A new look at the effects of unbalanced voltages upon synchronous and induction machines

Abstract

Recently developed polyphase machine demonstration and analysis software is used to explore a phenomenon whose effects have been observed for many years: namely, that under certain conditions, significant imbalances in stator currents of polyphase AC machines (and thus in the phase power distribution and the internal steady-state magnetic field) can result from relatively minor imbalances in machine terminal voltage at certain loading levels. Using standard steady-state equivalent circuit models of synchronous and induction machines, it is shown that the presence of severe levels of current imbalance can be easily and effectively demonstrated. It is also shown how these effects can be readily simulated and analyzed in order to help underscore the need for stringent voltage imbalance limits.