U.S. Electric Grid Narrowly Dodged Huge Collapse During Storm

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The unprecedented strain on the electrical grid during December’s frigid storm was threatening to trigger cascading blackouts across the Eastern US when Duke Energy Corp. called for rolling outages in North Carolina to stabilize the system, company officials said Tuesday.

Duke cut power to about 500,000 homes and businesses the day before Christmas as frigid weather sent demand surging as much as 10% above forecast while instruments froze at coal and natural gas-fired plants, forcing them to cut output.

The strain in North Carolina threatened to throw the flow of power off balance on the entire Eastern Interconnection grid, stretching from Maine to Oklahoma, and required Duke to institute outages on its own system to protect the grid at large, the executives said.

“If that doesn’t work, the stability of the Eastern Interconnection system is at risk,” Sam Holeman, Duke’s head of transmission system planning, said at a hearing Tuesday. “That risk comes in the form of uncontrolled loss of the system.”

After the lights came back on, North Carolina Gov. Roy Cooper asked Duke for a complete report on what went wrong and for changes to be made, prompting the hearing by the North Carolina Utilities Commission, which regulates electricity in the state.

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A handful of Duke executives gave a timeline of the demand surge, power supply failures and system failures that made blackouts last much longer than the 15 or 30 minutes of which customers initially had been warned.

As the cold front moved into North Carolina, instruments froze at two Duke coal plants and three natural gas plants, reducing generation at those facilities, the governor’s office said in a statement Tuesday afternoon. Once Duke started rotating outages, a software problem disrupted automatic restorations, making the blackouts last longer than planned.

“The outages did not occur because of renewable energy generation,” according to the statement.

Holeman added that other utilities were in the same situation at the time. For example, Tennessee Valley Authority, a federal agency that supplies power in the region, was forced for the first time to institute rotating outages on Dec. 23 and Dec. 24 as demand soared to a winter record.

Just north of Duke’s territories, PJM Interconnection was doing all it could to prevent rotating outages from rolling across its 13-state network that stretches from the mid-Atlantic to the Midwest. PJM reduced exports, including additional reserves Duke was hoping to tap for the Carolinas.