以上海500 kV静安地下变电站主变采用“电缆+主变+低抗”整合的“三位一体”运行方式为例，介绍了开关失灵启动及动作的保护原理，分析了主变500 kV开关采用RCS-921A失灵保护装置、主变220 kV开关采用RCS-923C中压侧失灵联跳装置的失灵保护逻辑，指出了正常运行方式和“三位一体”运行方式，在保护配合和动作出口的差异性，用以正确理解保护动作过程和在事故状况下迅速判明保护动作状况。对于线变串接线和电缆线路的变电站，倘若运行方式需要，开关须改非自动的，“三位一体”运行方式可作为借鉴。

In shanghai 500 kV Jingan underground substation main transformer adopts “three-in-one” operation mode integrating “cable+main transformer+reactor”. As an example, this paper introduces protection principles of starting breaker failure and action, the breaker failure protection logics of RCS-921A failure protection device adopted by main transformer 500 kV breaker and RCS-923C failure protection device adopted by 220 kV breaker are analyzed, the differences of protection coordination and action in normal and “three-in-one” operation mode are studied,which helps to understand the protection action process correctly and identifies the protection movement situation quickly under accident conditions. For substation of circuit transformer unit wiring and cable line,if the breaker must be changed to non automatic state with the need of operation mode, “three-in-one” operation mode can be used as a reference.