Experimental study of the effect of positive sequence voltage on the derating of induction motors under voltage unbalance

This paper presents the results of an experimental study on derating of an induction motor under different voltage unbalanced conditions and its comparison with the NEMA standard MG1 voltage unbalance derating graph. During the derating tests the 4 kW squirrel cage induction motor temperature rise was kept constant at the rated value and the windings temperature was measured on-line by means of an accurate digital thermal monitoring system with nine thermocouples positioned in both stator and rotor circuits. The obtained results show that the positive sequence voltage plays an important role in the derating performance of the induction motor under unbalanced conditions, and that the unbalance voltage indices currently used do not allow for accurately measuring this influence.