Analysis of induction motor performance under unbalanced supply voltage conditions and its impact on the network voltage unbalance propagation

Abstract

Voltage unbalance (VU) is regarded as a power quality problem of significant concern at the electricity distribution level. Influence of unbalanced supply voltages on the adverse performance of power system and its equipment is intensified by the fact that a small unbalance in the phase voltages can cause a disproportionately larger unbalance in phase currents. Naturally, three phase Induction Motor (IM) loads which are considered to be the main work horses of many industrial environments, are symmetrical devices and do not possess any inherent unbalance. However, the operation of three-phase induction motor is adversely affected by the supply source unbalance. Voltage unbalance causes a lot of adverse effects on induction motor such as Overheating, line-current unbalance, derating, torque pulsation, and inefficiency. The overheating leads to winding insulation degradation. Despite the degrading of motor performance, it has been found that the existing level of the voltage unbalance (VU) at the point of common coupling (PCC) is attenuated due to the presence of induction motor load. The following analysis shows how VU is attenuated by three phase induction motors at the point of evaluation (POE). Finally this paper presents a practical approach to evaluate VU propagation at different points of the network in terms of the Voltage Unbalance Factor (VUF) and hence the level of attenuation made by induction motor loads.