Current limiting circuit breaker

Abstract

Current limiting circuit breaker having for each pole, a pair of main contacts separable upon operation of a thermally and electromagnetically operable tripping device and a pair of auxiliary contacts for current limiting in series with the main contacts and in parallel with a transformable resistor having a positive temperature coefficient of resistance. The auxiliary contacts are separable when an electromagnet is energized by a fault current which simultaneously energizes a field magnet to produce a transverse magnetic field across the auxiliary contacts and the arc formed between them when separating. This simultaneous action of electromagnet and field magnet coacting for rapid contact separation and lengthening of the arc upon flow of a fault current serves to increase arc voltage almost instantaneously to that of the source, about which time the fault current is totally shunted into the resistor. A conductor system is associated with the electromagnet which includes two conductor turns, the first being connected in parallel with the auxiliary contacts and the second being connected in series with the auxiliary contacts and with the other conductor turn. The second produces magnetic flux in the magnet core when a fault current appears and while the auxiliary contacts are closed. The first and second conductor turns together continue to produce magnetic flux in the magnet core after the auxiliary contacts have opened to hold them apart and prevent contact welding.