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

With the gradual improvement of the requirements forthe safe andstable operation of gas-insulated equipment (GIE), the eco-friendlyinsulating gas C4F7N-CO2-O-2 has become the best choice to replace SF6 andapply it to various medium-voltage (MV) and high-voltage (HV) GIE.At present, the generation characteristics of solid decompositionproducts of the C4F7N-CO2-O-2 gas mixture under partial discharge (PD) fault need to bestudied. In this paper, a 96 h PD decomposition test was carried outby simulating metal protrusion defects in GIE with needle-plate electrodesto study the generation characteristics of C4F7N-CO2-O-2 gas mixture solid decompositionproducts under PD fault and their compatibility with metal conductors.It was found that obvious ring-shaped solid precipitates appearedin the central area of the surface of the plate electrode under theaction of long-term PD, mainly including metal oxides (CuO), silicates(CuSiO3), fluorides (CuF, CF (X) ), carbon oxides (CO, CO2), and nitrogen oxides (NO, NO2). The addition of 4% O-2 has little effect on theelement composition and valence state of PD solid precipitates, butit can reduce their yield to a certain extent. The corrosion effectof O-2 in the gas mixture on metal conductors is weakerthan that of C4F7N.