Study On Insulation Properties And Decomposition Characteristics Of Environmentally Friendly Insulating Gas C₆F₁₂O/CO₂ For Application

SF₆ is widely used in gas-insulated equipment due to its extremely high insulation properties,but it is a typical greenhouse gas.With the increasing demand for environmental protection,research on environmentally friendly gas insulating media in the power industry has also received increasing attention.With the continuous development of China's power grid construction,especially the distribution network,the demand for medium and low voltage gas insulation equipment has increased year by year.Finding economical and reliable environmentally friendly insulating media in switchgear is also an important issue to solve the research and development of environmentally friendly equipment in China's power industry.C₆F₁₂O is safe,non-toxic,environmentally friendly and has good dielectric strength,but is limited by liquefaction temperature and is considered to have potential for use in medium and low voltage gas insulated equipment.C₆F₁₂O needs to be used in combination with buffer gas due to the liquefaction temperature.In this paper,CO₂ is selected as the buffer gas,and the feasibility of using C₆F₁₂O/CO₂ mixed gas in 10kV switchgear equipment is explored from the aspects of physical property parameters,insulation properties,decomposition characteristics and compatibility with metals.The safety of the C₆F₁₂O used in the equipment was analyzed from the basic parameters and toxicity parameters.The thermodynamic properties and transport parameters of the gas during discharge were calculated based on the LTE conditions.According to the type of reaction in which the particles participate and the thermal parameters of the particles themselves,the number density of particles at different temperatures is obtained,and the thermodynamic parameters and transport parameters in the range of 300K?30000K are obtained by combining the partition function and the collision parameters.At higher temperatures(greater than 10000K),the difference in conductivity between the three gases C₆F₁₂O,CO₂ and N₂ is small,and the curves of the three are almost coincident with temperature,showing a difference at lower temperatures.C₆F₁₂O is higher than CO₂ and N₂.This law is consistent with the properties of most electronegative gases.The thermal conductivity of C₆F₁₂O has three distinct peaks,appearing at 3500K,5500K and 16000K.The relationship between the mixing ratio of C₆F₁₂O/CO₂ mixed gas and the liquefaction temperature was obtained by Antony's equation.The gas pressure of the insulation test was0.1?0.2Mpa,and the mixing ratio was 0%,2%,4%and 6%.The test measures the breakdown voltage and partial discharge voltage at the power frequency voltage,and analyzes the effects of different electric field uniformity,mixing ratio and pressure value on the insulation performance.The breakdown voltage of the mixed gas is significantly higher than that of pure CO₂,and the ratio of breakdown voltage to CO₂ gradually increases as the mixing ratio increases.Under the extremely uneven field,when the C₆F₁₂O mixing ratio is less than 4%,the breakdown voltage is almost linear with the increase of the mixing ratio.The PDIV+of the mixed gas is significantly larger than the PDIV-,and the PDIV is larger than the PDEV under the same polarity.Mixtures with the pressure greater than 0.14 MPa have the potential to be used in medium and low voltage equipment.The decomposition products of C₆F₁₂O mixed gas after multiple breakdown were measured,and the main decomposition paths and molecular properties of the products were calculated by DFT.It was found that breakdown voltage of the mixed gas after 50 times did not decrease.The main decomposition products after discharge are CF₄,C₂F₆,C₃F₈,C₃F₆,CF₂O and C₅F₁₂.CF₂O was not detected after 48h breakdown.The concentration of CF₄ and C₂F₆ gas remained unchanged after 48h,the concentration of C₃F₈ and C₃F₆ decreased to a certain extent.The product has minimal impact on the insulating properties,environment and safety of the mixed gas.Finally,the compatibility of C₆F₁₂O with copper,aluminum and silver was explored.The effects of C₆F₁₂O on the surface morphology and elemental composition of metal materials were obtained by SEM and XPS.The interaction between different metals and C₆F₁₂O was analyzed.Based on DFT,the physical and chemical adsorption models of C₆F₁₂O and copper,aluminum and silver were constructed.The adsorption energy,charge transfer,electronic structure characteristics(electronic state density,differential charge density)in the interaction process were discussed.Theoretically,the interaction mechanism between C₆F₁₂O and three metal materials was revealed.It was found that the compatibility of C₆F₁₂O with silver was greater than that of copper and aluminum,which provided a theoretical guide for the selection of metal materials in equipment.Through the research of experimental measurement and theoretical calculation,the feasibility of using C₆F₁₂O/CO₂ mixed gas in equipment is verified,which provides theoretical support and technical guidance for C₆F₁₂O/CO₂ mixed gas in low voltage application of 10kV switchgear.