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Since the environmental-friendly insulating gas C5F10O not only has good environmental compatibility, but also has excellent insulating properties, it has the potential to replace SF6 in equipment such as medium and low voltage switchgear. When a partial over-thermal fault occurs on metal material surface inside the gas-insulated equipment, the C5F10O can be decomposed by overheating, and the presence of the gas–solid interface has a certain influence on C5F10O decomposition process. To this end, this article uses the Density Functional Theory to study on C5F10O over-thermal decomposition mechanism on metal materials surface in the equipment. The results show that when it does not involve Cu atoms in the reaction, the energy barrier of C5F10O decomposed into C2F4O and C3F6 is reduced by about 14.7 kcal/mol compared with that in free space; when C5F10O decomposition involves Cu atoms in the reaction and chemical adsorption occurs, the reaction energy barrier is further reduced by about 7.4 kcal/mol. In addition, the participation of Cu surface reduces the reaction energy barrier of 2 C2F4O → CF2O + C3F6O and C2F4O → CF4 + CO by 8.4 kcal/mol and 26.6 kcal/mol respectively, and increases the reaction energy barrier of C3F6 + CF2O → C3F8 + CO by 23.4 kcal/mol. It is believed that copper material has the effect of promoting the C5F10O decomposition to some degree. The research conclusions in this article can provide theoretical guidance for selections of internal metal materials or surface coating for the design of environmentally friendly gas-insulated switchgear in the future.

During the breaking process of the self-blasting circuit breaker, the pressure characteristics greatly affect the action characteristics of the valve and the pressure in the expansion chamber, thus affecting the arc blowing effect. Therefore, a 550kV single-break selfblasting circuit breaker is taken as the research object. Based on the theory of magnetohydrodynamics (MHD), a two-dimensional transient model considering arc radiation is established, and the numerical calculation of the breaking process under two typical breaking conditions with short- circuit current of 63kA and 40kA and arcing time of 12ms is completed. The pressure and temperature distribution in the expansion chamber, and the action characteristics of the valve are obtained. Besides, combined with the test conditions, the 63kA short-circuit current, the pressure and temperature characteristics under short, medium and long arcing conditions are studied, and the valve action time under different conditions is obtained. The results show that the maximum temperature of the arc core region is 33219K at 63kA, which is about 3332K higher than the 40kA condition. The maximum pressure in the expansion chamber is 2.94MPa under the condition of 63kA and 2.36MPa at 40kA. The check valve is mainly affected by the temperature and pressure in expansion chamber side under the two breaking conditions, and the force received on the side of the cylinder is substantially same. The action time of the check valve under 63kA is 0.06ms earlier than the 40kA, and relief valve advance acts 0.05ms. Corresponding to different arcing time, the action time of check valve is 16.38ms, 16.28ms and 16.48ms and the time of relief valve is 17.52ms, 17.42ms and 17.67ms.

With the rapid development of UHV and smart grid, the breaking condition of SF 6 circuit breaker becomes more complicated. Along with the increasing of recovery voltage after arc extinguishing, breaking failures caused by the re-strike happened frequently. A two-temperature model about nonequilibrium SF 6 arc plasma was built according to basic equations of fluid mechanics and gas equation of state, forming a numerical computing method for the whole breaking process in SF6 circuit breaker. The whole breaking process in condition of no-load and breaking 1600A capacitive current were numerical calculated to obtain dielectric breakdown voltage of SF 6 . The accuracy and reliability of the numerical calculation method were verified compared with the experimental results of dynamic breakdown voltage of SF 6 gas between arcing contacts. The thermal dielectric recovery characteristics of SF 6 circuit breaker was analyzed in the condition of breaking 1600A capacity current and short arcing time. Influences of breaking phase angels, velocity and gas pressure were discussed at the same time. The optimization operating strategy of circuit breaker was given to improve the electrical life and reliability of circuit breaker.

High voltage SF 6 circuit breaker must meet the breaking requirement for large short-circuit current, and ensure absence of breakdown after breaking small current. A 126kV high voltage SF 6 circuit breaker was used as the research object in this paper. Based on the calculation results of non-equilibrium arc plasma material parameters, the distribution of pressure, temperature and density were calculated during the breaking progress. The electric field distribution was calculated in the course of flow movement, considering the influence of space charge on dielectric voltage. The change rule of the dielectric recovery progress was given based on the stream theory. The dynamic breakdown test circuit was built to measure the values of breakdown voltage under different open distance. The simulation results and experimental data are analyzed and the results show that: 1) Dielectric recovery speed (175kV/ms) is significantly faster than the voltage recovery rate (37.7kV/ms) during the arc extinguishing process. 2) The shorter the small current arcing time, the smaller the breakdown margin, so it is necessary to keep the arcing time longer than 0.5ms to ensure a large breakdown margin. 3) The calculated results are in good agreement with the experimental results. Since the breakdown voltage is less than the TRV in some test points, restrike may occur within 0.5ms after breaking, so arc extinguishment should be avoid in this time range.

The Redlich-Kwong state equation of the real gas and the governing equations of the flow field were combined to solve the problem. The distribution of physical parameters of the interrupter was attained under the condition of the circuit breaker in small capacitive current interruption by analysis of the 126kV capacitor group SF 6 gas circuit breaker arc extinguishing chamber in air flow field, which is according to enthalpy flow arc model and dynamic model of non-equilibrium arc energy built by microscopic parameters of plasma. The dielectric recovery characteristic curves in arc contacts after the arc extinguished were attained through the coupling calculation in the field of electric and gas flow. Calculation results show that: When the circuit breaker is opening the small capacitive current, the effect of breaking speed on arc burning time is very small and arc extinguished in advance. The arc gap conductivity is about 700S/m, and the thermal conductivity is about 1.1W/m-K at arc extinguishing time. The transient recovery voltage is always lower than that of the breakdown voltage, and the electric arc can successfully break without reburning. To make the short arcing time have a large arc distance, and the large nozzle should be open enough to be strong for the gas blowing condition, the optimum opening speed is 9.6m/s.