Combined Medium Voltage and Low Voltage simulation to accurately determine the location of voltage problems in large grids

Distribution Network Operators (DNOs) traditionally treat Low Voltage (LV) and Medium Voltage (MV) networks as two separate entities. Both voltage levels have their own set of assumptions and design policies. This paper proposes a fast load flow algorithm suitable to simulate both the LV and MV network in a single simulation. The algorithm is applied to the grid of Alliander DNO. Using this method, congestion problems in both the LV and MV grid can be determined with greater detail. Using a case study it was shown that identical customer load scenarios produce vastly differently results if the MV network is taken into account. While the absolute number of voltage problems was in the same order of magnitude, the location of these problems overlapped only 20\%. The lack of overlap has a severe implication, namely that searching for congestion by only simulating LV networks yields the wrong voltage problems. This conclusion calls for network design using integral MV/LV simulations.