POTENTIAL DISTRIBUTION ALONG SINGLE NEGATIVE CREEPING STREAMER IN TRANSFORMER OIL

A needle immersed in transformer oil is located just above a sheet of glass the opposite surface of which is conducting. By applying steps o f high voltage, streamers are generated which propagate radially with numerous branches. A technique for guiding the discharges gives single quasirectilinear streamers, which allows more accurate investigation. The characteristics of these discharges (mean propagation velocity, f inal extension, electric current and charge) are determined and the me asured charge is compared with the predictions of two simple models. T his indicates that the streamer channels are not equipotential. A capa citive probe technique with associated optical fibres allows one to ac curately determine the spatio-temporal variation of the potential alon g the streamer channels.