Surface flashover voltage and its improvement of dielectric specimens in vacuum

This paper describes the results of the flashover experiment under rather high pressure (0.001~0.13 Pa) in vacuum. The measurement of the flashover voltages was done applying DC or pulsed voltages to electrode. When the electric field strength was about 6 to 15 kV/mm, the flashover occurred under the gas pressure mentioned above. The condition to improve the surface flashover voltage was clarified by testing the various dielectric materials and electrodes which had either different geometries and dimensions. It was found that when a depression was made on electrode to shade the triple junction, the flashover voltage became 1.6 times higher than that obtained for ordinary electrode. Also, it was found that the flashover voltage became 2.6 times higher, when the dielectrics were shaped like a piece of truncated cone having the slope angle of 10 degree against the perpendicular direction of the ground electrode surface (cathode)