Impulse Surface Flashover along a Polycarbonate Plate with a Back Electrode in Vacuum

To study the effect of a large component of normal electric stress on surface flashover in vacuum, a high voltage electrode and its opposite one were mounted on a polycarbonate(PC) plate lying on an earthed metal plate (back electrode), the opposite electrode being connected to the back electrode. Experiments were also performed for composite insulators having laminate structures of PC, titanium dioxide and vacuum. Impulse voltages of 1×40 μs were applied. The flashover voltages were measured as a function of electrode separation, thickness and electrostatic capacity per unit area of the solid insulator. The flashover voltage was found to depend on the field distribution around the insulator surface. The results may be explained in terms of the electron emission from the cathode and their multiplication on the insulator surface.