Reliability Analysis and Prediction

1

• Reliability Analysis and Prediction
• of Wind Turbine Gearboxes
• K. Smolders, Hansen Transmissions International
• H. Long (speaker), Durham University
• Y. Feng, Durham University
• P. Tavner, Durham University

2
Outline of the Presentation

• Field reliability data from public sources
• Objectives of this study
• Generic WT gearbox configurations and modular
  structure
• Estimation of failure rates of critical
  components
• Reliability prediction of generic WT gearboxes.

3
Field Reliability and Downtime Data
4
Recent Reports on Gearbox Failures

• E.ON UK report on the first year of operation of
  an offshore wind farm in the UK (2005, 30
  turbines)
• There were 43 incidences of major unplanned work
• 39 were caused by failures within in the gearbox
• All of these were failures of the bearings
• 27 were in the intermediate speed shaft
• The remaining 12 were in the high speed shaft.
• Gear tooth failures were reported in 2.5 MW
  turbines
• 50 turbines were in need of repair and refit in
  August 2007.
• Design for Reliability to eliminate design faults
  and to improve operational performance.

5
Objectives of this Study

• To develop generic WT gearbox configurations
• To develop generic and flexible gearbox modular
  structure
• To develop reliability block diagrams
• To estimate failure rates of the critical
  components
• To provide quantitative reliability prediction of
  WT gearboxes at modular level, for different
  designs
• To identify reliability critical components in a
  WT gearbox.

6
Gearbox Generic Configurations

• Two WT configurations are considered R80 and
  R100
• Three gearbox designs GB-R80, GB-R100-S, and
  GB-R100-A

Characteristics R80 R100
Nominal Power (MW) 1.52.0 3.05.0
Rotor Diameter (m) 8090 120130
Hub Height (m) 60100 100120
Rotational Speed (rpm) 1020 1415

• GB-R80 1 planetary stage 2 parallel stages
  Ratio 100
• GB-R100-S 1 planetary (spur) 1 planetary
  (helical)Ratio 35
• GB-R100-A 2 planetary stages 1 parallel stage
  Ratio 126

7
Gearbox Modular Structure
8
Gearbox Configurations
GB-R100-A
GB-R80
9
Reliability Block Diagrams
10
Estimation of Failure Rates

• Require data of individual components of each
  module
• Consider R80 LS Planetary Module

• Handbook of Reliability Prediction Procedures
  for Mechanical Equipment
• Published by the US Naval Surface Warfare
  Centre (NSWC07)
• Provided prediction formulae and data sheets for
  gears, bearings, splines, shafts, ...

Components of R80 LS Planetary Module Failure Rate (failures/year) Quantity
LSS 0.0025 1
LSS Bearing RS 0.00009 1
LSS Bearing GS 0.00009 1
LS-PS 0.0025 3
LS-PS Bearing 0.00022 3
LS-PS Wheel 0.00017 3
LS Ring Wheel 0.00017 1
LS Sun Pinion 0.00017 1
LS Sun Shaft 0.0025 1
LS Sun Shaft Spline 0.00025 1
Total 0.01444 0.01444
11
Formulae for Gears and Bearings
Gears
Considering the base failure rate and
multiplication factors (operating speed, loading,
misalignment, viscosity of lubricant,
temperature, AGMA service factor).
Bearings
Where ?BE is the failure rate of the bearing
under specific operation conditions, calculated
by using the base failure rate of the bearing
?BE,B and the multiplication factors by
considering the applied load Cy, lubricant Cn,
water contamination CCW, and the operating
temperature Ct.
12
Failure Rates of R80 LS Planetary Module

• Assumptions
• Constant failure rates
• Base failure rates
• For shafts, keyways, structural components,
  joints, oils, pumps, sealings, piping, filters,
  coolers, heaters, sensors and breather

Components of R80 LS Planetary Module Failure Rate (failures/year) Quantity
LSS 0.0025 1
LSS Bearing RS 0.00009 1
LSS Bearing GS 0.00009 1
LS-PS 0.0025 3
LS-PS Bearing 0.00022 3
LS-PS Wheel 0.00017 3
LS Ring Wheel 0.00017 1
LS Sun Pinion 0.00017 1
LS Sun Shaft 0.0025 1
LS Sun Shaft Spline 0.00025 1
Total 0.01444 0.01444
13
Prediction of Failure Rates
14
Observations of the Predicted Results

• The high speed parallel stage is found to be the
  most unreliable module
• A planetary intermediate speed stage is less
  reliable than a parallel intermediate speed
  stage
• The planetary intermediate speed stage seems less
  reliable than the planetary low speed stage
• The lubrication subsystem has an important effect
  on reliability
• The housing and the accessories are the least
  reliability critical components.

15
Conclusions

• A reliability prediction method has been
  developed, based on Reliability Block Diagram and
  Gearbox Modular Structure
• Predicted results show that the high speed stage
  and planetary intermediate speed stage are less
  reliable
• Estimation of failure rates at component level is
  in need of improvement
• Field failure data through Life Data analysis or
  Weibull analysis can improve reliability
  prediction
• This requires collaborations between end-users,
  WT manufacturers, gearbox and bearing
  manufacturers.

16
Acknowledgement

• Financial support of the EC through the EU FP7
  Reliawind, Project No. 212966
• Reliawind project partners
• SKF
• Gamesa
• Alstom Ecotecnia
• Relex Italy
• Garrad Hassan
• ABB OY
• LM Glasfiber
• SZTAKI.