Investigation of Main Bearing Operating Conditions in a Three-Point Mount Wind Turbine Drivetrain

Olle Bankestrom, Yi Guo, Roger Bergua, Jonathan Keller, Mark Dunn

Research output: NRELPresentation


Wear related failures of spherical roller bearings in the main bearing position of three-point mount wind turbines have been higher than expected and can contribute to higher than anticipated operation-and-maintenance costs. In this paper, the operational conditions of such a main bearing, including measured axial displacement and velocity subject to the estimated axial loads are described for an instrumented, commercial wind turbine. The field measurements suggest a maximum axial speed between the bearing rings that is less than 2 millimeters per second. It is estimated that the axial speed between the ring and rollers is approximately 25% of this value. When compared to a speed of rolling from approximately 200-352 millimeters per second, the measured axial sliding is therefore significantly less than 1% of the speed of rolling. Previous numerical studies of lubricant film formation in rolling contacts have shown that the effect of axial sliding starts to be noticeable only when this ratio exceeds 10%; therefore, the axial velocity represents only a small disturbance to the nominal pure rolling case, and the influence on oil film building can be neglected. A simple analytic model of the main bearing motion was also developed and demonstrated similar displacement and velocity characteristics.
Original languageAmerican English
Number of pages13
StatePublished - 2021

Publication series

NamePresented at the Conference for Wind Power Drives, 9-11 March 2021

NREL Publication Number

  • NREL/PR-5000-79442


  • axial motion
  • main bearing
  • spherical roller bearing
  • wear


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