What we can do to Improve the Reliability of Offshore Wind Farms
Peter TavnerEmeritus Professor, Durham University, UK Past President, European Academy of Wind Energy
“I have only one eye; I have a right to be blind sometimes... I really do not see the signal!” Vice-Admiral Horatio Lord Nelson at the battle of Copenhagen
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 1
Keynotes
• Aim to reduce risk, raise turbine Reliability and Availability, Reduce offshore wind Cost of Energy;
• Wind Turbine Reliability from onshore experience;• What we know about WT reliability;• Wind Turbine Availability, what is happening
Offshore?
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 2
Bathtub Curve
Useful Life ( = 1)
Time, t
Failure intensity
Early Life( < 1)
Wear-out Period( > 1)
Select more reliable componentsPreventive maintenance
Reliability centred maintenanceCondition based maintenance
Major sub-assemblychangeout
More rigorous
pretesting
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 3
SCADA & Condition Monitoring in Context
SCADA, < 0.001 HzContinuous signals & alarms
Structural HealthMonitoring,
SHM,< 5 Hz
Not continuous
ConditionMonitoring,
CM,< 35 Hz
Continuous
Diagnosis,>10 kHz
Not continuous
Condition Monitoring in ContextConventional rotating machine
condition monitoringaccelerometers, proximeters
article in oilBlade &
pitch monitoringElectrical Systemmonitoring
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 6
WT Condition Monitoring Test Rig-WTCMTR
• 3-phase, 4-pole, 30kW wound rotor induction generator
• 5:1 two-stage helical gears parallel shaft gearbox• 54kW DC motor
• Control Interface• Instrumentation
• Signal Conditioning• Data Acquisition NI LabVIEW
SKF WindCon system
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 7
WTCMTR– Synchronous Generator (SG)
Synchronous Generator
Gearbox DC MotorTorque Transducer
~
Resistive Load Banks
Instrumentation& Control Interface
Current & Voltage
Transducers
Variable Speed Drive
DC Tachometer
PC Running NI LabVIEWData Acquisition & Control
X & Y Proximeters
Accelerometer(s)
USB
Synchronous Generator
Gearbox DC MotorTorque Transducer
~~
Resistive Load Banks
Instrumentation& Control Interface
Current & Voltage
Transducers
Variable Speed Drive
DC Tachometer
PC Running NI LabVIEWData Acquisition & Control
X & Y Proximeters
Accelerometer(s)
USB
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 8
SG Electrical Results
100 200 300 400 500 600 700 800 90015
20
25
spee
d / r
ev/m
in
100 200 300 400 500 600 700 800 900150
200
250
300
350
time /s
torq
ue /N
m
original torque signaldenoised torque signal
coilconnected
coilconnected
coilshorted
coilshorted
coilconnected
100 200 300 400 500 600 700 800 9009
10
11
12
13
14
15
time /s
C /
N*m
*min
/rev
using original torque signalusing denoised torque signal
coilconnected
coilconnected
coilconnected
coilshorted
coilshorted
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 9
SG Mechanical Results
0 50 100 150 200
24
26
28
30
spee
d / r
ev/m
in
0 50 100 150 200160180200220240260280
time /s
torq
ue /N
m
original torquedenoised torque
with imbalance faultno imbalance fault
20 40 60 80 100 120 140 160 180 2006
7
8
9
10
11
time /s
C / N
*m*m
in/re
v
using original torque signalusing denoised torque signal
no imbalance fault with imbalance fault
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 10
WTCMTR- Wound Rotor Induction Generator (WRIG) in open loop control
Wound Rotor Induction Machine
(Generator)
~
Resistive Load Banks (Rotor)
Grid Connection
Instrumentation& Control Interface
(NI DAQ Pads)
Current, Voltage & Power
Transducers
Variable Speed Drive
PC Running SKF ProCon& NI LabVIEW Data
Acquisition & Control
X & Y Proximeters
Accelerometer(s)
USB Link
Torque Transducer &
Shaft Tachometer
Gearbox DC Motor DC Tachometer
Experimental Balance Plane
3 Phase Supply
Experimental Balance Plane
Ethernet Link
SKF MasCon16
Unit
Wound Rotor Induction Machine
(Generator)
~~
Resistive Load Banks (Rotor)
Grid Connection
Instrumentation& Control Interface
(NI DAQ Pads)
Current, Voltage & Power
Transducers
Variable Speed Drive
PC Running SKF ProCon& NI LabVIEW Data
Acquisition & Control
X & Y Proximeters
Accelerometer(s)
