Studies on the propagation of an impulse breakdown across the surface of artificial acid rainwater by high-speed Schlieren method

Rain water polluted with natural and industrial contaminants, more commonly known as acid rain, has been used as an electrolyte to account for its effect on the flashover phenomenon across high voltage outdoor insulators. Optical and electrical techniques using high speed Schlieren photography and current measurement with LED were employed. The propagation of an impulse breakdown was then studied by varying the voltage waveforms. Experiments were also conducted with artificial acid rainwater of low pH value to determine the factor of safety over the actual rainwater characteristics. It was found in the present conditions, that given the same conductivity (sigma) neither the dissolved components nor the pH value of the rainwater influence significantly the discharge growth, while a substantial decrease of the propagation speed was measured with the increase of the front duration of the applied voltage.