An incremental analysis of spark paths in air using 3-dimensional image processing

A video camera has been used to record the path of spark breakdowns across a positive point/plane air-gap. By using a prism as a mirror, two images were obtained from which the path could be determined in three dimensions by subsequent computer processing and analysis. Images were analyzed for each of five angular positions of the point electrode´s axis, the gap remaining constant. The fractal dimension of each path was determined and found to increase slightly with the inclination of the pointed electrode. Each spark appeared to have propagated semi-randomly in a direction which included a `memory´ factor, that is, it tended to follow the previous direction while moving monotonically towards the opposite electrode. This was confirmed by an analysis of 400 spark paths which showed that each section has a specific relationship to the previous section, but that there is a wide variation around this mean which leads to the characteristic shape of a spark path. Simulations based on these results yield spark tracks which look similar to those measured and have similar fractal dimensions. These analyses strongly suggest that the development of spark paths in air is by successive steps and in a direction suggested by an angular probability distribution which is related to the field at the tip of the propagating leader