Spectral Detection of Decomposition Products of C4F7N/CO2/O2 Mixed Gas

Perfluoroisobutyronitrile (molecular formula C4F7N) is currently one of the best-known alternative environmentally friendly insulating gases for SF
6.
Due to the high liquefaction temperature of C
4
F
7
N gas, it needs to be mixed with N
2
, CO
2
, and dry air for use. GIS equipment using C
4
F
7
N/CO
2
/O
2
ternary mixture gas as insulation and arc extinguishing medium has been promoted and applied. However, the C
4
F
7
N/CO
2
/O
2
mixture gas will decompose under partial discharge and overheating faults, generating characteristic decomposition products such as CO, carbon-fluorine gas, fluoronitrile (C
x
F
y
CN), COF
2
, and CNCN. Qualitative and quantitative analysis of decomposition products can be used for gas decomposition state evaluation, equipment state diagnosis, and other fields. In this paper, Raman spectra of C
4
F
7
N/CO
2
/O
2
mixture gas and decomposition products under different electric fields were obtained through quantum chemical calculations. This provides basic data for the qualitative detection of C4F7N mixed gas and its decomposition products. The research results indicate that the Raman spectra of gas molecules under different electric fields exhibit characteristic peak shifts, which can be used for the simultaneous qualitative detection of multiple decomposition products. This study provides a new approach for the potential application of Raman spectroscopy in the detection of C4F7N mixed gas decomposition products.