High-temperature properties of dry air used as arc quenching medium and its mixture with vaporized C2F4 : reaction products and critical reduced electric field strength at 300–3000 K

Abstract

Recently, electric power equipment manufacturers released a joint statement to develop high-voltage electrical equipment completely free of fluorinated gases as fluoroketones and fluoronitriles, which are considered as alternatives to SF6 , are artificially produced compounds of F. 
 This paper considers air as a typical gas present naturally in the environment to investigate its high-temperature properties, including an air mixture with C2F4 vapor injected from a polytetrafluoroethylene nozzle, for application as an arc quenching medium in a high-voltage circuit breaker equipped with a nozzle. Chemical composition results for revealing reaction products at 3000-300 K show that the admixture of C2F4 vapor causes a decrease in the molar number of O2 contained in air, owing to the production of O-containing compounds such as CO2 and CO. Additionally, the results reveal that the admixture of C2F4 vapor lead to the production of CF4 as the predominant F-containing compound. Furthermore, the boundary condition for O2 production in terms of O2 molar number X O2 and C2F4 molar number X C2F4 is formulated. 
 Such evaluation of the mixture composition enables the determination of a reduced effective collision ionization coefficient λ/N and a critical reduced electric field strength E/N, resulting in λ/N=0. The strength E/N for the mixture with 30-100% C2F4 molar fraction rises to approximately 150 Td (1 Td=10-21 V m2 over 3000-300 K, which is 20-50 Td higher than that for high-temperature air unmixed with C2F4 vapor. The variation in E/N is discussed in terms of predominant electron impact processes and an electron energy distribution function in the mixture.