Induction Machine Phase Balancing by Unsymmetrical Thyristor Voltage Control

Abstract
High inrush currents and unbalanced supply voltages are two of the major causes for failure of polyphase induction machines. While thyristor voltage controllers, sometimes called static starters, are in widespread use to limit damaging inrush currents, little attention has been paid to the use of these controllers to balance the phases voltages of the machine. The technical feasibility of unsymmetric control to limit unbalanced currents is explored. A substantial reduction in losses is shown to be possible for two specific types of unbalance.

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