The Reignition of Short Arcs at High Pressures

An investigation has been made of the reignition of short a.c. arcs in air at pressures from one to eight atmospheres, for currents less than 3.25 amperes (and with a resistance circuit). Pure graphite electrodes were used and were separated by a distance of 1 mm. The reignition voltage under these conditions increases with pressure and decreases as the current is increased. The characteristic of reignition potential vs. current has been found to exhibit a discontinuity at a critical current. For this current the reignition potential decreases by about 1000 volts to a new characteristic typical of the higher currents. This critical current increases with the gas pressure to a maximum of 2.25 amp. As the r.m.s. current is increased from low values to values near the critical, the number of cycles during which the reignition potential has the value given by the higher characteristic decreases. For currents equal to, or greater than the critical value, only the low reignition potentials are obtained. This transition is accompanied by an increase in the burning voltage of the arc.