Analysis of Decomposition Products of Eco-friendly Gas C4F7N/CO2 under Spark Discharge

Abstract

In recent years, the g3 (C4F7N/CO2) gas produced by 3M has attracted widespread attention from scholars because of its good insulation properties and the greenhouse effect that is much lower than SF6^[1]-[5]. Preliminary research shows that this gas has a very good application prospect in power systems. In addition to the excellent electrical performance of replacing SF6, the decomposition characteristics of the new type of insulating gas under various operating conditions are also critical to the stable operation of electrical equipment ^[6],[7]. With the continuous development of partial discharges caused by various insulation defects in gas-insulated equipment, partial discharges may evolve into more serious spark discharges, which will cause serious deterioration of power equipment ^[8],[9]. At the same time, it also aggravates the decomposition process of the insulating gas. Aiming at the decomposition of C4F7N/CO2 mixed gas, this paper uses pulse capacitors as a power source which can charge and discharge stably to build a frequency-controlled spark discharge fault test platform, and uses gas chromatography-mass spectrometry to qualitatively and quantitatively detect decomposition products, exploring the changes in decomposition products under different energy levels and different pressure. The results show that: the decomposition products of the C4F7N/CO2 mixed gas under spark discharge fault are CO, CF4, C2F4, C2F6, C3F6, C3F8, CF3CN, C4F10, C2N2, C3HF7, C2F5CN and HCN. All decomposition products increase linearly with the accumulation of energy which comes from spark. The single spark discharge energy at different voltage levels is measured, which is a quadratic function relationship with the charging voltage value. The higher the energy of a single discharge, the faster the rate of decomposition products formation. The content of decomposition products under spark discharge continuously decreases with the increase of the total air pressure, and high air pressure has an inhibitory effect on the decomposition process.