A New Cross-Differential Protection Scheme for Parallel Transmission Lines Including UPFC

This paper proposes a new cross-differential protection scheme for a parallel transmission system in the presence of a unified power-flow controller (UPFC) in one line. A cumulative summation technique using three-phase current signals at the sending end is used for fault detection. The faulty phases are then identified by computing the spectral energies of the phase currents. The spectral energy of the phase currents is computed by applying a computationally fast efficient powerful tool known as first Discrete S-Transform (FDST), suitable for analyzing power system signals. The proposed scheme has been extensively tested on different fault conditions with a wide variation in operating parameters. The test results indicate that it can accurately detect and classify the faults with clear discrimination between internal and external faults on a transmission line with a response time of a maximum one cycle from fault inception.