Current and Emitted Light Characteristics of Streamers in Insulating Liquids under AC Voltages

This paper is aimed to investigate the streamer characteristics of a mineral oil – Gemini X and an ester liquid – Midel 7131 in a divergent AC electric field. A point-to-plane electrode configuration with a gap distance of 30 mm and etched tungsten wire with tip radius of 50 µm were used. Streamer current and emitted light signals were measured by adopting a current shunt and a photomultiplier tube (PMT), respectively. Both streamer initiation and propagation stages were studied. It was found that 50% streamer initiation voltage of the ester liquid is slightly lower than that of the mineral oil. Positive streamers those occurred during the positive half cycle of AC voltage contain a continuous dc component superimposed with intensive pulses for both current and light signals, whereas the…