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 first thyristor through a resistor when second and third thyristors are fired to pass a commutating current from a capacitor through the first thyristor. As a result the values of the resistor and the capacitor 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 fourth thyristor is fired to pass commutating current through the second thyristor to effect final interruption of the load current and the values of a parallel resistance-capacitance circuit in series with the second thyristor are chosen to reduce a second over-voltage which occurs when the second thyristor is commutated.