Diagnosis of induction motors operating under distorted and unbalanced voltages

Abstract

Connected to unbalanced and distorted voltages, three-phase induction motors operate below their nominal power, due to increasing losses and thermal solicitation. The present article intends to analyze this situation based on equivalent electric circuits, herein utilizing the theory of Symmetrical Components and the Fourier Series. To obtain the parameters of the equivalent circuits, both the influence of the frequency and the skin effect will be considered. This article shows that the reduction in a motor's power is not defined by the unbalance factor alone; it can result from endless combinations of values of modules and angles of unbalanced voltages. It also demonstrates that the necessary power reduction due to increasing losses stemming from the unbalance is determined by either the losses on the stator or the total losses. The obtained results demonstrate that voltage unbalance more strongly affects the stator winding, and harmonic distortions mainly affect the rotor circuit.