PERFORMANCE ASSESSMENT OF DIGITAL DISTANCE RELAY ALGORITHMS

With recent advancements in micro-computer technology, the use of micro-processors for distance protection has received much attention from power system research groups. Different algorithms have been developed over the years for use in digital distance relays. The performance of the al­gorithms need to be assessed off-line before any implementation in an actual system. Some of the general characteristics of the algorithms that can be examined are frequency reponse, effect of decaying dc on the accuracy of cal­culated phasors and noise suppression qualities. The performance of an algo­rithm can also be assessed using power system fault data. This thesis examines the suitability of four long window relay al­gorithms for protecting transmission lines. The frequency response, the effect of decaying dc on the accuracy of the calculated phasors and noise suppression characteristics of each algorithm is examined. The ability of each algo­rithm to accurately detect faults and to estimate the distances of the faults is also checked using data obtained by computer simulations. The speed with which the algorithms detect faults, that are in the operating zone of a relay, is illustrated using the movement of the trajectories of the calculated impedances from their pre-fault values to the post-fault values