交联聚乙烯电缆绝缘材料中电树枝的导电特性研究

利用光学显微观察、局部放电测量和共聚焦Raman光谱分析相结合的方法, 研究了交联聚乙烯(XLPE)电缆绝缘材料中两种典型电树枝的导电特性.尽管具有相似的培养条件, 两种电树枝却呈现出完全不同的形态,其中9 kV下典型电树枝为枝-松枝状, 11 kV下为枝状, 而且电树枝生长及局部放电规律呈现出明显的差异.枝-松枝状电树枝主干通道内存在无序石墨碳的沉积, 根据石墨碳G带与D带的相对强度,估算碳层厚度约为8 nm,树枝通道单位长度电阻小于 10 Ω· μm^-1,足以抑制电树枝内局部放电的发展,电树枝呈现出导电型电树枝特征. 枝状电树枝通道内观察到荧光背景,存在材料劣化的产物,但不存在无序石墨碳的聚集, 通道具有明显的非导电特性而不足以抑制电树枝内局部放电的连续作用. 最后提出了XLPE电缆绝缘材料中导电型和非导电型电树枝的单通道生长模型, 利用等效电路理论对XLPE电缆绝缘材料中两种不同导电特性电树枝的生长机理进行了探讨.

Study on conducting characteristics of electrical trees in cross-linked polyethylene cable insulation

The conducting characteristics of two typical electrical trees in cross-linked polyethylene (XLPE) cable insulation are studied by a combination of optical microscopy observation, partial discharge measurement and con-focal Raman spectroscopy analysis. Although they are grown under similar conditions, these two trees display very different shapes. One is a typical branch-pine tree grown at 9 kV, and the other is a branch tree grown at 11 kV. The growth and the partial discharge regularities show obvious differences. The disordered graphitic carbon is condensed in the main tree channels of the branch-pine tree. From the relative intensity of the graphitic carbon G band to D band, the graphitic domain is estimated to be about 8 nm in size. The tree channel resistance per unit length is less than 10 Ω· μm^-1, which is sufficient to prevent the partial discharge from developing within the tree structure. The branch-pine tree shows the features of the conducting tree. The fluorescence background is observed in the channels of branch tree, which shows the existence of the products of the material degradation, but no disordered graphitic carbon is observed in these tree channels. These tree channels display obvious non-conducting characteristics, which is not sufficient to prevent the continuous effect of the partial discharges. Finally, a single channel growth model is proposed for the conducting and non-conducting trees grown in XLPE cable insulation. Based on the equivalent circuit theory, the growth mechanisms of the two trees with different conducting characteristics in XLPE cable insulation are discussed.