Lightly ferromagnetic rotor bars for three-phase squirrel-cage induction machines

The concept of lightly ferromagnetic rotor bars to improve the starting performance of squirrel-cage induction motors is presented in this paper. Although the induction machines are popular for their ruggedness and simplicity, their starting torque is low and the starting current is 5-8 times higher than the rated current. A simple solution to this problem is the introduction of new rotor-bar material with lightly ferromagnetic properties, which in turn improves the starting power factor due to enhanced skin effect. Relevant electromagnetic theory supporting this is e presented in this paper. A computer simulation also produced expected results. A 1-hp induction machine has been tested to verify the proposed methodology.