光伏电站正极直流电缆频繁绝缘阻抗低故障分析

Fault Analysis of Low Frequent Insulation Impedance of Positive DC Cable in Photovoltaic Power Station

针对粤东某电站汇流箱频繁报正极直流电缆绝缘低故障问题,通过对现场情况检查发现:正极直流电缆绝缘下降比负极严重;正负极电缆埋地段的绝缘水平下降比架空段严重。针对直流电缆开展防PID功能投退比对试验、直流耐压试验、绝缘电阻试验并进行解剖检查。结果发现,直流电缆绝缘层存在水侵蚀,导致直流电缆绝缘性能下降,泄漏电流增大,导致局部温升,进而造成绝缘劣化,恶性循环,最终出现直流电缆被击穿。解剖检查结果证实,护埋地电缆的PVC套管非完全防水密封,雨水流入套管,直流电缆长期浸泡于积水中,水分子缓慢侵入至绝缘层,导致频繁出现绝缘阻抗低故障。对此类直流电缆绝缘阻抗低故障提出了纠正建议,为今后同类地面光伏电站项目的直流电缆施工、技改提供了参考。

In view of the low insulation failure of the positive DC cable frequently reported by the bus-box of a power station in eastern Guangdong,it is found that the insulation decline of the positive DC cable is more serious than that of the negative cable through field inspection.The comparison test of anti PID function on/off,DC withstand voltage test,insulation resistance test,and anatomical inspection were carried out for DC cables.The results showed that there was water erosion in the insulation layer of DC cables,which led to a decrease in the insulation performance of DC cables,an increase in leakage current,and a local temperature rise,leading to insulation degradation,a vicious cycle,and ultimately the breakdown of DC cables.The anatomical examination results confirmed that the PVC sleeve protecting the buried cable was not completely waterproof and sealed,and rainwater flowed into the sleeve.The DC cable was soaked in water for a long time,and water molecules slowly penetrated into the insulation layer,leading to frequent low insulation resistance failures.Suggestions for correcting the low insulation impedance faults of such DC cables are proposed,providing a reference for the construction and technical transformation of DC cables in similar ground photovoltaic power station projects in the future.