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1
Module 11: Operation & Maintenance
Gerard van Bussel
section Wind Energy
OPERATION & MAINTENANCE
Module 11: Operation & Maintenance
Typical contribution to energy cost
Decommissioning3%
O & M
23%Investment
74%
Opti-OWECS study (1998)
Investment &
~ 75 %
Decommissioning
25 - 30%O & M
CA-OWEE (2001)
2
Module 11: Operation & Maintenance
maintenance
correctivemaintenance
preventivemaintenance
periodicpreventive
maintenance
conditionbased
maintenance
conditionjudging
conditionmonitoring
batch wisecorrective
maintenance
correctivemaintenanceon demand
calendarbased
opportunitybased
repair service
Maintenance Concepts
Module 11: Operation & Maintenance
Tacke TW600 Enercon 40 Vestas V39/500
number of turbines 25 26 59
events/year events/year events/yearLightning 0 0.03 0Blade 0.76 0.42 0.32Rotor Brake 0 0 0Pitch Mechanism 0 0.30 0.03Brake 0.08 0 0Shaft/Bearing 0.04 0.03 0Gearbox 0.16 0 0.03Generator 0 0.03 0.33Hydraulic 0.32 0 0.27Yaw System 0.32 0.23 0.08Anemometry 0 0 0.01Electronics 0.04 0.42 0.33Electric 0.20 0.69 0.30Inverter 0 0 0Sensors 0.08 0.07 0.18Other 0.20 0.38 0.37Overall Total 2.2 2.6 2.25
Failure frequencies 500kW class
Failure frequencies 2.2 2.6 2.25For larger machines (onshore) => 2.2 /year
3
Module 11: Operation & Maintenance
Component Failure frequency(failures/year)
Shaft & Bearings 0.02Brake 0.05Generator 0.05Parking Brake 0.05Electric 0.14Blade 0.16Yaw System 0.23Blade tips 0.28Pitch Mechanism 0.28Gearbox 0.30Inverter 0.32Control 0.34Total 2.20
Failure frequencies multi MWW class
Total of all components: 2.20 failures/year
Module 11: Operation & Maintenance
reliability(failures/year)
maintainability(MTTR)
serviceability(PM demand)
accessibilityof the site
maintenancestrategy
theoreticalavailability
actualavailability
actualavailability
Reliability, Availability, Maintainability, Serviceability
4
Module 11: Operation & Maintenance
A measure for availability
time
staterunning
failedMTTF
Mean Time To FailureMTTR
Mean Time To Repair
Availability =MTTF
MTTR + MTTF
Module 11: Operation & Maintenance
Experienced Availability
1996 1997 199890.00%
92.00%
94.00%
96.00%
98.00%
100.00%
Tuno Knob availability
1996 1997 199890.00%
92.00%
94.00%
96.00%
98.00%
100.00%
Tuno Knob availabilityTuno Knob (inshore,Denmark)
97%
5
Module 11: Operation & Maintenance
Present maintenance demand
Visits perturbineperyear
Unplanned
1
3
0Planned
2
4
Module 11: Operation & Maintenance
Oct Nov Dec Jan Feb Mar Apr May June July TotalNominalWorking Days
23 21 20 22 20 22 19 19 21 23 210
Bad Weather(Days)
1 1 0 2 4 5 4 0 0 0 17
Bad Weather(o.5 Day)
5 2 2 4 1 3 1 0 0 0 18
Lack ofTransport
0 2 0 0 1.5 4 6 1 0 0 14.5
InaccessibleDays
3.5 4 1 4 6 10.5 10.5 1 0 0 40.5
% Total Time 15.2 19 5 18.2 30 47.7 55.3 5.3 0 0 19.3
Accessibility of site (Vessel)
Vindeby DK inshore
6
Module 11: Operation & Maintenance
Horns Rev versus Vindeby Accessibility
0.00%
20.00%
40.00%
60.00%
80.00%
100.00%
120.00%
jan
feb
mar ap
r
may jun jul
aug
sep
oct
nov
dec
Frac
tion
of ti
me
6 hours12 hours24 hoursVindeby
Accessibility of site (Vessel)Vindeby(inshore,Denmark)
Horns Rev(near shore,North Sea)
Module 11: Operation & Maintenance
Means of crew transport
• Helicopter- fast- expensive - helipad- large operational
window
• Tender vessel- fairly slow- cheap- boat landing - medium
window
7
Module 11: Operation & Maintenance
A “gol” boatHarbour pilots
A tender vesselFor crew transport
Means of crew transport 2
Module 11: Operation & Maintenance
With a Zodiacfor landing
A tender vesselFor crew transport
Means of crew transport 3
8
Module 11: Operation & Maintenance
With a Zodiacfor landing ??With a Zodiacfor landing ??
