Study on DC breakdown characteristics of epoxy insulating materials

With the rapid development of UHV DC transmission technology, the high voltage insulation of the epoxy support insulator as the key insulation is very important to UHV DC wall bushing. As an insulating material, epoxy resin is widely used in the power system. However, its DC breakdown characteristics have been the key problems restricting the development of high voltage direct current power equipment. In this paper, we used ANSYS to build up three-dimensional simulation model of epoxy sample, and calculated the DC electric field distributions under spherical electrodes. We also manufactured laminate neat epoxy resin and epoxy nanocomposites and epoxy microcomposites, with thickness of 1 mm as test samples and measured the dielectric constant, dielectric loss, volume resistivity and DC breakdown voltages, and then the influences of additives on DC breakdown voltages properties were analyzed. The study results show that: under the spherical electrode system, the electric field distribution of the epoxy insulating material is quite uniform, and the strength is about 10 kV/mm. The electric field strength at the three junction point is distorted, and up to 56.709 kV/mm; The DC breakdown strength of epoxy nanocomposite samples increase slightly, and the DC breakdown strength of Nano-AlOOH sample is the highest, and its DC breakdown strength is 184.14 kV/mm; The DC breakdown strength of epoxy microcomposite samples decreases, and the breakdown strength of Micro-69.4% sample is the minimum, and the strength is 126.68 kV/mm; With the increase of the dielectric constant, the DC breakdown strength decreases; With the increase of the volume resistivity, the DC breakdown strength increases.