The effect of slime pulp on electrical properties of insulation pressboard

摘要

Insulation pressboard is an important dielectric of oil-immersed transformers. During its production process, slime pulp is one of the common problems, which may become a potential risk of transformer insulation. In this paper, through measuring and comparing the electrical properties of sample with slime pulp and normal sample, the effect of slime pulp was studied. BX51-P polarizing microscope was used to observe the differences of microstructure between these two kinds of samples. The photos show that the fibers of the normal sample are orderly interwoven and clearly arranged, however, there is a mass of finer fibers around the interwoven fibers of slime pulp samples. Besides, frequency domain dielectric spectrum, volume resistivity and surface resistivity were measured. The results show that the relative permittivity and dielectric loss factor variation trend of slime pulp sample are basically consistent with those of the normal ones. The relative permittivity of slime pulp sample is lower slightly, and dielectric loss factor is higher. Slime pulp spots have little effect on volume resistivity, probably because the slime pulp is only a thin layer on the surface of the insulation pressboard. However, the slime pulp seriously affected the surface resistivity. The surface resistivity of slime pulp sample is much smaller than the normal ones, and it is more dispersive.