Formation mechanism of surface corona on dielectric plates under negative impulse voltage in atmospheric air

The formation mechanism of the surface corona on dielectric plates under negative impulse voltages has been investigated with a high-speed gated image intensifier in atmospheric air. An acrylic plate was inserted perpendicularly to the axis of a rod-plane electrode system, and as a backside electrode, a translucent electric conductive film was used to observe the luminosity of the surface corona. The size and shape of the negative surface corona were measured using acrylic plates of 1, 2, 5 and 10 mm thick and rod electrode with diameters of 10, 20, 50 and 125 mm. Experiments show that the negative surface corona occurred just after the impulse voltage application and formed a ring-like luminescence. The diameter of the ring increased with the thickness of the acrylic plate and the diameter of rod electrode. The formation mechanism of the negative surface corona is studied using a numerical analysis of the electron avalanche developing along the electric line of force around the rod electrode. As a result, it is found that the occurrence positions of the surface corona agree with the theoretical computed points of the maximum linear density of positive ion.