Power losses at low speed in a gearbox lubricated with wind turbine gear oils with special focus on churning losses

In this study gear oils were tested for power loss behaviour in a two stage multiplying gearbox, on a back-to-back test rig with recirculating power. The tests were performed at low input speeds and high input torques with oil sump temperature set free.A power loss model simulating the power loss mechanisms was implemented to evaluate gear power losses, but failed to correctly describe the gear churning.Two lubricant flow regimes were identified, which are related to the nature of the fluid circulation, as well as with the gearbox case. A calibration method for the gear churning loss is proposed based on these results and a method to identify the transition between the fluid flow regimes inside the gearbox.

► Four wind turbine gear oils were selected.
► Density and viscosities were measured.
► Efficiency tests were conducted on a gearbox at low speeds and high torques.
► Oil flow regimes were identified through thermal equilibrium temperatures analysis.
► A calibration method for a gear churning loss model is suggested.