Phase frame analysis of the effects of voltage unbalance on induction machines

Operating a three-phase induction motor with unbalanced voltages can lead to excessive heating. The traditional method of analyzing the operating conditions of the motor when unbalanced voltages have been applied has been to use the theory of symmetrical components. The purpose of this paper is to develop a method of analyzing the motor in the "phase frame". The method is then applied to a typical motor to demonstrate the results of operating a motor with unbalanced voltages and the reason why a motor must be derated under these conditions.