NREL is a national laboratory of the U.S. Department of Energy, Office of Energy Efficiency and Renewable Energy, operated by the Alliance for Sustainable Energy, LLC.

Presenter 

Francisco Oyague

May 23-26, 2010

Dallas, Texas

NREL/PR-500-48176

Gearbox Reliability Collaborative 

Experimental Data Overview & Analysis
National Renewable Energy Laboratory 2 Innovation for Our Energy Future

Drivetrain and the Cost of Energy

Wind turbine gearboxes fail to meet 20-year design life

• Premature failure of gearboxes increases cost of energy

– Turbine downtime

– Unplanned maintenance 

– Gearbox replacement and rebuild

– Increased warranty reserves

• The problem:

– Widespread

– Affecting many OEMs

– Not caused by manufacturing practices
National Renewable Energy Laboratory 3 Innovation for Our Energy Future

• Facilitate dialog among all parties

– Designers and consultants

– Suppliers and rebuilders

– Operations and maintenance 

organizations

• Understand gearbox response to 

specific loading

– Pure torque, bending, thrust 

(dynamometer)

– Turbulence (field)

• Understand physics of premature 

failure of wind turbine gearboxes 

• Identify gaps in design process 

• Suggest improvements in design 

practices and analytical tools 

Field Test Dynamometer Test

Analysis

• Load cases

• System loads

• Internal loads

• Test plan

• Test turbine

• Test setup & execution

Gearbox Reliability Collaborative (GRC)

• Test plan

• Test turbine

• Test setup & execution
National Renewable Energy Laboratory 4 Innovation for Our Energy Future

Failure Database Condition Monitoring

Accelerometer

Acoustic emission sensor

Proximity probe

Frequency range 

to above 20 kHz

Photo Sources: ProvibTech, Machine Condition Monitoring Ltd, Physical Acoustics Corporation

Gearbox Reliability Collaborative (GRC)
National Renewable Energy Laboratory 5 Innovation for Our Energy Future

Gearbox Redesign

Gearbox redesign to reflect MW fleet

• Floating sun

• Bearing arrangement 

• Lubrication 

• Gearing micro geometry 

DOE-owned GRC gearbox design distribution

• Detailed technical specifications

• Drawings and solid models 

• Material 

Round Robin Analysis

• Standardized analytical approaches

• Results from many commercial and in-house codes 
Instrumentation

National Renewable Energy Laboratory 6 Innovation for Our Energy Future

• Relative motion

– Planet carrier

– Sun 

– Planet 

– Housing 

• Forces, moments on main shaft

• Tooth load sharing between planet gears 

• Bearing roller load distribution

• Temperature gradients of bearings

• Planet bearing collective roller slip 
Planet Carrier Motion

National Renewable Energy Laboratory Innovation for Our Energy Future

• Implemented 4 sets of proximity sensor

• Machined Target surface

• Monitor of axis motions and angular motion

Planet Carrier

Planet Target surface
Planet Carrier Deformation

National Renewable Energy Laboratory Innovation for Our Energy Future

• Target surface deformation captured by the 

proximity sensors

• Deformation of planet carrier body 

correlated to planet pin misalignment
Planet Carrier Deformation

National Renewable Energy Laboratory Innovation for Our Energy Future

• Target surface deformation captured by the 

proximity sensors

• Deformation of planet carrier body 

correlated to planet pin misalignment
Analysis Versus Experimental Data 

• Finite element model validation using 

75% rated power 

• Two gearboxes produced slightly 

different behavior

• Boundary conditions are adjusted to 

account for the differences 

National Renewable Energy Laboratory Innovation for Our Energy Future

Experimental data 

Simulated results
National Renewable Energy Laboratory Innovation for Our Energy Future

Gear Tooth Contact Stress 

Force

Area

=

Load
National Renewable Energy Laboratory Innovation for Our Energy Future

Gear Tooth Contact Stress 

Force

Area

=

Load
Bearing Load 

National Renewable Energy Laboratory Innovation for Our Energy Future

• Equivalent load location => Bearing load distribution

• Life reduction of 8% due to gearbox manufacturing variability 

(planet pin misalignment only)

Up-wind BNG Down-wind BNG
National Renewable Energy Laboratory 14 Innovation for Our Energy Future

GRC Current and Future Work

• Facilitation and communication between the various 

parties involved in the design process 

• Multi-fidelity analysis validation through a round robin 

approach

• Acquisition of field and dynamometer test data for 

post-processing analysis

• Evaluation of analytical assumptions and other 

assumptions imbedded in the design process

• Implementation and population of database in order 

to truly understand the problem 
National Renewable Energy Laboratory 15 Innovation for Our Energy Future

GRC Current and Future Work

• Long term

– Produce multiple topical reports

– Provide reference data set for future testing of analytical 

tools and analysis approaches

– Provide support for standards updates 

• Redirect research and narrow focus by using the 

database statistics

• Expand project to include full drivetrain study

• Expand project to other drivetrain configurations