Reliability & Availability of Wind TurbineElectrical & Electronic ComponentsElectrical & Electronic Components

Peter Tavner, Professor of New & Renewable EnergyEnergy GroupEnergy GroupHead of School of Engineering, Durham University

“One has to consider causes rather than symptoms of undesirable events andOne has to consider causes rather than symptoms of undesirable events and avoid uncritical attitudes.” Prof Dr Alessandro Birolini

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Availability OperatorAvailability, Operator

Operability100%100%

MTBF

MTTFLogistic Delay

time

0% MTTRTime

%

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Availability ManufacturerAvailability, Manufacturer

Operability100%100%

MTBF

MTTF

0% MTTRTime

%

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Availability Manufacturer?Availability, Manufacturer?

Operability100%100%

MTBF

MTTFOp key

turned off

0% MTTRTime

%

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Availability & Reliability•• Mean Time To Failure, Mean Time To Failure, MTTFMTTF•• Mean Time to Repair, or downtime Mean Time to Repair, or downtime MTTRMTTR•• Mean Time Between Failures, Mean Time Between Failures,

MTTF ≈ MTBFMTTF ≈ MTBFMTBF≈MTTF+MTTR=1/MTBF≈MTTF+MTTR=1/λ +1/ μλ +1/ μμμMTBF=MTBF=MTTF+MTTR+LogisticMTTF+MTTR+Logistic Delay TimeDelay Time

•• Failure rate, Failure rate, λ λ λλ = 1/MTBF= 1/MTBFR i tR i t 1/MTTR1/MTTR•• Repair rate, Repair rate, μμ μμ=1/MTTR=1/MTTR

•• Manufacturer’s Availability, Manufacturer’s Availability, A=(MTBFA=(MTBF--MTTR)/MTBF=1MTTR)/MTBF=1−−(λ/μ)(λ/μ)

•• Operator’s or Technical Availability, Operator’s or Technical Availability, A=MTTF/MTBF < 1A=MTTF/MTBF < 1−−(λ/μ)(λ/μ)

•• Typical UK valuesTypical UK values–– Operators Availability Operators Availability 97%, 97%, –– Manufacturers Availability Manufacturers Availability 98%98%

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Capacity FactorCapacity Factor•• Energy generated in a year= C x Turbine rating xEnergy generated in a year= C x Turbine rating x•• Energy generated in a year= C x Turbine rating x Energy generated in a year= C x Turbine rating x

87608760C i FC i F CC•• Capacity Factor, Capacity Factor, CC

•• 8760 number of hours in a year8760 number of hours in a year•• Therefore:Therefore:•• C=Energy generated in a year/ Turbine rating xC=Energy generated in a year/ Turbine rating xC Energy generated in a year/ Turbine rating x C Energy generated in a year/ Turbine rating x

87608760•• CC incorporates the Availabilityincorporates the Availability AA and thereforeand therefore•• C C incorporates the Availability, incorporates the Availability, A, A, and therefore and therefore

the MTBF, the MTBF, 1/1/λλ

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Cost of Energy, COE•• COE, £/kWh= COE, £/kWh=

O&M+ {[(ICC*FCR) + LRC]/O&M+ {[(ICC*FCR) + LRC]/AEPnetAEPnet} } { ( ){ ( ) }}–– O&M=O&M=Cost of Operations & Maintenance, £Cost of Operations & Maintenance, £–– ICC=ICC=Initial Capital Cost, £Initial Capital Cost, £–– FCRFCR=Fixed Charge Rate, interest, %=Fixed Charge Rate, interest, %–– LCRLCR==LevelisedLevelised Cost of Replacement, replacing unavailable Cost of Replacement, replacing unavailable

ti £ti £generation, £generation, £–– AEPAEP=Annualised Energy Production, kWh=Annualised Energy Production, kWh

•• COE £/kWh =COE £/kWh =•• COE , £/kWh = COE , £/kWh = O&M(O&M(λλ, , 1/1/μ) μ) + {[(ICC*FCR) + LRC(+ {[(ICC*FCR) + LRC(λλ,, 1/1/μ)μ)]/]/AEPnetAEPnet(A((A(μμ, , 1/1/λλ)} )}

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Cost of Energy, COEgy,•• Reduce failure rate, Reduce failure rate, λ,λ,

Reliability MTBF, Reliability MTBF, 1/1/λ,λ, andandAvailabilityAvailability AA improveimproveAvailability, Availability, AA, improve, improve

•• Increase repair rate, Increase repair rate, μ,μ,p ,p , μ,μ,Downtime MTTF, Downtime MTTF, 1/1/μ μ reducesreduces,, andandA il biliA il bili AA iiAvailability, Availability, AA, improve, improve

•• ThereforeTherefore COECOE, reduces, reducesTherefore Therefore COECOE, reduces, reduces

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Root Causes & F il M d& Failure Modes

Failure Mode

H ?Why?

(Symptom)Main Shaft Failure

How?

Condition

Why?

