Fault Analysis of a Relay Protection Override Trip and Discussion on the Relay Protection Selectivity

Chen Ruzhong（Xiamen International Airport Co.，Ltd.，Xiamen 361006，Fujian Province，China）

        Abstract A large current short -circuit fault occurred in the low -voltage bus-tie switch cabinet at the substation of a central machinery factory，which led to the simultaneous override trip of the two stages of high -voltage circuit breaker of the superior 10 kV distribution substation. Analysis is conducted directing at the phenomena，reason，relay protection settings，and protection action value of this fault；meanwhile high -voltage relay protection is expounded；based on these，the paper comes to the conclusion that it is necessary and important to set gradation for relay protection actuation time and current start value in high -voltage distribution system including multi -grade substations.

         Key words　Bus-tie switch　Override trip　Relay protection　Protection selection

        摘　要　某中心机械厂变配电所低压母联开关柜发生大电流短路故障，导致上级 10 kV 配电所的两级高压断路器同时越级跳闸，针对这次故障的现象、原因、继保整定值、保护动作值进行分析，同时对高压继电保护进行阐述，得出在包含多级子站的高压配电系统中，继电保护动作时间及电流启动值设置级差的必要性与重要性。

       关键词　母联开关　越级跳闸　继电保护　保护选择