Impact of Interconnection Transformer Configuration on Operation of Inverter-Based DER

Abstract

DER interconnection transformers, especially their winding configurations can affect various aspects of system operations and protection. Among others, the selection of winding configuration can affect a DER plant’s response to faults and open phases including detection of events, coordination with other protection systems, levels of ground fault overvoltage and the potential for ferroresonance. Due to its significant impact, transformer winding configuration is a first order consideration. Therefore, the pros and cons of the commonly used transformer configurations need to be understood to inform selection considering application-specific system characteristics and needs. In this paper, four types of transformer winding configurations are evaluated. The studied winding configurations have been identified from a recent utility survey as the most used ones for three-phase inverter-based DER interconnections in the US. Some of the main concerns related to DER transformer configuration are addressed, including ground fault overvoltage, ferroresonance or overvoltage caused by open phase and open phase detection.