Impacts on the Grid-Side Voltage Due to the Current Unbalance Amplification Caused by Induction Motors

It is well known that supply voltage unbalance is detrimental to induction motors as it increases the losses, reduces the output torque and the overall efficiency, and increases stress on the insulation which can lead to machine failure. It is also well documented that current unbalance in induction motors is several times greater than the voltage unbalance. While induction motors are known to be victims of voltage unbalance, there has been little exploration of the converse. What impacts do IMs operating under unbalanced voltage have on the power system? This paper focuses on analyzing these effects via simulation using the Electromagnetic Transients Study Program (EMTP) by utilizing the model of a test power system with preexisting supply voltage unbalance and several induction motors. The distribution system under test is the IEEE 34-node test feeder with a nominal voltage of 24.9 kV and unbalanced loads. Induction motors are connected at nodes with highest unbalance to observe effects throughout the system and results pertaining to change in voltage and current unbalance are presented and analyzed.