PJM, Dominion Evaluate Large Load Rules After Record Data Center Disconnection

PJM Interconnection on Aug. 11 announced that it is evaluating changes to interconnection and ride-through requirements for large computational loads after nearly 4,000 megawatts of data center demand unexpectedly disconnected from the grid in Northern Virginia on July 22. The event marked the largest sudden transfer of large load in grid operator’s history and has prompted a joint review with Dominion Energy to examine how data centers and other computational facilities respond to system disturbances.

Dominion Energy’s preliminary investigation found that a mechanical failure removed a 230-kilovolt transmission line from service at 7:56 a.m., triggering an unexpected transfer of data center load to backup generation. An initial 2,970-megawatt load drop was followed by another 1,099 megawatts, resulting in about 3,800 megawatts of demand leaving the grid without warning. PJM’s total load fell from 99,984 megawatts to 96,205 megawatts.

The sudden imbalance caused significant swings in system voltage and frequency, although the grid did not experience major reliability impacts. PJM reduced generation, deployed reactive power resources and restored its operating balance within nine minutes, compared with the applicable 30-minute reliability requirement. Similar events in Dominion’s service area caused approximately 1,500-megawatt load transfers in February 2025 and July 2024, although neither reached the scale of the July event.

The incident highlights an emerging reliability challenge as rapidly growing data centers and cryptocurrency mining facilities increasingly rely on protection systems that can transfer operations to on-site generation during voltage or frequency disturbances. Such transfers can create sudden changes in grid demand and cause voltage and frequency to rise. PJM is considering the issue alongside earlier challenges involving wind and solar resources, which prompted voluntary ride-through guidelines for inverter-based generation in 2019.

The review also comes as federal regulators move toward mandatory requirements. On July 16, the Federal Energy Regulatory Commission directed the North American Electric Reliability Corporation to develop enforceable reliability standards and registration criteria for computational loads, with the first phase due by Dec. 31, 2026. Voltage and frequency ride-through requirements are expected to follow in 2027. PJM and Dominion will continue evaluating the July event, while the Planning Committee considers requirements that could be applied before new large-load facilities connect to the grid.