Dynamic simulation of eccentric squirrel cage induction motors by including saturable reluctances of individual teeth

Abstract

This study proposes an analytic model for three-phase squirrel cage induction motors (SCIMs) under general eccentricity fault with variable degree, including static, dynamic and mixed eccentricities. After defining general air gap function, the air gap length within each slot pitch is assumed to be constant and equal to its length at the centre of the slot pitch by approximation. Then, by using modified winding function theory, analytic equations are obtained for the motor inductances. A novel technique is introduced to calculate saturable reluctances of individual teeth in every simulation step. These reluctances are added to the model by proper increment of the air gap length in front of each tooth. Consequently, dynamic simulation of SCIMs with any eccentricity type and degree and with the effect of the teeth saturable reluctances is made possible in the frame of a single Matlab code. It is shown that by adding the teeth reluctances, the amplitudes of the side-band harmonics around the fundamental line current, as the eccentricity fault indices, are reduced towards the corresponding harmonic amplitudes obtained by experiments. Finally, the proposed method is extended to include axial asymmetries.