Direct modeling of the starting process of skewed rotor induction motors using a multi-slice technique

Both the starting current and the starting torque of induction motors cannot be evaluated and measured accurately and readily. In particular, the geometrical features of the skewed rotor bars are very difficult to study if a general 2-D finite element method is used. This paper presents an approach in using a multi-slice, time stepping 2-D eddy-current finite element method to study the starting processes of skewed rotor induction machines. The fields of the multi-slices are being solved en bloc simultaneously, and thus the eddy current effects can be taken into account directly. New forms of the governing equations for the multi-slice model are derived so as to allow the meshes of the multi-slices to be taken as one 2-D mesh. The resultant algorithm is then very similar to that of general 2-D problems. Special time stepping techniques for studying the starting process of motors are also presented. The performances of motors with skewed and nonskewed rotors are shown. It was found that the simulation results correlated very well with test data.