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Data centers received plaudits in recent winter storm Fern both for their ability to provide backup power and for voluntary ramp-downs.

Greater industry concern is being given to the effect of large loads like data centers when they unexpectedly trip off-line and ramp up again.

“Some of the plants that were 202(c) were running during Fern,” Alex Fitzsimmons, acting undersecretary of the U.S. Department of Energy, said at a conference this month.

Section 202 (c) of the Federal Power Act gives the department the ability to change operations on the U.S. electricity system on a temporary basis, intended for emergencies.

Fitzsimmons told the winter policy summit of the National Association of Regulatory Utility Commissioners in Washington that several balancing authorities and reliability coordinators requested 202(c) during Fern, but none were necessary.

He added that there is 35 GW of backup power at data centers. In late January before the storm, U.S. Energy Secretary Chris Wright asked many of the nation’s grid operators to prepare to use backup power at data centers and other major facilities.

The department said it received five requests and issued five orders in Texas, the Mid-Atlantic, the Carolinas, and Florida to leverage backup power.

The Electric Reliability Council of Texas (ERCOT) was one operator that requested that DOE issue a 202(c) order to allow the deployment of backup generation.

ERCOT Chairman Bill Flores said immediately after the storm last month that some data centers and cryptocurrency miners voluntarily curtailed power use during the recent winter storm that strained the state’s grid and others across the country.

“I think you have a group of large loads in Texas that want to be cooperative, and understand the value of working with the grid operator in the state,” Flores told the news service Bloomberg.

“Some large technology companies are building generation dedicated solely to supplying their data centers rather than feeding power into the broader grid, but ultimately, I see an interconnection for all these hyperscalers.”

A law passed in Texas last year directs the state utility commission to set standards that provide ERCOT with the authority to direct large loads to curtail their load prior to and during declared energy emergency situations.

Elsewhere, a recent report said that in the Midcontinent Independent System Operator, large load customers continue to evaluate their options for participation in the markets, including as demand responses resources during emergency conditions.

Moreso than providing generation to the grid, industry planners worry about the effect of data centers going off line unexpectedly.

These facilities already challenge the bulk power system with high and unpredictable loads that flatten peak periods, and because of their sensitivity to power quality.

Voltage-sensitive loads of this kind have increased and are expected to continue to grow rapidly, an incident review from the North American Reliability Corporation said.

“When considering large data centers and cryptocurrency miners, operators of the bulk electric system should be aware of the potential for large amounts of voltage sensitive load loss during normally cleared faults,” NERC concluded.

A 230-kV transmission line fault in July 2024 in the Eastern Interconnection led to a customer-initiated simultaneous loss of about 1,500 MW of voltage-sensitive load that was not anticipated.

“The grid has not historically experienced simultaneous load losses of this size in response to a fault,” according to NERC. “These faults have historically been planned losses of large generation.”

In this incident, voltage and frequency both rose unexpectedly, but not to levels that posed a reliability risk. Transmission system operators took action to reduce voltage to within normal levels.

The review detailed how a lightning arrestor failed, resulting in a permanent fault that “locked out” a 230-kV line. The auto-reclosing control on the line cleared the faults.

The auto-reclosing control was configured for three attempts staggered at each end of the line, resulting in six successive system faults in 82 seconds.

Most of the sustained load reduction occurred simultaneously with the third and final automatic reclosing attempt. Most of the load loss in the event can be attributed to the interaction between the reclosing sequence on the faulted line and the data center’s protection scheme that counts the voltage disturbances.

The typical parameters for transfer to backups on data center power systems are three interruptions in one minute, the review said.

About 1,260 MW of load dropped off the grid and did not return for hours. The local area had a load reduction about 1,500MW, disconnected on the customer side by its own controls.

The customers were “exclusively data center-type load” that transferred their load to backup power systems in response to the disturbance.

The review said there were no issues in reconnecting the large loads, “but the potential exists for future incidents if the load is not reconnected in a controlled manner. Ramp rates for load connection are just as critical to system operations as generation ramping.”

The NERC large load task force continues to review the general issue.

The NERC Long Term Resource Assessment released last month said new data centers account for most of the projected increase in demand over the next 10 years.

“These high-load, high-duty-factor customers could strain both generation and transmission resources if not adequately planned for,” the document said.

The assessment comprises long term research among the reliability coordinators in the U.S.

A study by the PJM Interconnection concluded that the bulk of expected voltage criteria flowgate violations in coming years will be driven by heavy west-to-east transmission interface flows caused by large load increases in the Dominion zone and in eastern PJM.  The significant load growth is attributed primarily to data centers, electrification, and electric vehicle developments.

The NERC assessment cited an event in ERCOT of approximately 1,500 MW of voltage-sensitive load reduction. Many different types of loads of varying size reduced consumption during an extended low-voltage period in West Texas due to a protection system mis-operation. The date of the event was not specified.

The industry is taking note of the potential threat to reliability.

“We’re talking about loads that we’ve never seen before behind the meter,” Dean Musser, director of digital products for energy and transportation at Caterpillar, said at a conference earlier this month.

“I am not sure how you bang a 1 GW watt load on and off the grid and still maintain grid stability,” he said during a panel discussion at the DistribuTECH conference in Atlanta. “The issue there becomes that most of those systems are not set up for it. I think we need time to digest that.

“What are the economics for the end use customer? How is the utility going to be involved versus the power pool? It is something that is going to happen more often than not.”