On-line load test for induction machine stator inter-turn fault detection under stator electrical asymmetries

The stator inter-turn faults and stator electrical asymmetries such as stator resistance and inductance unbalance generate similar negative sequence current signatures in the induction machine. Hence the stator inter-turn fault is one of the most difficult faults to discriminate and detect in an induction machine. Discrimination of the stator inter-turn fault from stator electrical asymmetry essentially helps to arrange maintenance in a proper schedule. In this paper, a simple on-line load test is proposed to detect the presence of stator inter-turn fault under stator electric asymmetrical condition of the machine. The proposed test is based on the observation of steady-state stator current locus with change in load. The test procedure does not require additional sensors, training and database, past history of the machine and speed measurement. It is also applicable to any unknown machine. This paper presents analytical studies and experiments on a faulted and electrically asymmetrical motors to confirm the simplicity and effectiveness of the proposed load test.