某电厂1 000 MW机组380 V PC段母线在负荷侧单相接地时，发生电压互感器（potential transformer，PT）烧毁事故。经对此次事故详细分析后发现，1 000 MW机组与300、600 MW机组低压厂用电系统接地方式不同，前者一般采用经电阻接地的小电流接地系统，后者一般采用直接接地的大电流接地系统。此次PT烧毁事故是设备选型不当造成的，大容量机组的设备选型要视实际情况区别对待。

For single-phase grounding on the load side of 380 V PC bus in a 1 000 MW unit of power plant, burnout accident of potential transformer(PT) occurs. It is found after a detailed analysis of the accident that the grounding ways of LV auxiliary power system are different for 1 000 MW, and 600 MW or 300 MW unit, where the former applies small current grounding system via resistance grounding, while the latter generally adopts large current system via direct grounding. Therefore, the PT burnout accident is caused by improper selection of equipment, and equipment selection of large capacity unit should depend on actual situation.