Amplification of Current Unbalance Due to Induction Motors

There is a plethora of studies in literature that focus on the impacts of voltage unbalance on the losses, efficiency, output torque, premature failure, and derating of induction motors. While it is known that the current unbalance in induction motors is generally greater than the voltage unbalance, this issue is seldom studied in detail. This paper focuses on the amplification of current unbalance due to induction motors by analyzing the motor currents at a variety of different voltage unbalance and loading scenarios. These scenarios include over-and under-voltage, as well as phase unbalance cases, affecting one to multiple phases, at varying levels of unbalance. For cases affecting multiple phases, scenarios where all phases are affected equally are also compared against those where they are not affected equally. Select tests are performed using a 6-pole, 10 HP, 230 V, squirrel-cage induction motor, which is also modeled in Matlab to obtain additional simulation results.