Generation Characteristics of Solid Byproducts of the C 4 F 7 N-CO 2 -O 2 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 CFN-CO-O has become the best choice to replace SF and apply it to various medium-voltage (MV) and high-voltage (HV) GIE. At present, the generation characteristics of solid decomposition products of the CFN-CO-O 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 CFN-CO-O 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 (CuSiO), fluorides (CuF, CF), carbon oxides (CO, CO), and nitrogen oxides (NO, NO). The addition of 4% O 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 O in the gas mixture on metal conductors is weaker than that of CFN.