OPERATION & MAINTENANCE

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Warren Francis
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1 OPERATION & MAINTENANCE Gerard van Bussel section Wind Energy Typical contribution to energy cost O & M 23% Decommissioning 3% Investment 74% O & M 25-30% Investment & Decommissioning ~ 75 % Opti-OWECS study (1998) CA-OWEE (2001) 1

2 Maintenance Concepts maintenance corrective maintenance repair preventive maintenance service batch wise corrective maintenance corrective maintenance on demand periodic preventive maintenance condition based maintenance opportunity based calendar based condition judging condition monitoring Failure frequencies 500kW class Tacke TW600 Enercon 40 Vestas V39/500 number of turbines events/year events/year events/year Lightning Blade Rotor Brake Pitch Mechanism Brake Shaft/Bearing Gearbox Generator Hydraulic Yaw System Anemometry Electronics Electric Inverter Sensors Other Overall Total Failure frequencies For larger machines (onshore) => 2.2 /year 2

3 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/year Reliability, Availability, Maintainability, Serviceability reliability (failures/year) maintainability (MTTR) serviceability (PM demand) accessibility of the site theoretical availability maintenance strategy actual availability 3

4 state running A measure for availability failed MTTR MTTF Mean Time To Repair Mean Time To Failure Availability = MTTF MTTR + MTTF time Experienced Availability Tuno Knob (inshore, Denmark) 97% Tuno Knob availability % % 98.00% 98.00% 96.00% 96.00% 94.00% 94.00% 92.00% 92.00% 90.00% 90.00%

5 Present maintenance demand 4 Visits per turbine per year Unplanned Planned Accessibility of site (Vessel) Vindeby DK inshore Oct Nov Dec Jan Feb Mar Apr May June July Total Nominal Working Days Bad Weather (Days) Bad Weather (o.5 Day) Lack of Transport Inaccessible Days % Total Time

6 Accessibility of site (Vessel) Horns Rev (near shore, North Sea) Vindeby (inshore, Denmark) Horns Rev versus Vindeby Accessibility % % 80.00% 60.00% 40.00% 20.00% 0.00% jan feb mar apr may jun jul aug sep oct nov dec Fraction of time 6 hours 12 hours 24 hours Vindeby Means of crew transport Helicopter - fast - expensive - helipad - large operational window Tender vessel - fairly slow - cheap - boat landing -medium window 6

7 Means of crew transport 2 A tender vessel For crew transport A gol boat Harbour pilots Means of crew transport 3 A tender vessel For crew transport With a Zodiac for landing 7

8 Means of crew transport 4 With a Zodiac for landing?? Means of crew transport 5 Crew transport by helicopter 8

9 Trends: Access methods Catamaran landing vessel / Abeking &Rasmussen Trends: Access methods Flexible gangway: OAS: P&R systems / Reinout Prins 9

10 Trends: Access methods Flexible gangway Flexible gangway OAS: P&R systems / Reinout Prins Trends: Access methods Ampelmann 10

11 Cost comparison transport Vessel/Helicopter Costs [euro] MW Wind turbine farm Distance Mantenance base to offshore wind farm [km] Vessel Helicopter Vessel+Downtime Heli+Downtime 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) transfers in 1.5 years (2 x /day/turbine) 11

Experiences in the real world Maintaining Horns Rev: Reasons: Design not well adapted for offshore Strategy not optimal Onshore crew Sophisticated

12 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? Lifting equipment Jack-up barge Crane vessels Helicopter Jack up vessel assisted with built-in facility (in wind turbine) 12

Rev Denmark Installation and O&M lifting facilities Jack

13 Installation & O&M lifting facilities Jack up vessels Utgrunden Wind farm, Sweden A2Sea Ocean Hanne at Horns Rev Denmark Installation and O&M lifting facilities Jack up vessels A2Sea Ocean Hanne at Horns Rev and at Nysted Denmark 13

14 Trends: Lifting at wind turbine Hoisting outside Picture: Enron (Utgrunden, Sweden) Internal cranes Picture: Nordex N80 Offshore Trends: Installation Ballast-Nedam NEG-Micon Dowec project 14

15 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 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 Importance of Reliability and Accessibility 100% Availability 90% 80% 70% 60% 50% 100 % (onshore) 80 % (nearshore) 60 % (offshore) Accessibility 40 % (remote offshore) Reliability highly improved improved onshore design Importance of (improved) Reliability 100% Availability 90% 80% 70% 60% Offshore designed Offshore adapted 50% 100 % (onshore) 80 % 60 % (near shore) (offshore) Vessel accessibility 40 % (remote offshore) Tuno & Vindeby (DK inshore) Horns Rev (North Sea) 16

17 Assessing reliability, availability and O&M in the design process Design evaluation Conceptual design Feasibility study RAMS targets on system level RAMS targets sub-system level RAMS targets on component level Waiting time analysis Expert system approach Monte Carlo Simulations Final design Systems specification RAMS targets sub-component level Full FMECA analysis Probabilistic Waiting time analysis Time To Repair IJmuiden Munitie Stortplaats Chance [%] CDF 100% 90% 80% 70% 60% T_mission: 24 h 50% 40% T_mission: 72 h 30% 20% T_mission: 168 h 10% 0% time [hrs] ECN/ Luc Rademakers Time [hrs] 17

18 Trend lines in expert system Availability [%] Availability as Function of Maximum (onshore) Availability and Storm Percentage Max.availability 99.0 % 98.0 % 97.0 % Symbols: simulations No access percentage 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 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) 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

