Calculation of the impedance of rotor cage end rings

The authors show that the resistance and leakage reactance of the end rings of a rotor cage can be evaluated from the impedance of an identical ring which carries a circulating current of the appropriate frequency. Two mathematical methods for calculating end-ring impedance using this physical model are described, the first based on the use of modal currents together with the method of images, and a second employing finite elements. The influence of skin effect is investigated, as is the proximity of the rings to the shaft and to the core-pack end. The method is also applied to the consideration of the impedance of the end rings in a double-cage machine