Detection of rotor asymmetries in induction motors at standstill

This paper addresses the detection of asymmetries in the squirrel cage rotor of an induction machine when the machine is at standstill. In case of a damaged bar, the use of a machine model that represents the rotor as a set of electrically and magnetically coupled coils allows the computation of the impedance that depends on the asymmetry in the damaged cage. The paper proposes a simple method, based on the measurement of the impedance of the motor for a single phase supply that uses the changes of the impedance along the rotor position as an indicator for the asymmetry. Experimental results prove the validity of the proposed technique.