Song Xiao

Experimental analysis of the feasibility of CF 3 I/CO 2 substituting SF 6 as insulation medium using needle-plate electrodes

CF₃I gas has low greenhouse effect and good insulation properties, so it can replace SF₆gas that has high greenhouse effect. In this study, the partial discharge inception voltage (PDIV) of CF₃I/CO₂ mixed gas is measured by power frequency test under different gas pressures, mixing ratios, and gap distances. The influence of these conditions on the partial discharge performance of CF₃I/CO₂ mixed gas is investigated. The PDIV of the CF₃I/CO₂ mixed gas is also comparatively analyzed with that of SF₆/CO₂ mixed gas. The results show that the PDIV of the CF₃I/CO₂ mixed gas is 1-1.2 times higher than that of SF₆/CO₂ mixed gas¿when the mixture ratio is between 10-30% and the gas pressure is between 0.1-0.3 MPa, which means the insulating ability of the CF₃I/CO₂ mixed gas is better than that of the SF₆/CO₂ mixed gas. By contrast, the PDIV of these two mixed gases exhibit similar variation trend with gas pressure when the mixing ratio is more than 20%. There is positive synergistic effect on the PDIV of CF₃I and CO₂. These results indicate that CF₃I/CO₂ (20 to 30%) mixed gas may be used to replace SF₆ gas for gas-insulated equipment applications.

Experimental studies on power frequency breakdown voltage of CF3I/N2 mixed gas under different electric fields

To verify the feasibility of replacing SF6 by CF3I/N2, we compared their power frequency breakdown performance with the influence of gas pressure, mixing ratio, and electric field utilization coefficient. Under different electric fields and mixing ratios, the power frequency breakdown voltage of CF3I/N2 increases linearly along with gas pressure. Besides, with the rise of the electric field utilization coefficient, the linear growth rate of breakdown voltage along with gas pressure gradually rises. The sensitivity of pure CF3I to electric field is particularly high and can be improved by the addition of N2. The mixture 30% CF3I/70% N2 at 0.3 MPa could replace pure SF6 in equipment requiring a low insulation, but the gas pressure or the content of CF3I need to be increased for higher insulation requirements.

Decomposition Mechanism of C5F10O: An Environmentally Friendly Insulation Medium

SF6, the most widely used electrical-equipment-insulation gas, has serious greenhouse effects. C5F10O has attracted much attention as an alternative gas in recent two years, but the environmental impact of its decomposition products is unclear. In this work, the decomposition characteristics of C5F10O were studied based on gas chromatography-mass spectrometry and density functional theory. We found that the amount of decomposition products of C5F10O, namely, CF4, C2F6, C3F6, C3F8, C4F10, and C6F14, increased with increased number of discharges. Under a high-energy electric field, the C-C bond of C5F10O between carbonyl carbon and α-carbon atoms was most likely to break and generate CF3CO•, C3F7• or C3F7CO•, CF3• free radicals. CF3•, and C3F7• free radicals produced by the breakage more easily recombined to form small molecular products. By analyzing the ionization parameters, toxicity, and environmental effects of C5F10O and its decomposition products, we found that C5F10O gas mixtures exhibit great decomposition and environmental characteristics with low toxicity, with great potential to replace SF6.

Effects of micro-water on decomposition of the environment-friendly insulating medium C5F10O

SF6 is widely used in all kinds of high-voltage electrical equipment because of its excellent insulation and arc-extinguishing performance. However, this compound leads to serious greenhouse effect, which harms the environment. Many research institutions are now actively in search of SF6 alternative gas. C5F10O has attracted much attention as an alternative gas with low global warming potential (GWP) and excellent dielectric strength. In this paper, we analyzed the possible decomposition paths of C5F10O under micro-water environment through density functional theory. We also evaluated the ionization parameters and toxicity of the decomposition products. The results show that OH• and H• produced by H2O exhibited a catalytic effect on the decomposition of C5F10O. CF4, C2F6, C3F6, C3F8, C4F10, C5F12, C6F14, C3F7COH, C3F7OH, CF3COH, C3F7H, and CF3OH were produced in the micro-water environment. Based on molecular configuration calculation, the ionization parameters of these products were inferior to perfluoro...

Reactive molecular dynamics study of the decomposition mechanism of the environmentally friendly insulating medium C3F7CN

The extensive use of sulfur hexafluoride (SF6) gas in the power industry has a strong greenhouse effect. Hence, many scholars are committed to studying SF6 alternative gases to achieve green power development. In the past two years, C3F7CN (heptafluoroisobutyronitrile) has attracted the attention of many scholars due to its excellent insulation and environmental protection characteristics as a potential alternative gas. This study theoretically explores the decomposition characteristics of C3F7CN and the C3F7CN/CO2 gas mixture based on the reactive molecular dynamics method and density functional theory. The main decomposition pathways of C3F7CN and the enthalpy of each path at different temperatures were analyzed. The yield of the main decomposition products was obtained under several temperature conditions. The decomposition of C3F7CN mainly produced CF3, C3F7, CN, CNF, CF2, CF, F, and other free radicals and a few molecular products, such as CF4 and C3F8. The C3F7CN/CO2 gas mixture has more excellent decomposition characteristics than that of the pure C3F7CN. The addition of CO2 effectively ensures that the gas mixture has a low liquefaction temperature, which is considerably suitable for use as a gas insulation medium. The relevant research results provide guidance for the further exploration on the electrical properties and practical engineering application of the C3F7CN gas mixture.

