一起母差保护误动事件的原因分析

按照双重化配置原则,某电厂500 kV母线配置了RCS-915A-G型和P740型各一套母差保护。该厂3号机主变高压侧出口开关在一次停机过程中,盆式绝缘子被击穿,造成母线接地,母差保护不正确动作。经对事件检查发现,故障是设计缺陷引起。P740保护跳母联开关5012的出口应该有而未设接复压闭锁接点,导致两套母线保护均动作。

Analysis of a Mal-operation Fault of Busbar Differential Protection

The 500 kV busbar in a hydropower plant is equipped with a RCS-915A-G type and a P740 type busbar differential protection following the dual configuration principle.During a shutdown process of the No.3 unit,the pot insulator of the outlet switch on the high voltage side of the main transformer was broken down,which caused the grounding of the busbar and thus the mal-operation of the busbar protection.Analysis shows that the fault is due to a design defect.In the outlet of the bus tie switch 5012 in P740 protection,a compound voltage blocking point should be arranged but not in practice,which leads to the operation of both protections.