A breakdown mechanism transition with increasing vacuum gaps

The objective of this paper is to determine a breakdown mechanism transition with increasing vacuum gaps. A rod-plane vacuum gap was designed in a vacuum interrupter. A current and voltage conditioning process was performed in order. Two shots of ac power frequency voltage were applied at different vacuum gaps until breakdown occurred, and the vacuum gaps were 1.0 mm, 0.8 mm and 0.5 mm, respectively. The field emission current and breakdown voltage were simultaneously measured. Whether the field emission current and voltage fitted the Fowler-Nordheim theory was used to distinguish the field emission induced breakdown and particles induced breakdown. The results showed that there was no mechanism transition between the two shots at 0.5 mm gap spacing, and there were mechanism transitions between two consecutive breakdowns at 0.8 mm and 1.0 mm gap spacings. The probability of a mechanism transition occurring also increased with the increase in gap spacing from 0.5 mm to 1.0 mm.