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Application of observer coil technique for detection of stator turn fault and damaged bearing in cage motors

This paper presents the distinct advantages of stator inter-turn and bearing faults detection using an internal radial flux sensing coil. External stray flux measurement based techniques have been effectively applied in a number of earlier studies for detection of various faults. In this paper a simple internal flux sensing observer coil (OC), located into stator slots, has been found to be more succinct in detection of stator inter-turn and bearing faults which constitutes nearly 80% of induction motor faults. Tools like THD, third harmonic component, and FFT analysis have been successfully applied in detection of these faults. The OC technique has been found to be more simple and effective compared to external flux sensors and current sensors employed in detection of these faults. The present work using OC technique has been implemented on a 0.746-kW three-phase four-pole 415-V squirrel-cage induction motor. Faults were experimentally created from stator winding tapings brought out on external board, and using an outer race cracked bearing.