Dual-setting directional over-current relays: An optimal coordination in multiple source meshed distribution networks

To guarantee a safe operating scheme against the probable faults, an accurate and fast relaying scheme is of high priority. This challenge seems to be more sophisticated in multiple source meshed distribution networks hosting distributed generations (DGs). In this case, the current experiences bidirectional flows. More recently, dual-setting over-current relays are evolved as competent countermeasures for such cases. In this way, establishing an optimal coordination strategy is recognized as the first prerequisite in assuring a safe protection scheme. To this end, the present study aims at minimizing the overall operating time of primary and backup relays. Typically, the coordination problem is carried out by adjusting two parameters namely, pick up current (Ip) and time dial setting (TDS). In contradiction, the proposed approach follows a user-defined settings supported by some operating rules. Thus, besides the aforementioned settings, the coefficients of the inverse-time characteristics are also optimized. In other words, more flexibility is attained in adjusting relay's characteristic in regard of the network's loading and topological changes. Furthermore, inclusion of operating rules in main objectives, not only reduces the sum of operating time of all relays, but also increases the efficiency of backup relays regarding the break points in meshed networks. In other words, the covering zone by each backup relay is increased. The proposed approach demonstrates a non-linear programming fashion which is tackled based on genetic algorithm (GA). Several numerical studies are carried out to interrogate the validity of the proposed approach encountering different fault scenarios. The obtained results are encouraging.