Impact of Voltage Unbalance on Application of IEEE Std 112 Test Procedure in North American Electric Motor Service Centers

Abstract

American standards like ANSI/NEMA MG 1 and IEEE Std 112 recommend test procedures for determination of polyphase induction machine losses which may be used for loss segregation and/or efficiency evaluation. All procedures described in those standards require balanced sinusoidal voltages, which can only be achieved in well-equipped laboratories. In real industrial environments, a balanced sinusoidal power supply is impossible. Thus, tests are generally conducted with a certain level of voltage unbalance and harmonic pollutions without any knowledge of how test accuracies are affected. This research work investigates the impact of voltage unbalance on the accuracy of the friction and windage loss, and core loss evaluations based on the IEEE Std 112 no-load test procedure. The impact is demonstrated and quantified by testing a 60 Hz, inverter-duty, premium efficiency, 3 hp induction motor under balanced voltages and with voltage unbalance in the range of 0.5%-5%. The objective of this technical paper is to update the current IEEE Std 112 with the findings of this research work.