A simple description of the tripping circuit and a connection diagram of it is shown in figure (54). C3, and C4 are n.o. contacts. contact from bus isolator2 of equipment’s 3, and 4 respectively, connected on bus 2 so contacts C3, C4 are closed and ready to transfer trip to trip coils of associated circuit breakers if differential coil is operated by differential current. The tripping process is executed through Aux contacts of isolators.
At fault, sum of I3+I4 not equals 0, so the differential coil will operate and transfer a trip signal to a trip bus and so to trip coils of equipments connected to the same bus.A similar circuit for bus1 (equipment 5,and 6) is exist .
Note
The previous examples assumes that the coupler is not connected . If the coupler is connected before fault occurrence, the circuit breaker of it is disconnected at the beginning of the fault to isolate bus1 From Bus2 and then identify which bus from1 and 2 is faulted and then trip all equipment’s connected to it and leave the healthy bus as it is.