Root Cause A l i Fracture Deformation

Monitoring

& Diagnosis

Analysis Fracture Deformation

High Cycle Fatigue Corrosion Low Cycle Fatigue orOverload Misalignment

Root Causes

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The Bathtub CurveFailure

Intensity, λ failures ofnumber Total

⎟⎟⎞

⎜⎜⎛λ

(years) Period OperatingPopulation Turbine ⎟⎟

⎠⎜⎜⎝=aλ

Most turbines

lie here

Time t

te)t( βρβλ −=

Early Life(β < 1)

Useful Life(β = 1)

Wear-out Period(β > 1)

Time, t

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(β < 1) (β = 1) (β > 1)

Trend in Turbine Failure Rates ith tiwith time

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Reliability & Size, EU

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Wind Turbine Subassemblies

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Wind Turbine ConfigurationsConfigurations

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Reliability & Subassemblies EUReliability & Subassemblies , EU

IndustrialReliability figures

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Reliability & Downtime & Subassemblies EUSubassemblies, EU

Electrical System LWK F il R t 6000 T bi Y

ISET Pivot Diagram Failure Rate and Downtime from 2 Large Surveys of European Wind Turbines

Other

Electrical Control

Electrical System LWK Failure Rate, approx 6000 Turbine Years

WMEP Failure Rate, approx 7800 Turbine YearsLWK Downtime, approx 6000 Turbine Years

Yaw System

Hydraulic System WMEP Downtime, approx 7800 Turbine Years

R t Bl d

Mechanical Brake

Rotor Hub

Generator

Gearbox

Rotor Blades

Drive Train

1 0.75 0.5 0.25 0 2 4 6 8 10 12 14 Annual failure frequency Downtime per failure (days)

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p ( y )

RELIAWIND Training Course, 1st June 2009, Helsinki

Reliability & Time, LWKy ,

LWK, E66, converter

1.0

ar]

9 y

ears

.60.

8

ilure

s / y

ea

apse

d tim

e: 9

0.4

0

ensi

ty [

fa

actu

al e

l

demonstrated reliabilitydemonstrated reliabilitydemonstrated reliability

0.2

failu

re in

t

industrial range

0 20 40 60 80 100

0.0

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Reliability & Time, LWK G tGenerators

81.

0

LWK, E40, generator

ear]

11 y

ears

81.

0

LWK, E66, generator

ear]

7 y

ears

0.4

0.6

0.8

e in

tens

ity [

failu

res

/ ye

actu

al e

laps

ed ti

me:

20.

40.

60.

8

re in

tens

ity [

failu

res

/ ye

actu

al e

laps

ed ti

me:

0 100 200 300 400 500

0.0

0.2

total test time [turbines * year]

failu

re

industrial range

0 20 40 60 80

0.0

0.2

total test time [turbines * year]

failu

r

industrial range

0.6

0.8

1.0

LWK, V27/225, generator

ailu

res

/ yea

r]

laps

ed ti

me:

12

yea

rs

0.6

0.8

1.0

LWK, V39/500, generator

ailu

res

/ yea

r]

elap

sed

time:

11

yea

rs

0.0

0.2

0.4

0

failu

re in

tens

ity [

fa

actu

al e

l

industrial range

0.0

0.2

0.4

0

failu

re in

tens

ity [

fa

actu

al e

industrial range

0 100 200 300 400

0

total test time [turbines * year]

0 100 200 300 400 500

total test time [turbines * year] Figure 4.4: Variation between the failure rates of generator subassemblies, in the LWK

population of German WTs, using the PLP model. The upper two are low speed direct drive generators while the lower two are high speed

i di t d i t

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indirect drive generators.

Reliability & Time, LWKG bGearboxes

1.0

LWK, TW600, gearbox

r] yea

rs 1.0

LWK, V39/500, gearbox

r] year

s

0.4

0.6

0.8

tens

ity [

failu

res

/ yea

r

actu

al e

laps

ed ti

me:

12

0.4

0.6

0.8

tens

ity [

failu

res

/ yea

r

actu

al e

laps

ed ti

me:

11

0 100 200 300

0.0

0.2

total test time [turbines * year]

failu

re in

t

industrial value

0 100 200 300 400 500

0.0

0.2

total test time [turbines * year]

failu

re in

t

industrial value

0.8

1.0

LWK, N52/N54, gearbox

s / y

ear]

d tim

e: 7

yea

rs

0.8

1.0

LWK, Micon M530, gearbox

s / y

ear]

time:

12

yea

rs

0.2

0.4

0.6

ailu

re in

tens

ity [

failu

res

actu

al e

laps

ed

industrial value

0.2

0.4

0.6

ailu

re in

tens

ity [

failu

res

actu

al e

laps

ed

industrial value

0 20 40 60 80 100

0.0

total test time [turbines * year]

fa industrial value

0 50 100 150 200 250

0.0

total test time [turbines * year]

fa industrial value

Figure 4.5: Variation between the failure rates of gearbox subassemblies, using the

PLP model in the LWK population of German WTs

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PLP model, in the LWK population of German WTs.

