This paper written by Jawad Faiz, H.Ebrahimpour, P.Pillay, investigates the negative effect of unbalanced voltage upon the losses and efficiency of a three phase squirrel cage induction motor. The financial losses caused by unbalanced voltage of the power supply are determined using an analytical–statistical method. The analytical method is verified by experimental test.
The performance of a three phase induction motor supplied by unbalanced voltage is undesirable and can damage the motor. The unbalance voltages has a negative sequence component which generates a reverse rotating air gap field in the opposite direction of normal rotor rotation. All undesirable effects of the unbalanced voltage upon the performance of the induction motor are caused by this reverse rotating field.
The unbalance voltage reduces the efficiency of an induction motor which leads to a considerable temperature rise and shorter life time of the machine. Induction motors supplied with unbalanced voltages likewise decreases the effective motor rating. This paper applied a simple and brief method to study the impact of unbalanced voltages on the losses and its negative effect on the insulation of the motor. Protection of the motor against these risks and adjusting the relays is essential.
The paper is available here