USB Link
Torque Transducer &
Shaft Tachometer
Gearbox DC Motor DC Tachometer
Experimental Balance Plane
3 Phase Supply
Experimental Balance Plane
Ethernet Link
SKF MasCon16
Unit
NTNU, EU FR7 MARE WINT ProjectSeptember 2013
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WTCMTR-Comparison of Rig & Model
10-1 100 101 102 10310-8
10-6
10-4
10-2
100
102
Frequency (Hz)
PS
D (P
ower
per
Hz)
MeasuredSimulated
121.3 Hz
0.30 Hz
0.35 Hz
22.90 Hz
23.20 Hz
121.62 Hz
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 12
Fault Detection: Previous work• Focus on non-stationary signals
– Wind turbines are variable speed, variable load systems– Test rig driving conditions derived from a highly detailed wind
turbine model and proscribed wind/turbulence conditions
• Mechanical and electrical fault investigation under controlled environment
• Post-processing LabVIEW data collected during the tests
• Development of signal analysis method: Iterative Localised Discrete Fourier Transform (IDFTlocal)
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 13
WRIG Electrical Asymmetry Results
Wound rotor induction generator rotor electrical asymmetry– For example, brush gear fault/unbalance
Line current analysis– (1-2s)fse
Total power analysis– 2sfse
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 14
WRIG Mass Unbalance Results
High speed shaft mass unbalance– Mass applied near generator drive end
High speed shaft displacement analysis
– frm, machine rotational speed
Gearbox high speed end accelerometer analysis
– frm, machine rotational speed
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 15
Current research SKF WindCon unit configured to record and process the measured signals
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 16
Why an SKF WindCon System?• Commercially available system used
in wind industry• Flexible analogue inputs• Mechanical frequencies calculated by
machine information• Frequency analysis and alarms• Faults have been successful detected
in the field• Opportunity to investigate the system
in a controlled environment• Could the system be used for power
signal analysis?NTNU, EU FR7 MARE WINT Project
September 2013 17
Tests: Gearbox Gear Tooth DamageAIM: Investigate the effect of High Speed Shaft Pinion missing tooth on the
gearbox vibration signature
Accel 2
Accel 1
Healthy Tooth Damaged Tooth Missing ToothNTNU, EU FR7 MARE WINT Project
September 2013 18
Gearbox Vibration Signature• Fast Fourier Transform (FFT) analysis
• Identify frequencies or harmonic patterns indicative of a specific fault
• HEALTHY GEARS: characteristic fairly stable vibration pattern 2 gear meshing frequencies
fmesh,1 = 13.23 Xfmesh,2 = 58 X
their harmonics small amplitude sidebands
• FAULTY GEARS: what are the changes in the vibration signature?
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 19
Healthy Tooth Vibration Results
fmesh,1 2 X fmesh,1 2 X fmesh,2fmesh,2
WindCon (HSS) Accel2 Order Vibration FFT Spectrum(1560 rev/min)
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 20
Damaged Tooth Vibration Results
WindCon (HSS) Accel2 Order Vibration FFT Spectrum(1560 rev/min)
fmesh,1 2 X fmesh,1 2 X fmesh,2fmesh,2
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 21
Missing Tooth Vibration Results
fmesh,1 2 X fmesh,1 2 X fmesh,2fmesh,2
WindCon (HSS) Accel2 Order Vibration FFT Spectrum(1560 rev/min)
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 22
Spectra Comparison Harmonic content increase
More prominent 2 X fmesh,2sidebands spaced at the pinion rotational frequency (fHSS = 1X)
caused by the progressive damage introduced
The severity level of the tooth damage affects the
sideband amplitudes
Amplitude increases as a result of the 2 X fmesh,2
modulation by the faulted pinion impact per revolution
Healthy tooth
Damaged tooth
Missing tooth
0 20 40 60 80 100 120 140 160 180 200
0
0.1
0.2
0.3
0.4
0.5
0.6
Frequency (Order)
Am
plitu
de (g
Rm
s)
Healthy tooth
Damaged tooth
Missing tooth
110 112 114 116 118 120 122
0
0.05
0.1
0.15
0.2
0.25
Frequency (Order)
Am
plitu
de (g
Rm
s)
2 X fmesh,2
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 23
Power tracking algorithm Avoid time-consuming manual analysis for spectra comparison