Means of crew transport 4
Module 11: Operation & Maintenance
Means of crew transport 5
Crew transportby helicopter
9
Module 11: Operation & MaintenanceTrends: Access methods
Catamaran landing vessel
SWATH@A&R / Abeking &Rasmussen
Module 11: Operation & MaintenanceTrends: Access methods
Flexible gangway:
OAS: P&R systems / Reinout Prins
10
Module 11: Operation & Maintenance
Trends: Access methods
OAS: P&R systems / Reinout Prins
Flexible gangwayFlexible gangway
Module 11: Operation & Maintenance
Trends: Access methods
AmpelmannAmpelmann
11
Module 11: Operation & Maintenance
Cost comparison transport Vessel/Helicopter
2 MW Wind turbine farm
010002000300040005000600070008000
0 10 20 30 40 50 60 70 80
Distance Mantenance base to offshore wind farm [km]
Cos
ts [e
uro]
VesselHelicopterVessel+DowntimeHeli+Downtime
Module 11: Operation & Maintenance
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)
Experiences in the real world
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
• Jack-up barge• Crane vessels• Helicopter
• Jack up vesselassisted with built-in facility (in wind turbine)
Lifting equipment
13
Module 11: Operation & Maintenance
Installation & O&M lifting facilities
Utgrunden Wind farm, Sweden A2Sea Ocean Hanne at Horns Rev Denmark
Jack up vessels
Module 11: Operation & MaintenanceInstallation and O&M lifting facilities
A2Sea Ocean Hanne at Horns Rev and at NystedDenmark
Jack up vessels
14
Module 11: Operation & Maintenance
Internal cranes
Picture: Enron (Utgrunden, Sweden)
Picture: Nordex N80 Offshore
Hoisting outside
Trends: Lifting at wind turbine
Module 11: Operation & Maintenance
Trends: Installation
Ballast-Nedam NEG-Micon Dowec project
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 maintenance
Module 11: Operation & Maintenance
• 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)
Maintenance strategies
16
Module 11: Operation & Maintenance
50%
60%
70%
80%
90%
100%
40 % (remoteoffshore)
60 %(offshore)
80 %(nearshore)
100 %(onshore)
highlyimproved
improved
onshoredesign
Accessibility
Ava
ilabi
lity ReliabilityReliability
Importance of Reliability and Accessibility
Module 11: Operation & Maintenance
Importance of (improved) Reliability
50%
60%
70%
80%
90%
100%
40 % (remoteoffshore)
60 %(offshore)
80 %(near shore)
100 %(onshore)
OffshoreadaptedA
vaila
bilit
y
Vessel accessibility
50%
60%
70%
80%
90%
100%
40 % (remoteoffshore)
60 %(offshore)
80 %(near shore)
100 %(onshore)
Offshoreadapted
Vessel accessibility
Horns Rev(North Sea)
Tuno & Vindeby(DK inshore)
Offshoredesigned
17
Module 11: Operation & Maintenance
Assessing reliability, availability and O&M in the design process
Systems
specification
Conceptual design
Feasibilitystudy
RAMS targets on system
level
RAMS targets
sub-system level
RAMS targets on component level
RAMS targetssub-component level
Design evaluation
Final design
Expert system approach
Waiting time analysis
Full FMECA analysis
Monte Carlo Simulations
Module 11: Operation & Maintenance
Probabilistic Waiting time analysisTime To Repair
IJmuiden Munitie Stortplaats
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
0 100 200 300 400 500 600 700 800 900 1000
time [hrs]
CDF T_mission: 24 h
T_mission: 72 h
T_mission: 168 h
Time [hrs]
Chance[%]
ECN/ Luc Rademakers
18
Module 11: Operation & Maintenance
50 100 1500
20406080
100120
Max.availability
99.0 %98.0 %
97.0 %
Symbols: simulations
0No access percentage
Ava
ilabi
lity
[%]
Availability as Function of Maximum(onshore) Availability and Storm Percentage
Trend lines in expert system
Module 11: Operation & Maintenance
• 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
Monte Carlo simulations
19
Module 11: Operation & Maintenance
• 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)
FMECA: Failure Mode Effect and Criticality Analysis
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 !?
