Observation of cathode streamer initiation in dielectric liquids under high magnification

The cathode-streamer initiation process in cyclohexane under nonuniform field was observed. An impulse voltage was applied to a tungsten needle of 0.5 μm radius. The streamer growth was photographed using a high-magnification, high-speed shadowgraph system. The streamer initiation voltage was determined to be -5.18 kV. The initial streamer structure was filamentary. Within 100 ns of inception it changed to a bushlike structure which increased with increasing voltage until a secondary stem appeared and the process appeared to repeat itself. After their expansion process stopped they were noted to break into small bubbles. Partial discharges (PDs) were measured using an LED (light-emitting diode) current measurement system. The relation between PD and streamer growth is discussed