Relay Coordination in the Protection of Radially-Connected Power System Network
Protective relays detect intolerable or unwanted conditions within an assigned area, and then trip or open one or more circuit breakers to isolate the problem area before it can damage or otherwise interfere with the eective operation of the rest of the power system. It often happens that a substation feeder relay and supply-side relay both trip for the same feeder fault. This occurrence, known as over-trip is undesirable, and is usually blamed on poor relay coordination. The relay and breaker nearest to the point of fault must be able to see the fault and operate before other relays in the system so that healthy parts of the system will not be interrupted. How to achieve this is the subject of this paper.