Temperature Gradient effect on the space charge behaviour in thick oil and oil-impregnated pressboard

Space charge formation within oil and oil-impregnated pressboard can distort electric field distributions within converter transformers. Electric field distortion may lead to materials partially overstressed. Therefore, it is important to analyze influential factors on space charge behavior such as temperature, moisture, aging and electric field. Temperature gradient is existing across insulation materials as the joule heating and stray losses[1], leading to the electric field severely distorted. Therefore, this paper mainly focuses on the temperature gradient effect on the space charge behavior of both one layer pressboard and two layers oil and oil-impregnated pressboard. The space charge characteristic under temperature gradient has been investigated using the modified pulsed electroacoustic (PEA) technique. The space charge recovery method for two layers materials is proposed in the paper. It has been found that the maximum electric field locates at the bottom electrode due to space charge behavior for one layer pressboard under temperature gradient. Moreover, for two layers oil and oil-impregnated pressboard with 20 °C of bottom electrode, the electric field of the oil is increasing under the temperature gradient while that is decreasing under the room temperature.