高压电力电缆护层电流在线监测及故障诊断技术

Sheath Current in HV Cable Systems and Its On-line Monitoring for Cable Fault Diagnosis

通过监测护层电流可及早发现高压电力电缆线路的潜在故障,有效避免非计划性停电。为此,提出了1种可用于诊断故障与非故障情况下3相交叉互联高压电力电缆中护层电流的研究方案。通过建立数学模型详细分析了2种典型的电缆故障,并基于1条线路长度为1.5 km、电压等级为110 k V的隧道电缆的仿真计算,提出了1套适用于12种电缆故障的诊断及定位标准。仿真分析结果显示:当电缆接地系统中存在开路故障时,故障回路中的护层电流会降低;而当电缆交叉互联箱进水或电缆接头内环氧预制件击穿时,故障护层回路中将产生高于正常水平的护层电流值。基于故障仿真,所提出的故障诊断标准可准确识别并定位指定的3种电缆故障:接头松动导致护层开路、交叉互联箱进水和接头内环氧预制件击穿。仿真表明地电阻的大幅度变化会导致诊断标准发生变化。

Cable sheath currents can be utilized to identify cable faults at an early stage and avoid unplanned power outages. We put forward a methodology to analyze the sheath currents in three-phase cross-bonded cable system with cable link boxes under either normal or fault conditions. Firstly, we established a numerical model to analyze two selected joint faults in detail. Then, on the basis of the calculation of a 1.5 km long 110 kV underground power cable system installed in a cable tunnel, we proposed a set of criteria for the fault diagnosis and localization of 12 kinds of faults that could significantly cause changes in sheath currents. The simulation results indicate that the sheath current decreases when the open-circuit fault occurs in the cable sheath loop, however, in the case of flooded cable link box or insulation breakdown between sheaths at both sides of a cable joint, the sheath current gets higher than its normal. According to the criteria, it is able to determine and locate three kinds of cable faults, namely, sheath open circuit induced by loosen joints, flooded cable link box, and prefabricated epoxy component breakdown in joints, though the criteria may vary due to large changes in earth resistance.