In many countries the distribution system is rapidly approaching the critical point beyond that the passive operation is no longer feasible and economic. The active distribution network aims at enabling producers and consumers to play in the energy market. The strategic goal of active distribution is a low carbon, competitive, reliable and cost effective distribution system. The paper focuses on an Optimal Power Flow algorithm for the operation of active distribution network embedded in the centralized Distribution Management System model developed within the framework of the ATLANTIDE project. Preliminary studies on the application of this model are presented and discussed in the paper. (7 pages)