Consider Sub-1 & Sub-2. A fault is exits in the Sub-1 bus.
In this condition a line is energized by closing the other end Sub-2 Line breaker.
The Sub-1 bus is trying to energize by close the Line breaker. Minimum 50ms will take to close the CB poles and CB status contacts. During this operation the fault current will start to follow through the arec between CB poles.This fault current seance by Other end relay as Zone -2 faults and it will send a carrier to the Sub-1 relay with in 20 ms.Sub-1 relay will sense this fault current as reverse Zone -4 fault and it will not trip the won breaker.Sub-1 relay will receive the carrier and reply back to Sub-2 relay and conform two thinks ones Zone 4 reverse current and CB open.with in 20 ms this carrier will reach the the Sub -2 relay and relay will trip the breaker.
