Research On Modeling And Simulation Of The Gearbox Of Wind Turbine With Cracked Tooth

As the core components of non-direct drive wind turbine, gearboxes are strongly affected by alternating load and fail easily. Researches of gearbox fault dynamics help people to understand mechanism of failure in-depth, and provide some guidance for the optimal design and fault diagnosis of gearbox. In this paper, the wind turbine gearbox is the study object, the following tasks are carried out around the gearbox fault modeling and simulation:The one-stage planetary gear and two-stage spur gear fixed axis system of wind turbine are chosen as the research object, using the coordinate transformation to deal with the motion analysis contradiction between planetary gear train and fixed gear train; using lumped parameter method, the 25-dimensional differential motion equations of gearbox reverse- lateral vibration are established. The simulation analysis on the gearbox model combined with wind turbine generator system(WTGS) model was carried out and the results revealed that the absolute speed of the various components was in full compliance with the law of the transmission ratio, it indicates the validity of the model.On the condition that materials and geometrical parameters of the gear were determined, the analytical expression of the meshing stiffness of the gear with perfect teeth varies from the turning angle was derived using potential energy method based on the theory of cantilever beam with variable cross section. Through the influence of crack failure to mesh stiffness parameters, meshing stiffness is derived in the case that there is crack in pitch circle and tooth root of the gear, from which two faults are simulated. From the gear meshing curves of these two kinds of typical crack fault, we can know the variation trend of gear meshing stiffness in any position when there is crack fault: with the position of cracks from the tooth root to the top, the pressure angle(turning angle) when meshing stiffness began to decline is increasing, the impact of faults on the meshing stiffness is decreasing. In addition, wherever the cracks occur, integrated meshing stiffness decreased when the degree of cracking increases.The fault characteristic frequencies of fixed axis gear trains and planetary gear trains were obtained through analyzing the vibration signals of gear in normal and localized fault condition. The local fault characteristic frequency is rotating frequency of the fault gear for fixed axis gear trains; while for planetary gear trains, it is relative rotation frequency of the fault gear in the moving coordinate following the planet carrier. Especially, to the fault components of the planetary gear trains, amplitude modulation effects of vibration signals is caused by the asymmetric load of the planet gear when fault tooth is in the meshing process. As a result, the modulation sideband which is composed by rotating frequency of the planet carrier, fault characteristic frequencies and their combination would appear around the meshing frequencies and their harmonics in the fault vibration signals. Analysis in time and frequency domains was applied to simulated vibration signals of the wind turbine model under the tooth root crack fault and the results were consistent with conclusions from the theoretical analysis of the vibration signals of gear in localized fault condition.