## 4 Overcurrent Protection Coordination Results, Analysis and Discussion
### Protection Coordination Results in Scenario 4  
Scenario 4 is a distribution network topology of the third FISR plan after the 3 ph-G fault at Bus 2 is cleared. As referred to the two dashed lines (c) and (d) in Figure 10, the REC Hao-Vo recloser is opened to isolate the fault at Bus 2. The LBS Can-Thanh 97 is then closed to restore the power of interrupted customers while the REC Can-Thanh-Hao-Vo recloser and the CB GEN circuit breaker are closed to allow the interlinking operation of both the feeder supplied by the 110/22 kV An-Nghia power substation and the other feeder supplied by the DG sources. The optimal protection coordination results of the OCRs in Scenario 4 which are calculated by the GA, GSA and hybrid PSO-GSA are indicated in Table 7. In this table, \(I_{f}\) is the tripping-current threshold selected for the 50P and 50G functions of the OCRs including the REC Can-Thanh 36 OCR, the REC Can-Thanh-Hao-Vo OCR, the CB GEN OCR and the REC Can-Thanh 163 OCR. \(t_{trip}^{defined}\) is the pre-defined tripping time of the 50P and 50G functions of these OCRs. Moreover, the TDS multiplier and \(A\), \(B\), and \(C\) coefficients of the 51P and 51G OC functions of the above OCRs are shown in the table. The CTI is still selected to 0.30-0.35 s. It is worth noting that the parameter settings of the REC Can-Thanh 163 OCR must be simultaneously updated to be adaptable to Scenario 4 instead of Scenario 1, Scenario 2, or Scenario 3. To validate the optimal setting parameters obtained by the ASPC system for the above OCRs, a 3 ph-G fault is given at Bus 3. The REC Can-Thanh 163 OCR operates as the primary protection to detect and clear this fault while the CB GEN OCR operates as the backup protection on the feeder supplied by the DG sources and the REC Can-Thanh 36 OCR and the REC Can-Thanh-Hao-Vo OCR are the backup relays on the other feeder supplied by the 110/22 kV An-Nghia power substation. Their tripping time \(t_{trip}\) to clear the 3 ph-G fault at Bus 3 are also indicated in Table 7. The achieved results have demonstrated that the CTI constraints from Equations (3)-(5) are completely satisfied. Figure 13 shows the optimal protection characteristic curves of the OC relays in Scenario 4 of the real 22 kV DG-contained DN. Regarding the obtained coordination results of 51P/G and 50P/G functions, Relay 1 represents the OC protection function embedded into the REC Can-Thanh 163 recloser; Relay 2 represents the OC protection function integrated into the REC Can Thanh-Hao Vo recloser; and Relay 3 indicates the OC protection function used to control the REC Can-Thanh 36 OCR recloser. When the 3 ph-G fault occurs at Bus 3, the maximum 3 ph-G fault current is 2.9 kA as indicated in Table 3, so the primary operation time of the REC Can-Thanh 163 OCR is 0.01 s. The backup operation times of the REC Can-Thanh Hao-Vo OCR and the REC Can-Thanh 36 OCR are about 0.31-0.33 s and 0.63-0.65 s, respectively, according to results of three different algorithms as seen in the table and Figure 13. The backup operation time of the CB GEN OCR is about 0.35 s. Additionally,\(I_{trip}\) represents the tripping-current threshold of 50P/G