Separation harmonics for detecting broken bar fault in case of load torque oscillation

This paper presents separation harmonics to discriminate rotor failure from low frequency load torque oscillations in three phase induction motors. The most common method for detecting broken rotor bar faults is to analyze the corresponding sidebands through motor current signature analysis (MCSA). If a motor is subjected to load fluctuation, then the oscillation related sidebands exhibit similar behaviors as well. Particularly, when the load fluctuation frequency is close or equal to that of broken bars, the stator current spectrum analysis can be misleading. In this study, torque and motor phase voltage waveforms are exhaustively analyzed to discriminate broken rotor bar fault from low frequency load torque oscillation in three phase induction motors. In order to extract and justify the separation patterns, 2-D Time Stepping Finite Element Method (TSFEM) is used. The simulation and experimental results show that the proposed approach can successfully be applied to fault separation process in star connected motors.