Breakdown and Prebreakdown Conduction in Plain Vacuum Gaps under Variable Frequency Alternating Excitations

Results of experimental investigations leading towards a better understanding of breakdown and prebreakdown behavior of vacuum gaps under variable frequency a.c excitations is presented in this paper. The frequency variation is in the range of 30 to 300 Hz in steps of 10 Hz. The results indicate that the pre-breakdown currents show an inverse relation with the breakdown voltage in general though erratic behavior was observed over a certain range of frequencies. A peaking of breakdown voltage was observed at 130 Hz. This was pronounced when the pair of electrodes was of stainless steel and less pronounced when copper and aluminum electrodes were used. The experimental findings are explained based on F-N emission, I-F emission and also thermal interaction due to quasi-continuous shower of anode micro-particles.