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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]

The decomposition characteristics of SF6 gas-insulated equipment remarkably vary under different working pressures (0.3?0.7 MPa). Thus, the influence of pressure should be considered when adopting decomposed components for spark discharge fault diagnosis. A series of experiments on SF6 spark discharge decomposition under various pressures were performed on the spark discharge simulation experimental platform. The influence of pressure on SF6 spark discharge decomposed components were analyzed quantitatively combined with molecule chemical decomposition mechanisms. Results show that the species of spark decomposed components do not vary under different pressures. However, pressure directly affects the accumulated energy of the electrons in the spark channel, leading to diverse dissociation intensities of electrons on SF6. This phenomenon further affects the rate of neutral-neutral molecule and ion-molecule reactions responsible for the decomposed components. Finally, the yields and effective generation rates of decomposed components CF4, SOF4, SO2F2, SOF2, and SO2 decline with varying degrees under increasing pressure. Moreover, mathematic regression equations were derived for the effective generation rates of the components influenced by pressure. [ABSTRACT FROM AUTHOR]

To figure out the influence rules of trace H2O on SF6 decomposition characteristic components under spark discharge, a series of spark discharge decomposition experiments with various H2O contents were performed using needle-plate electrode to simulate metal protrusion insulation defect. The changing rules and mechanisms of five decomposition characteristic components were achieved quantitatively, indicating that no matter how much H2O was, there exist five main decomposition components: CF4, SOF2, SO2, SOF4 and SO2F2. The contents of the five decomposition components increased with the time extended, and resulting in the contents of SF6 spark decomposition components by the order: SOF2 > SO2F2 > SOF4 > SO2 > CF4. Additionally, the higher H2O content is, the stronger promoting effect on the generation of SO2F2, SOF2, SOF4 and SO2 is. [ABSTRACT FROM AUTHOR]

SF6 decomposition characteristics under partial discharge (PD) are not only associated with insulation fault type and its severity but also closely related to the H2O content of in the equipment. This paper studies the decomposition characteristics of mixture gas SF6/H2O with six different gradients of trace H2O under the same PD energy, selects SO2F2, SOF2, CO2, and CF4 as the characteristic components, and analyzes the influence regularity of trace H2O on each of the component concentration, effective formation rate and characteristic ratio. Results show that H2O creates favorable conditions for generating SO2F2 and SOF2 owing to the capacity to capture F atom and inhibit low fluorine sulfides from recombining into SF6. As a result, the concentration and effective formation rate of SO2F2 and SOF2is positively related with H2O. Whereas H2O has no evident influence on CO2, it can consume intermediate by-products CF2 and CF3 which restrain CF4 generation. Each characteristic ratio decreases sharply and then becomes stable with increment of H2O. The defined effective characteristic ratio effectively reflects its relationship with H2O, whereas obtained mathematical expression between each effective characteristic ratio and trace H2O lays solid foundation for fault diagnosis of SF6 insulated equipment based on SF62 decomposition characteristics. [ABSTRACT FROM AUTHOR]

To obtain relationship between concentration of SF6 decomposed characteristic components (or their concentration ratio) during the formation process and partial discharge qualities and pulse repetition rate, this paper used needle-plate electrode to simulate outthrust insulation fault and conducted a serial of experiments. First, the SF6 decomposition characteristic under different PD strengths is obtained. Then this paper defines average discharge qualities per second as QSEC. It considers both apparent discharge qualities and discharge pulse repetition rate, and analyzes the relation feature between SF6 decomposition characteristic (both concentration of component and their effective formation rates RRMS) and QSEC. Besides, it proposes C(SO2F2)/C(SOF2) as the energy characteristic ratio (ER) to represent PD energy, and defines the effective energy characteristic ratio as (ERRMS). Moreover, it achieves the inner correlation feature between QSEC and all the characteristic component concentration, the RRMS of each characteristic component and ERRMS. The results show that: since number of C atoms from stainless steel surface and content of trace H2O and O2 in gas chamber were limited, both decomposed component concentration and component concentration ratio accords with the famous "Logistic Population Model" growth trend in ecology, which means they present ???S???-curve increase with QSEC. The proposed ER can effectively indicate the amount of PD energy and the defined ERRMS can objectively reveal the variance regularity of PD energy with QSEC. Hence, the correlation mathematic formula between ERRMS and QSEC is obtained and ERRMS can be used as the new characteristic parameter to represent PD energy. It establishes the foundation for the further fault diagnosis research. [ABSTRACT FROM PUBLISHER]