The dual configured transmission line protection with fiber channels has the risk of refuse operation when fiber channels are both abnormal during the internal fault. Once endangered

the fault clearing time will be delayed and the non-selective tripping of the adjacent line will occur to bring about serious consequences of enlarged fault area and destroyed power grid stability. In view of the above risky situation

an adaptive technology for shortening the time of the zone Ⅱ backup protection is proposed and verified by experiment. The technology makes it possible to achieve rapid tripping time while avoiding non-selective tripping of zone Ⅱ backup protection of the adjacent line by accelerating the zone Ⅱback-up protection. It can also improve the stability and reliability of power grid operation.