Dielectric-recovery characteristics of large air gaps

In contrast to power arcs in air, for which the dielectric-recovery voltage decreases with increasing arc current, arcs in air produced by surge currents of several hundred microseconds´ duration possess dielectric-recovery characteristics that vary only slightly with current magnitude and wave shape. Even when the discharge current is prolonged at low magnitude for as long as a thousand microseconds, the rate of dielectric recovery is little affected. For this condition at times when current as high as one ampere is flowing, the transient voltage required to convert to a high current arc is quite high. The mechanism for such a discharge is different than for the breakdown of virgin air, and the initial arc drop is sufficiently high to record its transient character. It is about ten times the steady-state value at the time the crest current is reached and drops about 50 per cent in the first 20 microseconds.