Overvoltages in polyphase induction motors during single-phase operation

Introduction IN the course of the starting, reversal, or normal operation of a polyphase wound-rotor induction motor, it occasionally happens that either the stator or the rotor or both may be allowed to operate single phase. In some cases it has been noted that the voltage of the open terminal or terminals under these conditions has a steady-state peak value well above its normal maximum. While scattered references to this effect may be found in the literature, and though the general subject of single-phase operation of polyphase induction motors has been discussed from time to time, apparently the magnitude of these voltages has not been the subject of a thorough and organized investigation. This paper is based on the results of a study, undertaken to determine analytically the maximum theoretical voltages of a three-phase induction motor under single-phase operating conditions, and, so far as possible, to check these calculated figures against actual test results.