A new coordination scheme of directional overcurrent and distance protection relays considering time-voltage-current characteristics

The power transmission systems are mainly protected by distance relays (DisRs) as a primary protection and directional overcurrent relays (DOCRs) as a backup protection. These two types of relays have a different operation principle that, sometimes, leads to miscoordination problems. In this paper, a new approach for DOCRs and DisRs coordination considering the DOCRs time-voltage-current characteristic (TVC-C) is proposed to fully eliminate the miscoordination problems found in the already published works. The coordination problem is formulated as a mixed-integer nonlinear programming (MINLP) considering a new proposed objective function. Furthermore, two new decision variables related to TVC-Cs are proposed namely: the type and the voltage control variable. An enhanced version of the hybrid GSA-SQP method is proposed to solve the developed opti-mization problem. In order to check the applicability of the proposed relays coordination method on small and large and more complex systems, the IEEE 9-bus and IEEE 39-bus are used for this task. The obtained results are compared with the published works which show the superiority of the proposed method in terms of satisfaction of all coordination constraints.