TRANSMISSION ROUTE CHANGEOVER CIRCUIT FOR CARRIER PROTECTIVE RELAY DEVICE

PURPOSE:To elevate reliability by providing transmission fault detecting functions in every transmission route, and preventing the changeover to the transmission route where the transmission fault is detected. CONSTITUTION:If transmission fault occurs on the side of a down signal A route, a transmission fault detection circuit 13 detects the transmission inferiority, and it outputs a transmission fault signal 16 and an A route transmission infault signal 21 to a transmission route changeover circuit 14. The transmission route changeover circuit 14, due to the materialization of the condition of an AND circuit 211, sets the flip flop circuit 224 through an on delay timer 231 and an OR circuit 221, and a route changeover circuit 24 gets on 1 level from 0 level, and performs the changeover from A route to B route. At the same time, it sends out a route changeover signal 25 to the counterpart terminal, and the counterpart terminal also seeks to perform the changeover from A route to B route, but with the counterpart terminal, the B route is in maintenance and inspection, and B route transmission fault is being detected, so the route changeover is locked, and it can be operated with A route intact.