This paper presents the Dynamic Voltage Restorer (DVR) response study in cases of voltage sags occurrence in the electrical distribution networks with connection substation topology. Usually, these voltage disturbances are caused by faults that can occur on the lines connected to the same bus bar as the main feeder or even on main feeder of connection substation. A DVR that uses a diode based rectifier as a DC voltage source, supplied by the back-up feeder of connection substation, has been modeled in Matlab/Simulink. Severe faults on the lines adjacent to main feeder and back-up feeder and also faults on main feeder, with real impact for the magnitude of voltage supplied to end-users connected to the electrical network downstream of the connection substation bus bars, have been simulated. The DVR response has been studied for these fault conditions. The obtained results prove the effectiveness of the chosen topology of this series Custom Power device for voltage magnitude disturbances mitigation in distribution networks.