Switching Transients in Single-Phase Induction Motors with Constant Speed

Abstract

In the past, the problem of switching transients in polyphase induction motors has been studied in great detail by several investigators. There is, however, no published literature dealing with the analysis of the problem of transient conditions in single-phase induction motors of the split-phase variety with constant speed. In this paper, the method of symmetrical components of instantaneous potentials and currents has been applied to the analysis of transient conditions in a capacitor-start capacitor-run single-phase induction motor with constant speed, and with special reference to reclosing and plugging. Detailed computation has been carried out for the transient currents and torque produced when a capacitor motor running at full speed is suddenly taken off the lines, and then put back after an extremely brief interval. The problems of sudden short circuiting of stator terminals and plugging have also been analyzed. It has been found that if the motor is reclosed when the applied potential passes through its zero value there is a fundamental frequency slowly decaying torque superimposed on the average steady-state unidirectional torque. If, on the other hand, the motor is switched on to the supply when the applied potential passes through its maximum value, the developed electromagnetic torque settles down to its final value before the end of the third cycle of the applied a-c potential. In order to plug the motor satisfactorily it is absolutely necessary to first replace the running condenser by the starting condenser before the electric connections for one of the windings are interchanged.