Abstract: A significant factor for property designing the protection scheme of a smart grid is the fault current contribution from the converter interfaced distributed energy resources. The fault current direction and magnitude is difficult to be defined, since the currents injected by the converters affect it considerably. The fault situation is even more complicated considering. The case of islanded looped micro-grids with conventional protection devices. In such micro-grids, all protection devices are settled to the same rated current. In order to overcome these issues, this paper proposes a new method for detecting and clearing faults, without utilizing and communication means. The fault identification process is carried out by measuring indirectly the micro grid impedance, while each converter adapts the internal control method and injects a fault current proportional to the sensed impedance. Therefore, the sources being closer to the fault inject relatively larger currents enabling the relative coordination of conventional protection devices. In order to enhance even more the relative coordination of the protection devices, a time delay is also incorporated in the fault control, the proposed strategy is validated a looped micro grid, protected by simple over current relays.

Keywords: Directional Over current, ETAP, LINKNET, Relay coordination.