交联聚乙烯中丛状电树枝的生长机制

The Growth Mechanism of Brush-type Electrical Tree in XLPE

为了研究交联聚乙烯（cross-linked polyethylene,XLPE）中丛状电树枝的生长机理,采用XLPE薄片试样进行电树枝老化实验,通过实时显微观测系统完整记录了在工频高压下电树枝从引发到击穿的全过程,利用扫描电镜观察丛状电树枝的微观结构,并对电树枝通道进行能谱分析。通过构建丛状电树枝不同阶段的有限元电场仿真模型,进一步分析丛状电树枝生长特性与微观结构的关系。研究表明：电树枝引发初期,气体的迅速膨胀促使非导电型电树枝沿无定形区快速生长;碳颗粒周围产生的局部放电和电-机械应力导致电树枝进一步分叉和生长,碳颗粒的不断聚集使非导电型电树枝逐渐转化为导电型电树枝;丛状电树枝团端部场强相对较小以及电树枝内部局部放电减少,是丛状电树枝滞长的主要原因;电树枝团端部由于电-机械应力作用可能形成新的微孔或裂纹,易形成新的电树枝,最终导致绝缘击穿。

To study the mechanism of brush-type electrical tree growing in cross-linked polyethylene（XLPE）, the electrical tree aging experiments in XLPE slice samples were made. Under power frequency and high voltage, the whole process of electrical tree aging from initiation to breakdown was recorded by the real-time microscopic observation system. The microstructure of electrical tree was observed by scanning electron microscope and the energy spectrum of the electrical tree channel was analyzed. The relationship between electrical tree growing characteristics and microstructure was analyzed based on the finite element simulation models of electrical tree at different stages of electrical tree aging. The results show that the rapid expansion of gas in the early stage of electrical tree initiation leads to the rapid growing of non-conducting electrical trees along amorphous regions. Due to strong electrical-mechanical stress and partial discharges around carbon particles, electrical trees are growing and bifurcating ceaselessly. In addition, with the continuous accumulation of carbon particles, non-conductive electrical trees are gradually transformed into conductive electrical trees. The lesser electric field strength at the end of electrical tree group and the decrease of partial discharges in the electrical tree channels lead to the stagnation of electrical trees. However, with the passage of time, some new micro cracks can be formed due to the accumulation of fatigue by electrical-mechanical stress. New electrical trees begin to grow and the insulation was broken eventually.