Motor current signature analysis apply for external mechanical fault and cage asymmetry in induction motors

The aim of this paper is to recognize if the differences between effects due to external mechanical faults and internal electrical faults in induction motors can be diagnosed through Motor Current Signature Analysis (MCSA) techniques applying Fourier analysis. For that purpose an alternative algorithm to traditional Fast Fourier Transform was used. Positive and negative frequency spectra have been studied. The paper shows a comparison between frequency spectra of the symmetrical and natural components of stator currents for internal electrical fault (rotor cage asymmetry) and external mechanical fault represented by a periodical oscillating torque. Cage asymmetry is defined by symmetrical and asymmetrical factors. The study is based on the classical model of induction machine considering only effects of Main Magneto-motive Forces. Result shown corresponds to the steady-state performance of the motor supplied directly from the net as a sinusoidal voltage source. The advantages of the algorithm use for Fourier analysis have also been discussed.