In this paper, an improved smart meter data-based three-stage algorithm to calculate the power/energy losses in three-phase networks with the voltage level below 0.4 kV (low voltage-LV) is presented. In the first stage, the input data regarding the hourly active and reactive powers of the consumers and producers are introduced. The powers are loaded from the database of the smart metering system (SMS) for the consumers and producers integrated in this system or files containing the characteristic load profiles established by the Distribution Network Operator for the consumers, which have installed the conventional meters non-integrated in the SMS. In the second stage, a function, which is based on the work with the structure vectors, was implemented to easily identify the configuration of analysed networks. In the third stage, an improved version of a forward/backward sweep-based algorithm was proposed to quickly calculate the power/energy losses to three-phase LV distribution networks in a balanced and unbalanced regime. A real LV rural distribution network from a pilot zone belonging to a Distribution Network Operator from Romania was used to confirm the accuracy of the proposed algorithm. The comparison with the results obtained using the DigSilent PowerFactory Simulation Package certified the performance of the algorithm, with the mean absolute percentage error (MAPE) being 0.94%.Energies 2019, 12, 3008 2 of 27 with the help of information provided by smart meters from consumers and producers for improving the energy efficiency in LV distribution networks. The benefits of smart meters consist of the fact that, in addition to the metering function, they also provide a whole range of applications such as the following [6,7]:• Secure transmission of data to the consumers, the DNOs, or another operator (for example Metering Operator); • Bidirectional communication between the smart meters installed at consumer/producers and the data concentrators (information management points) belonging to the DNO; • Remote controlled connection/disconnection from the network or demand limitation at the consumers; • Implementing differentiated time-of-use tariffs.In these circumstances, the DNOs can obtain accurate online information regarding the energy consumptions and productions from the renewable sources, which allows them to calculate the energy losses and then to take some technical measures which will enable the low voltage networks to operate more energy efficiently and better plan their investments. For LV electrical networks, the information needed to calculate the power and energy losses is easily obtained if consumers are integrated into the SMS. In this context, the DNOs should use accurate methods and take into account all components (lines and transformers) in order to have a correct evaluation regarding the efficiency of their own LV distribution networks. Thus, an accurate analysis of the steady-state regimes corresponding the LV distribution network can be made through real-time monitoring using the smart mete...