Transport and radiation properties of C₄F₇N-CO₂ gas mixtures with added oxygen

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.

High-Throughput Compatibility Screening of Materials for SF6-Alternative Insulation

“…C 4 F 7 N/CO 2 gas mixtures, considered the most promising SF 6 -alternative solution, − provide a good example. On one hand, C 4 F 7 N/CO 2 gas mixtures demonstrate many desirable properties critically needed in the replacement of SF 6 , such as high dielectric strength, a low GWP, a satisfactory liquefaction temperature, nontoxicity, etc., − but on the other hand, issues of C 4 F 7 N/materials incompatibility due to the relatively high reactivity of C 4 F 7 N have already been reported. For instance, while C 4 F 7 N was found stable up to 650 °C in ideal conditions, it decomposed into C 3 F 6 and C 2 N 2 at ∼220 °C, or even lower temperatures, in the presence of incompatible materials. , It was also reported that certain rubber products can react with C 4 F 7 N at a low temperature of 125 °C, producing yellow oily substances .…”

Generation and optimization of cross-sections for electron-C4F7N collisions

“…Owing to this interest, C 4 F 7 N has received much attention in research. Studies reporting its chemical decomposition pathways [9][10][11], transport [12], thermal plasma properties * Author to whom any correspondence should be addressed. [13,14], electrical breakdown [15,16], toxicity [17], and materials compatibility [18] have been reported.…”