Investigation of reductions in motor efficiency caused by stator faults when operated from an inverter drive

Inverter driven motor systems have seen wider use in industry as energy reduction methods. Studies have been undertaken previously to understand the effects of voltage imbalances on motor efficiency and deratings. However, this has not been covered in much detail on inverter-driven motor systems. This paper aims to study the effect that motor stator resistance imbalances have on motor efficiency when used on inverter-driven systems. Motor imbalances may remain undetected by the inverter drive and can result in overheating and premature failure of the motor. Motor efficiency monitoring is now of greater interest due to new IEC standards defining new AC motor efficiency classes and this is also reviewed along with the standards for motor efficiency and inverter-operated motors.