Effect of Micro-Grid Renewable Micro-sources on Short Circuit Capacity of Hosting Distribution Networks

Fault occurrence and protection against faults impede heavy penetration of distributed generation (DG) into distribution networks, particularly at medium and low voltage levels. This paper is aimed at assessing how the short circuit capacity (SCC) of hosted distribution network is influenced by the short circuit-current contributions from DG micro sources. A case study indicates that the micro sources have a significant effect on SCC of the hosted distribution grid. In absence of micro sources, the value of SCC is found equal to 157 MVA against 215 MVA when considering micro sources injected short-circuit currents. Thus, the SCC of the distribution network experiences 37% increase. Also, this paper calculated the SCC of distribution network including micro sources using three different method. The first method is the voltage source and impedance method. The second method is using IEC standard method. While the third method is an improved proposed method, which considered real conditions (prefault voltages and currents) of the investigated power system. Therefore, the protection system of the grid hosting micro-sources calls for different settings and already installed protection system should be updated to meet the new levels of short circuit currents.