General Electric Company

Loyal N Stallard

John H Cutler

Each of the three phase power source voltages coupled to a three phase (3.0.) thyristor power converter are respectively half-wave rectified to provide both positive and negative voltages. Signals representing the largest positive rectified voltage and the smallest positive rectified voltage are developed as are signals representing the largest negative rectified voltage and the smallest negative rectified voltage. Using signals from both the positive and negative rectified voltages, at least one comparison is made to determine a difference which, when in excess of a predetermined limit, effects a logic signal to provide an indication that an asymmetrical fault exists either phase to neutral or phase to phase across the power converter and the power lines connecting the converter to a polyphase alternating current (AC) source. Following a suitable delay, protective action is initiated, which action comprises either phasing back of gating to the converter thyristors and/or tripping of a circuit breaker or contactor which operates to interrupt the supply of AC power to the converter.

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Daleville, VA, United States of America

Loyal N Stallard