Automated Method to Verify Industry Standards on Derating of a Three-Phase Induction Motor due to Thermal Stress Caused by Voltage Unbalance

This paper presents an automated technique to verify the NEMA standard MG-1 voltage unbalance derating graph using temperature sensors embedded in a 5 hp motor. This two step process initially identifies the reference coil temperature. Once the reference temperature is found, the system automatically regulates the load to maintain the reference temperature at the single hottest coil for a wide range of incoming voltage unbalances. This testing system provides a highly controllable platform in which to investigate motor derating according to voltage unbalance, in addition to providing a basis for evaluation of IEEE vs. IEC style voltage unbalance calculations.