Discriminating time-varying loads and rotor cage fault in induction motors

Diagnosis of electrical machines are becoming more and more important issues in the field of electrical machines as new data processing technique. Motor Current Stator Analysis (MCSA) are usually used to detect the broken bars. In several industrial applications, the motor is subjected to load torque variations of low frequencies, which have effects similar to rotor faults in the current spectrum and result of diagnostic procedure may be ambigues. Discriminating rotor cage fault from oscillating load effects in Induction motors must be considered. In this paper, we present a study based on the application of the active and reactive power signature analyses for discriminating broken rotor bars from mechanical load oscillation effects in operating three-phase squirrel cage induction motors. This method is attractive because it does not need to interrupt the operating system. Finite element method was used to perform dynamical simulation, which leads to more precise results than other models, as the reel geometry and winding layout of the machine are used. The computer simulations and laboratory experiments results show the interest and the efficiency of this technique for the correct distinction between broken rotor bars and load oscillations.