Computation of the performance of large cage induction motors during starting

The starting performance of small cage induction motors can be computed by 2-D FEM accurately. For large cage induction motors, because of the complexity of end structure, this method can not give results with necessary accuracy. Though the use of 3-D FEM can improve the computation, the computing time and computer storage would bring many difficulties if it were used for the whole region analysis of motors. In this paper, a new mixed model of 2-D and 3-D FEM is proposed, by which the rotor 3-D and 2-D eddy current fields are calculated. Through the comparison of these two fields the end parameters of impedance can be obtained. Putting these parameters into the nonlinear 2-D eddy current field computation system of the whole region of the stator and rotor, the starting currents and torques of motors can be calculated. Two numerical examples are given. It is shown that the relative computation errors in currents and torques are less than 10% compared with the experiment results. In addition, the influence of rotor winding temperature on the starting parameters of motors is also discussed.