H. Shad - Department of Electrical Engineering, College of Electrical Engineering and Computer,‎ Saveh Branch, Islamic Azad University, Saveh, Iran
M. Gandomkar - Department of Electrical Engineering, College of Electrical Engineering and Computer,‎ Saveh Branch, Islamic Azad University, Saveh, Iran
J. Nikoukar - Department of Electrical Engineering, College of Electrical Engineering and Computer,‎ Saveh Branch, Islamic Azad University, Saveh, Iran

To assure the security and optimal protection coordination in meshed distribution networks, clearing faults swiftly and selectively is an essential priority. This priority, when hosting distributed generations (DGs), becomes the main challenge in order to avoid the unintentional DGs tripping. To overcome the mentioned challenge, this paper establishes a truth table to select new settings of directional overcurrent relays (DOCRs) characteristics which can be defined by users. It concentrates on minimizing the overall relays operating time. Typically, the conventional coordination between pair relays is achieved by two settings: time dial setting (TDS) and pickup current (Ip). Besides these adjustments, the suggested approach, considered the two coefficient constant of the inverse-time characteristics, namely the relay characteristics (A) and the inverse-time type (B), as continuous to optimize. Thus, more flexibility is attained in adjusting relays features. In addition, the inclusion of user-defined settings on numerical DOCRs, not only decreases the overall operating time of relays, but also improves the performance of the backup relays against the fault points. This approach illustrates a constrained non-linear programming model tackled by the combined particle swarm optimization (PSO) and whale optimization algorithm (WOA). The efficiency of the suggested approach is assessed though the IEEE ۸-bus and the distribution portion of IEEE ۳۰-bus system with synchronous-based DG units. The obtained results demonstrate the performance of approach and will be discussed in depth.

Protection Coordination, Numerical DOCRs, Meshed Distribution Networks, synchronous-based DG, Combined PSO-‎WOA.‎