Analysis of the voltage phasors characteristics for motor unbalanced supplies under constant voltage level

This article presents an analytical and graphical study of the supply characteristics of a three-phase induction motor operating under constant average voltage in unbalanced conditions. Till now, researchers have addressed the unbalance analysis of induction motors without paying attention to the accuracy on the voltage level issue. This work develops the loci of voltage phasors and their symmetrical components, and calculates the variation ranges of voltages and voltage unbalance factor (IEC) for an induction motor operating under constant line average voltage and constant percent voltage unbalance (NEMA). The results are applied to the variation limits established in the electrotechnical standards.