| An experimental study is performed to determine the nature of events which lead to the breakdown of a solid/liquid interface parallel to the electric field when subject to an impulse voltage in a point sphere electrode configuration.;By means of a shadowgraph optical system in conjunction with a high speed camera, recordings of spatial and temporal streamer propagation at and over a solid interface have been made for various spacer materials and test liquids. The results show a strong correlation between the breakdown strength and the permittivity mismatch between the liquid and solid. Glass-like insulators exhibit a general trend towards providing better performances than those of comparable geometry fabricated from high permittivity ceramic materials. A strong polarity effect was also observed. For a given gap setting, the breakdown voltage of an insulating system was considerably lower when using a point cathode. For a point cathode, an improvement in performance was achieved by roughening the surface of the insulator. |
