Streamer injection and growth under impulse voltage: a comparison of cyclohexane, Midel 7131 and Nytro 10X

Streamer growth and charge injection vs. applied impulse voltage has been studied in cyclohexane, Midel 7131 (ester based transformer liquid) and Nytro 10X (mineral transformer oil). Experiments were conducted in point-plane geometry under 50 ns/740 μs impulse voltage. The tip electrodes were electrochemically etched to 2.0 μm and 2.3 μm with electrode gaps of respectively 19.5 mm and 17 mm. Shadowgraphic imaging and a sensitive differential charge measurement technique were used to detect the streamer shape and charge. The experimental setup used can detect charge injections as low as 0.1 pC, and has an image resolution of 4.5 μm. When comparing Midel 7131 to Nytro 10X similar streamer shape and length under positive and negative polarities at the same voltage were found, but Midel 7131 had a higher initiation voltage and less charge was injected into this liquid compared to Nytro 10X at the same voltage.