Reducing Microgrids Integration Complexity in Distribution Networks Considering Bidirectional Power Flow in SFCLs

In this paper, investigations are carried out to explore the application of the well-known unique bidirectional power flow nature of superconducting fault current limiters (SFCLs) to reduce the complexities of integrating microgrids into distribution networks. More specifically, their adverse impact on the coordination of existing protection of distribution networks, as well as the complexity of setting their internal protection to handle the change in fault current due different modes of operation. In this context, the capability of the proposed SFCL scheme is tested while demonstrating the tandem operation of the utility distribution network and microgrid protection systems and problems related to sensitivity and selectivity are addressed. In addition, different fault contingencies are considered, namely, faults located on the incoming main-lateral connecting the microgrid to the distribution network (where the fault is between the distribution substation protection and the microgrid) and on an adjacent main-lateral from the same main feeder (where the microgrid is located between the distribution substation protection and the fault). Moreover, other faults are located inside the microgrid on a local-line and at a local end-user. Results have shown the efficiency of the proposed SFCL scheme in reducing the short circuit contributions of both the microgrid and the utility network within the coordination limits depending on the direction of flow into the point of connection (PoC). Thus, it allowed a safe continuous integration of microgrids in distribution networks during faulted conditions, while, simultaneously permitted the microgrid to utilize a single protection setting to handle the changes in short circuit current levels when transitioning between grid-connected and islanded modes of operation. The time-domain simulation studies are conducted using PSCAD/EMTDC software.