Studies of Spark Formation at High Switching Voltages of Positive Polarity

Studies of the development of pre-discharges with large air gaps and positive switching voltages of 1.5 and 2.0 MV are reported. Measurements of the charge flowing into the gap and recordings obtained with a high-resolution image converter have shown that the origin of the filamentary brush-like discharges moves forward at an almost constant rate of a few cm/Ms, and that variations in luminosity are accompanied by similar fluctuations in the transfer of charge. The space behind the streamers remains without light except when a leader is formed for a short time in the event of a charge step. The discussion is illustrated by numerous photographs and oscillograms.