A novel algorithm for differential protection of untransposed transmission line using synchronized measurements

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.