Migration Characteristics of Moisture in Epoxy-impregnated Paper Materials and Its Influence on Surface Insulation Characteristics

At present, the wall bushing and converter transformer bushing in domestic high-voltage DC projects mostly use epoxy impregnated paper dry casing. Epoxy impregnated paper materials are easy to absorb water, so it is urgent to study the water migration law of epoxy impregnated paper materials during moisture exposure and the DC surface insulation performance before and after moisture. In this paper, the surface insulation strength of the surface painted and unpainted epoxy impregnated paper specimens before and after moisture is obtained by AC/DC flashover test, and the moisture migration characteristics of epoxy impregnated paper are obtained by micro-water content measurement. It is found that the flashover field strength of painted specimens along the AC and DC surfaces before and after moisture is at least 2.9% higher than that of unpainted specimens; compared with the unpainted sample, the water absorption rate of epoxy impregnated paper material after painting is reduced by 22.1%; due to the water absorption of polyamide, the humidity of the surface layer is high, and the insulation performance along the surface of the painted specimen still decreases significantly after a long period of moisture. The results of this paper can provide theoretical support for the moisture resistance of epoxy impregnated paper core and the improvement of its insulation performance along the surface. ©2023 Chin.Soc.for Elec.Eng. 4811.