Method for tracking a gear tooth meshing angle of a gearbox of a wind turbine

A method for tracking a gear tooth meshing angle of a gearbox of a wind turbine, the method comprising the steps of:

• setting a reference virtual gear tooth meshing angle of the gearbox,
• monitoring an angular position of a high speed shaft and/or a low speed shaft of the gearbox,
• estimating a virtual gear tooth meshing angle relative to the reference virtual gear tooth meshing angle, based on the monitored angular position of the high speed shaft and/or the low speed shaft and on information regarding topology of the gearbox,
• calculating a number of full rotations of the high speed shaft and/or the low speed shaft which corresponds to an integer number of full periods of gear meshing of the gearbox, based on information regarding topology of the gearbox,
• resetting the reference virtual gear tooth meshing angle each time the high speed shaft and/or the low speed shaft has performed the calculated number of full rotations, and continuing monitoring the angular position of the high speed shaft and/or the low speed shaft and continuing estimating the virtual gear tooth meshing angle relative to the reference virtual gear tooth meshing angle that has been reset, and
• applying the estimated virtual gear tooth meshing angle to a periodic noise signal of the wind turbine.