A new approach to detect broken rotor bars in induction machines by current spectrum analysis

This paper deals with a new technique to detect broken rotor bars in polyphase induction machines. Like most techniques, we employ the Fourier Transform of the stator current to make detection. But where the other methods use the Fourier Transform modulus, this alternative approach proposes to analyse 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 but the method robustness decreases for a half-broken rotor bar. So, in order to improve the diagnosis and to permit the detection of incipient broken rotor bar, the analysis is completed 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 the final decision on the rotor cage state is took without the healthy motor reference.