20
Module 11: Operation & Maintenance
Recent wind turbine failures
NEG Micon
YttreStengrunden
V 80 at Tjaereborg
Nordex N 80Blyth offshore
Module 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 aspectsin the context of the whole wind farm
21
Module 11: Operation & Maintenance
Yearlyfailurefreq.
Present500 kW
DOWECtarget (5 MW)
Assumed1.5 - 2 MW
1
2
0
Wind turbine’s reliability
Module 11: Operation & Maintenance
Reduction of failure frequencies
• 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
Components factor events/year
22
Module 11: Operation & Maintenance
Base line
Active Stall
3 blades
2 speed
Tubular tower
Piled (tripod)
Up wind
Advanced
Pitch
3 blades
Var. speed(30%)
Tubular tower
Piled (tripod)
Up wind
Robust
Stall
2 blades
Fixed speed
Tubular tower
Monopile
Up wind
Stall-teeter
Stall
2 blades
Var. speed(full)
Truss tower
Gravity
Down wind(teetered hub)
Smart stall
Stall
3 blades
Var. speed(full)
Tubular tower
Piled (tripod)
Up wind
Direct drive
pitch
3 blades
Var. speed(full)
Tubular tower
Piled (tripod)
Up wind
DOWEC concepts
Module 11: Operation & Maintenance
basic control concepts: yearly failure frequencies
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
Base Line Advanced Robust Stall-teeter
Smart-stall
Directdrive
Cum
ulat
ive
failu
re fr
eque
ncy
ControlInverterGearboxPitch Mechanismblade tipsYaw SystemBladeElectricBrakesGeneratorShaft & Bearings
DOWEC concepts: reliability
target
23
Module 11: Operation & Maintenance
DOWEC concepts: failure classesbasic control concepts: yearly failure frequencies
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
Base Line Advanced Robust Stall-teeter
Smart-stall
Directdrive
Cum
ulat
ive
failu
re fr
eque
ncy
Cat. 4: Small orno parts, 24 hrs
Cat. 3: Smallparts, 48 hrs
Cat. 2: Largecomponentsinternal crane
Cat. 1: Heavycomponents,external crane
target
Module 11: Operation & Maintenance
Numerical Monte Carlo SimulationQuantity of Spare Parts in Stock
0
5
10
15
20
25
1
1231
2461
3691
4921
6151
7381
8611
9841
1107
1
1230
1
1353
1
1476
1
1599
1
1722
1
time [hours]
quan
tity
Spare Part 1Spare Part 2Spare Part 3Spare Part 4
Accumulative Availability of Wind Farm against Time
96.00%
97.00%
98.00%
99.00%
100.00%
101.00%
1
941
1881
2821
3761
4701
5641
6581
7521
8461
9401
1034
1
1128
1
1222
1
1316
1
1410
1
1504
1
1598
1
1692
1
time [hours]
Availability of Turbines
93.00%
94.00%
95.00%
96.00%
97.00%
98.00%
99.00%
100.00%
101.00%
turbine 1turbine 2turbine 3turbine 4turbine 5turbine 6turbine 7turbine 8turbine 9turbine 10turbine 11turbine 12
• Site conditions(wind and waves)
• Failurescomponents of turbine, and wind farm
• Maintenance strategy- ships and crew- immediate/batch repair- overhaul- stock keeping
24
Module 11: Operation & Maintenance
DOWEC 500 MW wind farm
Accessibility 80 %
Base L
ine
Advance
d
Robust
Stall-te
eter
Smart-st
all
Direct
drive
80.00%
85.00%
90.00%
95.00%
100.00%
1.60E+09
1.70E+09
1.80E+09
1.90E+09
2.00E+09
2.10E+09
Year
ly y
ield
[kW
h]
target
Module 11: Operation & Maintenance
DOWEC 500 MW wind farmAccessibility 60 %
Base L
ine
Advance
d
Robust
