500 kV三林变电站在对电容器充电操作时，发生1号主变3号电容器爆炸起火事故。通过分析发生事故时的保护动作报告、查看原始设计图纸以及对照现场电容器组接线，确诊3号电容器发生爆炸的主要原因，是设备安装人员将安装于绝缘台架上的电容器放电线圈外壳接地线，直接与接地铜牌相连了。为此，建议在设备安装说明书和设计图纸中，应该强调“放电线圈安装于绝缘台架上，外壳不得接地”的警示语，并提出了防止发生类似爆炸事故的技术措施。

No. 3 capacitor of San Lin substation occurred an explosion and fire accident when doing the charging operation. Analyzing on protection action report, the original design drawings and wiring of capacitor group, reason of the accident is found. That is the discharge coil installed on the insulation bench connected to the earth terminal by mistake. In this paper the settlements are proposed, such as adding the warnings to installation specifications and design drawings, and careful examination before operating.