Rerating Factors of Polyphase Induction Motors Under Unbalanced Line Voltage Conditions

The load on the induction motors is to be reduced under unbalanced voltage conditions so as to limit the temperature rise to the normal value. The rerating factors are determined experimentally and compared with four methods of prediction. The first two methods are drawn from previously published work and have failed to correlate the experimental and predicted values. An attempt to incorporate the effect of winding details and heat conduction is made in the third and fourth methods, respectively. Based on the third method, generalized curves are presented which can be applied to any motor having short-chorded windings. This method has its own limitations. The fourth method is a new approach, the results of which agree very closely with the experimental data on two types of motors tested.