Transmission line pilot protection based on frequency-domain model identification of distributed parameter

To eliminate the capacitive current's influence on line protection of long-distance and high-voltage transmission lines, this paper proposed a novel transmission line protection scheme based on model identification method and on the point that matrix pencil algorithm can extract the characteristic frequencies of the transmission line reliably. By studying the fault network topology of distributed parameter lines, the frequency-domain models of external and internal fault states were built. The fault model for external fault states is a distributed capacitive model, while the fault model for internal fault state is an equivalent system impedance model. The two kinds of unbalanced currents were defined as two model errors to identify different fault models. When an external fault occurs, the fault data corresponds with the distributed capacitive model and its unbalanced current is smaller than that of the equivalent system impedance model. When an internal fault occurs, fault data corresponds with the equivalent system impedance model and its unbalanced current is smaller than that of the distributed capacitive model. Therefore, external and internal faults are distinguished. Theoretical analysis and simulation results show that the new principle can remove internal fault quickly and reliably, free from the influence of capacitive current and transition resistances. © 2013 Chin. Soc. for Elec. Eng.