Research Project on the Gas Insulation Using a Gas Mixture

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SF_6 is widely used in important electric power systems such as gas-insulated switchgear (GIS). Recently, however, very high global warming potential (GWP) of SF_6 gas has become a very serious problem. This research project has proposed the "non-SF_6 (or SF_6-less) gas insulation" by substituting a gas mixture with PFC (perfluorocarbon) for SF_6. We have principally investigated the possibility of applying a gas mixture consisting of c-C_4F_8 (perfluorocyclobutan) and N_2 or CO_2.(1) We have derived the expression for the release rate or loss rate at the liquefaction recovery process of a gas mixture containing an electronegative gas. By applying this derivation, we have made clear that the release rate of c-C_4F_8 from c-C_4F_8 /N_2 is much lower than that of SF_6 from SF_6/N_2 at the same mixing ratio.(2) We have studied the insulation characteristics of c-C_4F_8 /N_2(or CO_2) in various conditions, and compared them with those of pure SF_6 and SF_6/N_2. Main experimental conditions … More are as follows :Gas pressure : 0.1〜0.4MPaApplied voltage : dc, 60Hz ac, lightning impulseMixingraito : 0, 5, 10, 20,100 %(vol %) of an electronegative gasIt has been shown that compared with SF_6/N_2, gas mixtures containing c-C_4F_8 have reasonably good insulation ability under quasi-homogeneous electric field conditions.Nonlinearity, or synergism, in discharge voltage relative to mixing ratio, increases with Pd (gas pressure x gap length) for gas mixtures containing c-C_4F_8.(3) Under extremely inhomogeneous conditions simulating sharp conducting particles in practice, the gas mixtures with c-C_4F_8 show almost equivalent insulation characteristics compared with SF_6/N_2. The ac sparkover voltage of c-C_4F_8 /N_2 is even higher at a pressure above 0.3MPa than that of pure SF_6.(4) We estimate that by applying a gas mixture with c-C_4F_8 having the insulation strength, comparable to pure SF_6, the GWP (global warming potential) can be reduced to less 10%. This value is about a half of the GWP in the case SF_6/N_2 is applied at the same mixing ratio. Less