Spark breakdown in air/PP-film composite with point-sphere electrode system

A description is given of the spark breakdown in a point-sphere air gap with polypropylene film inserted between the electrodes and subjected to a linearly rising DC voltage. No appreciable polarity effect on the breakdown voltage of the composite was observed at any position of the film. The spark breakdown voltage V/sub b/ increased with increasing distance x of the film from the sphere electrode, to a critical position x/sub c/ at a distance just less than half of the gap length d, at which point it dropped suddenly, and then increased again as x increased to d. In the region xx/sub c/. The breakdown mechanism for both regions is discussed.<>