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Inception and breakdown voltages of insulating liquids under DC stress

This paper investigated the streamer inception and breakdown properties of a mineral oil and a synthetic ester liquid under DC stress up to 100 kV. To observe the effect of tip radius on streamer inception, the point-plane electrodes configuration with a fixed gap distance of 10 mm and point electrode with the radii of 5 μm, 10 μm, 20 μm and 50 μm were used. To observe the effect of gap distance on breakdown voltage, a point-to-plane electrode configuration with a fixed tip radius of 10 μm and variable gap distances of 2 mm, 5 mm, 10 mm, 20 mm and 30 mm were used. Streamer current and emitted light signals were measured by using a 10 Ω current shunt and photomultiplier tube (PMT) respectively. The results indicated that initiation voltages of the synthetic ester liquid are slightly lower than those of the mineral oil for all the tip radii under both positive and negative polarities. Moreover, the synthetic ester liquid has lower breakdown voltages than the mineral oil for all the gap distance under both positive and negative polarities.