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Dielectric barrier discharge in helium at atmospheric pressure was studied by taking fast images of the discharge during one current pulse using an intensified charge couple device. It was observed that there appears a weakly luminous layer close to the anode at the very beginning of the discharge, then the luminous area gradually expands into the entire gap as the anode layer moves toward the cathode, and finally a highly luminous layer forms close to the cathode at the time around the maximum of the current pulse. The evolution of the discharge pattern indicates a transition from Townsend discharge to glow discharge.

The radial evolution of dielectric barrier discharge in helium at atmospheric pressure was studied by taking end-view photographs of the discharge during one current pulse using a fast-gated intensified charge coupled device. The photographs were transformed into three-dimensional images that make the radial evolution of the discharge more visualized. It was found that the discharge begins with a weak Townsend discharge covering the entire electrode surface, develops much more rapidly in the central part where the electric field is higher, and spreads radially outward.

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Research on dynamics of streamer propagation along different dielectric materials under a uniform electric field is presented. In the three-electrode arrangement, the variation of the streamer propagation probability, velocity and light intensity with electric field in the air and along the different dielectric materials was measured through three photomultipliers. The photographs of the streamer propagation in the air and along the different dielectric materials were taken with an ultraviolet camera. The test results have shown that the electric field required for streamer propagation in air alone is less than along the insulation surface. Furthermore, for electric fields higher than streamer 'stability' propagation fields, the streamer propagates along insulation surface with a 'fast' and a 'slow' component. However, the streamer propagates in air alone without a 'fast' component, only with a 'slow' component. The velocity of the streamer propagating in air alone is significantly less than the velocity of the 'fast' component, and is higher than the velocity of the 'slow' component. The streamer 'stability' propagation field and velocity depend upon the nature of the dielectric material. Specifically, higher electric fields are required for streamers to propagate along a dielectric material with larger permittivity. The velocity of streamer propagation along the dielectric material is also affected by attachment of charge to the surface and photoemission of secondary electrons from the surface so much. Consequently, under the same electric field, the relationship between streamer propagation velocity and permittivity of dielectric material is not very evident, roughly inverse proportion.Index Terms -Streamer propagation, dielectric material, three-electrode arrangement, streamer propagation electric field, streamer propagation velocity, streamer propagation light intensity.

Ice accumulation on high voltage insulators can cause accidents by flashover across the ice-covered insulators. The ice accumulation can be reduced by changing the insulator surface properties by application of a semiconducting RTV silicone coating. This method is based on the hydrophobicity and semiconductivity properties of the coating. The mechanism for reducing ice accretion is analyzed theoretically. Experimental results are presented to validate the effectiveness of the semiconducting RTV coating at reducing ice on insulator strings. The results show that the coating on the insulators delays ice formation and reduces the amount of ice.