Research on C4F7N gas mixture detection based on infrared spectroscopy

Abstract

As a promising insulated gas to replace SF6, C4F7N gas mixture has gradually been put into practical application. It has great practical significance for condition monitoring and fault diagnosis of electrical equipment with C4F7N gas mixture. In this paper, molecular structure of C4F7N has been optimized by density functional theory using GGA-PBE functional with DZP basis set, and vibrational assignments have been calculated. The mixing ratio detection and leakage detection for the equipment based on infrared spectroscopy is proposed. The results show that: the calculated results and the experimental results have good agreement; the band of 750˜780 cm−1 can be used for mixing ratio detection, the error of mixing ratio inversion of 1˜10% C4F7N gas mixture using peak value as eigenvalue is less than 5%; after peak fitting processing, the error is less than 3% by using peak area as eigenvalue; 1240˜1290 cm−1 is the strongest infrared absorption band of C4F7N which has a good linear relationship between different concentrations, and it can be used for leakage detection. The calculated results and experimental results provide important theoretical support for the mixing ratio detection and leakage detection for the electrical equipment with C4F7N gas mixture.