Effect of Electric Field Uniformity on Streamer and Breakdown Characteristics in a Gas-to-Liquid Oil under Positive Lightning Impulse

This paper presents an experimental study on the streamer characteristics of a gas-to-liquid (GTL) oil in a semi-uniform field under positive lightning impulse. To realize the semi-uniform field, a plane-needle-plane electrode geometry was applied. The needle-plane geometry, non-uniform field, with the same oil gap distance was also employed for comparison. The streamers propagate farther when the applied voltage increases in both fields, however compared to the nonuniform field, the streamers in semi-uniform field are constrained along the axial direction with less side branches. Additionally, the streamer initiation voltage and breakdown voltage are higher in semi-uniform field while the streamer propagation is facilitated compared to the non-uniform field. Meanwhile, two more electrode geometries with different field uniformities were used to measure the streamer initiation voltages and breakdown voltages in the GTL oil. The results were also compared with conventional mineral oil, and GTL oil shows similar streamer initiation voltages and breakdown voltages as the mineral oil in the present investigation, which provides additional reference for the application of GTL oil in power transformers.