Deconstructing Direct Transfer Trip: A Comprehensive Assessment of DER Islanding Risks, Safety Concerns, and Mitigations
This study evaluates the various utility justifications for requiring direct transfer trip (DTT) and outlines a suite of alternative grid protection strategies that can effectively address grid safety and reliability concerns for inverter DERs.
(Updated December 2025)
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.
Webinar
Hear key findings from the study’s authors as they highlight how state regulators and utilities can adopt a modern and risk-informed approach to UI mitigation that ensures safe grid operations while accelerating the clean energy transition. Watch the webinar on-demand below.
