Protection coordination of an inverter generation based microgrid for an unbalanced distribution system

Abstract

In this paper we examine the protection issues that must be dealt with, to successfully operate a microgrid when the utility experiences a grid outage. Changes in fault current levels within microgrids under grid-tied and islanded conditions present challenges to developing robust and reliable protection schemes. These schemes must provide an effective response in both gridconnected and islanded mode and the transition between these modes. In this study, a section of an actual residential community located in the western part of the United States (U.S.) was considered as part of the microgrid evaluation. A sizing analysis was conducted to select the appropriate sizes of DER; simulated using DER-CAM analysis. The two DERs considered for the study included solar PV and Battery Energy Storage System (BESS). This paper highlights the protection coordination issues when an existing unbalanced distribution system encompassing a residential subdivision is converted into a microgrid with generation sources with low fault contribution. It further explains the strategy to coordinate protection devices during grid connected and islanded microgrid operating regimes.