交联聚乙烯电缆水树缺陷的修复方法研究

Study on the Repair of Water Tree Defect in XLPE Cables

采用硅氧烷修复液修复交联聚乙烯电缆老化试样中的水树,进而分析修复效果及机理。将介质损耗因数为4%～6%,绝缘电阻7 500～10 000 MΩ的短电缆在7.5 kV 450 Hz交流电压下老化至介质损耗因数达到20%左右,绝缘电阻3 500～5 000 MΩ。然后用压力注入式修复装置把修复液注入缆芯对水树缺陷进行修复。以介质损耗因数、绝缘电阻和击穿电压为指标对修复效果进行评判;通过显微镜切片观察修复前后水树微观形态;通过仿真修复前后水树附近电场分布来分析和验证水树的修复机理。实验结果证明,修复液可以充分与电缆水树中的水发生反应生成胶状聚合物填充水树通道;修复后电缆介质损耗因数、绝缘电阻和击穿电压恢复到新电缆水平;改善了绝缘层电场分布;有效地抑制了水树生长。实验表明,该修复液可有效修复电缆中的水树缺陷,提高电缆绝缘水平。

In this paper, a siloxane liquid is utilized to repair the water trees in ageing XLPE cables, and the results and mechanisms of the repair are analyzed. The short cables, whose dielectric loss factor is from 4% to 6% and insulation resistance is from 7 500 MΩ to 10 000 MΩ, are aging with 7.5 kV and 450 Hz AC until the dielectric loss factor of them grows up to around 20% and the insulation resistance decreases to 3 500-5 000 MΩ. Then the siloxane repair liquid is injected into water tree cables with a pressurized injection systenL The effects of repairing experiment are analyzed through dielectric loss factor, insulation resistance and breakdown voltage. The micro morphology of water trees in cables before and after repairing is observed with microscope observation. The repair mechanism is verified though the simulation of the distribution of electric field nearby water trees before and after repairing. The experimental results show that the siloxane liquid fully reacts with the water in water trees to form a gel polymer which is filled the water trees with. After repairing, the dielectric loss factor, the insulation resistance and the breakdown voltage is restored to those of the new cables; the electric field in cable insulating barrier becomes well-distributed; and the growth of water trees is greatly inhibit. Verified by experiments, the water trees in ageing XLPE cables can be effectively repaired by the siloxane liquid, and the insulation level of cables can be significantly improved.