Experimental studies on the power–frequency breakdown voltage of CF3I/N2/CO2 gas mixture

Trifluoroiodomethane is a promising alternative to SF6 because of its good insulation properties and much less serious greenhouse effect than SF6. Previous studies have shown that the insulation performance of CF3I mixed with CO2 or N2 can equal that of SF6. This study explored the frequency breakdown characteristics of CF3I and SF6 mixed with two buffer gases. The effects of air pressure and field strength were analyzed. The fixed mixing ratio of CF3I and SF6 was 30% in the experiment. The breakdown experiment was conducted by changing the mixing ratio of CO2 and N2. Results showed that the CO2/N2 mixture ratio did not exert a synergetic effect, and the CF3I/CO2 breakdown performance was better than that of CF3I/N2 in the quasi-uniform and highly non-uniform electric fields. CO2 possibly provided the C atoms for the entire system to maintain a certain balance in C, and this balance inhibited the decomposition of CF3I. The breakdown performance of SF6/N2 was good in quasi-uniform field, whereas that of SF...

The influence of Cu, Al, or Fe on the insulating capacity of CF3I

SF6 is widely used in electrical equipment as an insulating medium. However, SF6 is a serious greenhouse gas. CF3I is considered as one of its potential alternatives. This study verifies whether free metal particle (Cu, Al, or Fe) defects adversely affect CF3I insulation and investigates the incidence from different types and numbers of metal particles. This study is also devoted to calculating specific heat at constant pressure and electrical conductivity of CF3I–metal mixtures. The calculation results prove that with the increase of metal ions, temperature rises faster in the CF3I–Cu plasma or in the CF3I–Fe plasma than in the CF3I plasma without metal absorbing the same energy. The fast development of ionization can promote the increase of free electrons and the rise of electric conductivity. On the basis of the experiments and theoretical analysis, the influence of Cu and Al on the insulating capacity of CF3I is greater than that of Fe.

Partial discharge decomposition characteristics of typical defects in the gas chamber of SF 6 insulated ring network cabinet

The decomposition products of SF6 partial discharge (PD) were experimented to detect PD fault in the gas chamber of SF6 gas insulated ring network cabinet. The SF6 decomposition products and the decomposition characteristics of typical defects (i.e., metal protrusion and metal particle) were investigated. Two models of typical defects were constructed in the simulated gas chamber. Various discharge intensities were generated by applying different voltages, and the samples were collected and detected by gas chromatography mass spectrometry. Experimental results showed that the stable SF6 decomposition components under PD were CO2, SO2F2, SOF2, and SO2. The concentration of the four components increased with time and were saturated. In addition, the increase in discharge intensity significantly affected the decomposition process. Decomposition characteristics under different defects were analyzed according to the different electric field characteristics. Research showed that CO2 formation rate in the two kinds of defects under similar discharge intensity exhibited minimal difference. Furthermore, sulfide formation rate under metal protrusion defects was higher than that of metal particle defects. The same experiment was carried out in the ring network cabinet chamber, and the results were consistent with that in the simulation chamber.

Insights on decomposition process of c-C4F8 and c-C4F8/N2 mixture as substitutes for SF6

In recent years, many scholars have carried out studies on c-C4F8 and its gas mixture and found it has potential to be used as an environment-friendly insulating medium to replace SF6 in medium-voltage equipment. In this paper, the c-C4F8 and c-C4F8/N2 gas mixture models were built to study its decomposition process by the combination of reactive molecular dynamics method and density functional theory. The yield of the main decomposition products, the reaction pathways and enthalpy under different temperatures were explored. It was found that the decomposition of c-C4F8/N2 mainly produces CF2, F, CF3, CF, C, CF4 and C2F4. c-C4F8 can decompose to C2F4 by absorbing 43.28 kcal/mol, which is the main decomposition path and this process easily occurs under high temperature. There is a dynamic equilibrium process among the various produced radicals, which ensures the insulation performance of system to a certain extent. The decomposition performance of c-C4F8/N2 mixture is better than that of pure c-C4F8 at the same temperature. Relevant results provide guidance for engineering application of the c-C4F8/N2 gas mixture.

Theoretical study on the interaction of heptafluoro-iso-butyronitrile decomposition products with Al (1 1 1)

ABSTRACT Seeking environmentally friendly gas-insulated medium has become a research hotspot in recent years. At present, C3F7CN (Heptafluoro-iso-butyronitrile) is considered to be a potential SF6 environment-friendly alternative gas and some achievements have been made in the study of its insulation and decomposition characteristics, but there are few reports on the compatibility between its characteristic decomposition products and materials. The investigation of compatibility between gas-insulated medium and material is an important part of evaluating its comprehensive performance. In this paper, we investigated the interaction between C2F5CN, CF3CN, COF2 and CF4 with the aluminium widely used in electrical equipment. It was found that the interaction between C2F5CN, CF3CN and Al (1 1 1) surface is strong. There are obvious charge transfer and electron orbital overlap between the C atom, N atom in CN group and Al (1 1 1). The interaction between COF2, CF4 and Al (1 1 1) surface is weak and van der Waal’s forces play the major role. Relevant results reveal the characteristics of C3F7CN decomposition products and provide theoretical guidance for evaluating the material compatibility between C3F7CN decomposition products and aluminium. GRAPHICAL ABSTRACT