一起由接地工艺引起的 220 kV 高压电缆故障分析

Fault Analysis of a 220 kV High － voltage Cable Caused by Grounding Technique

摘要:

以某 220 kV 高压电缆线路故障为例，分析了电缆的放电通道和施工工艺等问题，最后对电缆接头的接地工艺 进行了探讨。对故障的电缆进行解体后，发现电缆接头的铜壳与铝护套间的焊接工艺不规范，接头两侧的焊点处存 在接触面积不足、虚焊、脱焊等现象。由于电缆铜壳未能与铝护套有效连接，导致铝护套与铜壳在运行中长期存在异 常放电。此外，这种接地情况导致本该从铜壳流走的电流，会从绝缘预制件外表面缠绕的薄铜网中流过，并在接触电 阻较大的铝护套断口附近引起发热。长期发热会逐渐灼伤电缆本体，并最终引起绝缘击穿故障。

Abstract:

Taking insulation breakdown of a 220 kV high － voltage cable for example，the discharge channel，installation procedure and so on are analyzed to find out the main reason of cable fault，and the grounding technique of high － voltage cable is discussed too． After dismantling the broken － down cable joint，it is found that welding technology between copper shell and aluminum sheath is not standard，and there are some phenomena such as false welding，welding off，and inadequate contact area in welding points at the two sides of cable joints． This connection between copper shell and aluminum sheath is not effective，and the abnormal discharge exists for a long time in the running． Besides，the current which is designed to flow through the copper shell，would flow through copper mesh from the outside of insulating prefabricated part，which would lead to abnormal heating at the edge of aluminum sheath where the contact resistance is larger． The long － term heating would burn the cable，and cause insulation breakdown finally．