Properties of C₄F₇N–CO₂thermal plasmas: thermodynamic properties, transport coefficients and emission coefficients

Abstract

The thermophysical properties, including composition, thermodynamic properties, transport coefficients and net emission coefficients, of thermal plasmas formed from pure iso-C4 perfluoronitrile C4F7N and C4F7N–CO2 mixtures are calculated for temperatures from 300 to 30 000 K and pressures from 0.1 to 20 atm. These gases have received much attention as alternatives to SF6 for use in circuit breakers, due to the low global warming potential and good dielectric properties of C4F7N. Since the parameters of the large molecules formed in the dissociation of C4F7N are unavailable, the partition function and enthalpy of formation were calculated using computational chemistry methods. From the equilibrium composition calculations, it was found that when C4F7N is mixed with CO2, CO2 can capture C atoms from C4F7N, producing CO, since the system consisting of small molecules such as CF4 and CO has lower energy at room temperature. This is in agreement with previous experimental results, which show that CO dominates the decomposition products of C4F7N–CO2 mixtures; it could limit the repeated breaking performance of C4F7N. From the point of view of chemical stability, the mixing ratio of CO2 should therefore be chosen carefully. Through comparison with common arc quenching gases (including SF6, CF3I and C5F10O), it is found that for the temperature range for which electrical conductivity remains low, pure C4F7N has similar ρCp (product of mass density and specific heat) properties to SF6, and higher radiative emission coefficient, properties that are correlated with good arc extinguishing capability. For C4F7N–CO2 mixtures, the electrical conductivity is very close to that of SF6 while the ρCp peak at 7000 K caused by decomposition of CO implies inferior interruption capability to that of SF6. The calculated properties will be useful in arc simulations.

Ablation-Dominated Arcs in CO2 Atmosphere - Part I: Temperature Determination near Current Zero

“…However, only a limited selection remains in the actual investigations. Gas mixtures containing fluoro-nitriles (C 4 F 7 N) or fluoro-ketones (C 5 F 10 O) as minority components (<20 %) have been identified as most promising alternatives to SF in high-voltage gas-insulated switchgear applications, because of their low global warming potential together with their dielectric strength values being comparable to SF 6 [5][6][7]. Due to high boiling points (at 1 bar) of the fluoro-ketones (27 • C) and fluoro-nitriles (-4.7 • C), gas mixtures with carbon dioxide CO 2 as buffer gas prevent liquefaction at temperatures below -30 • C. One of the most promising alternatives that has less limitations concerning temperature range and greenhouse effect but reasonable electrical insulation is CO 2 [8][9][10].…”

Adsorption Behavior of γ-Al2O3 Toward Heptafluoroisobutyronitrile and its Decompositions: Theoretical and Experimental Insights

“…Beroual et al found that the synergistic effect of 3.7% C 3 F 7 CN -96.3% CO 2 was the strongest by breakdown test under power frequency and impulse voltage [9]. Wang et al carried out the calculations on the arc extinguishing performance of C 3 F 7 CN and its gas mixtures, and confirmed that its decomposition products will reduce the arc extinguishing ability [10]. Zhang et al combined simulation and experimental research on the decomposition products of C 3 F 7 CN and its gas mixtures under discharge, and found that there are toxic gases in the products.…”

Experimental study on the partial discharge and AC breakdown properties of C 4 F 7 N/CO 2 mixture

“…In addition, Kieffel et al [11] studied the switching performance of 4% C 4 F 7 N/96% CO 2 gas mixture using a 420 kV disconnector and found that the average arcing time over 100 times operations is about 12 ms (lower than the typical value of 15 ms for SF 6 ). The decomposition process during the arc process and the transport properties of C 4 F 7 N/CO 2 gas mixture were also revealed theoretically [12,13].…”