The authors explored the thermal decomposition characteristics of perfluoroisobutyronitrile-carbon dioxide (C 4 F 7 N-CO 2) gas mixture as eco-friendly dielectric medium. The main by-products and decomposition mechanism of C 4 F 7 N-CO 2 gas mixture under different temperature and gas pressure conditions were revealed and analysed. It was found that the thermal decomposition of 6%C 4 F 7 N-94%CO 2 gas mixture starts at about 350°C (0.15 MPa), producing C 3 F 6 and CO first. Some other characteristic by-products such as CF 4 , C 2 F 6 , CF 3 CN, COF 2 and (CN) 2 could also be detected at higher temperature. The yield of C 3 F 6 , (CN) 2 increased with the temperature (lower than 450°C) first and then decreased when it reached to 500°C. While the yield of CO, C 3 F 8 , COF 2 and CF 3 CN increased with temperature (350-550°C). The generation of CF 4 and C 2 F 6 begins at temperatures higher than 500°C, which can be used as the feature component of severe overheating fault. The thermal decomposition amount and by-products yield of C 4 F 7 N-CO 2 gas mixture slowed down with the increase of gas pressure, indicating that C 4 F 7 N-CO 2 gas mixture is quite suitable used at high-pressure equipment, especially high-voltage devices such as gas insulated switchgear.
The
C4F7N (fluorinated nitrile) gas mixture
has been recognized as the most potential substitute gas to SF6 used in gas-insulated equipment. In this paper, we explored
the thermal stability and decomposition properties of the C4F7N–N2–O2 gas mixture.
The influence mechanism of oxygen content and temperature on the byproduct
generation was obtained and analyzed. It was found that thermal decomposition
of the C4F7N–N2–O2 gas mixture mainly produces CO, C3F6, C3F8, CF3CN, (CN)2,
and COF2. The addition of oxygen could accelerate the decomposition
of C4F7N. The content of C3F6 and (CN)2 decreases, while the yield of CF4, CO, C3F8, and COF2 increases
with the oxygen content. Thermal decomposition of the C4F7N–N2–O2 gas mixture
at temperatures lower than 425 °C results from the interaction
between C4F7N and the metal heating element,
while the bond cleavage reactions occur at higher temperature. As
for engineering application, the oxygen added in the 6%C4F7N–94%N2 gas mixture should not exceed
6% to avoid the negative effect of oxygen on the thermal stability
of C4F7N.
The eco-friendly insulating medium C 5 F 10 O gas has attracted the attention of many researchers due to its superior environmental protection and insulation properties. However, there are few studies on the compatibility of C 5 F 10 O gas with sealing materials for the gas-insulated equipment (GIE), which will bury hidden dangers for its engineering application. In this study, the compatibility of C 5 F 10 O gas with an ethylene propylene diene monomer (EPDM) sealing material which is most used in equipment was tested, and its reaction mechanism was simulated. The study found that the O element on the carbonyl group of C 5 F 10 O gas has high chemical reactivity and will interact with EPDM rubber. During the interaction process, EPDM rubber will also react with the C 3 F 6 gas generated by the decomposition of C 5 F 10 O gas, and at the same time, it will also decompose C 5 F 10 O gas to produce more C 3 F 6 O and C 3 HF 7 . The surface of EPDM rubber will produce oily substances and a large number of crystal particles, which will cause its mechanical properties to deteriorate and shorten its service life. Therefore, it is necessary to carry out anti-corrosion treatment on the surface of EPDM rubber or replace the sealing material with better compatibility when designing and manufacturing GIE.
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