Effects of voltage unbalance on induction motors

This paper investigates the effects of different voltage magnitude unbalances with the same voltage unbalance factor (VUF) on the stator loss and rotor copper loss and total copper loss of three classes of three-phase induction motor. Under six different voltage magnitudes unbalance conditions, the copper losses of three different three-phase induction motor under full load conditions has been analyzed through simulation. Following the investigations, the importance of the positive-sequence voltage and the negative-sequence voltage has been pointed out. In the present work, the relative percentage increase in the stator copper loss, rotor copper loss and total copper losses have been computed for the motor working under unbalanced and balanced voltages. For this analysis Matlab environment using Simulink toolbox has been used. In this paper the three definitions (line voltage unbalance in percent-LVUR, phase voltage unbalance in percent-PVUR and voltage unbalance factor-VUF) of voltage magnitude unbalance have been considered. The operation of the induction motor has been considered at full load. The analysis shows the effects of resulting losses during unbalanced voltage supply. The increase in losses under unbalanced voltages leads to the necessity of derating the motor.