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Distance relays used for transmission line protection can mal-operate on power swing. This paper presents protection schemes for out of step detection based on synchronized phasor measurement. Voltages and currents at both the ends of a transmission line are used to derive the parameters required for designing these schemes. The proposed schemes can distinguish stable and unstable power swing and can prohibit tripping of distance relays on stable power swings. The schemes are also compared with conventional power swing detection schemes. Simulations are carried out on single machine infinite bus system (SMIB) using PSCAD. (4 pages)

Although there has been a practice of transposition of transmission lines, most of the real life EHV/UHV lines are untransposed. The distance protection of such lines becomes very complicated. With the advent of Global Positioning System (GPS) and Fiber optics technology, current differential protection can be a better choice for such lines. This paper proposes current differential protection scheme for protection of untransposed transmission lines based on equivalent-π line model. The proposed differential relay basically works on difference of currents in series branch (computed) from equivalent-π line model. As the measurements are time synchronized, the performance of relay is immune to line charging current. The analysis has been carried out in phase coordinates. ATP/EMTP programs have been used to simulate system disturbance and algorithm is implemented MATLAB. The result shows the efficacy and robustness of proposed algorithm. (4 pages)