对某电厂一起220 kV线路接地故障进行分析，依据现场记录的甲线“高频距离、距离 I 段”保护动作和220 kV 5号母线母差动作的情况，对线路保护动作录波图、母差保护动作录波图进行分析，初步判定故障为 L3相接地故障，同时从其发展趋势判定其为发展性故障。为确定故障点位置，对5号母线、厂站甲线间隔绝缘情况和线路上设备进行了检查，发现甲线L3相断路器动弧触头断裂，缓冲器油缸(外壳)底部焊口有砂眼，并有油迹。为此，分析了区外故障(甲线53号铁塔L3相接地故障)转换为区内故障(甲线L3相断路器)的原因，认为缓冲器油缸底部焊口有砂眼，变压器油从砂眼处渗出挥发，油量逐渐减少，导致缓冲效果下降是引起故障的主要因素。建议加强220 kV气体绝缘金属封闭式开关设备日常维护和变压器油油位监视或渗漏监视。%One 220 kV line grounding fault in some power plant was analyzed. According to protection action of recorded high frequency distance and distanceⅠsection of A line and No. 5 busbar differential protection of 220 kV,wave record fig-ures of line protection action and busbar differential protection action were analyzed and L3 phase grounding fault was ini-tially judged. Meanwhile,developmental fault was judged in aspect of its development trend. For confirming fault point po-sition,No. 5 busbar,insulation of A line gap and equipments on the line were examined and dynamic arc contact of the breaker was found broken. In addition,there was sand hole and oil stains on bottom crater of the bumper oil cylinder (shell).Therefore,reason for transform of external fault into internal fault was analyzed and main factors for the fault were discovered that included sand hole on bottom crater of the bumper oil cylinder,transformer oil oozing and volatilizing from the sand hole and gradually reduction of oil which might result in decreasing buffering. Suggestions of strengthening daily maintenance for 220 kV gas insulated metal enclosed switchgear and monitoring on transformer oil level or leakage were proposed.
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