Induction motors play a very important part in the safe and efficient running of any industrial plant. Early detection of abnormalities in the motor would help to avoid costly breakdowns. Accordingly, this work presents a technique for the diagnosis of broken rotor bars in induction motor. Stator voltage and current in an induction motor were measured and employed for computation of the input power of one stator phase. Waveforms of the instantaneous power and line current were subsequently analyzed using the Bartlett periodogram. We evaluate different global fault indexes on the instantaneous power spectrum and on the line current spectrum for the fault detection. Several rotor cage faults of increasing severity were studied with various load effects. Experimental results prove the efficiency of the employed method.

In this paper, a new technique to detect broken rotor bars in polyphase induction machines is presented. Like most techniques, we employ the Fourier Transform of one stator current to make detection. But where the other methods use the Fourier Transform modulus, we propose an alternative approach by analyzing its phase. As shown by results, the Fourier Transform phase allows to detect one broken rotor bar when the motor operates under a low load. In order to improve the diagnosis and to permit the detection of incipient broken rotor bar, we complete the analysis with the Hilbert Transform. This transform provides good results and a partially broken rotor bar can be detected when the load torque is equal or greater than 25%. The main advantage of these methods is that it does not require a healthy motor reference to take the final decision on the rotor cage state.

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