Abstract :
A new technique for investigating the recovery period is described. A rectangular pulse of arc current is used and a probing voltage impulse is applied to the decaying arc channel at varied delay times after current interruption. The method has certain advantages over the normal a.c. method of testing. Reignition-voltage/time curves are presented for different conditions of electrode material, gas, gap length, arc current, arc duration and reignition polarity, with gas pressures at or near atmospheric. Observations are also made on the dynamic characteristics of the electrical discharge following reignition. Polished-copper and polished-tungsten electrodes require a reignition voltage of 355 volts within 3 microsec after current interruption for arc currents of 20 amp and less. Pipped-copper, pipped-tungsten, mild-steel, aluminium and graphite electrodes show continuing emission of electrons after current interruption to a varying degree, with corresponding reduction of the reignition voltage. The reignition phenomena are markedly affected by the polarity of the reignition. The arc anode normally attains a higher temperature than the cathode, so that continuing thermionic emission of electrons is more prevalent. Thus reignitions of reverse polarity from the original arc discharge tend to be lower than those of the same polarity. Different gases recover electric strength in the order: sulphur hexafluoride, carbon dioxide, oxygen, air, nitrogen and argon.
