Optimal Feeder Routing in Urban Distribution Networks Planning with Layout Constraints and Losses

We address the problem of optimally re-routing the feeders of urban distribution network in Milano, Italy, which presents some peculiarities and significant design challenges. Milano has two separate medium-voltage (MV) distribution networks, previously operated by two different utilities, which grew up independently and incoordinately. This results in a system layout which is inefficient, redundant, and difficult to manage due to different operating procedures. The current utility UNARETI, which is in charge of the overall distribution system, aims at optimally integrating the two MV distribution networks and moving to a new specific layout that offers advantages from the perspectives of reliability and flexibility. We present a mixed-integer programming (MIP) approach for the design of a new network configuration satisfying the so-called 2-step ladder layout required by the planner. The model accounts for the main electrical constraints such as power flow equations, thermal limits of high-voltage (HV)/MV substation transformers, line thermal limits, and the maximum number of customers per feeder. Real power losses are taken into account via a quadratic formulation and a piecewise linear approximation. Computational tests on a small-scale system and on a part of the Milano distribution network are reported.