Effect of area on surface flashover voltage in vacuum

It is known that the breakdown voltage in a vacuum insulation system drops with an increase in linear dimension of electrodes and with an increase in the number of insulating spacers bridging the gap. Normally this is explained to be the result of the increase in the number of so-called weak links in the system. The influence of an external capacitance on the flashover voltage of an electrode gap bridged by a spacer was investigated. When a capacitor was connected inside the vacuum chamber near the discharge site in parallel with the gap, it was found that the additional capacitance lowered the breakdown voltage in a manner similar to that observed with an increase in electrode area. This supports the energy explanation of the area effect. A larger external capacitor, far from the discharge site, had no influence on the breakdown voltage.