Arc decomposition behavior of C 4 F 7 N/Air gas mixture and biosafety evaluation of its by‐products

Abstract

At present, reports on the arc interruption and decomposition behaviour of a C4F7N/air gas mixture especially the biosafety of its by-products are limited. Herein, a 57% C4F7N/43% air gas mixture was employed as an arc-quenching medium to conduct 200 breaking tests on a load switch (630 A/24 kV). The arc interruption and decomposition behaviour of the gas mixture were evaluated, and the biosafety of the decomposition products was assessed based on an acute inhalation toxicity test. It was found that the average arcing time of the 200 breakings was about 10.1 ms and that breakings were basically completed at the zero-crossing of the second or third current half-cycle. The gas mixture after breaking decomposed dramatically (the C4F7N content decreased by 75.6%), generating a large number of gaseous by-products (CO, CF4, C2F6, C3F8, CF3CN, C4F8, CO2, C4F10N2, C3F6, C2N2, etc.) as well as solid by-products (carbon particles). The lethal concentration (LC50) of 50% (LC50, 4 h) of C4F7N/air after 200 breakings was 31 ppm (male mice) and 34 ppm (female mice), respectively, and the toxicity was classified as Grade 1. In general, C4F7N has an arc interruption capability, albeit weaker than that of SF6 under the same conditions. After breaking, the C4F7N gas mixture has a relatively high acute inhalation toxicity, and relevant safety protection measures for research or operation personnel are strictly needed.