PJM Interconnection is considering new requirements for data centers and other large computational loads to remain connected during grid disturbances after nearly 3,800 megawatts of Northern Virginia data center demand was transferred to onsite generation last month.. The July 22 event demonstrated that large data centers are becoming an active variable in bulk-system operations, not simply another source of electricity demand for grid planners to forecast..
“A nearly 3.8 GW transfer from grid supply to onsite generation following a transmission disturbance is large enough that planners should be asking not only, ‘How much load is connected?’ but also, ‘How will that load behave when the system is disturbed?’” said Neil Osnato, founder of Persistence Analytics Group.. The event occurred after a mechanical failure caused a 230-kilovolt transmission line in Northern Virginia to automatically come out of service.
The fault was properly cleared, according to PJM, but data centers in the Dominion zone subsequently transferred from the grid to onsite generation.. Related:House Bill Would Put Federal Electricity Tax on Data Centers. About 2,970 MW of load was transferred in the first wave, followed by another 1,099 MW as the system voltage increased..
The sudden reduction in demand forced PJM operators to quickly cut generation and deploy reactive power resources as voltage and frequency rose. PJM restored its balancing-authority-area control error within nine minutes, well inside the 30-minute NERC requirement.. The grid remained reliable, but the event was the largest sudden large-load transfer PJM has experienced..
“A large load can therefore create reliability consequences both when it arrives and when it suddenly leaves,” Osnato said.. Large Loads Become a Reliability Variable. The event highlights a growing reliability challenge as data centers account for an increasing share of electricity demand..
Data centers use sophisticated protection and control systems to safeguard sensitive computing equipment against voltage and frequency fluctuations. Those systems can transfer a facility to onsite generation when they detect conditions that could threaten equipment.. For an individual facility, that can be an appropriate protective response.
However, across several gigawatts of load, simultaneous transfers can create a system-level event.. PJM is now examining whether large computational loads need ride-through requirements similar in concept to requirements imposed on generation resources.. With inverter-based generation, reliability standards evolved in response to the risk that large amounts of generation could disconnect simultaneously during voltage or frequency disturbances..
Related:Why Data Center Development Is Facing a Legal Reckoning. The emerging computational-load problem is the inverse: Large amounts of demand can suddenly disappear from the grid, be transferred behind the meter, or materially change their consumption in response to the same disturbance..
“The core reliability principle is similar,” Osnato said. “A normally cleared grid disturbance should not automatically trigger a second, much larger system disturbance because thousands of megawatts of resources or load react in the same direction.”. PJM Operating Committee Chair Emanuel Bernabeu made a similar point during an August 6 committee meeting, saying the data centers involved in the July event “should not disconnect from the grid.”.
The July event was not the first such incident in Dominion’s territory.. PJM said similar events resulted in approximately 1,500 MW of load transfers in July 2024 and February 2025.. The latest event was more than twice the size of either of the previous events..
PJM Is Considering Ride-Through Requirements. PJM and Dominion are reviewing the July 22 event and considering enhancements to reliability requirements for existing and future large loads.. “We are currently evaluating potential enhancements to reliability requirements, with consideration of existing and future industry ride-through standards and practices,” Matthew Wharton, PJM’s manager of reliability engineering, said..
Related:Ofgem Fee Aims to Clear Grid Queue – Who Benefits?. PJM said the work will proceed through its stakeholder process, including the Planning Committee.. The potential requirements could go beyond a simple voltage or frequency threshold..
Osnato said large-load requirements should address voltage and frequency ride-through, protection coordination, the behavior of onsite generation and storage during a grid disturbance, and how facilities reconnect to the grid.. Telemetry and event recording will also be important, he said, because PJM needs visibility into how large facilities respond to disturbances..
The goal would be to prevent a facility’s protection system from responding to a normally cleared transmission event in a way that creates a much larger disturbance for the bulk power system.. Federal Rules Are Also Taking Shape. PJM’s review comes as federal regulators are developing reliability requirements specifically for computational loads..
In July, the Federal Energy Regulatory Commission directed the North American Electric Reliability Corporation to develop reliability standards addressing the integration of large computational loads into the bulk power system.. PJM does not necessarily have to wait for those national standards before addressing the operating characteristics of large loads on its system..
Osnato said PJM can address issues including connection and service requirements, protection-setting disclosure, dynamic load models, event telemetry, disturbance reporting, operating protocols and transfer-to-onsite-generation behavior through its existing planning and interconnection processes.. “NERC should eventually establish the common reliability floor,” Osnato said.
“PJM may need requirements above that floor where the characteristics and concentration of its large-load fleet warrant them.”. That could become particularly important for new data centers, where ride-through, telemetry, modeling and protection requirements can be incorporated before a facility is energized..
Existing facilities pose a harder problem because their protection systems and contractual arrangements are already in place.. But Osnato said the reliability implications cannot simply be eliminated by grandfathering existing facilities.. “If an existing site can change grid demand by hundreds of megawatts in seconds, grandfathering that behavior indefinitely does not eliminate the reliability consequence,” he said..
He suggested a risk-based approach beginning with facilities whose size, location and disturbance response could materially affect bulk-power-system reliability.. The 1 GW Data Center Is No Longer Just 1 GW. The July event also complicates how planners evaluate the enormous data center pipeline developing across PJM..
A facility’s nameplate demand does not necessarily describe its behavior under all operating conditions.. Osnato said planners increasingly need to understand the sequence from routine grid import through disturbance response, onsite transfer, restoration and reconnection.. “We have spent much of the large-load debate asking whether projected data-center demand will actually materialize,” he said.
“This event adds another dimension: even once the facility is real and energized, planners need to know how much load remains electrically dependent on the grid under different operating conditions.”. That means planners may need to distinguish between gross facility demand, routine grid imports, maximum grid imports, disturbance-response load, emergency grid dependency and flexible or curtailable load..
“The headline ‘1 GW data center’ is becoming increasingly inadequate,” Osnato said.. The July 22 event provides a concrete example of why.. PJM needs to know not only how much demand will connect to its system, but what that demand will do when the system is disturbed..
For data center developers, that could make protection settings, ride-through capability, telemetry and transfer behavior part of the technical requirements for operating large computational facilities on the PJM system.
