Lightning impulse surface flashover characteristics of insulators in SF6/N2 and SF6/air below 0.25 MPa

SF₆ gas is used as the insulating medium in cubicle gas insulated switchgear (C-GIS) in low pressure (below 0.25 MPa). SF₆ gas has several shortcomings, such as expensive price, significant greenhouse effect, therefore, exploring alternative media of SF₆ gas is of important theoretical value and practical application significance. This paper focuses on the C-GIS switchgear which uses SF₆ gas as insulating medium and works below 0.25 MPa pressure, and by using self-designed GIS test platform, the negative lightning impulse surface flashover characteristics of insulator models in SF₆ with N₂, air binary mixed gases have been tested under various mixing ratios and various pressures. The test results show that: in the test gas pressure range, the insulators´ surface flashover strengths always increase with the increasing of air pressure in all kinds of gas mixtures, and the specific variation trends are related to the gas pressure and mixing ratio of gas mixtures; the content of SF₆ in gas mixture has a great impact on the surface flashover strength, when a little SF₆ is added to pure N₂ or pure air, the insulators´ surface flashover strength can be obviously improved, however, with the increase of the content of SF₆, the rise of insulators´ surface flashover strength has a saturated trend; SF₆/N₂ or SF₆ /air gas mixtures with higher pressure can be used as insulating medium to replace pure SF₆ gas with lower pressure.