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

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. keywords : Phase analysis, Fourier Transform, Hilbert Transform, Fault diagnosis, Induction machines.