Fault detection system to trigger the microgrid disconnection procedures

The microgrid disconnection from the main grid can be driven by a fault in the main grid that occurs close to the microgrid. Typical protective devices based on overcurrent are not suitable since they could fail in detect this fault due to the low short circuit capability of the sources in the microgrid. Thus, a fault detection system based on voltage, instead of current, is proposed in this paper. The voltage-based detector by itself is not suitable because it cannot distinguish if the fault is inside or outside the microgrid. Therefore, the proposed fault detector also has a directional element based on the impedance at the microgrid connection point. Such impedance is estimated through the three-phase voltages and currents using space vector approach which results in a very fast response time. As a result, the proposed fault detector can act quickly for faults outside the microgrid and its actuation is intentionally delayed when the faults are inside the microgrid. Simulations results are presented to demonstrate the feasibility of the proposed scheme.