METHOD AND APPARATUS FOR SYMMETRICAL CURRENT STARTING OF POLYPHASE INDUCTION MOTORS

A motor starter minimizes transient asymmetrical current to an A.C. induction motor during start-up. Desired timing of closing each phase is calculated using the reactance/resistance ratio (X/R) of the motor and calculated capacitive (X.sub.C) and inductive (X.sub.L) reactances and resistances (R) of the motor circuit cable. A target closing angle of the first phase that crosses zero potential of the voltage cycle is determined based on the system X/R ratio, and that phase of the starter is closed individually. After the first phase is closed, the power frequency is used to determine closing of the other phases at 60 degrees intervals corresponding to the X/R-based target timing.