Deconstructing Direct Transfer Trip: A Comprehensive Assessment of DER Islanding Risks, Safety Concerns, and Mitigations

As the adoption of inverter distributed energy resources (DERs) like solar and energy storage systems accelerates, utility concerns regarding unintentional islands (UIs)-which occur when a segment of the electric grid remains energized by a DER for a period after being electrically isolated from the rest of the grid-have led to the development of several grid protection strategies to mitigate risks and maintain system safety and reliability. One such strategy that has commonly been deployed is direct transfer trip.

This study evaluates the various utility justifications for requiring DTT, analyzes the risk of UI, critiques existing utility screening practices, and outlines a suite of alternative grid protection strategies that can effectively address grid safety and reliability concerns for inverter DERs.