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 behavior of a C 4 F 7 N/air gas mixture especially the biosafety of its by-products are limited. Herein, a 57% C 4 F 7 N/ 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 behavior 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 C 4 F 7 N content decreased by 75.6%), generating a large number of gaseous by-products (CO, CF 4 , C 2 F 6 , C 3 F 8 , CF 3 CN, C 4 F 8 , CO 2 , C 4 F 10 N 2 , C 3 F 6 , C 2 N 2 , etc.) as well as solid by-products (carbon particles). The lethal concentration of 50% (LC50, 4 h) of C 4 F 7 N/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, C 4 F 7 N has an arc interruption capability, albeit weaker than that of SF 6 under the same conditions. After breaking, the C 4 F 7 N gas mixture has a relatively high acute inhalation toxicity, and relevant safety protection measures for research or operation personnel are strictly needed.

Trifluoromethyl Fluorosulfonate (CF3OSO2F) and Trifluoromethoxy Sulfur Pentafluoride (CF3OSF5) – Two Gaseous Sulfur(VI) Compounds with Insulating Properties

“…For other dielectrics such as (CF 3 ) 2 CFCN, the decomposition is much more favored. A mixture of (CF 3 ) 2 CFCN (53 %) in air (47 %) shows a degradation of the nitrile of 61.7 % after 200 breakdown processes with a duration of ~10 ms each, while only a small amount (1.6 %) of SF 6 is decomposed under the same conditions [32] . This can be explained by a lower recombination rate of the more complex nitrile and the thermodynamically favored formation of other reaction products.…”

“…Some of the decomposition products like CF 4 , C 2 F 6 , or C 2 N 2 have a high GWP, while several are also highly toxic like CF 3 CN, C 4 F 8 , and HF. This leads to a drastically increased acute toxicity with a lethal concentration (LC 50 ) of the nitrile mixture that is around 1100 times lower than that of pure SF 6 after 200 breakdown processes [32] …”

“…A mixture of (CF 3 ) 2 CFCN (53 %) in air (47 %) shows a degradation of the nitrile of 61.7 % after 200 breakdown processes with a duration of ~10 ms each, while only a small amount (1.6 %) of SF 6 is decomposed under the same conditions. [32] This can be explained by a lower recombination rate of the more complex nitrile and the thermodynamically favored formation of other reaction products. Some of the decomposition products like CF 4 , C 2 F 6 , or C 2 N 2 have a high GWP, while several are also highly toxic like CF 3 CN, C 4 F 8 , and HF.…”

“…This leads to a drastically increased acute toxicity with a lethal concentration (LC 50 ) of the nitrile mixture that is around 1100 times lower than that of pure SF 6 after 200 breakdown processes. [32] To analyze the decomposition behavior of CF 3 OSO 2 F and CF 3 OSF 5 , experiments were conducted at their breakdown voltages. The gas was exposed to a stable arc over a period of 10 s at an initial pressure of p i = 0.1 bara, which corresponds to 1000 breakdown processes with a duration of 10 ms each.…”

Assessment on gas‐polyethylene terephthalate solid interface partial discharge properties of C4F7N/CO2 gas mixture for eco‐friendly gas insulating transformer

“…Its GWP is 2090 and its dielectric strength is more than twice than that of SF 6 [12][13][14]. Due to the high liquefaction temperature (−4.7°C), C 4 F 7 N needs to be mixed with buffer gases such as CO 2 to meet the minimum operating temperature requirements of the equipment [15,16]. Scholars have carried out systematic research on the basic insulation, stability and decomposition, material compatibility, biosafety etc.…”