Detecting the Origin of the Voltage Sags Measured in the Smart Grids

Two different hybrid methods (HM) were considered and compared in distribution systems with distributed generation (DG) units for ascertaining the systems where measured voltage sags originated. These methods, namely M1 and M2, use only the measured voltage during the fault at the medium voltage (MV) busbars of the high voltage/medium voltage (HVIMV) substations. Two main aspects, typical of distribution systems with DG, were considered: the presence of on load tap changer (OLTC) of the HVIMV transformers and the action of the DG units in support of the local voltage. The methods M1 and M2 were applied and compared on a part of a real HVIMV system. We used time-domain simulations, and forced short circuits in several nodes of the system. In such conditions, in which the origin of the voltage sags was known, we were able to appreciate the reliability of the methods.