HARTFORD, Conn. (AP) -- A malfunctioning relay has been identified as the cause of a weekend power outage at Connecticut's nuclear plant, which supplies half of all power in the state and 12 percent throughout New England, a spokesman said Tuesday.
The Millstone Power Station is still not operating though power has been restored. Officials don't know yet when operations will resume and it will have to go through many steps before it does.
Ken Holt, a spokesman for the Millstone plant in Waterford, said the culprit was a relay on a transmission line that carries power to and from the Waterford plant.
"It didn't do what it's supposed to do," he said.
An "unusual event," the lowest of four levels of emergency classification used by the federal Nuclear Regulatory Commission, was declared at 7:15 a.m. Sunday.
The plant's emergency diesel generators activated and powered safety systems. Electrical power was restored several hours after it failed at the plant, owned by Dominion Resources Inc.
The outage, which affected both units at the plant, was Millstone's first, Holt said.
ISO-New England, which runs the region's grid, operates with a daily margin of reserve of about 2,200 to 2,600 megawatts for the possibility that plants could lose power, spokeswoman Marcia Blomberg said.
"We could lose resources and we routinely manage through unexpected and unplanned resource outages," she said.
One megawatt powers about 1,000 homes.
No emergency actions were needed and the reliability of the region's high-voltage power grid was maintained, Blomberg said.
Frank Poirot, a spokesman for Connecticut Light & Power, said the relay problem was tracked to equipment at an electrical substation and the results of a detailed investigation are not expected for a month.
Dominion, ISO-New England and CL&P are looking at what caused the equipment to fail and the broader impact on the system at Millstone, he said.