Impact of a microgrid on utility grid under symmetrical and unsymmetrical fault conditions

Microgrid is becoming one of the popular architectures for accommodation of distributed energy sources into conventional distribution network. A microgrid structure consists of various renewable energy sources which includes non linear solid state devices for interfacing. Presence of non-linear components in distribution network may change the behavior of main utility grid both under steady and transient state of operation. This paper investigates the transient behavior of a utility grid connected with a microgrid under symmetrical and unsymmetrical fault conditions. The system under study consists of a microgrid fed from solar PV and wind turbine generator (WTG) based energy sources. Microgrid is connected to main grid which maintains a constant voltage and frequency at point of common coupling (PCC). Effect of presence of microgrid under occurrence of symmetrical and unsymmetrical faults at point of common coupling have been analyzed and presented through voltage drop and magnitude of fault current at point of common coupling (PCC). Results are indicative that the fault current levels changes with microgrid interface and hence the protection scheme needs to be designed accordingly. The simulations are carried out with PSCAD. The results are demonstrated on 300 MVA, 34.5 kV, 50 Hz radial distribution network.