Reduced losses in die-cast machines with insulated rotors

This paper reports an investigation into the influence of interbar currents on the performance of die-cast cage induction machines. This work is based on an extensive set of experimental measurements using a series of specially made die-cast cage induction motors with bars insulated using alternate processes. Experimental measurements were undertaken separately by the industrial manufacturer and at the university laboratories, and these clearly demonstrate that increasing the insulation of the rotor cage inhibits the flow of interbar current and reduces the total motor losses and increases the motor efficiency as a consequence. The experimental measurements were further validated using an analytical interbar model. Further experimental measurements also demonstrate that insulating the rotor cage also modifies the stator torque in a counterintuitive fashion.