高压XLPE电缆阻水缓冲层烧蚀机理

Ablation Mechanism of Water-blocking Buffer Layer in HV XLPE Cables

近年来,高压XLPE电缆阻水缓冲层烧蚀故障频发,引起了行业内广泛关注。为了探索缓冲层烧蚀机理,搭建简化试验平台并对应电缆实际运行工况条件,开展了对比试验研究;同时,基于110 k V电缆典型结构建立轴向有限元仿真模型,按照阻水缓冲带的实测性能参数进行赋值;最后调节波纹铝护套与缓冲层的接触形式,开展了电势及电场分布模拟分析。研究发现:缓冲带受潮将导致其电阻率增大,介电常数升高,并在外加电流下引发白色物质生成;白色物质中包含阻水粉成分及铝反应产物,其不导电性易导致铝护套与绝缘屏蔽之间电气接触不良;当阻水缓冲层与波纹铝护套连续接触不良的轴向长度达到0.4m,在尺寸为0.1mm气隙中的场强已超过3 k V/mm,足以引发放电。缓冲层受潮是发生烧蚀故障的主要原因,缓冲层与铝护套的间隙也会影响气隙放电的发生,因此建议高压电缆在制造和施工阶段应避免缓冲层受潮,同时应严格保障缓冲层与铝护套有效连续的电气接触。

In recent years, ablation failures of the water-blocking buffer layer in HV XLPE cables occur frequently, which has attracted widespread attention in the industry. In order to study the ablation mechanism of the water-blocking buffer layer, a simplified test platform was set up and comparative experiments were carried out corresponding to the actual operating conditions of the cable. Besides, a finite element simulation model was established for a 110 k V cable, with the dielectric parameters of the buffer layer assigned according to the measured data. Finally, the electric potential and field distribution were analyzed when the corrugated aluminum sheath and the buffer layer were contacted in different forms.The results show that, with the buffer layer getting damp, its resistivity and permittivity both increase, and the white substance appears under the applied current. The white substance containes water blocking powder and aluminum oxide products, and its non-conductivity will lead to the poor electric contact between the aluminum sheath and the insulation screen. When the axial length of the poor contact between the water-blocking buffer layer and the corrugated aluminum sheath reaches 0.4 m, the field strength in an air gap with a height of 0.1 mm will exceed 3 k V/mm, which can trigger the discharge. Damp of the buffer layer is the main reason of ablation failures, and the gap between the buffer layer and the aluminum sheath also affects the occurrence of air gap discharge. Therefore, it is suggested that the damp of the buffer layer should be avoided in the manufacturing and construction stages of HV cables, and the effective and continuous electrical contact between the buffer layer and the aluminum sheath should be strictly guaranteed.