Wind turbine planetary gearbox health diagnostic using time-varying meshing stiffness

In wind turbine planetary gearbox, the ability to identify ring-planet-sun gears meshing stiffness from the real data of vibration responses makes it possible to determine the physical existed planet gear defects which are used for severity assessments. There are limitations for vibration based gear diagnostic methods. Vibrations are secondary effects in the sense that they are dynamic responses of a gearbox excited by meshing stiffness and other excitations. The aim of this work is to diagnose the level of defects (gear tooth crack, gear tooth spalling and gear tooth breakage) in wind turbine gearbox using gears meshing stiffness. Time-varying meshing stiffness is used, where, a technique consists of a non-linear numerical optimisation is applied. The optimisation uses a dynamic model of the gears mesh and forms an estimate of both time-varying and frequency-varying mesh stiffness that best corresponds to the given set of vibration data. Multi-hour tests were conducted and recordings were acquired using translation vibration monitoring, where the optimum meshing stiffness was computed. The optimum meshing stiffness with the recording time was highlighted suggesting critical changes in the operation of the gearbox. The results indicate that if one tooth is defected due to cracks, spalling and breakage to reach the setting maximum level, the maintenance regime will be called despite a new damage is prone in the adjacent tooth to save time and cost.