Effects of unbalanced voltage on the operation performance of a three-phase induction motor

This paper uses a real load test to investigate the effects of an unbalanced voltage supply on an induction motor´s performance. Based upon various experiments, including: (1) cases with the same unbalance voltage factor but different unbalanced voltages; (2) cases with only one unbalanced voltage but different degrees of unbalance; and (3) cases with the same positive-sequence voltage but different negative-sequence voltages, the importance of the positive-sequence voltage in the motor´s apparent performance and of the negative-sequence voltage in the hidden damage are pointed out. Finally, it is strongly suggested that the related regulations, and a motor´s derating factor and temperature rise curves should be based on not only a voltage unbalance factor, but also the magnitude of the positive-sequence voltage