Surface Corona Aging of Epoxy/SiO2 Nanocomposites

Abstract

Epoxy resin has been widely used in electronic and electrical equipment due to its excellent electrical and mechanical properties. However, prolonged corona discharge may cause deterioration of the surface, and finally lead to failure of insulation structure. Extensive researches have indicated that addition of nano fillers can improve corona resistance of polymers. In this paper, epoxy/SiO 2 nanocomposites are prepared to study the micro development of corona erosion and surface trapping performance during corona aging. AC breakdown strength of epoxy/SiO 2 nanocomposites is measured firstly and 2 wt% epoxy/SiO 2 nanocomposite with highest AC breakdown strength of 64.11 kV/mm is selected to conduct corona resistance test with pure epoxy. It was observed by polarizing microscope that the degradation was severer for pure epoxy resin with corrosion area from about 0.27 mm2 at 10 min to 0.57 mm2 at 30 min, while the area of 2 wt% nano-SiO 2 nanocomposite is nearly invariable about 0.21 mm2. With the increase of corona duration, the corrosion regions become darker which indicates thicker channel and more intensive corrosion density. Additionally, the corona damage extends from the center to edge of samples in shape of “branch”, and “branch” channels of degradation develop denser in the center. The isothermal surface potential decay (ISPD) results show that shallow trap ranges from 0.90 to 1.00 eV, whereas the deep trap locates at 1.05∼1.15 eV. The deep energy density of pure epoxy decreases dramatically from 7.2x1014 m−3 to 4.9x1014 m−3 with corona aging time, while that of 2 wt% epoxy/SiO 2 nanocomposite maintains constant about 6.9x1014 m−3. Both of the shallow trap density of epoxy and nanocomposite increases after corona aging, while pure epoxy increases more obvious from 1.6x1013 m−3 to 3.8x1013 m−3. Therefore, charges are more difficult to inject and move in epoxy nanocomposites because of more deep traps even after corona exposure, which illustrates why nanocomposites have higher corona resistance.