## 5 Simulation Analysis
### Defense Strategy Simulation  
According to the results of Sections 5.1 and 5.2, it is shown that the most likely fault locations are lines 9-12, 67-68, and 29-39. If no action is taken, the amount of loads loss will reach 294,320 kW, which will bring huge losses. In order to avoid the impact of the faults on the distribution network, the different strategies are adopted and simulated in this paper for comparison. Figures 9-11 are network structures of different defense strategies adopted before these lines fail. Among them, the red nodes represent loads blackout when the line fails, and the defense strategy cannot help them work normally. Yellow nodes indicate that if no strategy is taken, these nodes will also lose power, but the network topology can be changed through defense scheme to ensure the safe and stable operation of the loads. The blue line indicates that the tie line switch and BPS switch are closed.  
The network structures with only the load transfer strategy and only the islands strategy are shown in Figures 9 and 10:  
Figure 8: Three types of risk index of each distribution line after standardization.  
Figure 9: Network structure after transferring loads.  
As shown in Figure 9, the tie line switches ZL1 and ZL2 are closed, and segment switches Z9, Z29, Z55, and Z58 are opened at the same time. Yellow nodes represent loads that can be transferred. The red nodes represent loads that have not been transferred, and all of these loads will lose power.  
It can be seen from Figure 10 that Z1, Z2, and Z3 are closed, so island 1 consists of the BPS 1 and the loads of yellow nodes (9, 10, 11), island 2 consists of the BPS 2 and the loads of yellow nodes (55, 56, 58, 59, 61), island 3 consists of the BPS 3 and the loads of yellow nodes (62, 63, 65, 66, 67). The yellow nodes represent the loads that were incorporated into the island. Red nodes represent loads that have not been included in the island, which means all of these nodes will lose power once the line occurs faults.  
The network structure which CADS adopted is shown in Figure 11:  
It can be seen from Figure 11 that after closing ZL1, ZL2, Z2, Z3 and opening Z9, Z29, Z64, Z67. When the CADS is adopted, the tie line ZL1 is used to transform nodes 9, 10, and 11, the island is established by the BPS 3 and nodes 62, 63, 65, 66, 67. At the same time, the tie line ZL2 and the BPS 2 cooperate with each other, the DG that connected the ADN and tie line ZL2 are used to defend the risk area.  
Compare the results of the three defense strategies, as shown in Table 4.  
Figure 11: The network structure after CADS.  
Figure 10: Network structure after islands strategy.  
As shown in Table 4, the number of switch operations is the least when the load transfer strategy is adopted. However, the capacity of the tie-line ZL2 is limited, the loads are transferred to node 61 at most, so the load loss is much larger than the CADS. On the contrary, all nodes can avoid the danger of power failure except 64 if the CADS is used. When the island strategy is adopted, the number of switches operations is more than the load transfer strategy. Furthermore, because of the limited capacity of the BPS 2, there are so many red nodes that cannot be included in the islands in Figure 10. Similarly, the node 64 cannot be protected by the BPS 3, it makes it that the load loss is largest among three strategies.  
Through simulation analysis, the advantage of using this strategy is that load loss is minimized. Moreover, the maintenance department can use the ice melting device to melt ice on high-risk lines or use artificial de-icing teams to reduce the risk of these lines. Since the goal of active defense is to pursue the least amount of load loss under certain constraints, the method proposed in this paper is more reasonable in the natural disaster environment.