配网电缆接头内部缺陷电场特征研究及电树发展分析

配网交联聚乙烯(cross linked polyethylene，XLPE)电缆的严重击穿故障大多发生在电缆接头处，主要由电缆接头在制造和安装过程中的工艺缺陷引起。文中采用模拟电荷法研究电缆接头4种典型缺陷，即气隙、水膜、金属碎屑和金属外破附近的电场分布特征；然后采用电场计算与随机漫步理论相结合的方法，分析缺陷引发的电树枝的分布规律。同时，测量带缺陷配网XLPE电缆接头样本周围的实际电场分布，并比较测量结果与计算结果。结果表明，采用电场测量的方法可以直接有效地识别电缆接头内部缺陷类型，相比气隙、水膜缺陷，导电缺陷造成的电场畸变更为显著。缺陷引发的电场畸变大于临界电场值时会引起电树发展，电树发展的轨迹长度与场强大小呈正相关，导电缺陷引发的电树枝有较大概率向缆芯方向发展，更易引起XLPE绝缘击穿。

Electric field characteristics investigation and electrical tree propagation of distributed network cable joint with defects

Most serious breakdown faults of cross linked polyethylene(XLPE) cables in distribution network occur at cable joints,which are mainly caused by process defects in the manufacturing and installation of cable joints. In this paper,the charge simulation method is used to study the characteristics of electric field distribution near four typical defects of cable joints,namely,air gap,water film,metal debris and metal breakout. The electric field calculation and random walk theory are combined to analyze the distribution of electrical tree caused by several defects. At the same time,the actual electric field distribution around the sample of XLPE cable joints in the distribution network with defects is measured,and the measured results are compared with the calculated results. The results show that the electric field measurement method can directly and effectively identify the types of internal defects of cable joints,and the electric field distortion caused by conductive defects is more significant than that caused by air gap and water film defects. When the electric field distortion caused by defects is greater than the critical electric field value,the electric tree will develop. The track length of the electric tree development is positively related to the field strength. The electrical tree caused by conductive defects is more likely to develop towards the cable core,which is more likely to cause the breakdown of XLPE insulation.