Track the spectra power change in the 2 X fmesh,2 sideband narrowband
Power increase even in the case of low severity tooth damage
NTNU, EU FR7 MARE WINT ProjectSeptember 2013
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Vibration Results
• The signal harmonic content increases with the progressive gearbox HSS pinion damage
• Experimental data show that the presence of a faulty tooth results in more prominent sideband components of the 2 X fmesh,2 harmonic in
the vibration signal
• A detection algorithm has been proposed to track the overall power in the 2 X fmesh,2 sideband frequency
• Automatic detection may be possible during early stages of fault development using the power algorithm
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 25
Doubly-Fed Induction Generator
~
Data Acquisition Hardware
C urrent & Voltage Transducers
Variable Speed Drive
Data Acquisition & Control Environment
X & Y Proximeters
Accelerometer
Torque Transducer &
Shaft Tachometer
Gearbox DC Motor
Experimental Balance Plane
3 phase
Grid Connection
Experimental Balance Plane
3 phase
Grid Connection
DCTachometer
Converter Controller
~
~
Converter
Incremental Encoder
Torque
WTCMTR–Doubly-Fed Induction Generator in closed loop control
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 26
WTCMTR–DFIG Converter
Current & Voltage
Transducers
~
~
Current Transducers Clarke
Transformation(αβ)
ClarkeTransformation
(Ir_αβ)
Stator flux Calculation
(αβ)
Stator flux Angle calculation
(qs)
Magnetizingcurrent
Stator flux speed(ωs)
Rotorspeed(ωr)
Rotorangle(qr)
ParkTransformation
(Ir_dq)
Rotor current Reference
(Iqr_ref)
Rotor current Reference(Idr_ref=0)
PI Controller
Cross-Magnetisatio
n Compensatio
n terms
Rotor voltage Calculation
(Vr_dq)
Rotor voltage transformation
(Vr_abc)
Incremental Encoder
High speed shaft
Converter
Doubly-Fed Induction Generator
3 phase
Grid Connection
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 27
Future work • Define magnitude thresholds for various levels of fault severity to
refine the algorithm
• Incorporate the power algorithm in WindCon to automate the detection process
• Investigate electrical fault conditions (i.e. generator electrical asymmetry)
• Investigate mechanical fault conditions (i.e. LSS and HSS mass unbalance)
• Development of fault detection algorithms and their incorporation into WindCon to automatically track faulty frequencies
• Test the developed automated detection processes on data from wind turbines operating in the field
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 30
O&M Research• What are the offshore challenges?
• How do SCADA and condition monitoring fit into a wider picture of operations?
• What is the benefit of condition monitoring?
• Is monitoring justified?
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 31
Performance: Capacity Factor
Scroby Sands (30 x V80‐2MW ‐ UK Offshore) North Hoyle (30 x V80‐2MW ‐ UK Offshore)
Kentish Flats (30 x V90‐3MW ‐ UK Offshore) Barrow (30 × V90‐3MW ‐ UK Offshore)
Egmond aan Zee (36 × V90‐3MW ‐ NL Offshore)
0
10
20
30
40
50
60
70
80
90
100
Jul‐0
4Aug
‐04
Sep‐04
Oct‐04
Nov
‐04
Dec‐04
Jan‐05
Feb‐05
Mar‐05
Apr‐05
May‐05
Jun‐05
Jul‐0
5Aug
‐05
Sep‐05
Oct‐05
Nov
‐05
Dec‐05
Jan‐06
Feb‐06
Mar‐06
Apr‐06
May‐06
Jun‐06
Jul‐0
6Aug
‐06
Sep‐06
Oct‐06
Nov
‐06
Dec‐06
Jan‐07
Feb‐07
Mar‐07
Apr‐07
May‐07
Jun‐07
Jul‐0
7Aug
‐07
Sep‐07
Oct‐07
Nov
‐07
Dec‐07
Jan‐08
Feb‐08
Mar‐08
Apr‐08
May‐08
Jun‐08
Jul‐0
8Aug
‐08
Sep‐08
Oct‐08
Nov
‐08
Dec‐08
Jan‐09
Feb‐09
Mar‐09
Apr‐09
May‐09
Jun‐09
Jul‐0
9Aug
‐09
Sep‐09
Oct‐09
Nov
‐09
Dec‐09
Capacity F
actor (%)
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Performance: Availability
0
10
20
30
40
50
60
70
80
90
100
Jul‐0
4Au
g‐04
Sep‐04
Oct‐04
Nov‐04
Dec‐04
Jan‐05
Feb‐05
Mar‐05
Apr‐05
May‐05
Jun‐05
Jul‐0
5Au
g‐05
Sep‐05
Oct‐05
Nov‐05
Dec‐05
Jan‐06
Feb‐06
Mar‐06
Apr‐06
May‐06
Jun‐06
Jul‐0
6Au
g‐06
Sep‐06
Oct‐06
Nov‐06
Dec‐06
Jan‐07
Feb‐07
Mar‐07
Apr‐07
May‐07
Jun‐07
Jul‐0
7Au
g‐07
Sep‐07
Oct‐07
Nov‐07
Dec‐07
Jan‐08
Feb‐08
Mar‐08
Apr‐08
May‐08
Jun‐08
Jul‐0
8Au
g‐08
Sep‐08
Oct‐08
Nov‐08
Dec‐08
Jan‐09
Feb‐09
Mar‐09
Apr‐09
May‐09
Jun‐09
Jul‐0
9Au
g‐09
Sep‐09
Oct‐09
Nov‐09
Dec‐09
Availability (%
)