Recent wind turbine failures NEG Micon Yttre

Project: ~ 500 MW offshore wind farm Location:

turbines Turbine design for large scale wind

20 Recent wind turbine failures NEG Micon Yttre Stengrunden V 80 at Tjaereborg Nordex N 80 Blyth offshore 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 Wind turbine s reliability Yearly failure freq Present 500 kw Assumed MW DOWEC target (5 MW) Reduction of failure frequencies Components factor events/year Electric system Blades / 0.11 Yaw System blade tips Pitch Mechanism / 0.14 Gearbox / 0.15 Inverter Control system /

22 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 Tubular tower Var. speed (30%) Tubular tower Fixed speed Var. speed Tubular tower (full) Truss tower Var. speed (full) Tubular tower Var. speed (full) Tubular tower Piled (tripod) Up wind Piled (tripod) Up wind Monopile Up wind Gravity Down wind (teetered hub) Piled (tripod) Up wind Piled (tripod) Up wind DOWEC concepts: reliability basic control concepts: yearly failure frequencies 1.40 target Cumulative failure frequency Control Inverter Gearbox Pitch Mechanism blade tips Yaw System Blade Electric Brakes Generator Shaft & Bearings 0.00 Base Line Advanced Robust Stallteeter Smartstall Direct drive 22

23 1 1 DOWEC concepts: failure classes basic control concepts: yearly failure frequencies target Cumulative failure frequency Cat. 4: Small or no parts, 24 hrs Cat. 3: Small parts, 48 hrs Cat. 2: Large components internal crane Cat. 1: Heavy components, external crane 0.00 Base Line Advanced Robust Stallteeter Smartstall Direct drive Numerical Monte Carlo Simulation Site conditions (wind and waves) Failures components of turbine, and wind farm Maintenance strategy - ships and crew - immediate/batch repair - overhaul - stock keeping quantity Quantity of Spare Parts in Stock Spare Part 1 15 Spare Part 2 10 Spare Part 3 5 Spare Part time [hours] Accumulative Availability of Wind Farm against Time % % 99.00% 98.00% 97.00% 96.00% time [hours] turbine 1 Availability of Turbines turbine 2 turbine % turbine % turbine % turbine % turbine % turbine % turbine % turbine % turbine % turbine 12 23

24 DOWEC 500 MW wind farm % Accessibility 80 % 2.10E+09 target 95.00% 90.00% 85.00% 80.00% Base Line Advanced Robust Stall-teeter Smart-stall Direct drive 2.00E E E E E+09 Yearly yield [kwh] DOWEC 500 MW wind farm % Accessibility 60 % 2.10E+09 target 95.00% 90.00% 85.00% 80.00% Base Line Advanced Robust Stall-teeter Smart-stall Direct drive 2.00E E E E E+09 Yearly yield [kwh] 24

25 DOWEC 500 MW wind farm Yearly O&M costs of wind farm [Euro] Euro 45,000,000 40,000,000 35,000,000 30,000,000 25,000,000 20,000,000 15,000,000 10,000,000 5,000,000 0 Base Line Advanced Robust Stall-teeter Smart-stall Fixed costs Transport costs Crew costs Cat 4: No parts Direct drive Cat 3: Small parts Cat 2: Large comp. Cat 1: Heavy lift 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 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 hours Access systems considered No Access system Significant wave height [m] Average (1-hour) wind speed [m/s] 1 Fictitious 0.75 N.A. 2 Rubber boat, jump onto ladder 3 Offshore Access System (OAS) 4 Offshore Access System (optimistic assumption) 5 Helicopter NA 20 26

27 Wind & waves from the NESS/NEXT database North European Storm Study consortium of oil companies ( 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) NL7 location + 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 θ V wind direction (degrees) H s significant wave height (m) T z mean zero upcrossing period (s) Θ m wave direction (degrees) 9 years of consecutive data 27

28 pdf From 3 D scatter plot pdf Vw Hs? pdf Tz NEXT database: built-in (long term) correlation between wind and wave data To 2 D relations V Hs 28

29 NESS/NEXT database relation for NL7 V Zodiac OAS+ OAS Helicopter Hs Example: Uninterrupted time intervals H s < 1.25 m Weather windows 1 Windows: 6 hours 12 hours 24 hours... hours 29

30 Weather windows 2 % Percentage Heli summer Heli winter OAS+ summer OAS summer OAS+ winter Zodiac summer OAS winter Zodiac winter Fictitious summer Fictitious winter Weather window [hours] Weather Window [hours] Availability of the DOWEC wind farm Availability [%] Zodiac OAS+ Heli OAS Accessibility [%] [%] 30

31 Immediate maintenance action Direct action and compltetion % [%] Accessibility [%] Accessibility [%] 12 hours 24 hours 48 hours 168 hours 336 hours 12 hours 24 hours 48 hours 168 hours 336 hours 336 Average waiting time Average nr of waiting hours Waiting hours hours 24 hours 48 hours 168 hours 336 hours Accessibility [%] [%] 31

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

32 CONTOFAX overall results DOWEC reference wind farm: one shift with two crews No Access system Accessibility Availability [%] [%] 1 Fictitious Rubber boat, jump onto ladder 3 Offshore Access System Offshore Access System (optimistic assumption) 5 Helicopter 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 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

The impact of different means of transport on the operation and maintenance strategy for offshore wind farms

The impact of different means of transport on the operation and maintenance strategy for offshore wind farms W.A.A.M. Bierbooms, M Sc.; G.J.W. van Bussel, PhD * Section Wind Energy, Faculty Civil Engineering