Abstract: A current differential relay device is described. The device has two transmission parts provided in parallel and communicating with an other end of a power transmission line through two transmission paths and transmitting and receiving a quantity data of electricity of each of the terminals to and from an other end in the form of the digital data obtained through analog/digital conversion. Two current differential operation parts are connected to each of the two transmission parts and perform a current differential operation independently for each of the transmission paths by using the digital data of the quantity data of electricity of the one end of the power transmission line and of the other end of the power transmission line. A signal generation part generates a trip signal from the current differential operation result of the two current differential operation parts.

Abstract: Two current differential relay devices 1 are installed at each terminal 3 of a two-terminal power transmission line 2, and connected to each other via two transmission paths 5 and 6, and perform current differential operations by transmitting and receiving the quantity data of electricity to each other. In the current differential relay device 1, two transmission means 14 normally each perform communications with the current differential relay device 1 of the other end of the power transmission line in parallel through the two transmission paths 5 and 6. Two current differential operation means 14 are connected to the two transmission means 14 respectively and perform independently two-series of current differential operations independently for each series associated with each of the transmission paths 5 and 6.