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The grid in the Mid-Atlantic region needed alternate supply sources to make up for a transformer failure that shut two reactors at a nuclear plant in Maryland and briefly cut electricity to the White House and Capitol Hill.

Pepco, the DC electric services provider, initially said it had scattered reports of outages for “unknown” reasons, and that it was looking into the matter. Government officials later pointed to an explosion at a southern Maryland power facility as the likely cause for the regional issue.

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Department of Homeland Security officials said just after the outage began they were looking into the outage, but believed at the time there was no reason to believe the power failure had any connection to terrorism or other criminal activity.

Officials believe the outage was the result of an explosion at a Southern Maryland Electric Cooperative (SMECO) power plant several miles south of nation’s capital. The explosion had no known link to terrorism, and appeared to have been the result of a high-voltage conductor falling to the ground, according to a SMECO official. No one suffered an injury, company officials said.

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Shortly before 1 p.m. a Pepco 230-kilovolt (kV) transmission conductor located at SMECO’s Ryceville switching station in Charles County broke free from its support structure and fell to the ground. This failure resulted in the loss of supply to SMECO’s Ryceville and Hewitt Road stations. The Pepco supply to the Morgantown and Chalk Point interconnect locations also ended up interrupted.

As a result, Calvert Cliffs Nuclear Power Plant shut down automatically as a result of a localized grid disturbance that caused power outages in the Washington, D.C./Maryland area.

As a part of its design, Calvert Cliffs automatically shuts down during significant electrical disturbances. The plant shut down safely and without incident. Both reactors will remain in “hot shut-down,” which means the reactor remains ready to resume power production, until the offsite grid disturbance ends up addressed.

A U.S. official said the White House was without power for a few minutes. The daily press briefing ended up delayed because of the outage. By 2:15 p.m. ET, the White House had gone back to its normal power source, White House Press Secretary Josh Earnest said.

The State Department’s daily news briefing, meanwhile, ended up suspended after power was lost. A department announcement said the main building and other nearby buildings remained affected because electricity feeders were down.

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