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Abstract:A high-temperature oil-paper insulation system offers an opportunity to improve the overloading capability of distribution transformers facing seasonal load variation. A high-temperature electrical insulation system (EIS) was chosen due to thermal calculation based on a typical loading curve on the China Southern Power Grid. In order to evaluate candidate high-temperature insulation systems, Nomex ® T910 (aramid-enhanced cellulose) immersed in FR3 (natural ester) was investigated by a dual-temperature thermal aging test compared with a conventional insulation system, Kraft paper impregnated with mineral oil. Throughout the thermal aging test, mechanical, chemical, and dielectric parameters of both paper and insulating oil were investigated in each aging cycle. The thermal aging results determined that the thermal class of the FR3-T910 insulation system meets the request of overloading transformer needs.

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This paper presents an experimental study on the streamer characteristics of a gas-to-liquid (GTL) oil in a semiuniform 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.