Performance Analysis of a Three-Phase Squirrel-Cage Induction Motor under Unbalanced Sinusoidal and Balanced Non-Sinusoidal Supply Voltages

As a result of the increasing use of electronic devices and other non-linear loads, the waveforms of the electricity supply voltage are being distorted and inequalities are appearing between the phases. This deterioration is associated with problems of electromagnetic incompatibility and reductions in the efficiency of loads such as motors. This paper investigates the negative effects of unbalanced sinusoidal voltage (0.96% unbalance and 2.9% THD) which always present in the power supply over balanced (inverter supply) non-sinusoidal voltage (23.7% THD) on the performance of induction motor in terms of line currents, power factor and efficiency. Under both supply conditions, the performance of a 5 HP three-phase squirrel cage induction motor was measured through a real load test. According to the test results and analysis, the negative effects of unbalanced sinusoidal voltage are more than the balanced non-sinusoidal voltage on the motor´s performance. The financial losses caused by unbalanced voltage of the same motor are determined.