The effect of end windings and the bearing labyrinth seals on stray capacitances and bearing voltage ratio of AC motors

The bearing voltage brings premature failure of the motor bearings in the subway traction system, which is related to the stray capacitance of the motor. Therefore, the accurate calculation of stray capacitance parameters is of great significance for predicting bearing voltage. In previous studies, stray capacitances generally were acquired from simplified model of the motor. The effect of stator end-winding and the bearing labyrinth seal on stray capacitance was usually ignored. In this study, the stray capacitance is analysed and the finite element calculation is carried out, and the improved finite element model of motor is proposed, which includes the end-winding treatment and the bearing labyrinth seal. Then the feasibility of the improved model is verified by the measurement, and it is found that the accurate modelling of end windings has a great influence on the capacitance, and the bearing seal capacitance cannot be ignored while it is used in the motor. Finally, the influence of labyrinth seal parameters on the bearing voltage ratio of the motor is analysed, and it is concluded that the reduction of the radial gap width or the axial gap width of labyrinth seal can effectively reduce the risk of baring current.