Stall-te
eter
Smart-st
all
Direct
drive
80.00%
85.00%
90.00%
95.00%
100.00%
1.60E+09
1.70E+09
1.80E+09
1.90E+09
2.00E+09
2.10E+09
Year
ly y
ield
[kW
h]
target
25
Module 11: Operation & Maintenance
Yearly O&M costs of wind farm [Euro]
€ 0€ 5,000,000
€ 10,000,000€ 15,000,000€ 20,000,000€ 25,000,000€ 30,000,000€ 35,000,000€ 40,000,000€ 45,000,000
Base Line
Advanc
ed
Robust
Stall-te
eter
Smart-s
tall
Direct
drive
Euro
Fixed costsTransport costsCrew costsCat 4: No partsCat 3: Small partsCat 2: Large comp.Cat 1: Heavy lift
DOWEC 500 MW wind farm
Module 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
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 hours
Module 11: Operation & Maintenance
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 1.5 10
3 Offshore Access System (OAS)
2 11.5
4 Offshore Access System + (optimistic assumption)
3 15
5 Helicopter NA 20
27
Module 11: Operation & Maintenance
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
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
28
Module 11: Operation & Maintenance
From 3 D scatter plot
NEXT database: built-in (long term)correlation between wind and wave data
• ?• ⇒
Hs →
pdf→
Vw→
pdf→
Tz →
pdf→
Module 11: Operation & Maintenance
To 2 D relations
V
Hs
29
Module 11: Operation & Maintenance
NESS/NEXT database relation for NL7
V
Hs1 2 3 4 5
5
10
15
20
25
Zodiac
OAS+
Helicopter
OAS
Module 11: Operation & Maintenance
Weather windows 1Example:• Uninterrupted time
intervals Hs < 1.25 m
Windows:• 6 hours• 12 hours• 24 hours• ...... hours
30
Module 11: Operation & Maintenance
Weather windows 2
0
20
40
60
80
100
120
0 10 20 30 40 50 60
Weather window [hours]
Perc
enta
geHeli summerHeli winterOAS+ summerOAS summerOAS+ winterZodiac summerOAS winterZodiac winterFictitious summerFictitious winter
Weather Window [hours]
%
Module 11: Operation & Maintenance
Availability of the DOWEC wind farm
0.0
20.0
40.0
60.0
80.0
100.0
120.0
0 20 40 60 80 100
Accessibility [%]
Ava
ilabi
lity
[%]
Accessibility [%]
Ava
ilabi
lity
[%]
HeliOAS+OAS
Zodiac
31
Module 11: Operation & Maintenance
Immediate maintenance action
0102030405060708090
100
20 40 60 80 100
Accessibility [%]
Dire
ct a
ctio
n an
d co
mpl
tetio
n % 12 hours
24 hours 48 hours 168 hours 336 hours 12 hours 24 hours 48 hours168 hours336 hours
Accessibility [%]
[%]
Module 11: Operation & Maintenance
Average waiting time
0
48
96
144
192
240
288
336
40 50 60 70 80 90 100
Accessibility [%]
Ave
rage
nr
of w
aitin
g ho
urs
12 hours 24 hours 48 hours168 hours336 hours
Accessibility [%]
Wai
ting
hour
s
32
Module 11: Operation & Maintenance
CONTOFAX overall results
No Access system Accessibility [%]
Availability [%]
1 Fictitious 34 49 2 Rubber boat, jump onto
ladder 71 83
3 Offshore Access System 84 91 4 Offshore Access System+
(optimistic assumption) 95 95
5 Helicopter 100 96
DOWEC reference wind farm: one shift with two crews
Module 11: Operation & Maintenance
DOWECcrew 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 maintenanceactions (<48h) is limited (10 to 20 h)
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