+09 t ll er d e e us ta n iv ce et Li t-s ob dr n e l-t va e ar R ct as al Ad Sm ire B St D 24
  • 25. Module 11: Operation & Maintenance DOWEC 500 MW wind farm Yearly O&M costs of wind farm [Euro] € 45,000,000 € 40,000,000 € 35,000,000 € 30,000,000 Euro € 25,000,000 € 20,000,000 Fixed costs € 15,000,000 Transport costs € 10,000,000 Crew costs € 5,000,000 €0 Cat 4: No parts Cat 3: Small parts ed e ll ne t r us te iv ta Cat 2: Large comp. nc Li ee dr t-s ob va e l- t ct ar Cat 1: Heavy lift R as Ad al re Sm B St DiModule 11: Operation & Maintenance Context of the project • Consortium of industries and institutes • Project: ~ 500 MW offshore wind farm • Location: North Sea > 12 mile zone • Concepts of 5 MW wind turbines • Turbine design for large scale wind farm Develop optimal crew transport strategy 25
  • 26. Module 11: Operation & Maintenance The Target Develop an optimal O&M strategy for crew transport in the DOWEC offshore wind farm • 80 * 6 MW wind turbines • 43 km off the Dutch coast (“NL7”) • 40 PM operations per year • 1.5 failure per year per turbine (120 (averaged) CM operations per year) • 1 shift (12h) per 24 hoursModule 11: Operation & Maintenance Access systems considered Significant Average (1-hour) No Access system wave height wind speed [m] [m/s] 1 Fictitious 0.75 N.A. 2 Rubber boat, jump onto 1.5 10 ladder 3 Offshore Access System 2 11.5 (OAS) 4 Offshore Access System 3 15 + (optimistic assumption) 5 Helicopter NA 20 26
  • 27. Module 11: Operation & Maintenance Wind & waves from the NESS/NEXT database• North European Storm Study• consortium of oil companies ‘NL7’ location (“NL7“ data made available by Shell)• “hindcast“ data • wind fields based on pressure data • application of wave models • verification with measurements• 3- hours interval; 30*30 km grid• 30 years; 9 years complete + (long term correlation of wind and waves)Module 11: Operation & Maintenance Variables in the NESS/NEXT database Characteristic values for each 3-hour period: •V (1-hour) mean wind speed (m/s) at 10 m height • θV wind direction (degrees) • Hs significant wave height (m) • Tz mean zero upcrossing period (s) • Θm wave direction (degrees) 9 years of consecutive data 27
  • 28. Module 11: Operation & Maintenance From 3 D scatter plot pdf → Vw → • ? pdf → •⇒ Hs → pdf → NEXT database: built-in (long term) correlation between wind and wave data Tz →Module 11: Operation & Maintenance To 2 D relations V Hs 28
  • 29. Module 11: Operation & Maintenance NESS/NEXT database relation for NL7 V 25 20 Helicopter 15 OAS+ 10 Zodiac 5 OAS 1 2 3 4 5 HsModule 11: Operation & Maintenance Weather windows 1 Example: • Uninterrupted time intervals Hs < 1.25 m Windows: • 6 hours • 12 hours • 24 hours • ...... hours 29
  • 30. Module 11: Operation & Maintenance Weather windows 2 120 Heli summer Heli winter OAS+ summer 100 OAS summer OAS+ winter 80 Zodiac summer OAS winter Percentage % 60 Zodiac winter Fictitious summer Fictitious winter 40 20 0 0 10 20 30 40 50 60 Weather window [hours] Weather Window [hours]Module 11: Operation & Maintenance Availability of the DOWEC wind farm 120.0 OAS+Heli 100.0 OAS Zodiac Availability [%] Availability [%] 80.0 60.0 40.0 20.0 0.0 0 20 40 60 80 100 Accessibility Accessibility [%] [%] 30
  • 31. Module 11: Operation & Maintenance Immediate maintenance action 100 Direct action and compltetion % 90 12 hours 80 24 hours 48 hours 70 168 hours 60 336 hours 50 12 hours 40 [%] 24 hours 30 48 hours 20 168 hours 10 336 hours 0 20 40 60 80 100 Accessibility Accessibility [%] [%]Module 11: Operation & Maintenance Average waiting time 336 Average nr of waiting hours 288 12 hours 24 hours Waiting hours 240 48 hours 168 hours 192 336 hours 144 96 48 0 40 50 60 70 80 90 100 Accessibility [%] Accessibility [%] 31
  • 32. Module 11: Operation & Maintenance CONTOFAX overall results DOWEC reference wind farm: one shift with two crews No Access system Accessibility Availability [%] [%] 1 Fictitious 34 49 2 Rubber boat, jump onto 71 83 ladder 3 Offshore Access System 84 91 4 Offshore Access System+ 95 95 (optimistic assumption) 5 Helicopter 100 96Module 11: Operation & Maintenance DOWEC crew transport conclusions • Rubber boat landing strategy not feasible • OAS wind farm availability > 90% • OAS+ availability > 95% • OAS+ and heli comparable availability • Average waiting time for short maintenance actions (<48h) is limited (10 to 20 h) 32
  • 33. Module 11: Operation & Maintenance O&M Conclusions • Present wind turbine reliability insufficient • Certainly for wind farms at remote sites • Different maintenance strategy needed • Opportunity based (flexible service intervals) • Condition based maintenance • High impact of heavy lifting operations on costs • Large offshore wind farms need integrated design • Wind turbines designed for marine maintenance (and installation !!) operations • Special purpose O&M hardware 33