32 / 2018-08-10 11:23:16

Research on the feasibility of 10%c-C4F8/CO2/N2 as SF6 alternatives in UHV GIS and GIL Equipments at low temperature

c-C4F8 binary gas mixtures, c-C4F8 ternary gas mixtures, dielectric strength, Global Warming Potential, Liquefaction temperature

Sulfhur hexafluoride (SF6) is an insulating medium for compact substation components and gas insulated cables due to its high dielectric strength and good heat transfer properties. SF6 has been widely used in UHV (Ultra High Voltage) GIS (Gas Insulation Substation) and GIL(Gas-Insulated metal-enclosed Line). But SF6 does great harm to the environment and its global warming potential (GWP) is very high, and 239000 times as the one of CO2. SF6 has been listed as one of the restricted gas for its high GWP in the ordination of Kyoto protocol signed in 1997. Before 2020, the use of SF6 will be reduced significantly in power industry and even be abandoned. Searching for a gas or gas mixtures with lower environment impact to substitute SF6 and its mixtures as the insulation gases has become more and more urgent. Among all the possible substitutes, c-C4F8 has the features of entirely nontoxic, no ozone depletion, lower GWP (only 36% of SF6), strong electronegative, and high insulation ability. Therefore, c-C4F8 is one of the most promising component gases of a mixture for gas insulation to substitute SF6 and its mixtures. However, the liquefaction temperature (Tb) of pure c-C4F8 is high. Considering the possible use of c-C4F8 mixtures in environment with low temperature, this paper studied the insulation characteristcs of 10%c-C4F8/CO2/N2.
When choosing the substitutes to SF6, high dielectric strength (E/N)lim, GWP and liquefaction temperature (Tb) should be considered. Though few scholars home and abroad have studied the insulation characteristcs of c-C4F8 gas mixtures, they only analyzed the GWP and Tb qualitatively or even ignored these two indexes when analyzing the insulation characteristics of c-C4F8 gas mixtures. In this paper, (E/N)lim, GWP and Tb these three indexes of 10%c-C4F8/CO2/N2 were analyzed quantitatively synchronously for the first time. When studying the discharge characteristics in c-C4F8 and its mixtures, Steady State Townsend (SST) experiment method and Boltzmann equation analysis method can be adopted. SST experiment method needs large quantity of work, and experimental accuracy will be affected by the experimental device. So in this paper Boltzmann equation analysis method was used to calculate the discharge parameters (the swarm parameters including ionization coefficient, attachment coefficient and effective ionization coefficient) in 10%c-C4F8/CO2/N2 over the wide range of 180 In this paper, GWP and Tb were also calculated in pure c-C4F8, c-C4F8 binary mixtures and 10% c-C4F8 ternary mixtures when their (E/N)lim were comparable to SF6. Calculated results show that, it is not feasible for pure c-C4F8 substituting SF6 because of its high Tb, when the environment temperature is over 0℃, c-C4F8/ N2 and c-C4F8/ N2O in c-C4F8 binary mixtures are better substitutes than c-C4F8/CO2 and c-C4F8/CF4 to SF6 for the ratios of c-C4F8 in these two mixtures are low, and GWP are also low, and 10%c-C4F8/N2O/N2 are suitable substitutes to SF6 under the environment temperature lower than -20℃. (E/N)lim、GWP and Tb in 10% c-C4F8 ternary mixtures obtained in this thesis can provide reference for practical engineering use. Detailed data were showed in the following table.