The influence of a cylindrical shield electrode on the dielectric strength of large vacuum gaps

Breakdown voltages of three-electrode arrangements have been determined. The shield electrode shows a significant influence on the breakdown behavior of the electrode arrangement at the investigated gap distances between 10 and 20 mm and at shield diameters of 100 to 120 mm. Confirming former investigations, the breakdown voltages increase according to the material in the order: copper, stainless steel, aluminium. The amplitudes of the AC prebreakdown conditioning voltages are of great importance if the measured breakdown voltages are compared. The electrical strength of three-electrode arrangements can be increased by 30% if field-optimized electrodes are used. The breakdown of a three-electrode gap is normally not included by a charging or discharging of the shield electrode