Impulse breakdown of small air gap in electric field Part II: Statistical analysis of shot distribution

The patterns of shot distribution and maximum coverage at impulse breakdown voltage for positive point electr-odes (needle and cone electrodes) in small air gaps in non-uniform electric fields were investigated. During the breakdown test, a sheet of paper was placed on the plate electrode (-ve), and each breakdown shot punched a hole on the paper. Due to the main and filamentary avalanches, the breakdown occurred within an area around the point electrodes. Circles were drawn enclosing all punched holes with the tip of the point electrode at the ce-ntre, each circle separated by 5 mm intervals and frequency of shots determined for gap distances of 5, 8 and 12 cm. The shots pattern exhibited Gaussian frequency distribution, and the maximum spread and coverage were determined