Flow transferring identification algorithm with consideration of transient period

Cascading trips caused by flow transferring are crucial for lots of well-known blackouts. For a power system with heavy load flow, once there is a fault, the system might suffer flow transferring after the fault clearing. However, for relays, they cannot know the sensing overcurrent is caused by internal faults or flow transferring. The relays will trip the overcurrent after the predefined time delay, which might result in flow transferring again and worsen the system state. Therefore, if relays pickup due to flow transferring, the back-up relay should be blocked until the thermal limit of the line reaches. In this paper, Flow Transferring Relativity Factor (FTRF) is suggested to estimate the flow distribution after a line is tripped. Moreover, based on the relationship of node injection and branch currents, the impact of transient period on the flow distribution is analyzed. Finally, a flow transferring identification algorithm is presented to distinguish flow transferring from internal fault caused by fault clearing. The simulation results of 10-generator 39-bus New England system show that the proposed flow transferring identification algorithm works well.