On the Numerical Transient in Time-Stepping Finite Element Analysis of Induction Motors: Fundamental Concepts

Time-stepping finite element (TS-FE) analysis when employed for induction motor modeling, results in a long and time-consuming numerical transient before it reaches a steady-state solution. During this numerical transient stage, no useful and reliable performance characteristics can be extracted from the TS-FE data. When a steady-state magnetic field distribution is reached throughout the magnetic circuit of the machine, performance characterization can be calculated in such a device by TS-FE algorithms. The resulting computations will correspond to the operating point at a given frequency, slip and load torque. This long transient profile is dependent on the chosen operating point and the electric and magnetic circuits material parameters and configurations. In this paper, the focus is on the study of such numerical transient responses under various supply frequencies, slips, and materials of rotor bar cage conductivities. Through this study, the behavior of this transient phenomenon is examined in terms of actual CPU time and required electrical cycles to reach steady state. The studies conducted in this paper are pursued for both voltage source and current source excitations. The emphasis in this paper is on better understanding of the problem, while in a companion paper the emphasis is on proceeding further and providing approaches that shorten this lengthy numerical transient.