High permittivity electroluminescence coating for improving flashover strength and visualizing surface defects

Abstract In gas-insulated switchgear, the metallic particles on spacers initiate discharges and significantly reduce flashover strength. It is crucial to sensitively detect surface defects and improve the flashover strength. In this work, a high permittivity electroluminescence coating with ZnS:Cu as fillers and cyanoethyl cellulose (CEC) as polymer matrix was developed to improve flashover strength and visualize surface defects. The dielectric constant, flashover strength, and electroluminescence properties of ZnS:Cu/CEC coatings with different concentrations of ZnS:Cu fillers were tested and the underlying mechanism was investigated. Due to the strong-polarity cyanide group in CEC and the effect of ZnS:Cu fillers on polymer chains, a high-permittivity coating was obtained, which can effectively mitigate the electric field distortion on spacers, and improve the flashover performance. For the basin insulator, maximum increments of flashover strength were realized by doping 12.5 wt% ZnS:Cu fillers, with 11.36%, 31.22%, and 5.83% improvements in air, 0.3 MPa air, and SF 6 gas, respectively. Moreover, the electroluminescence coating can effectively indicate the location of defects and the distribution of electric field on the surface of insulators. This paper provides new insight into the electroluminescent materials used in non-destructive self-testing of surface defects and enhancement of flashover strength.