Charging of dielectric barriers in rod-plane gaps

The electric properties of an air gap between a hemisphere-rod covered with 3 mm thick silicone rubber and plane metal electrode have been examined. Observation of discharge activity and measurement of the discharge current have been made under impulse voltage stress. When applying an impulse voltage close to the inception voltage, discharge activity is observed around the hemispheric tip of the rod. Observed light emission seems to be evenly distributed along the hemispheric tip comprising a number of independent discharges similar to discharges in a homogeneous electrode configuration. Applying a conductive layer at the rod tip reduces the discharge activity and measured discharge current considerably. The discharge activity was concentrated close to the tip end of the rod. Relaxation time constant for the deposited charge was measured to be about 4 h. By comparing conductivity of the insulation material, the dominating relaxation mechanism was found to be conduction through the solid insulation.