# Optimization of Active Distribution Network Operation with SOP Considering Reverse Power Flow
## 3 Actual Maximum Transfer Capacity of Reverse Power Flow in the Distribution Network
### Case Analysis  
To verify that the reverse power flow transmission capacity is insufficient in the DG high-penetration distribution networks, and by operating multiple distribution networks jointly through the SOP, the reverse power flow transmission capacity can be increased to reduce wind and solar curtailment, thus improving the operational efficiency of distribution networks. The following optimization scheme is established:  
1. Distribution networks A, B, and C operate independently.
2. Distribution networks A and B operate jointly through a dual-port SOP.
3. Distribution networks A, B, and C operate jointly through a tri-port SOP.
4. Serves as the original scheme. It examines the distribution network under varying operational characteristics such as the DG output, load demand, and topology. It analyzes the actions of the OLTC and CB, as well as wind and solar curtailment and network losses during independent operation. This serves as a reference for subsequent Scenarios (2 and 3) which involve the combined operation of two distribution networks. However, they differ in operational characteristics to explore optimization effects after interconnection. Scenario 4 involves three distribution networks operating jointly, allowing the exploration of how the number of interconnected distribution networks impacts optimization results. Specifically, it assesses whether more interconnected networks lead to improved optimization outcomes.  
Figure 12: The load and DG output conditions of distribution networks A, B, and C, and (**a–c**) respectively represent distribution networks A, B, and C.  
Comparing the operation of distribution networks A, B, and C, one can observe distinct DG placements. While network A's DG lies closest to the OLTC and network B's DG is  
Figure 14: Scenario 1 presents the operational results of distribution network B, **(a)** as the operational status of the OLTC, **(b)** as the curtailment of wind and solar, **(c)** as the CB action status, and **(d)** as operational costs. The phenomenon of wind and solar curtailment is less prominent in distribution network B due to smaller reverse power flows. Consequently, operational costs primarily depend on network losses. When reverse power flow is minimal, OLTC tap positions can be lowered. Although this may increase the operation costs of the OLTC and CB, it elevates voltage in subsequent lines, thereby reducing overall active power losses.  
Figure 15: Scenario 1 presents the operational results of distribution network C, **(a)** as the operational status of the OLTC, **(b)** as the curtailment of wind and solar, **(c)** as the CB action status, and **(d)** as operational costs. In distribution network C, due to the minimal reverse power flow, there is almost no curtailment of wind or solar energy.  
further, all three networks show a similar active per unit value of maximal reverse power flow transfer capacity, approximately 0.37. Furthermore, permissible reverse power flow capacity varies directly with the tap changer ratio; a larger ratio increases capacity yet demands more reactive power compensation. Even at maximum tap ratio, reverse flow capacity remains below 50% of the OLTC's rated capacity, significantly lower than the 80% target set in the design phase.