## 3 Preliminary Work
### Algorithm to Calculate Mileage Matrix

Table 6: Positions and rated power of added generators. Figure 11: Comparison of the voltage profiles for every node in the IEEE 123-bus system. Figure 10: The resulting two power grids of the IEEE 123-bus case generated by the network optimization algorithm. ## 6 Conclusions

In this paper, the problem of adding transmission lines is first discussed. Unlike a well-designed power grid in a big city, power grids in remote areas always include large power stations that supply the demand of local loads. However, with the development of REs and national poverty alleviation programs, these areas usually have a large number of RESs. Without good planning, voltage overshoot and bad voltage quality become the norm. It is difficult to use traditional methods to overcome such problems due to the large amount of energy being managed. However, adding transmission lines is a promising method. In our study, a network optimization algorithm is proposed to present a guideline for adding transmission lines. In this process, the sub-graph that is far from the national grid and imbalanced between the power supply and demand is separated and connected to the national grid directly. To measure the quality of a network partition and facilitate the calculation, the power mileage value is deduced from the voltage drop equation. It has a linear relationship with the power flow and can indicate the voltage quality of a power grid. Then, an iterative algorithm is proposed to perform the network optimization. The algorithm can automatically choose the number of sub-graphs, and the effectiveness of the terminal conditions were verified by several case studies. We evaluated the algorithm using a real grid with 17 nodes and the IEEE 123-bus grid. Our results show a great improvement in the voltage profile for both cases and proves the utility of the power mileage value. Conceptualization, C.W. and M.C. ; methodology, C.W. and Q.L. ; software, C.W. ; validation, C.W. and Q.L. ; formal analysis, C.W. and Q.L. ; investigation, C.W. and W.K. ; resources, C.W. and W.K. ; data curation, H.L. ; writing--original draft preparation, C.W. ; writing--review and editing, Q.L. ; visualization, Q.L. ; supervision, M.C. ; project administration, M.C. ; funding acquisition, M.C. This research was funded by The Science and Technology Project of State Grid Zhejiang Electric Power Company under grant number 5211W4180001. The authors declare no conflict of interest. ## References

* [PERSON] and [PERSON] (2015) [PERSON]; [PERSON] A Novel Bus-Aggregation-Based Structure-Preserving Power System Equivalent. _IEEE Trans. Power Syst._**2015**, _30_, 1977-1986. [CrossRef]
* [PERSON] et al. (2014) [PERSON]; [PERSON]; [PERSON] Does a detailed model of the electricity grid matter? estimating the impacts of the regional greenhouse gas initiative. _Resource Energy Econom._**2014**, _36_, 191-207. [CrossRef]
* [PERSON] et al. (2013) [PERSON]; [PERSON]; [PERSON]; [PERSON] A novel hybrid algorithm for reconfiguration problem of the distribution networks. In Proceedings of the 22 nd International Conference and Exhibition on Electricity Distribution, Stockholm, Sweden, 10-13 June 2013; pp. 1-4. [CrossRef]
* [PERSON] et al. (2018) [PERSON]; [PERSON] [PERSON]; [PERSON]; [PERSON] [PERSON]; [PERSON] [PERSON] Study on Dynamic Reconfiguration of Active Distribution Network Considering Intermittent DG. _Zhejiang Electric Power_**2018**, _37_, 70-78. * [PERSON] et al. (2017) [PERSON]; [PERSON]; [PERSON]; [PERSON] Reconfiguration of smart distribution network considering variation of load and local renewable generation. In Proceedings of the 2017 IEEE International Conference on Environment and Electrical Engineering and 2017 IEEE Industrial and Commercial Power Systems Europe (EEEIC / I&CPS Europe), Milan, Italy, 6-9 June 2017; pp. 1-5. [CrossRef]
* [PERSON] et al. (2015) [PERSON]; [PERSON]; [PERSON] Multi-objective reconfiguration of distribution network with wind power generators considering network survivability. _Power Syst. Prot. Control_**2015**, _43_, 57-62.