A mass power outage in Central Maryland was avoided on Monday, following a transmission failure at a local Baltimore Gas and Electric Company substation.

Nearly 1.3 million electric customers in the BGE territory were bracing for a blackout after the facility connected to the Brandon Shores and H. A. Wagner power plants in Anne Arundel County failed. Only an estimated 4,000 customers in Howard County were without power for around 30 minutes, according to Maryland Senate President Bill Ferguson.

The outage was a result of the local power plants experiencing “an unplanned disconnection from the BGE electric system” and had “the potential to cause a temporary outage this afternoon and evening to protect the grid,” BGE said in an email sent Monday afternoon.

The problems started at around 3 a.m. Monday, when the BGE transmission facility cut power to the Brandon Shores and H. A. Wagner power stations, according to Taryne Williams, a spokesperson for Talen Energy, which owns both plants.

The outage caused Brandon Shores Units 1 and 2 to automatically shut down. Wagner’s two units and Brandon Shores Unit 2 could only start producing electricity again once they went through the startup process, if PJM Interconnection, the region’s grid operator, requested it, Williams said.

At 3:52 p.m., PJM gave BGE a “load shed directive” to help reduce electricity flow on overloaded lines. Shortly after the directive, BGE reported that the “portions of the transmission system that were inoperable for most of the day had been restored,” Jeffery Shields, spokesperson for PJM, said in an emailed statement.

PJM canceled the directive at 4:20 p.m. as they were able to bring enough power into the Baltimore area.

“Continued reliable operation of the local transmission system will depend upon the operability of the transmission facilities that tripped this morning, but for now, the system is in a place such that we can serve our peak evening demand in the area,” Shields said.

In a statement Monday afternoon, the Maryland Freedom Caucus, a group of conservative state legislators, pointed to a failure at the substation tied to the Brandon Shores power plant in Anne Arundel County.

Paul Pinsky, director of the Maryland Energy Administration, confirmed in an email that the issue was connected to Brandon Shores. And Ferguson told reporters on Monday afternoon he was briefed by BGE that the problem started at a substation near the power plant and “was not a matter of a lack of supply.”

BGE has electric customers in Baltimore City, in Baltimore, Harford, Carroll, Howard and Anne Arundel counties, and parts of Montgomery and Prince George’s counties.

Local officials, including in Anne Arundel County, the City of Annapolis and Baltimore Mayor Brandon Scott, warned residents of the potential outage. Baltimore-Washington International Thurgood Marshall Airport said in a statement Monday afternoon that it was not affected, but was taking “precautionary measures to conserve energy and lessen the demands to the power grid.”

How to prepare for possible power outage

BGE is asking its customers to conserve power until the evening. It also recommended that those in the service area should take the following precautions:

• Store a supply of bottled water and easy-to-prepare, nonperishable foods.
• Charge cellphones, computers, electric vehicles and other battery-powered electronic equipment.
• Customers with landlines should keep a corded phone to report outages if cellphones lose power.
• Have a flashlight with fresh batteries on each floor of your home.
• Customers requiring refrigeration for medication or electricity for medical equipment should have alternate arrangements in place in the event of an extended power outage.
• Monitor thermostats.
• Turn on ceiling fans or standalone fans.
• Close blinds, shades and drapes.
• Delay the use of major, heat-generating household appliances such as ovens, stoves, dishwashers and dryers.
• Turn off nonessential appliances, electronics and other devices.

Banner reporters Adam Willis and Pamela Wood contributed to this story.