Arc structure, arc motion and gas pressure between laterally enclosed arc runners

Abstract

Arc motion along parallel arc runners tightly enclosed by lateral walls was investigated experimentally, both with and without an exhaust barrier at the outlet. High speed movies (33000 frames/s) were taken and the gas pressure was measured at several locations along the path of arc motion. The measurements show how both arc shape and motion depend on the parameters arc length (5-15 mm), arc current (1-5 kA), magnetic blast field (40-100 mT), and exhaust constriction. In many cases both are shape and are motion were influenced by a plasma volume forming a "nose" in front of the arc next one of the electrodes. Spontaneous formation of an anode spot and/or a cathode spot in front of the arc may ignite a parallel current path and initiate a commutation process. The plasma volume in front of the arc is less significant at low electrode distance, high arc current, high blast field, and in more realistic chamber geometries with an exhaust barrier. Cold gas shock waves hitting the arc strongly influence both arc motion and shape. Simulation of arc motion may be a helpful tool in order to save expensive experiments when designing low voltage miniature circuit breakers. The high speed movies showed that the arc motion is sometimes strongly influenced by commutation processes requiring a very complex arc model.