New digital distance relaying scheme for phase faults on doubly fed transmission lines

Performance of conventional non-pilot phase distance relay is affected by series capacitor (SC), remote infeed/outfeed, prefault system conditions and arc resistance. The work presented in this study addresses the problems encountered by conventional non-pilot phase distance relay when protecting doubly fed series compensated transmission lines. One of the key points of this study is the detailed analysis of the apparent impedance as seen from the relaying point taking into account the effects of transmission line parameter uncertainties, behaviour of SC, arc resistance and variations in the system parameters external to the protected line. Based on extensive computer simulations of the infeed/outfeed, arc resistance and effects of SC on the relay characteristics, a new digital distance relaying scheme is proposed. It is based on digital computation of impedance of faulted portion of transmission line using symmetrical components of currents and voltages measured at local end only. To validate the proposed scheme, numerous computer simulations have been carried out on an existing Indian 400 kV, 300 km long series compensated transmission line using MATLAB/SIMULINK software. Simulation results demonstrate the effectiveness of the proposed scheme as the percentage error is within 5 .