Reliability & Time, LWK El t iElectronics

81.

0

LWK, E40, electronics

year

]

: 11

yea

rs

81.

0

LWK, E66, electronics

ear]

7 y

ears

0.2

0.4

0.6

0.

ure

inte

nsity

[fa

ilure

s / y

actu

al e

laps

ed ti

me:

20.

40.

60.

8

re in

tens

ity [

failu

res

/ ye

actu

al e

laps

ed ti

me:

0 100 200 300 400 500

0.0

0

total test time [turbines * year]

failu

industrial range

0 20 40 60 80

0.0

0.

total test time [turbines * year]

failu

r

industrial range

LWK TW 1 5s electronics

0.6

0.8

1.0

LWK, TW 1.5s, electronics

y [f

ailu

res

/ yea

r]

tual

ela

psed

tim

e: 5

yea

rs

0 10 20 30 40 50

0.0

0.2

0.4

failu

re in

tens

ity act

industrial range

total test time [turbines * year] Figure 4.6: Variation between the failure rates of electronics subassemblies, or converter,

using the PLP model, in the LWK population of German WTs. The upper two are low speed direct drive generators with fully rated converters while the lower

two are high speed indirect drive generators with partially rated converters.

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g p g p y

Reliability of Electronicsy

Failure root cause distribution for power electronicsFailure root cause distribution for power electronicsfrom E Wolfgang, 2007

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Variable Load of Wind PowerLi Sid I tLine Side Inverter

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Variable Load of Wind PowerG t Sid I tGenerator Side Inverter

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ConclusionsConclusions•• Definitions of Availability are open to interpretationDefinitions of Availability are open to interpretation•• Unreliability > 1 failure/turbine/year is commonUnreliability > 1 failure/turbine/year is common•• Unreliability increases with turbine sizeUnreliability increases with turbine size•• Unreliability increases with turbine sizeUnreliability increases with turbine size•• Such unreliability will be unacceptable offshoreSuch unreliability will be unacceptable offshore•• Offshore we need unreliability < 0.5 failure/turbine/yearOffshore we need unreliability < 0.5 failure/turbine/year•• Unreliability concentrated mainly in the Drive Train including electricsUnreliability concentrated mainly in the Drive Train including electrics•• Unreliability concentrated mainly in the Drive Train including electricsUnreliability concentrated mainly in the Drive Train including electrics•• Some unreliable subassemblies are surprising:Some unreliable subassemblies are surprising:

–– For example gearboxes are not unreliableFor example gearboxes are not unreliable–– But gearbox failures cause large downtime and costsBut gearbox failures cause large downtime and costsBut gearbox failures cause large downtime and costsBut gearbox failures cause large downtime and costs–– But electrical parts are unreliableBut electrical parts are unreliable–– Cause less downtime but significant costs, their downtime will increase Cause less downtime but significant costs, their downtime will increase

offshoreoffshore•• For electrical parts the root causes from these surveys are not clear:For electrical parts the root causes from these surveys are not clear:

–– ComponentsComponents–– SystemsSystems–– ControlsControls

•• But the highly variable loading from the turbine is clearly a factorBut the highly variable loading from the turbine is clearly a factor•• PrePre--testing is essential to eliminate early life failurestesting is essential to eliminate early life failures

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Thank you• P. J. Tavner, C. Edwards, A. Brinkman, and F. Spinato. Inuence of wind

d i d t bi li bilit Wi d E i i 30(1) 2006speed on wind turbine reliability. Wind Engineering, 30(1), 2006.• P. J. Tavner, J. P.Xiang, and F. Spinato. Reliability analysis for wind

turbines. Wind Energy, 10(1), 2007.• F. Spinato, P. J. Tavner, and G.J.W van Bussel. Reliability-growth

l i f i d t bi f fi ld d t P di f AR2TSanalysis of wind turbines from field data. Proceedings of AR2TS conference, Loughborough, 2007.

• Tavner, P J, van Bussel, G J W, Spinato, F, Machine and converter reliabilities in WTs. Proceedings of IEE PEMD Conference, Dublin, April 2006April 2006.

• Hansen, A D., Hansen, L H. ,Wind turbine concept market penetration over 10 years (1995–2004), Wind Energy, 2007; 10:81–97

• Ribrant J., Bertling L.M.: Survey of failures in wind power systems with f S di h i d l t d i 1997 2005 IEEE Tfocus on Swedish wind power plants during 1997–2005, IEEE Trans. Energy Conversion, 2007, EC22 (1), pp. 167–173

• Wolfgang, E. Examples for failures in power electronics systems, in EPE Tutorial ‘Reliability of Power Electronic Systems’, April 2007.B k d hl P Skii I lli b P M d l f i d bi• Beckendahl, P, Skiip, an Intelligenb Power Module for wind turbine inverters, EPE Wind Chapter Mtg, Stockholm, May 2009

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