4.2.3. Discussion of the Meshed Network Results

In this section, the performance of proposed NSTCC and approaches from the literature (STCC and NSTCC with constant coefficient A) on the IEEE 9- and 30-bus meshed networks are presented. The overall OTs for operation modes are shown in Figure 15 and were obtained by using the hybrid GSA–SQP algorithm. The previous subsections show that the NSTCC approach reduced the overall OT of OCRs for all modes compared to approaches from the literature. For example, the NSTCC reduced the overall OT in the meshed 30-bus test system by 54.4% and 37.9% compared to the literature approaches STCC and NSTCC with constant coefficient A, respectively.

**Figure 15.** The overall OT in NSTCC with constant coefficient A, STCC by Radosavljevi´c et al., 2016 [8], and NSTCC for the meshed 9- and 30-bus MGs.

#### **5. Conclusions**

An approach for the optimal coordination of OCRs in MGs that integrate DGs has been presented in this article. The approach has been successful in sustaining constant CTI between the primary and backup relay pairs and offering lower tripping times than the recent NSS introduced in the literature for different fault currents. The proposed NSTCC applies to long radial feeders and large meshed grids. The NSTCC is implementable when there is sufficient variance in the maximum and minimum fault currents. The GA algorithm was applied with several tests in radial networks, including the IEEE 9-bus test system and benchmark IEC MG that both integrate DGs under various operational modes. In all operational modes (grid-connected and islanding mode), better total operational times have been obtained by the proposed approach. Additionally, the hybrid GSA– SQP algorithm was carried out based on the proposed scheme in the 9- and 30-bus IEEE standard meshed power system to solve the OCR coordination optimization problem. This illustrates the superiority of the NSTCC in reducing operational time in meshed networks; hence, it is effective in both radial structures and meshed systems. These results broaden our understanding of the concept of using nonstandard curves in industrial relays to obtain optimal, flexible, and reliable outcomes. Regardless, future research could continue to explore the extent of applicability this proposed scheme has in the coordination of overcurrent relays with distance relays in radial networks. In addition, applying the proposed approach to hardware in the loop to confirm its reliability is possible.

**Author Contributions:** Conceptualization, S.A. and Y.H.; methodology, S.A. and Y.H.; software S.A. and Y.H.; validation, F.A., N.E.-N. and S.A.; formal analysis, F.A., N.E.-N. and S.A.; investigation, S.A. and Y.H.; resources, all authors; data curation, all authors; writing—original draft preparation, F.A., N.E.-N. and S.A.; writing—review and editing, all authors; visualization, all authors; supervision, all authors; project administration, S.A. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Data Availability Statement:** Not available.

**Conflicts of Interest:** The authors declare no conflict of interest.
