Methodology to assess performance indexes for sensitivity, selectivity, and speed of coordination of directional overcurrent protections

Abstract

Many algorithms for the coordination of directional overcurrent protections (DOCP) have been proposed in literature claiming that optimal solutions are reached, even though there are different reported solutions for the same problem. A new method to evaluate the quality of solutions for the coordination of DOCP is proposed. Three indexes are defined for selectivity, sensitivity, and speed, as desirable features of the coordination of protections. The use of performance indexes to evaluate the response of DOCP systems has not been previously considered in the literature. Given time dial and pick-up settings provided by any program or algorithm, uniformly distributed fault locations are simulated in each transmission line in order to determine the operation times as well as the separation times between main and backup relays. For each fault, the trip sequence of each relay pair is identified and classified according to 15 possible outcomes. To illustrate the method, indexes were computed from seven different coordination solutions reported in literature over the same test system. Results show interesting trade-offs among the three indexes, suitable to be presented as three independent axes; consequently, a given solution could be better in one feature (e.g., speed) but worse in others (e.g., selectivity and/or sensitivity). • There was no method to evaluate the quality of protection coordination solutions. • A novel and integral assessment of sensitivity, selectivity, and speed of solutions is shown. • The assessment is performed using an exhaustive analysis of possible fault locations. • Seven existing coordination solutions over the same case study are impartially assessed. • Conflicts among resulting sensitivity, selectivity and speed indexes are analyzed.