Diagnosis and characterization of effects of broken bars and connectors in squirrel-cage induction motors by a time-stepping coupled finite element-state space modeling approach

In this paper, a comprehensive presentation of a time-stepping coupled finite element-state space modeling approach for diagnosis and characterization of effects of rotor (cage) broken bars and connectors in squirrel-cage induction motors is given. The model is used to compute/predict the characteristic frequency components which are indicative of rotor bar and connector breakages in the armature current waveforms and developed torque profiles, respectively. It was found that failures due to rotor connector breakages tend to degrade the developed torque of the machine considerably more than failures due to rotor bar breakages. Also, the effects and implications of rotor breakages on core loss distributions are quantified and described. Furthermore, this model has great potential in future applications to generate databases for use in overall noninvasive diagnostics of faults or troubleshooting in relation to quality assessments of the state of the motor and the overall drive.