An algorithm determining stationary electromechanical interactions in faulty AC machines

This paper presents a new method for analysis of the electromechanical interactions in induction motors due to internal faults. These faults generate often electromechanical torque with rather low pulsations causing speed ripples, which change to the Fourier spectra of phase currents. The MCSA method uses those spectra for diagnosis. It is important to predict the spectra precisely, both qualitatively and quantitatively. The presented method allows determining the current spectra directly for steady-states by using an iterative algorithm. It is composed in two steps. Firstly, the electrical motor equations are solved by harmonic balance method and next speed perturbations are calculated from the equation of motion and this procedure is repeated until the stable results are obtained. The algorithm is tested by an example of a motor with cage asymmetry. The electromechanical interactions for that case are well recognized and can be used for validation of the algorithm.