Flashover discharge propagation on polluted insulators

In view of the vital importance of the current distribution at the tip of a flashover discharge, a new analytical approach to the problem of flashover discharge propagation on polluted insulating surfaces has been extended to the case of semiconducting surfaces. A simple model based on direct measurements of the current distribution at the pollution-discharge interface using a recently developed experimental technique has helped to shed some light on the critical physical mechanisms responsible for the highly unstable conditions leading to flashover. In this context the case of the semiconductive-glaze insulator is a good candidate to illustrate the different discharge elongation modes. In particular, the relationship between the key electrical parameters (i.e. current, voltage, discharge length and pollution-surface resistivity ratio) is clearly demonstrated using a set of non-dimensional computer-generated plots covering a wide range of conditions. From the practical point of view, these results prove useful for comparing the projected performance of different insulators under varying pollution severity.