A New Differential Current Protection Algorithm for Three-Terminal Line

In general, conventional differential scheme (CDS) is used for the three-terminal transmission line protection; however, because of CT saturation under external faults, the relay loses its security. Further, adaptive direct under reaching transfer trip (DUTT)-based algorithms are reliable until the overlappings between zone-1 settings are ensured. However, the overlapping of zone-1 may vanish due to infeed current and under high resistance fault, resulting in an unprotected region in the line. Hence, in this paper, a new differential current circle diagram-based protection algorithm is proposed by utilizing the magnitude and phase angle of three-terminal currents instead of the only magnitude as in CDS. The effectiveness of the proposed algorithm is tested on 400 kV, 50 Hz using PSCAD/EMTDC and MATLAB, and the corresponding results show the authenticity of this algorithm to discriminate and classify the faults correctly. Finally, the comparative section reveals that the proposed algorithm provides reliable results compared to the CDS and adaptive DUTT protection schemes.