Detection of decomposition products of C4F7N-CO2 gas mixture based on infrared spectroscopy

Heptafluoroisobutyronitrile (C4F7N)-carbon dioxide (CO2) gas mixture has been gradually applied as an excellent environment-friendly insulating medium. The research on the decomposition characteristics of C4F7N-CO2 gas mixture not only helps to better understand its decomposition mechanism under insulation fault, but also provides effective basis for monitoring the insulation state of electrical equipment based on decomposition products analysis. Due to infrared spectroscopy has good potential for on-line monitoring of electrical equipment, this paper studies the feasibility of the decomposition products detection by infrared spectroscopy. The infrared spectrum of C4F7N and its decomposition products were obtained by theoretical calculation. The possibility of detection by infrared spectroscopy was theoretically analyzed. The experimental platform for overheating decomposition of C4F7N-CO2 gas mixture was built, and a long path gas cell with 4 m light path was developed for the detection of trace decomposition products. The results show that C3F6, COF2 and CO can be effectively detected by infrared spectroscopy with the long path gas cell. At last, the decomposition experiments under different temperature and pressure have been employed and the decomposition products growth trend has been analyzed. The study illustrates the detection feasibility of decomposition products of C4F7N-CO2 gas mixture by infrared spectroscopy, and lays a foundation for future on-line monitoring technology of electrical equipment with the gas mixture based on infrared spectroscopy.