Novel Distance Protection Algorithm for Long Transmission Line

The fault location algorithm is commonly used to measure the distance between the measurement point and the fault point in a transmission line. One of the feasible techniques is the impedance -based methods, in which the single-end fault location algorithms are widely used in distance relays with the consideration of their simple theory and efficient cost. However, most of the existing single-ended fault location algorithms are based on the equivalent RL line model. They are relatively accurate for the short transmission line case, while this may be not true in a long transmission system due to the mismatching of the RL model and the real transmission line. To overcome this demerit, a modified impedance-based fault location algorithm is developed for estimating the fault distance in this paper. The core idea of the new method is to applying the Bergeron method to compute the voltage and current at the setting point of the distance relay, which make the setting point a virtual starting point when building the distance measurement equation. Then, the voltage drop equation between the setting point and the fault point is built based on equivalent RL line model. Finally, the conventional
fault location is adopted to solve the fault distance. By this way, the new method shows a higher computation accuracy than the conventional method for the faults occurring near the protective boundary. Besides, with the coordination of the directional element, the distance relay can achieve a reliable operation along the whole protective zone. The simulation model is built in DIgSILENT/PowerFactory and the data are processed in Matlab. The results from both the conventional algorithm and the proposed new one are compared with each other and the accuracy has been investigated in simulation results. The results verify that the proposed new fault location method performs higher accuracy for remote faults than the conventional Takagi method, which can improve the reliability of the impedance -based distance protection to remote faults in a long transmission system.