Letteratura scientifica selezionata sul tema "C4F7N-CO2-O2 mixture"

Sulfur hexafluoride (SF6) shows excellent insulation performance as an insulating gas. It is suitable for various climate conditions due to its low boiling point (−64 °C). Therefore, it has been widely used in power grid equipment. However, its global warming potential (GWP) is 23,500 times higher than that of CO2. Thus, it is imperative to find an environmentally friendly insulating gas with excellent insulation performance, lower GWP, and which is harmless to equipment and workers to replace SF6. In this review, four possible alternatives, including perfluorocarbons, trifluoroiodomethane, perfluorinated ketones, and fluoronitrile are reviewed in terms of basic physicochemical properties, insulation properties, decomposition properties, and compatibility with metals. The influences of trace H2O or O2 on their insulation performances are also discussed. The insulation strengths of these insulating gases were comparable to or higher than that of SF6. The GWPs of these insulating gases were lower than that of SF6. Due to their relatively high boiling point, they should be used as a mixture with buffering gases with low boiling points. Based on these four characteristics, perfluorinated ketones (C5F10O and C6F12O) and fluoronitrile (C4F7N) could partially substitute SF6 in some electrical equipment. Finally, some future needs and perspectives of environmentally friendly insulating gases are addressed for further studies.

Negative and positive partial discharge inception voltages and breakdown measurements are reported in a needle-plane electrode system as a function of pressure under AC voltage for natural gases (N2, CO2, and O2/CO2), pure NovecTM gases (C4F7N and C5F10O) and NovecTM in different natural gas admixtures. For compressed 4% C4F7N–96% CO2 and 6% C5F10O–12% O2–82% CO2 gas mixtures, the positive-streamer mode is identified as the breakdown mechanism. Breakdown and negative partial discharge inception voltages of 6% C5F10O–12% O2–82% CO2 are higher than those of 4% C4F7N–96% CO2. At 8.8 bar abs, the breakdown voltage of 6% C5F10O–12% O2–82% CO2 is equal to that of 12.77% O2–87.23% CO2 (buffer gas). Synergism in negative partial discharge inception voltage/electric field fits with the mean value and the sum of each partial pressure individually component for a 20% C4F7N–80% CO2 and 6% C5F10O–12% O2–82% CO2, respectively. In 9% C4F7N–91% CO2, the comparison of partial discharge inception electric fields is Emax (CO2) = Emax(C4F7N), and Emax (12.77% O2–87.23% CO2) = Emax(C5F10O) in 19% C5F10O–81%(12.77% O2–87.23% CO2). Polarity reversal occurs under AC voltage when the breakdown polarity changes from negative to positive cycle. Polarity reversal electric field EPR was quantified. Fitting results show that EPR (CO2) = EPR(9% C4F7N–91% CO2) and EPR(SF6) = EPR (22% C4F7N–78% CO2). EPR (4% C4F7N–96% CO2) = EPR (12.77% O2–87.23% CO2) and EPR (6% C5F10O–12% O2–82% CO2) < EPR (4% C4F7N–96% CO2) < EPR (CO2).

C₄F₇N and C₄F₇N-CO₂ mixtures are considered as alternatives to SF₆ for use in medium voltage gas insulated switchgear applications (GIS), due to the low global warming potential and good dielectric properties of C₄F₇N. Current work is focused on the calculation of radiative properties (absorption coefficients) of C₄F₇N-CO₂ thermal plasma and computational fluid dynamics (CFD) simulations of free burning C₄F₇N-CO₂ arcs that are stabilized by natural convection. Absorption coefficients of C₄F₇N-CO₂ plasma used in the CFD model are derived from spectral absorption coefficients by Planck averaging. An optimization procedure has been applied to find the optimal number of spectral bands as well as spectral band interval boundaries. Radiation and flow model results for C₄F₇N-CO₂ in comparison to SF₆ and air are provided and discussed.

C4F7N/CO2 gas mixtures have attracted extensive attention because of their excellent insulating properties and environmental friendliness. High electrical and thermal stability is an important indicator for evaluating their performance, but there have been few molecular dynamics studies of their decomposition mechanisms. In this study, using ReaxFF molecular dynamics simulations and quantum chemistry theory, the decomposition mechanism of a C4F7N/CO2 gas mixture and the effect of the O2 content on the decomposition of the mixture were simulated on the microscopic level. It was found that there are three main decomposition pathways of C4F7N molecules, of which the generation of C3F4N⋅ and CF3⋅ free radicals is the most likely to occur. COF2 is the main oxygen-containing product of the C4F7N/CO2 gas mixture, and its generation is significantly affected by the simulation time and temperature. COF2 can be regarded as the characteristic decomposition product of the C4F7N/CO2 gas mixture. The addition of O2 slightly promotes the decomposition of C4F7N, whereas the maximum decomposition rate of CO2 decreases by 0.3% and 1% after the addition of 2% and 8% O2, respectively. Relevant results of this research can provide a theoretical basis and guidance for research into the performance of C4F7N/CO2 gas mixtures and practical engineering applications of these mixtures in the future.

