European Wind Energy Conference

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Improving Wind Turbine Gearbox Reliability

• Walt Musial
• National Renewable Energy Laboratory
• Golden, Colorado USA
• walter_musial_at_nrel.gov
• Coauthors Sandy Butterfield and Brian McNiff

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Observations on the basic problems

• Actual life is below expected design life.
• Problems are generic in nature.
• Poor quality is not the primary cause.
• Most failures initiate in the bearings.
• Problems are more dependent on bearing
  configuration than size.

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Bearing Failure Observations

• General adherence to design standards
• ISO 2812007
• Proprietary codes prevent design transparency.
• Bearing manufacturers are not equipped to solve
  the problem on their own.
• No single, simple solution is expected.
• Collaborative approach is needed.
• Weaknesses in the design process are suspected.

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Possible Design Process Weaknesses

• Missing Load Cases
• Irregular or unanticipated bearing responses
• Excessive flexibility of gearbox mount.
• Non-uniform safety applied to gearbox
  subcomponents.

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Typical Wind Turbine Architecture
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Typical Gearbox Mounting
Hub
Main Low Speed Shaft Bearing
Gearbox
Trunnion Mounts
Mainshaft
Bedplate
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Trouble Spots

• Planet bearings
• Intermediate shaft-locating bearings
• High-speed locating bearings

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2
1
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Test Articles (phase I)

• Test platform between 600-kW and 900-kW.
• 2 gearboxes with identical instrumentation.
• Upgrade both units to state-of-the art.
• Cooling, filtration, gear finish, lubrication,
  and bearing types.
• Measure External and internal loads and
  displacements.
• Thermal measurements
• Condition monitoring
• Expert failure analysis and forensics

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Three Point Approach
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NREL Dynamometer Specifications

• 2.5 MW power delivery
• Full power regeneration at 480/575/690 or 4160
  volts
• Torque input range 0 - 1.62 million N-m.
• Speed range from 0 - 2250 RPM
• 500 kN non-torque shaft loads capacity.
• SCADA and automated torque/speed controls

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Dynamometer Testing

• Measure bearing responses to controlled load
  cases.
• Increase load complexity and build confidence.
• Develop non-torque load capability and simulate
  actual operating conditions.
• Establish transfer functions between shaft
  loading and bearing responses.

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Field Testing

• Ponnequin Windfarm in Northern Colorado USA
• Extensive measurements on a single turbine.
• Characterize load events
• Correlate loads with component internal gearbox
  responses.
• Site-wide failures and statistics.

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Drivetrain Analysis

• Multi-body dynamic analysis of test article.
• Codes FAST, Simpack, LVR
• Model bearing response under various load
  conditions measured in Dyno and Field.
• Model drivetrain solutions with tuned model.

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Summary

• Bearing failures are contributing to fleet-wide
  reductions in wind turbine gearbox life.
• A comprehensive three-part program to identify
  and fix weaknesses in the design process was
  initiated at NREL.
• A collaborative long-term approach is required
  involving all stakeholders.

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Panel Questions
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Panel Questions 1

• What is different with the Wind Turbine
  application compared to other industries
• What efforts (technical) are happening with your
  part of the industry to improve reliability
  (changes, research, design tools etc)
• Is there something in the design process that is
  lacking or needs more emphasis (loads
  description, rating methods, design tools

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Panel Questions 2

• Where do uncertainties exist in the loads,
  design, rating and system integration?
• For prototype validation what should be tested/
  validated/ verified to improve confidence in
  designs
• What future research needs to be done to improve
  reliability