1. European Wind Energy Conference Milan, Italy May 7-11, 2007 Improving Wind Turbine Gearbox Reliability Walt Musial National Renewable Energy Laboratory Golden, Colorado USA walter_musial@nrel.gov Coauthors: Sandy Butterfield and Brian McNiff

2. European Wind Energy Conference Milan, Italy May 7-11, 2007 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.

3. European Wind Energy Conference Milan, Italy May 7-11, 2007 Bearing Failure Observations  General adherence to design standards  ISO 281:2007  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.

4. European Wind Energy Conference Milan, Italy May 7-11, 2007 Possible Design Process Weaknesses  Missing Load Cases  Irregular or unanticipated bearing responses  Excessive flexibility of gearbox mount.  Non-uniform safety applied to gearbox subcomponents.

5. European Wind Energy Conference Milan, Italy May 7-11, 2007 Typical Wind Turbine Architecture

6. European Wind Energy Conference Milan, Italy May 7-11, 2007 Hub Main Low Speed Shaft Bearing Trunnion Mounts Gearbox Bedplate Mainshaft Typical Gearbox Mounting

7. European Wind Energy Conference Milan, Italy May 7-11, 2007 Trouble Spots 1.Planet bearings 2.Intermediate shaft-locating bearings 3.High-speed locating bearings 1 3 2

8. European Wind Energy Conference Milan, Italy May 7-11, 2007 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

9. European Wind Energy Conference Milan, Italy May 7-11, 2007 Three Point Approach

10. European Wind Energy Conference Milan, Italy May 7-11, 2007 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

11. European Wind Energy Conference Milan, Italy May 7-11, 2007 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.

12. European Wind Energy Conference Milan, Italy May 7-11, 2007 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.

13. European Wind Energy Conference Milan, Italy May 7-11, 2007 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.

14. European Wind Energy Conference Milan, Italy May 7-11, 2007 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.

15. Panel Questions

16. 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

17. 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