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In this work, we explored the ac breakdown characteristics of C5F10O/CO2 mixtures under different electrode surface roughness. It was found that sulphur hexafluoride (SF6) outperforms C5F10O/CO2 mixtures in the ac breakdown experiments. The breakdown voltages of C5F10O/CO2 and SF6 are negatively correlated with the surface roughness, while SF6 is more sensitive to the electrode surface roughness than C5F10O/CO2. To reach the dielectric strength of SF6, an increase in pressure or mixing ratio of C5F10O/CO2 is needed, while the liquefaction temperature of C5F10O/CO2 will increase simultaneously. Considering the limitation of 20% drop in dielectric strength, the maximum acceptable surface roughness of the gases is determined. The controlling requirement of electrode surface roughness ${R}_{t}$ of 30 $\mu \text{m}$ in SF6 equipment is suitable for the design of C5F10O/CO2 equipment. [ABSTRACT FROM AUTHOR]

$\text{C}_{{5}}\text{F}_{{10}}\text{O}$ gas mixture is one of the most promising SF6 replacement gases with outstanding electrical performance and excellent environmental characteristics. Its switching impulse (SI) breakdown characteristics are important for future insulation design and insulation coordination. In this article, factors that can influence SI withstand voltage and the synergy of the gas mixture such as gas pressure, and the type and content of the buffer gas, are experimentally studied. According to the experimental results, $\text{C}_{{5}}\text{F}_{{10}}\text{O}$ gas mixtures under nonuniform electric field show significant polarity effects under SI voltage. When the polarity of the applied voltage is negative, its $U_{\mathrm {50\%}}$ tends to increase linearly with the increase in gas pressure, while the “hump phenomenon” is observed under positive SIs as the gas pressure increases, which can be explained by the enhanced electric field distortion by the space charge. The insulation strength of the two gas mixtures increases more obviously with the increase in $\text{C}_{{5}}\text{F}_{{10}}\text{O}$ content at lower mixing ratios and shows a saturation trend at higher mixing ratios. Based on the calculation, CO2 in discharge processes is likely to produce more low-energy electrons than that can be produced by N2 under the same conditions, so that SI withstand voltage of $\text{C}_{{5}}\text{F}_{{10}}\text{O}$ /CO2 is higher than that of $\text{C}_{{5}}\text{F}_{{10}}\text{O} / \text{N}_{2}$ according to the attachment of low-energy electrons by $\text{C}_{{5}}\text{F}_{{10}}\text{O}$. On this basis, the synergistic effects between different gas components are calculated. The synergy between the components of a gas mixture is related to the gas pressure and $\text{C}_{{5}}\text{F}_{{10}}\text{O}$ content, and the synergistic effects are more significant in $\text{C}_{{5}}\text{F}_{{10}}\text{O} / \text{N}_{{2}}$ mixture than in $\text{C}_{{5}}\text{F}_{{10}}\text{O}$ /CO2 mixture. The results show that SI withstand voltage of $\text{C}_{{5}}\text{F}_{{10}}\text{O}$ gas mixtures under a nonuniform electric field can be improved by increasing the gas pressure or $\text{C}_{{5}}\text{F}_{{10}}\text{O}$ content. $\text{C}_{{5}}\text{F}_{{10}}\text{O}$ gas mixture has the potential to replace SF6 in certain mixing ratio and under certain gas pressure. [ABSTRACT FROM AUTHOR]

Self-recovery ability after over thermal fault decomposition is a fundamental factor determining the stability of environmentally friendly insulation medium C5F10O in engineering applications. This article proposes 42 possible reaction pathways for the decomposition products of C5F10O to reform C5F10O after overheating fault based on its thermal decomposition and industrial synthesis pathways. Dominant reaction paths and reactants in the recovery process at temperature of 298–1000 K are theoretically analyzed according to the chemical equilibrium constant and rate constant, which were calculated based on the density functional theory using the thermodynamics properties of the reactions such as activation energy and enthalpy. According to the results, at low temperatures, 26 of the 42 proposed reactions have the equilibrium constants greater than 1, and the rate constants of them are much higher than that of the decomposition reactions, proving that decomposed C5F10O can be partly recovered after the overheating fault is removed. Among the recovery pathways, reactions with primary or secondary decomposition products of C5F10O as the reactants hold higher equilibrium constants and are the dominant reactions for the recovery process. R11, R8, and R5 hold the largest rate constants in similar reactions and contribute the most to the restoration of C5F10O, that is, (CF3)2CFCO $\cdot $ , (CF3)2CFCOF $\cdot $ , and CF3OCCF(CF3)2 are the dominant reactants for the formation of C5F10O. And the synthesis reactions R22, R17, R7, and R15 of these reactants are also necessary for the self-recovery process of C5F10O. [ABSTRACT FROM AUTHOR]

Poor contact is one of the main causes of the internal fault of SF6 gas insulated equipment. Taking the most common over-thermal decomposition process of SF6 caused by poor silver-plated copper contacts as an example, this article combines with density functional theory (DFT) and establishes the gas–solid contact interface adsorption model of SF6 and its main decomposition characteristic products (SO2F2, SO2, SOF2, HF, and H2S) with solid silver. Adsorption energy, charge transfer, and density of electronic state were used to analyze the reaction activity of SF6 and its main decomposition products with the Ag surface. It is found that SF6 and SO2 are chemically adsorbed on the Ag surface, and the reaction activity is relatively strong. When chemical adsorption occurs, SF6 bonds with the metal surface by the 2p orbitals of F atoms, and SO2 is bonded to the metal surface by the 2p orbitals of O atoms. There is also a strong reaction trend between HF and Ag (1 1 1), while SO2F2, SOF2, and H2S only physically absorbed with the Ag (1 1 1) surface. This indicates that under the local overheating failure caused by metal contacts, SF6 will first undergo chemical adsorption in the SF6/Ag (1 1 1) system and then undergo a decomposition reaction near the metal surface rather than in free space. The participation of Ag reduces the difficulty of the decomposition reaction to some extent. The results lay a foundation for finally revealing the interfacial reaction process of SF6-Ag. [ABSTRACT FROM AUTHOR]

As a promising environmentally friendly insulating medium, C5F10O needs to be mixed with buffer gases such as technical air to avoid liquefaction. Notably, such a high proportion of oxygen can promote the decomposition of C5F10O and may even eradicate its stability under over-thermal fault. At present, there is still a lack of experimental research investigating the influence of oxygen on the thermal stability of C5F10O, and the mechanism is still unclear. To this end, experiments are carried out on the thermal decomposition properties of C5F10O while mixed with different proportions of O2. And to reveal the mechanism, the dissociation of C5F10O and the reaction of O2 with CF3CO $\cdot $ radical are studied theoretically based on the density functional theory (DFT) and transition state theory (TST). The results signify that oxygen of 4% and above ravages the thermal stability of C5F10O medium, causing it to decompose in a large amount at high temperature, which generates stable products such as CO2, C3F6, C3F8, and C2F6. The mechanism is that O2 is extremely easy to combine with CF3CO $\cdot $ radical to form a complex, which further decomposes, leading to the continuous development of the decomposition of C5F10O. The study revealed the important mechanism of O2 during the decomposition process of C5F10O, providing experimental and theoretical support for the use of C5F10O mixed gas. [ABSTRACT FROM AUTHOR]