Dependence of field enhancement factor on power frequency voltage in vacuum

Abstract

The objective of this paper is to determine the dependence of field enhancement factor β on power frequency (50 Hz) voltage in vacuum. A rod-plane vacuum gap was designed in a vacuum interrupter. Shots of ac power frequency voltage were applied at three vacuum gaps till breakdown occurred and the three vacuum gaps were 1.0 mm, 0.8 mm and 0.5 mm, respectively. The field emission current and applied voltage were measured at the same time. Through Fowler-Nordheim theory analysis, the electric field enhancement factor is obtained to represent a physical change of the emitters. The results showed the dependence of the field enhancement factor β on the applied voltage followed a “V” shape curve. The minimum β value, a turning point of the “V” shape curve, corresponded to a turning point voltage. The turning point voltage was about 90.1% ∼ 95.7% of the breakdown voltage. It could be an indication to predict a breakdown in vacuum.