In this paper a new approach for a three-phase Distribution System State Estimator (DSSE) is presented. It utilizes the most types of analog real time measurements (including voltage and current magnitude, active and reactive power measurements). The correct utilization is supported by topology analysis and creation of measurement areas. Loads are modeled based on historical or AMR information. The estimation problem is solved by weighted least squares error method. Applying traditional state estimation on distribution networks, by using load data as pseudo measurement, causes state estimation formulations that have very large size. Approach presented in this paper is based on network reduction which reduces size of the problem. The approach is very fast and provides feasible results.