温度梯度下双层油纸绝缘系统的空间电荷分布特性

换流变压器为直流高压输电系统中的重要设备,但因其运行工况的特殊性,其内部油纸等绝缘材料往往承受较大的内外温度差异作用。针对换流变压器中双层油纸绝缘系统存在的内外温度不同的温度梯度效应对油纸绝缘中空间电荷分布的影响,利用电声脉冲法测量了不同温度梯度下（Δθ=0、20、40°C）,电压分别为-3.4、-10.2、-20.4kV（即平均电场强度分别为10、30、60MV/m）时双层油纸中空间电荷在20min内随时间变化规律及电场分布。实验结果表明：在低场强下,上下电极均有明显的同极性电荷注入;温度梯度使低温侧出现异极性电荷,并且随着温度梯度的增大、电压的升高,低温侧异极性电荷越来越多,从而使低温侧的场强畸变越来越大;加压后,2层油纸界面处开始积累与上电极相同极性的电荷,并且界面处电荷量随温度梯度及电压的增大而增大,但电荷密度出现饱和现象。经分析可知,油纸界面起到阻挡正负电荷通过的作用,而温度对电极注入特性及试样电导特性的影响为温度梯度影响空间电荷分布的主要原因。

Space Charge Distribution Characteristic in Double-layer Oil Impregnated Papers Under Temperature Gradient

Temperature gradient existing in the oil impregnated paper insulation such as converting transformer or DC bushing affects the space charge distribution.The space charge profiles and field distributions in double layers of oil impregnated paper within 20 minutes were measured by the pulse electro-acoustic method under different temperature differences(Δθ=0,20,40 °C),and DC voltage of-3.4,-10.2,-20.4 kV(DC electric field intensity of 10,30,60 MV/m),respectively.The test results show that homocharge exists in both electrodes when the electric field intensity was low,and the heterocharge appears in the low temperature side due to the temperature difference.Moreover,the more remarkable the temperature difference and electric filed intensity were,the more the heterocharge at the low temperature side is,resulting in a greater field distortion.The homocharge of the up-electrode starts to accumulate in the space between two layers of oil impregnated paper.The higher the temperature and electric field intensity were,the more the space charge were while the density of the charge is saturated.The result suggests that the oil paper interface plays the role in preventing the charge from passing by,and the temperature is the main factor which affects the space charge distribution and the electricity conduction of the sample.