Effect of voltage unbalance and distortion on the loss characteristics of three-phase cage induction motor

Voltage unbalance and distortion become one of the most common power quality problems in industrial utilities, which cause significant increase of the electromagnetic losses in induction motors. For energy saving of the induction motor system, there is a need for a detailed research of the loss characteristics of induction motor under unbalanced and distorted supply voltage. For accurate and fast prediction of the induction motor losses, this study proposes a method to identify rotor harmonics using the data from one supply cycle. The slip-frequency rotor harmonics are determined by using the space-time symmetrical characteristics of the induction motor. And based on a numerical method, the higher order harmonics of rotor flux density or current density are determined from data within one supply cycle. The electromagnetic losses are then calculated from those harmonics. With this method, the electromagnetic losses of a 5.5kW induction motor under unbalanced and distorted supply voltage are calculated and analyzed. The proposed method and the analysis results are validated by comparing the predicted and measured motor losses of the 5.5kW induction motor under different supply conditions.