Dtt Under Light-Load Conditions

When the generation capacity of a DER approaches or exceeds local load, the risk of unintentional islanding increases significantly. In such scenarios, customer-owned generation may continue to energize portions of the grid without Dominion Energy’s control over voltage and frequency. This could potentially lead to sustained faults, overvoltage conditions, and unsafe working environments for field personnel. These risks are compounded by the dynamic nature of load profiles, especially in distribution systems where real-time load visibility is limited.

As part of maintaining a safe and reliable electric grid, Dominion Energy requires the implementation of Direct Transfer Trip (DTT) protection when a Distributed Energy Resource (DER) interconnection results in a load-to-generation ratio of less than three to one (3:1). This threshold is a conservative engineering standard designed to mitigate the risks associated with high DER penetration, particularly in areas where minimum load data is highly variable.

To address these challenges, Direct Transfer Trip (DTT) is deployed using fiber-based communication between protection relays, enabling rapid and reliable disconnection of DERs during fault conditions. This ensures effective fault isolation and prevents DERs from contributing to abnormal grid conditions. The three to one (3:1) ratio serves as a practical safeguard, aligning with industry best practices and providing a buffer against uncertainties in load behavior.

By enforcing this requirement, Dominion Energy reinforces its commitment to grid stability, operational safety, and the seamless integration of renewable energy and energy storage systems.