*4.2. Meshed Networks*

In this section, IEEE 9- and 30-bus meshed networks have been implemented to evaluate the proposed NSTCC approach. Figure 12 shows the flowchart for the implementation of NSTCC in radial networks. Afterwards, the short-circuit calculations in various modes and locations were performed. The MATLAB software is used to implement the proposed equation with the constant coefficient 5.8 and with the variable coefficient A for obtaining the short-circuit calculations. The optimal setting, TMS, the coefficient A, and Ip for OCRs have been obtained by using the MATLAB software and applying the hybrid GSA–SQP algorithm for the NSTCC approach. Finally, the NSTCC with a constant coefficient 5.8 and a variable constant A has been compared with the STCC to show the effectiveness of the proposed approach in terms of reducing the OT considerably and ensuring the CTI selectivity.

The main steps of using the hybrid GSA–SQP by applying it in the MATLAB software can be shown as follows:


**Figure 12.** Meshed Networks Flowchart of the Proposed NSTCC.

**Figure 13.** IEEE 9-Bus MG system, meshed network.

4.2.1. Description of the Meshed 9-Bus Test Systems under Study

For solving the OCR coordination problem, the NSTCC is applied to this 9-bus test system by using the hybrid GSA–SQP algorithm. This grid consists of 12 lines and 24 OCRs, and every line has two relays at both ends as illustrated in Figure 13. The power is received via bus 1, which is represented by a source of 100 MVA, 33 KV and more details about this grid are given in [48]. Twelve fault points have been considered, indicated from A to L (one on each line) as shown in Figure 13. For these fault points, Table 9 shows the primary–backup relationship of relays and the CTI is taken at a minimum of 0.2 s. In case of fault at different points, the short-circuit analysis has been conducted to find the current seen by the relays.


**Table 9.** CTI for the Meshed 9-bus Test System.

The optimized TMS and Ip values and OTs based on a hybrid GSA–SQP algorithm are compared with obtained results in ref. [8]. The NSTCC reduces the overall operational time of primary OCRs to 1.869 s compared to the results that are illustrated in Table 10. The coefficient A's optimized value is selected to be approximately 6.25 by MATLAB software operations in this case to obtain the lowest OT. The corresponding values of CTI are shown in the Table 9. The optimum results ensure the coordination between primary and backup relays. Further, the CTI is improved by using the NSTCC approach; the sum of CTI values equals 7.392, which is reduced compared with the sum of CTI values in ref. [8], which equals 8.892. The NSTCC scheme results in the best settings.
