The moisture diffusion between oil-paper foil layer of transformer bushing by temperature gradient field

Non-uniform dampness of main insulation is a serious defect for the oil-impregnated paper bushing (OIPB) in the transformer, which causes its electric parameters unusually rising, insulation failure and explosion. Temperature gradient field is one of the main factors in the moisture diffusion in transformer bushing accidents. In this paper, by using the method of physical field finite element modeling analysis, the moisture migration patterns under different temperature gradient of oil-impregnated paper insulation bushing was studied from the most intuitionistic image observation. The damp location and diffusion process of water concentration under the temperature were obtained. The results show as follows: 1) at the temperature from 20°C to 40°C, the moisture migration speed in bushing under the action of each increasing 10°C is much less than that of 50°C to 70°C. At the same diffusion time, the increment of temperature accelerates the degree of moisture diffusion. 2) There is an obvious asymmetry in the upper and lower parts of the bushing in the concentration visual cloud picture of moisture content. 3) The aluminum foil inside the core blocks unevenly the water diffusion among multi-layer oil-paper core, forming several local dry and wet areas, which eventually leads to severe local insulation failure of the bushing.