Patent ID: 8462475

Claim:
A multi-terminal power line protective relay system comprising: a power transmission line having four or more terminals which is divided into two or more power line sections, each of which is composed of three adjacent terminals and portions of the power transmission line lying among the three adjacent terminals, and at least one of the three adjacent terminals being shared by two of the adjacent power line sections; protective relays installed at the respective terminals included in the power line sections and each including a current-driven differential protective relay element for detecting a fault occurring in a power line section through current-differential calculation by using currents measured at the terminals included in the power line sections; inter-terminal communication channels to share data necessary to perform the current-differential calculation in the protective relays; and intra-terminal communication channels each linking two protective relays each being installed at a shared terminal being shared by two of the adjacent power line sections; wherein each protective relay that detected a fault occurring in a power line section transfers a signal indicating the fault to other protective relays via the inter-terminal and the intra-terminal communication channels and causes the other protective relays to trip circuit breakers installed at the terminals; and wherein each protective relay is configured digitally; and current data for the current-driven differential protective relay elements belonging to the same power line section is synchronously sampled, while current data for the current-driven differential protective relay elements belonging to different power line sections is asynchronously sampled.