Generation Characteristics of Solid Byproducts of the C4F7N-CO2-O2 Gas Mixture under PD Fault.

With the gradual improvement of the requirements for the safe and stable operation of gas-insulated equipment (GIE), the eco-friendly insulating gas C4F7N-CO2-O2 has become the best choice to replace SF6 and apply it to various medium-voltage (MV) and high-voltage (HV) GIE. At present, the generation characteristics of solid decomposition products of the C4F7N-CO2-O2 gas mixture under partial discharge (PD) fault need to be studied. In this paper, a 96 h PD decomposition test was carried out by simulating metal protrusion defects in GIE with needle-plate electrodes to study the generation characteristics of C4F7N-CO2-O2 gas mixture solid decomposition products under PD fault and their compatibility with metal conductors. It was found that obvious ring-shaped solid precipitates appeared in the central area of the surface of the plate electrode under the action of long-term PD, mainly including metal oxides (CuO), silicates (CuSiO3), fluorides (CuF, CFX), carbon oxides (CO, CO2), and nitrogen oxides (NO, NO2). The addition of 4% O2 has little effect on the element composition and valence state of PD solid precipitates, but it can reduce their yield to a certain extent. The corrosion effect of O2 in the gas mixture on metal conductors is weaker than that of C4F7N.