OREANDA-NEWS. A power outage that utility Pepco has traced to faulty transmission line equipment in Maryland temporarily cut off electricity supply to hundreds of customers in Washington, DC, including federal government institutions, and forced 2GW of generating capacity off line in the mid-Atlantic region.

Pepco is investigating the cause of the trip at the facility in Charles County, Maryland, located southeast of Washington. The disturbance on the transmission line, which started at 12:30pm ET, resulted in a dip in voltage and forced off line several transmission lines and power plants in the Pepco service territory.

PJM, the regional transmission organization that includes Washington, DC and 13 states in the mid-Atlantic and Great Lakes region, said the transmission grid is stable and the problems appear limited to the Washington, DC, area.

PJM estimated cumulative retail-level outages at 200-500MW while three power plants with 2,000MW of capacity shut down.

Real-time wholesale power prices in the Pepco territory shot to \$400/MWh in the hour ended 2pm ET while prices at the PJM West hub, which aggregates load across a large swath of the mid-Atlantic region, reached \$300/MWh.

The outage occured even as utility regulators in Washington, DC, and Maryland are reviewing a takeover bid for Pepco by utility holding company Exelon. Maryland regulators have expresed reservations about the deal, citing its impact on customers.

Pepco has cited access to Exelon's expertise in retail customer service as a reason for the merger. The Washington utility still is battling bad publicity after it took weeks to restore power to customers in the wake of a massive outage in June 2012.