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.
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