The Influence of O2 on Decomposition Characteristics of c-C4F8/N2 Environmental Friendly Insulating Gas

Abstract

The c-C4F8 gas is considered to have great potential as a gaseous medium for gas-insulated equipment, due to its good insulation properties and its relatively low greenhouse gas potential (GWP) relative to SF6. However, the decomposition is an important indicator of its use in equipment. In this paper, the decomposition characteristics of c-C4F8 and the influence by oxygen have been explored through experiments and theoretical calculations. Firstly, the breakdown test of mixed gas was carried out and the precipitated elements of the electrodes and breakdown products of gas mixture were analyzed by X-ray photoelectron spectroscopy (XPS) and gas chromatography mass spectrometry (GC-MS). At the same time, the differences in decomposition products have also been studied when a small amount of O2 was present. The path and mechanism of c-C4F8 decomposition is then discussed, based on density functional theory (DFT). The results show that the black powdery substance descends on the electrode surface after the breakdown of the mixture of c-C4F8/N2 gas containing O2, and its main constituent elements are C, O and F. O2 can promote the decomposition of c-C4F8. The mixture with O2 produced a large number of additional toxic and corrosive COF2 in addition to generating more CF4, C2F4, C2F6, C3F6 and C3F8. The GWP values of the products are lower than SF6. Comprehensive insulation properties and decomposition characteristics, c-C4F8 should not be mixed with dry air for use, and the oxygen content should be strictly controlled in c-C4F8 mixed gas.