New Algorithm for Protection of Double Circuit Transmission Lines Using Modal Currents

This paper presents a new protection algorithm for double circuit transmission lines using the sum of ratios of modal currents. Relay-operating characteristics is proposed using the complex ratio of modal currents. The proposed algorithm estimates modal domain line parameters and identifies the faulty phases for single pole-tripping applications even during inter-circuit faults. The scheme is sensitive to high resistance internal faults and also detects internal faults with outfeed. The proposed scheme is immune to mutual coupling and is found robust to uncertainties in parameter estimation due to measurement inaccuracies. The scheme is tested for its effectiveness to deal with current transformer saturation and synchronisation error. The scheme protects series compensated double circuit transmission lines even in the presence of current inversion. Exhaustive case studies in electromagnetic transient program (EMTP)/alternate transient program are performed on 400 kV, 300 km, double circuit transmission lines and the proposed protection algorithm is implemented in MATLAB. The results confirm the superiority of the proposed scheme.