improving wind turbine gearbox reliability

European Wind Energy Conference

Milan, ItalyMay 7-11, 2007

Improving Wind Turbine Gearbox Reliability

Walt MusialNational Renewable Energy Laboratory

Golden, Colorado [email protected]

Coauthors: Sandy Butterfield and Brian McNiff

mailto:[email protected]



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.



Bearing Failure Observations

General 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 Weaknesses

Missing Load Cases

Irregular or unanticipated bearing responses

Excessive flexibility of gearbox mount.

Non-uniform safety applied to gearbox

subcomponents.



Typical Wind Turbine Architecture



HubMain Low

Speed Shaft Bearing Trunnion

Mounts

Gearbox

Bedplate

Mainshaft

Typical Gearbox Mounting



Trouble Spots

1. Planet bearings2. Intermediate shaft-locating bearings3. High-speed locating bearings

1

3

2



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 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.



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.



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.



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.

Panel Questions

Panel Questions 1

1. What is different with the Wind Turbine application compared to other industries

2. What efforts (technical) are happening with your part of the industry to improve reliability (changes, research, design tools etc)

3. Is there something in the design process that is lacking or needs more emphasis (loads description, rating methods, design tools

Panel Questions 2

4. Where do uncertainties exist in the loads, design, rating and system integration?

5. For prototype validation what should be tested/ validated/ verified to improve confidence in designs

6. What future research needs to be done to improve reliability

improving wind turbine gearbox reliability

Documents