Dc circuit interrupter

Abstract

To avoid arcing when the breaker is opened, load current is diverted from a circuit breaker, before it opens, to a pulse forming circuit containing a precharged capacitor and a switch. Load current normally flows from a source of electric power to a load through a network comprising the breaker and a series connected controlled impedance. The pulse forming circuit is connected across the network. When load current is to be interrupted, the switch is closed to discharge a current pulse through the network, and the impedance of the controlled impedance is increased. These actions divert load current from the network to the pulse forming circuit. The breaker is then opened. The voltage across the capacitor first linearly increases from the precharge voltage to zero and then tends to increase in magnitude with an opposite polarity, i.e. that of the source of electric power. The voltage magnitude with opposite polarity then attainable across the capacitor is limited to a very low value, such as by a diode or SCR connected in parallel circuit with the capacitor. This limits the voltage across the opening breaker to avoid voltage breakdown across its contacts. It also permits use of a unipolar, e.g. electrolytic capacitor to increase the time during which the breaker can fully open. After the breaker is opened, the switch is opened, i.e. turned off, and remaining energy in the circuit is dissipated by a varistor. Various switching turn on and turn off circuits are disclosed.