Time-stepping finite element analysis on the influence of skewed rotors and different skew angles on the losses of squirrel cage asynchronous motors

Abstract

To study the influence of skewed rotors and different skew angles on the losses of squirrel cage asynchronous motors, a 5.5-kW motor was taken as an example and the multi-sliced field-circuit coupled time stepping finite element method (T-S FEM) was used to analyze the axially non-uniform fundamental and harmonic field distribution characteristics at typical locations in the stator and rotor cores. The major conclusions are: firstly the skewed rotor exhibits a decrease in the harmonic copper losses caused by slot harmonic currents in the stator winding and rotor bars. Secondly, the skewed rotor shifts the non-uniform distribution of field in the axial direction, which leads to more severe saturation and an increase in iron losses. The heavier the load, the more pronounced the increase in iron losses. Furthermore, the influences of different skew angles on motor losses are studied systematically, with skew angles from 0.5 to 1.5 stator tooth pitch. It is found that the lowest total loss occurs at 0.8 stator tooth pitch, and the slot harmonics can be decreased effectively.