Coordination of directional overcurrent relays in transmission systems-a subsystem approach

A new concept, called subsystem coordination, for efficiently computing proper settings of directional overcurrent relays on transmission systems in response to changes in system topology and load levels is proposed. An automatic window identification and coordination algorithm has been developed, implemented, and tested on a realistic transmission system. The test results have been validated through a full system coordination study, and the significant reduction in computer time required by the subsystem approach has been demonstrated