An investigation into the characteristics of large scale surface discharges

A surface discharge is a form of electrical breakdown which occurs across insulated surfaces in the presence of high voltage stress. This work is concerned with the measurement and analysis of the properties of a surface discharge which propagates one metre across a polymer surface. The work reported in this paper extends investigations originally carried out on a four metre surface discharge (see Farish et al., Eng. Sci. Educ. J., p.277-86, 1994) constructed on a one metre system designed for quantitative measurements. Results were previously given for the velocity and discharge length of the flashover as a function of the applied voltages using a diagnostic system consisting of a number of fibre optic cables positioned above the polymer surface. When the discharge passed the fibre optic cable the light emitted by the discharge was detected by photodetectors placed at the end of the fibre. By determining the time of arrival of the light pulse from the fibre optic cable the velocity of the discharge could be found. The main advantage in analysing a four metre discharge system is that the effects of the parameters influencing the surface discharge should be amplified. This would make their measurement simpler when compared to the measurements obtained over several centimetres using the standard cylindrical sample and plain parallel electrode configuration, as described by Allen et al. (1995). The present research involved scaling down the four metre apparatus to a one metre system