A new PQ method to diagnose rotor faults in three-phase induction motors coupled to time-varying loads

This paper presents a new method to diagnose rotor faults in operating three-phase induction motors coupled to time-varying loads. The method relies on the simultaneous analysis of the amplitude and phase spectra of the instantaneous active and reactive powers of the motor, and allows to effectively distinguishing a true rotor fault from an oscillating load torque of low-frequency even when these two phenomena occur simultaneously. A theoretical analysis carried out using a linearized model of the induction motor in a synchronous reference frame, complemented with experimental results, confirm the validity of the proposed diagnostic approach.