Comparison of DC and AC Surface Breakdown Characteristics of GFRP and Epoxy Nanocomposites in Liquid Nitrogen

Glass-fiber-reinforced plastic (GFRP) is one of the most extensively used material for high-temperature superconducting power equipment. However, GFRP has the difficulty not only of having precise fabrication but also of developing a crack in liquid nitrogen due to the severe thermal gradient. A newly developed epoxy resin with nanofillers, which is referred to as an epoxy nanocomposite, has received much attention as a new insulating material for high-voltage insulation. In addition, epoxy nanocomposites are easy to fabricate compared with GFRP. The insulating characteristics of epoxy resin with nanofillers in liquid nitrogen should be evaluated to determine the possible use of an epoxy nanocomposite in a cryogenic environment. To verify the possibility of the application of an epoxy nanocomposite as an insulating material in liquid nitrogen, thermal stress tests and the ac and dc surface breakdown of epoxy resin with different nanofillers, including a SiO2 nanofiller and an Al2O3 nanofiller, were performed. From the experimental results, it was found that the dc surface breakdown voltage is about two times higher than the ac surface breakdown voltage, but there was no significant increase in the breakdown voltage with the adoption of nanofillers. In addition, the epoxy nanocomposite showed better performance in the thermal test.