A Protective Relaying Scheme for a Microgrid with High Penetration of PV Systems

Currently, most of the PV systems installed in Europe are required to fulfill the DIN VDE 0126-1-1 standard that requires the PV systems to drop out from the grid within 0.2 seconds when the voltage decreases below 0.8 p.u. However, with the rising number of integrated PV systems, a sudden disconnection of a large amount of PV systems may inversely affect the stability of the grid and also prevent the formation of islanded microgrid. Hence either the existing network protection system or the current PV protection system shall be revised. The paper develops a new protection scheme that can deal with these issues. This scheme considers the coordination of the protective devices in both medium-voltage and low-voltage networks in such way that can support the PV systems in riding through external faults. The effectiveness of the protection system is demonstrated via the application for protecting a typical urban medium-voltage network containing a low-voltage microgid by using Matlab/Simulink.