The flexibility and controllability of the distribution network is only possible if control centre tools and control engineers have a more accurate representation of the grid in real-time. Therefore, one of the main objectives of new Distribution Management Systems (DMS) is to enhance the observability of MV networks in order to run new automation functions such as Volt and Var control or network reconfiguration. To do so, Distribution State Estimation (DSE) functions can be used in order to assess voltage profiles near to real-time with a minimal number of sensors. However, applying classical DSE to distribution networks leads to ill conditioned problems and long computation times due to the size and the characteristics of these networks. Therefore, this article presents a method which helps overcome these issues. It is based on a scalable zonal approach which leads to accurate state estimation results while decreasing computation times.