高温下110kV交联聚乙烯电缆电树枝生长及局部放电特性

利用实时显微数字摄像与局部放电连续测量系统,采用典型针-板电极结构,研究了高温下不同外施工频电压作用时110kV级交联聚乙烯(XLPE)电缆绝缘中典型电树枝的形态特征、引发、生长规律及其局部放电特性。实验结果表明,温度对XLPE电缆绝缘中典型电树枝的形态、引发与生长时间具有非常重要的影响。在高温下,不同外施工频电压作用时电树枝的形态呈现出多样性的特点,50°C下典型电树枝形态为枝状、枝-松枝状和丛状,70°C下为枝状,90°C下为滞长型和枝状。高温下电树枝引发时间随外施电压升高而减小,而且在同一外施电压下,电树枝引发时间随温度升高而减小,这是由于在高温下XLPE电缆绝缘中片晶熔化,无定形相增加,介质中自由体积扩大,从而更有利于电树枝引发。研究发现在低电压(9kV)下,电树枝生长过程中由于通道电导率增加而抑制了通道内局部放电的发展,局部放电作用减小,电树枝生长速度减慢,分形维数较高;而11kV以上电压作用时,电树枝在局部放电的连续作用下呈枝状向对面电极快速生长,同时高温下XLPE弹性模量下降,击穿场强降低,局部放电作用加剧,电树枝生长明显加速,电树枝分形维数较低。

Propagation and Partial Discharge Characteristics of Electrical Trees in 110 kV XLPE Cable Insulation at High Temperature

Using the real-time microscopy digital imaging and partial discharge(PD) continuous measuring system,we studied the electrical tree shape properties,initiation,growth law,as well as PD characteristics in 110 kV cross-linked polyethylene(XLPE) power cable insulation under different applied voltages at high temperature by the typical needle-plane electrode geometry.The experimental results indicated that the effect of temperature on the shape,initiation and growth time of the typical electrical trees in XLPE cable insulation was dominant.The electrical tree shapes displayed the features of diversity under different stressing voltages at an elevated temperature.The typical tree shapes at 50°C are branch tree,branch-pine tree and bush tree.The trees at 70°C are branch trees,and the trees at 90°C are stagnation-type tree and branch tree.The electrical tree initial time declined with the increase of the applied voltages,and decreased with the increase of the temperature at the same applied voltage,which was due to the melting of the lamella in XLPE cable insulation at high temperatures,and the increase of the amorphous regions and free volumes in dielectrics.It was found that the electrical tree growth rate at low voltage(9 kV) declined due to the increase of the tree channel conductivity,which suppressed the PD activity in the tree structure.The tree growth rate decreased with higher fractal dimension.However,the electrical trees grew rapidly to the counter electrode in branch-type with the continuous PD activity under higher applied voltages(≥11 kV).Meanwhile,the elastic modulus of XLPE decreased at high temperatures,the dielectric strength declined,the effect of PD activity was fiercer,which accelerated greatly the electrical tree growth at high temperatures,and the fractal dimension of the tree was lower.