The reignition voltage characteristics of freely recovering arcs

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Abstract
Advances in the knowledge of arc interruption have been achieved by simplifying the arc and its interruption condition, and studying the recovery of the arc free from the presence of restriking voltage. The arc investigated is a d.c. pulsed discharge of about 100 millisec duration burning freely between carbon electrodes. The reignition voltage of the arc at a given time after sudden interruption is obtained by pulsing with a unit function voltage. By varying the voltage magnitude a 50% reignition value is found, and by repeating at different delay times after interruption, full reignition characteristics have been obtained to an accuracy of within ±5%. Characteristics are given for 10–50 amp arcs in air, nitrogen, argon and hydrogen at pressures from 100 to 750mm Hg. and with gap separations of 1–5mm.The results show that full recovery takes about 1 sec and that breakdown occurs in different forms. For delays of 0–100 microsec thermal breakdown occurs owing to the low resistivity of the decaying arc column and electrode regions. From about 0.1 to 1 sec true spark breakdown is observed. At intermediate times the breakdown is affected both by free charge and reduced gas density.The spark breakdown voltages are found to follow closely an extended Paschen law, and give useful derived gas temperatures. A new phenomenon of a recovery pause is observed and is explained in terms of breakdown at the minimum spark voltage. The results also show the effects of energy exchange between gas and electrodes, and the improvement of recovery with current reduction and increased electrode mass. Only small differences are observed between the recovery of horizontal and vertical arcs. In general, the rapidity of recovery increases in the following order: argon, air, nitrogen and hydrogen.

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