Long 60-Cycle Arcs in Air

Volt-ampere characteristics of 60-cycle arcs in still air with lengths and currents such as occur in power systems have been investigated under laboratory conditions. The arcs varied in peak current from 68 to 21,750 amperes and in length from 1/8 to 48 inches. Typical oscillograms and volt-ampere curves of these tests are presented. The voltage gradient in the arc is affected very little by current magnitude. Through-out the entire range all gradients remained between 21.5 and 50 volts per inch, with 35 per cent of all values in a 5 volt per inch interval having an average value of 34 volts per inch. The increase in apparent gradient due to voltage drop at the electrodes was found to be negligible where the arc length exceeds several feet. The decrease in short-circuit current of a power system through a series arc as compared with that for the same system with a metallic short circuit has been investigated. Data are presented showing the actual reductions observed for various conditions of circuit voltage and impedance.