Dc flashover performance and surface discharge resistance of the fluorinated epoxy insulator in nitrogen gas
The surface of the epoxy insulator was modified by direct fluorination in a laboratory vessel using a F2/N2 mixture with 12.5% F2 by volume at 55 °C and 0.1 MPa for 30 min. The modified surface was examined by ATR-FTIR and SEM techniques. ATR-FTIR results show substantial changes in chemical composition and structure of the surface layer by the fluorination, and SEM observations reveal the fluorinated surface layer having a thickness of 0.76 μm and a roughed surface. Dc flashover performance and surface discharge resistance of the fluorinated surface layer in nitrogen gas were simultaneously evaluated using a simple sample/finger electrode arrangement in a stainless steel chamber at room temperature. The test results indicate a definite improvement in dc flashover voltage and a great increase in tracking resistance to the flashover discharge. The former is mainly attributed to easy leakage and dispersion of the charge from the cathode triple junction on the fluorinated surface due to high conductivity of the fluorinated layer, and the latter is due to the formation of C-F bonds and the disappearance of conjugated double bonds in the surface layer by the substitution and addition of fluorine atoms.