Planetary Load Sharing in Three-Point- Mounted Wind Turbine Gearboxes: Preprint

Research output: Contribution to conferencePaper


Wind turbine gearboxes do not achieve their expected design life. The cost of gearbox replacements and rebuilds and the downtime associated with these failures increase the cost of wind energy. In 2007, the U.S. Department of Energy established the National Renewable Energy Laboratory (NREL) Gearbox Reliability Collaborative (GRC). Its goals are to understand the root causes of premature gearbox failures and improve their reliability. To date, the GRC has focused on a 750-kW drivetrain with a three-stage, three-point-mounted gearbox. A nonproprietary version of the gearbox containing CRBs with C3 clearances in the planetary stage was customized. Two of these gearboxes, GB1 and GB2, were manufactured and then tested in the National Wind Technology Center's 2.5-MW dynamometer and in the field. Major GRC findings include the detrimental effect of rotor moments on planetary load sharing and predicted fatigue, and the risk of bearing sliding in low-torque conditions for three-point configuration drivetrains. Based on the knowledge gained from testing and analysis of the original design, the GRC gearbox was redesigned to improve its load-sharing characteristics and predicted fatigue. This new gearbox is named GB3. As shown in Figure 1, its key improvement is the incorporation of preloaded TRBs that support the planet carrier and planets. Roller loads can be optimized and bearing life maximized with a small preload [4]. These preloaded bearings, along with interference-fitted planet pins, improve alignments and load-sharing characteristics. A semi-integrated planet bearing design also increases capacity and eliminates outer race fretting. Romax Technology, with Powertrain Engineers and the Timken Company (Timken), completed the redesign. Timken manufactured and instrumented the planet gears and bearings. Brad Foote Gearing manufactured the other gearing and assembled the gearbox.
Original languageAmerican English
Number of pages5
StatePublished - 2017
Event2017 American Society of Mechanical Engineers (ASME) International Design Engineering Technical Conference (IDETC) - Cleveland, Ohio
Duration: 6 Aug 20179 Aug 2017


Conference2017 American Society of Mechanical Engineers (ASME) International Design Engineering Technical Conference (IDETC)
CityCleveland, Ohio

NREL Publication Number

  • NREL/CP-5000-68221


  • gearbox
  • Gearbox Reliability Collaborative
  • gearboxes
  • GRC
  • NREL
  • wind energy
  • wind turbine


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