DC Flashover Performance of GIS Spacers Fluorinated at Different Temperatures

In order to verify the effectiveness of direct fluorination in improving the dc flashover performance of gas insulated switchgear (GIS) actual spacers and explore the effect of fluorination conditions, 126-kV disk spacers were surface fluorinated in the laboratory at the different temperatures of 35 °C, 55 °C, or 80 °C. The evaluation of surface physicochemical characteristics and basic electrical properties of the fluorinated disk spacers are realized by using the epoxy samples of the same material and simultaneously fluorinated with the disk spacers. Flashover tests indicate that direct fluorination significantly increases the dc flashover voltage of the actual spacer in SF
₆
gas and reduces the dispersion of flashover voltage, fluorination temperature has a significant effect on the enhancement of the flashover voltage, and the fluorination at higher temperatures can produce a larger improvement in the flashover performance. In addition, these fluorinated spacers can withstand heat treatment at 120 °C, with unchanged flashover performance. Infrared analysis and scanning electron microscopy observation show that the fluorination at different temperatures changes surface chemistry of the disk spacer substantially, forming the fluorinated layers with different thicknesses, compositions, and structures. Measurements of surface conductivity and surface potential decay consistently show that direct fluorination increases surface conduction of the spacer, and the fluorination at higher temperatures leads to a more significant increase in surface conduction. The improvement in dc flashover performance, caused by direct fluorination, is mainly attributed to the suppression of surface charge accumulation by the increase in surface conduction of the spacer.