Improving Wind Turbine Gearbox ReliabilityWalt MusialNational Renewable Energy LaboratoryGolden, Colorado USAwalter_musial@nrel.gov

Coauthors: Sandy Butterfield and Brian McNiff

Observations on the basic problemsActual 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.

Bearing Failure ObservationsGeneral adherence to design standardsISO 281:2007Proprietary 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.

Possible Design Process WeaknessesMissing Load CasesIrregular or unanticipated bearing responses Excessive flexibility of gearbox mount.Non-uniform safety applied to gearbox subcomponents.

Typical Wind Turbine Architecture

Typical Gearbox MountingHubMain Low Speed Shaft BearingTrunnion MountsGearboxBedplateMainshaft

Trouble SpotsPlanet bearingsIntermediate shaft-locating bearingsHigh-speed locating bearings132

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 measurementsCondition monitoringExpert failure analysis and forensics

Three Point Approach

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

Dynamometer TestingMeasure 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.

Field TestingPonnequin Windfarm in Northern Colorado USAExtensive measurements on a single turbine.Characterize load events Correlate loads with component internal gearbox responses. Site-wide failures and statistics.

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

SummaryBearing 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.

Panel Questions

Panel Questions 1What is different with the Wind Turbine application compared to other industriesWhat 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

Panel Questions 2Where do uncertainties exist in the loads, design, rating and system integration?For prototype validation what should be tested/ validated/ verified to improve confidence in designsWhat future research needs to be done to improve reliability