Arc Extinction Phenomena in Vacuum

Abstract

Experiments have been performed to study the manner in which an arc between copper electrodes in vacuum extinguishes. In an ac circuit where current is limited to less than 1000 A peak, resistively, the extinctions are often prolonged over a period of many microseconds by successive reignitions of the arc caused by circuit-recovery voltage. These reignitions tend to be suppressed by capacitance paralleling the discharge thus raising the current at which the arc is extingusihed. In a similar circuit where the current is limited by inductance, the extinction most often occurs at a minimum in high-frequency oscillations of discharge current superimposed upon the 60-Hz arc current near the end of the half-cycle period. These oscillations occur at a frequency determined by the capacitance in parallel with the gap and the inductance of the wires used to connect the capacitors to the gap. For the inductive circuit with low values of capacitance, the oscillations are not apparent and extinction times of 10−7 to 10−8 sec are observed.