Secondary Circuit Parameter Calculation for Induction Motor with Closed Rotor Slots and Torque Characteristic Calculation

Abstract

Closed rotor slots are widely employed in low-power squirrel-cage induction motors with die-cast aluminum cage rotors. Die-cast aluminum cages with closed rotor slots can be manufactured commercially. They help reduce flux pulsation in air gaps and attenuate acoustic noises and surface loss. However, it is difficult to calculate the characteristic of a squirrel cage induction motor with closed rotor slots accurately because the secondary leakage inductance changes greatly with the slip.In this study, the secondary circuit parameter (secondary leakage inductance and secondary resistance) and torque characteristic as a function of the slip were investigated by FEM analysis. The secondary leakage inductance was calculated using magnetic energy and/or magnetic co-energy of a rotor bar, end-ring, and bridge. The secondary resistance was calculated using Joule loss of the rotor bar and end-ring. Moreover, the torque characteristic was calculated using a Steinmetz motor equivalent circuit with the secondary circuit parameter. The results were compared with the experimental value by using a 4P-0.75kW motor with closed rotor slots. From these analyses, it is seen that the measured values of the secondary circuit parameter and torque characteristic are in good agreement with the values calculated by FEM. It is confirmed that the torque characteristic that is calculated using the Steinmetz motor equivalent circuit with the secondary circuit parameter based on the proposed method is more accurate than the conventional characteristic calculation result because the variation of the secondary circuit parameter is taken into account.