Impact of the Supply Voltage on the Stray Load Losses in Induction Motors

In this paper, the effects of the sinusoidal supply voltage amplitude on the stray-load losses in small/medium-size induction motors are analyzed and discussed using a simplified per-phase equivalent circuit, which has recently been proposed by the authors. In this circuit, the stray-load losses due to the airgap spatial harmonics effects on the rotor squirrel cage are modeled using a suitable additional resistance connected in series with the stator impedance. Then, this paper's main aim is to further prove the validity and the accuracy of the proposed model and to increase the familiarity with the new equivalent circuit parameter. By an experimental campaign conducted on a four-pole 7.5-kW totally enclosed fan-cooled induction motor, several data have been collected and used to determine the stray-load losses for different values of the supply voltage, in accordance to the IEEE Std. 112-B. The same data have been used to determine the additional resistance as a function of the supply voltage. The obtained results show that, also in conditions different from the rated ones, the additional resistance is reasonably able to take into account the considered stray-load losses in the machine power balance.