500 kV SF_(6)气体绝缘电流互感器绝缘故障的分析

Insulation Fault Analysis of 500 kV SF_(6) Gas Insulated Current Transformer

本文介绍了500 kV主变压器差动保护动作的异常情况,现场检查发现5013 SF_(6)气体绝缘电流互感器C相底座固定螺栓及接地连接处有过流痕迹,解体检查盆式绝缘子表面可见明显裂纹。对比故障相、正常相设备解体及盆式绝缘子射线层析检测结果,推断C相盆式绝缘子生产制造中存在杂质隐性缺陷,造成其局部内应力和电场不均匀,长期运行过程中,镶嵌件部位应力集中形成裂纹,逐步发生局部放电至贯穿性击穿,导致底座基础及接地螺栓处放电,主变差动保护动作。据此,提出增强盆式绝缘子入厂品控,加强同类型同批次设备巡视维护,严格落实运输要求等运检预防措施,以保障设备安全运行。

The abnormal situation of differential protection of 500 kVmian transformer is introduced in this paper.It is found by inspection at site that over-current traces exist at the fixing bolts and the ground connection in phase C of 5013 SF_(6) gas insulated current transformer and surface of insulting spacer has visible crack after disassembly inspection.It is judged by comparing the detection results of the equipment with normal and faulty phase after disassembly as well as X-ray tomography of the insulating spacer that the insulating spacer in phase C has hidden defects of impurities in the production,which causes uneven local internal stress and electric field.During the long-term operation,the concentration of stress of the inserts forms cracks and the partial discharge gradually occurs till the penetration breakdown,leading to discharge at the base foundation and the grounding bolt as well as the differential protection action of the main transformer.Accordingly,such preventive measures as strengthening quality control of incoming insulating spacer,strengthening the inspection and maintenance of equipment with the same type and strictly implementing the transportation requirement strictly are proposed so to ensure safe operation of the equipment.