Abstract Owing to global and local legislative mandates pertaining to greenhouse gas emission reduction targets, the focus of industries dealing with electrical power management has shifted towards SF6 replacement within electrical or electromechanical equipment since 2010. In particular, fluoronitrile- (C4F7N) or fluoroketone- (C5F10O) based gas mixtures have been identified as the most promising candidates for this purpose in both medium-voltage (MV) and high-voltage (HV) gas insulated switchgear (GIS). The temperature and pressure ranges of interest are 300 K-30 kK and 1-5 bars respectively, which are relevant to the short-circuit current arcing conditions within an MV-GIS. In this work, we focus on a gas mixture with a fluoronitrile mole fraction lower than 20%, with or without O2 having a mole fraction lower than 20% and the rest of the mixture was carbon dioxide (CO2). Throughout this work, we validate our calculation results with published data for 10% and 20% C4F7N-CO2 mixtures at 1 bar and 5 bars and hint at the possible sources of discrepancies. Our local thermodynamic equilibrium (LTE) based chemical composition results indicate that the addition of 20% O2 to C4F7N-CO2 mixtures significantly reduced CO formation while increasing COF2 formation. However, the addition of 20% O2 induced marginal modifications to the thermodynamic, transport and radiation properties of 10% and 20% C4F7N-CO2 mixtures. Finally, after utilizing the properties database to calculate steady-state temperature proles for a low-current (10 A) free-burning arc without metallic vapor, we demonstrate that the arc columns of 10% and 20% C4F7N-CO2 mixtures with or without O2 are less diffuse compared to air but more diffuse compared to SF6. We explain the order of diffuse-to-constricted proles and arc interruption capabilities for different gases in terms of their thermal conductivities and diffusivities.

Abstract Effective ionization rate, bulk drift velocity and bulk longitudinal diffusion coefficient for electron swarms in mixtures consisting of either C4F7N or C5F10O in atmospheric gases - CO2, N2 and O2 are measured using a Pulsed Townsend setup. Measurements are carried out between 100 Td and 1800 Td.

Abstract During the arc breaking process of high-voltage circuit breaker, the eco-friendly SF6-alternative gases will inevitably decompose and generate various decomposition products. In some cases, it will contain solid by-products such as solid carbon, which will have a deterioration effect on the electrical insulation performance of the equipment. It has been found that adding a proper amount of O2 can effectively inhibit the formation of solid carbon. In this paper, based on the improved Gibbs free energy minimization method, a calculation model considering the solid decomposition products was established, and the arc plasma composition of CO2/O2 mixtures with the new eco-friendly gases, such as C4F7N, C5F10O, HFO-1234ze(E) and HFO-1336mzz(E), in LTE state was calculated. The change of decomposition products with the initial O2 ratio is studied, and the criterion expression of inhibiting solid carbon formation is obtained. We also applied the method to the calculation of other SF6-alternative gases containing sulfur atoms such as NSF3 and CF3SO2F. Finally, we showed that solid carbon can be inhibited when proper molecule formula is satisfied. This work may provide a new idea for further exploring the potential SF6-alternative gases.&#xD;

Dans ce travail de doctorat, une étude théorique et expérimentale systématique a été menée sur l'isolation du mélange de gaz C4F7N-CO2-O2 respectueux de l'environnement et ses caractéristiques de décomposition et de biosécurité sous défauts électriques et thermiques. Sur la base de la méthode de dynamique moléculaire ReaxFF, le processus de décomposition thermique du mélange gazeux sous différentes teneurs en O2 et températures est simulé. En combinant les résultats simulés avec des essais de décomposition thermique, le processus cinétique de décomposition thermique du mélange gazeux et le mécanisme d'évolution de ses sous-produits dans différentes conditions sont révélés. En même temps, le mécanisme d'influence de la teneur en O2 sur la tension de claquage et les valeurs caractéristiques statistiques du mélange C4F7N-CO2-O2 pour des décharges partielles sont analysés et le mécanisme d'influence de différents facteurs sur la génération et l'inhibition des gaz et des sous-produits solides au cours du processus de décomposition par décharge du mélange gazeux est clarifié. En conclusion, sur la base des résultats de simulation et expérimentaux, nous proposons la quantité optimale d'additif O2 et les composants caractéristiques de diagnostic du mélange gazeux C4F7N-CO2-O2 pour les défauts des équipements isolés au gaz moyenne tension ; nous testons la biosécurité du C4F7N et de ses produits de décomposition après l'exposition à l'arc, puis évaluons la faisabilité, la sécurité de l'application du mélange de gaz C4F7N-CO2-O2 dans l'équipement en combinant avec les caractéristiques isolantes et de décomposition électrique et thermique du mélange de gaz C4F7N-CO2-O2 et, les résultats de la biosécurité
In this doctoral work, a systematic theoretical and experimental study has been carried out on the insulation of environmentally friendly C4F7N-CO2-O2 gas mixture and on its decomposition characteristics and biosafety under electrical and thermal faults. Based on the ReaxFF molecular dynamics method, the thermal decomposition process of the gas mixture under different O2 contents and temperatures is simulated. The kinetic process of the thermal decomposition of the gas mixture and the evolution mechanism of its by-products under different conditions are revealed by combining with thermal decomposition tests. Meanwhile, the influence mechanism of O2 content on the breakdown voltage and partial discharge statistical characteristic values of the C4F7N-CO2-O2 mixture is analyzed, and the influence mechanism of different factors on the generation and inhibition of gas and solid by-products during the discharge decomposition process of the gas mixture is clarified. In conclusion, based on the simulation and experimental results, we propose the optimal O2 additive amount and fault diagnosis characteristic components of C4F7N-CO2-O2 gas mixture for medium-voltage gas-insulated equipmentwe test the biosafety of C4F7N and its arc decomposition products, and then evaluate the feasibility and safety of applying C4F7N-CO2-O2 gas mixture in equipment by combining with the insulating and electrical and thermal decomposition characteristics of C4F7N-CO2-O2 gas mixture and the results of the biosafety