Dc electrical breakdown between a metal electrode and a water surface

Dc electrical breakdown between a metal pin and a water surface in atmospheric pressure air is investigated by fast framing and high frequency current and voltage measurements. To investigate the influence of the water surface on spark formation, the measurements are compared with the breakdown characteristics between a metal pin and a metal plate electrode. In the case of negative polarity of the pin a glow-to-spark transition occurs. The spark is broadened near the water surface due to an incomplete constriction of the glow phase. When the anode is a metal plate the spark is a narrow filament. In the case of positive polarity of the pin and a water cathode a streamer-to-spark transition occurs. The streamers are clearly branched. When the cathode is a metal plate, mostly one thick streamer is observed with constricted cathode spot which develops into a spark.