Abstract：In recent years, gas insulated transmission lines (GILs) have been widely applied in power systems because of their excellent performances including high transmission capacity, low power loss, strong environmental adaptability, etc. Under the current carrying condition, the joule heat generated from the central conductor can raise the conductor temperature to 70~80 ℃, causing a radial temperature gradient between the conductor and the shell. Under temperature gradient, SF6 gas convection is formed, changing the designed insulation margin of tri-post insulators, which threats the safe operation of UHV-GIL. At present, more attention is paid to the problem of electric field distribution during checking the insulation performance of UHV-GIL, and the influence of thermal-fluid field distribution on gas dielectric strength is seldom considered. Therefore, this paper analyzed the insulation margin of the UHV-GIL tri-post insulator considering the non-uniform gas convection effect. The simulation model of the electric-thermal-fluid field in a horizontally laid 1 100kV GIL was established to explore the effects of the temperature and the gas density distributions inside the GIL on the breakdown strength of the insulation gas. Then, the insulation margin analysis for the tri-post insulator was conducted based on the current reference values of the designed electric field considering the gas convection effect. Finally, the discharge inception voltage based on the volume-time theory was calculated considering the electric field and the gas density. Results show that under the large current-carrying condition (8 000A), the GIL conductor temperature reaches 78.1 °C, reducing the local gas density and the dielectric strength by 15%. To keep the insulation margin, the reference value of the designed electric field should be lowered accordingly. The revised allowable electric field strength considering the gas convection is 20.4 kV/mm in the SF6 gap, is 10.2 kV/mm on the insulator surface and is 3 kV/mm inside the insulator and on the insert surface, respectively. At the peak time of the lightning impulse voltage, the tangential electric field along the tri-post insulator is concentrated in the post leg region of the insulator, whose maximum value is 8.9 kV/mm and is below the revised allowable electric field strength. While the normal electric field along the tri-post insulator is concentrated in the spherical area of the insulator, whose maximum value is 18.5 kV/mm. The synthetic field strength in the SF6 gap is up to 20.5kV/mm at the connecting sleeve, which exceeds the revised allowable electric field strength under the large current-carrying condition. Under the rated power frequency voltage, the electric field strength on the insert surface is 3.25 kV/mm, which does not meet the electric field design specification. The load induces the discharge inception voltage to drop by 11.6%. Gas discharge easily occurs around the upper post of the insulator, because the warm SF6 gas with low density and dielectric strength goes up by buoyancy. Since the gas convection has an evident impact on the insulation performance of GIL, the structure and parameter of the tri-post insulator should be adjusted to satisfy the current carrying condition. The research results are expected to provide references for the optimization design of GIL tri-post insulators.
杜伯学, 董佳楠, 梁虎成. 特高压GIL非均匀热气流特性与三支柱绝缘子绝缘裕度分析[J]. 电工技术学报, 2023, 38(6): 1678-1686.
Du Boxue, Dong Jia′nan, Liang Hucheng. Non-Uniform Gas Convection in UHV-GIL and Insulation Margin Analysis for Tri-Post Insulator. Transactions of China Electrotechnical Society, 2023, 38(6): 1678-1686.
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