STREAMER PROPAGATION OVER A LIQUID-SOLID INTERFACE

A needle immersed in transformer oil is located just above a sheet of glass of which the opposite surface is conducting. By applying HV step s, streamers are generated which propagate radially with numerous bran ches. The characteristics of these discharges (mean propagation veloci ty, final extension, electric current and charge) are determined and t he measured charge is compared with the predictions of two simple mode ls. A technique for guiding the discharges gives single quasi-rectilin ear streamers, which allows a more accurate investigation. The mean el ectric current and the final charge indicate that the streamers channe ls are, to a first approximation, at the potential of the needle. The simple picture of a finite potential gradient along the channels is di scussed with reference to the intermittent character of the discharge phenomena.