A Three-Terminal Line ProtectionScheme Immune to Power Swing

Abstract

Communication-assisted distance protection schemes are widely used for three-terminal line protection and are susceptible to power swings. The available differential protection scheme is also considered to be suited to protect three-terminal lines and is free from problems associated with the power swing. However, the performance of the current differential protection scheme may be affected if an outfeed condition occurs during an internal fault. This paper presents a new technique for protecting three-terminal transmission lines immune to power swing. The technique uses synchronized voltage and current measurements from three terminals for calculating voltage at the tee-point. The maximum magnitude of the superimposed component of positive-sequence voltage estimated at the tee-point is compared with the maximum magnitude of superimposed componentas of the positive-sequence voltage measured at three terminals of the line to discriminate a fault from power swing. The method is accurate even for an outfeed condition during the internal fault, current-transformer saturation during severe internal or external faults, large load rejection, and different prefault loading conditions occur during the power swing. The proposed algorithm is verified using data simulated through EMTDC/PSCAD for a 400-kV double-circuit three-terminal system.