Scroby Sands (30 x V80‐2MW ‐ UK Offshore) North Hoyle (30 x V80‐2MW ‐ UK Offshore)
Kentish Flats (30 x V90‐3MW ‐ UK Offshore) Barrow (30 × V90‐3MW ‐ UK Offshore)
Egmond aan Zee (36 × V90‐3MW ‐ NL Offshore)
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 33
0102030405060708090
100
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
Availability (%)
Wind Speed (m/s)
0102030405060708090
100
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
Availability (%)
Wind Speed (m/s)
0102030405060708090
100
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
Availability (%)
Wind Speed (m/s)
0102030405060708090
100
0.0 2.0 4.0 6.0 8.0 10.0 12.0 14.0
Availability (%)
Wind Speed (m/s)
Availability with Wind Speed
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 34
Generated and Lost Energy
0%
20%
40%
60%
80%
100%
5 6 7 8 9 10 11 12 13
Energy (M
Wh)
0%
20%
40%
60%
80%
100%
5 6 7 8 9 10 11 12 13
Energy (M
Wh)
0%
20%
40%
60%
80%
100%
5 6 7 8 9 10 11 12 13
Energy (M
Wh)
0%
20%
40%
60%
80%
100%
5 6 7 8 9 10 11 12 13
Energy (M
Wh)
Energy Generated Theoretical Lost Energy due to Unavailability
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 35
Cost of Condition Monitoring• CM often seen as too expensive
• Are the benefits worth the expense?
• SKF WindCon (Observer) ≈ £17,600
• Lost energy from an unplanned 24 hour stop:
• Conventional coal-fired plant with CCS ≈ £486,000
• 2MW onshore WT at 27% capacity ≈ £620
• Impractical
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 36
Cost of Failure• 2MW offshore gearbox failure
• Replacement gearbox ≈ £500,000
• Failure rate > 0.134 failures/turbine/year
• A 30 WT offshore farm can expect £2,500,000 failure costs at current rates
• Add £700,600 for generator failures
... ... ...
• SKF WindCon (Observer) ≈ £17,600 per turbine = £528,000
• Is it worth the cost of condition monitoring now...?
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 37
Operations Structure• How could we facilitate successful large wind farm operation?
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Future Work• Identify the causes of lost energy
• Are there problems with how we operate WTs?
• Do we fully understand large, multi-gigawatt offshore sites?
• Integration of condition monitoring and SCADA
• Link detection results to operation and maintenance structures
• How can results be presented and utilised?
• Quantify the benefits to industry of monitoring
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 40
Conclusions• For onshore WTs 75% faults cause 5% downtime, 25% faults cause
95% downtime• Pitch and Main Converters suffer from many faults but with low
downtimes.• Pitch and Main Converters represent a significant part of the 75%.• This behaviour could be problematic offshore.• WT reliability is affecting offshore performance• Sub-assemblies with high failure rates are consistent• Turbulence seems to be causing failures• Analysis of SCADA wind speeds, torques & shaft speeds is showing
ample evidence of turbulent effects• Link between turbulence and failures is difficult to prove• The mathematical tools to be used are not yet clear
NTNU, EU FR7 MARE WINT ProjectSeptember 2013 41
ReferencesTavner PJ, Xiang JP and Spinato F, Reliability analysis for wind turbines. Wind Energy 10(1): 1-18, 2006.Spinato F, Tavner PJ, van Bussel GJW and Koutoulakos E, Reliability of wind turbine subassemblies. IET Renewable, Power Generation 3(4): 1–15, 2009.Wilkinson M, Hendriks B, Spinato F, Gomez E, Bulacio H, Roca J, Tavner P J, Feng Y, Long H, Methodology and results of the ReliaWind reliability field study, Scientific Track, European Wind Energy Conference, Warsaw, 2010.Feng Y, Tavner PJ and Long H, Early experiences with UK round 1 offshore wind farms, Proc Institution of Civil Engineers – Energy, 163(EN4): 167–181, 2010.Tavner, P J, Faulstich, S, Hahn, B, van Bussel, G J W, Reliability & availability of wind turbine electrical & electronic components, European Power Electronics Journal, 20(4): 1-6, 2010.Faulstich, S., Hahn B., Tavner, P. J., Wind turbine downtime and its importance for offshore deployment, Wind Energy, DOI: 10.1002/we.421, published on early view.
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