施工缺陷对超导电缆中间接头内电场分布的影响

中间接头在高温超导电缆中是最薄弱的环节,制造和施工环节中造成的任何缺陷都有可能在运行时产生电场畸变,缩短中间接头使用寿命,施工缺陷严重时可能引发电缆局部放电、击穿等事故。为此本文利用有限元仿真软件分析了绝缘层划伤、绝缘层杂质、超导带焊接毛刺三种典型施工缺陷对接头内电场分布的影响规律。研究结果表明,绝缘层划伤存在空气隙时,最大电场强度随着空气隙厚度增加而减小；而当空气隙厚度保持不变时,最大场强与空气隙长度呈正相关增大。绝缘层残留杂质时,半导电层切断处、超导带焊接部位附近的绝缘层杂质周围电场畸变最严重,且超导带焊接部位周围最大场强大于半导电层切断处。此外,杂质大小、位置及带电与否均会对电场造成很大影响。随着杂质半径增加,超导带焊接部位和半导电层切断附近杂质周围场强近似呈正比例增长；杂质不同电荷量和电性对电场畸变程度同样有重大影响,特别是当部分杂质为电负性时,周围最大场强均超过5MV/m。超导带焊接毛刺的位置及大小对场强有较大影响,其中在超导带焊接部位与绝缘层分界面处场强最大,且沿超导带焊接部位径向的毛刺周围场强高于沿轴向的场强。研究成果为分析超导电缆故障原因,制定接头施工工艺提供一定参考。

Influence of construction defects on electric field distribution of superconducting cable intermediate joints

The high temperature superconducting cable intermediate joints, as the insulation weak link, may cause any electric field distortion, which may lead to the decrease of the joint life, partial discharge and breakdown of the cable. Therefore, this paper uses the finite element method to analyze the influence of three typical construction defects on the electric field distribution in the joint, such as the scratch of insulation layer, the impurity of insulation layer and the welding burr of superconducting tape. The result shows that the maximum electric field intensity decreases with the increase of air gap thickness when there is air gap caused by scratch of the insulating layer. When the air gap thickness is constant, the maximum field strength increases as the air gap length increases. When the insulating layer has the impurities, the electric field distortion, which is around the insulating layer of the semi-conductive layer and the superconducting layer near the welding site, is most serious, and the maximum field strength around the superconducting zone is greater than that of the half conducting layer. In addition, the impurity size, location, and charge or not has great impact on the electric field. With the increase of the impurity radius, the field strength that located in superconducting welds and semi-conductive layer cut near the impurity is approximately proportional increase; Impurities with different charge and electricity also has great influence on the electric field distortion, especially when the part of impurity is electronegative and the maximum field intensity reaches more than 5MV/m. The tape welding position and the size of burr have great influence on the field intensity of the welded area: The boundary between superconducting tapes and the insulating layer have the maximum field intensity, and the field strength along the radial burr of the superconducting zone is higher than the axial. The research results can provide a reference for analyzing the cause of superconducting cable fault and establishing the joint construction technology.