Novel Transient Differential Protection Based on Distributed Parameters For EHV Transmission Lines

A novel scheme and algorithm of differential protection, which employs not only the power frequency component but the transient components based on distributed parameter line model, is proposed, as well as the distributed capacitive current is taken into account accordingly. The operating travelling waves F_com and B_com are defined as the forward and backward travelling wave that calculated with the voltage and current data at the other terminal under the assumption that the whole line is healthy. By comparing the measured forward and backward travelling wave with the operating travelling waves, we proposed the differential protection criterion, which matches not only the steady state component but the high frequency transients. The EMTP simulation tests associated with the typical extra high voltage power network show that the new differential protection has the capability of instantaneously identifying internal and external faults as well as higher reliability and security, in general, the trip order can be sent within 10 ms. The new criterion is not sensitive to transient components, fault resistance, fault inception angle, fault types and system swing.