An incremental 3-dimensional analysis of spark paths in air

A video camera has been used to record the paths 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 in three dimensions could be computed. Three-dimensional analysis of 400 spark paths showed that each section was consistently related to the previous section; and allowed the determination of the ratio of the mean angle to the vertical of one section to that of the next section. In addition there is a wide, but definable, variation around this mean, which in turn leads to the characteristic shape of spark paths. Knowing the probability of each possible direction for the next section should allow the prediction of the probability of a spark from a high-voltage conductor striking any particular point on the earthed conductor. This has potential applications in the design of high-voltage equipment and lightning protection schemes. Some simulations were developed for a different electrode system with two earthed rods replacing the earthed plane, based on this approach. These compared well with experimental results.