Effect of AC Pre-Charging of Epoxy Insulator on Flashover Properties in Eco-Friendly Binary Gas Mixtures

Metal particles and surface charge accumulation are considered the key factors that could trigger unexpected flashovers of insulators equipped in gas-insulated switchgear (GIS). In eco-friendly gases, the flashover properties and the synergistic effect of the surface charge and the metal particle on flashover remain unclear. This study investigates the flashover properties of down-scaled 252 kV GIS basin-type epoxy insulators with metal particles in C4F7N/CO2 mixtures, with and without AC pre-charging. Tests considered various particle adherence locations and a particle-free control group. The results indicated that metal particles at the high-voltage (HV) electrode or middle area reduce flashover voltage, with the HV electrode and concave surface being most critical. Surface charges, induced by pre-charging and metal particle attachment, interact synergistically with the metal particle during the flashover process, increasing the flashover voltage and redirecting arcs away from them. Such findings enhance understanding of flashover mechanisms in eco-friendly gas-insulated systems and inform insulator design.