Circuit breakers for direct and alternating current.

摘要

Circuit breakers which employ a capacitor to pass a current in opposition to a load current through a thyristor when interruption is required suffer from the disadvantage that high switching over-voltages occur. In the present invention current is diverted from the main thyristor T1 through a resistor R1 when thyristor T2 and T3 are fired to pass a commutating current from a capacitor Ck through the thyristor T1. As a result the values of the resistor R1 and the capacitor Ck control the over-voltage and they are chosen to reduce it to approximately half the value obtained with equivalently rated conventional thyristor-based circuit breakers. In a second stage of commutation a thyristor T2' is fired to pass commutating current through the thyristor T2 to effect final interruption of the load current and the values of a parallel resistance-capacitance circuit (C2, R2) in series with the thyristor T2 are chosen to reduce a second over-voltage which occurs when the thyristor T2 is commutated.