Lessons learned from previous events, close coordination with the local utility, and effective use of both demand response programs and a voltage reduction action greatly reduced the magnitude and duration of a load shed event in the Baltimore area on Aug. 11, PJM told stakeholders at the Sept. 11 meeting of the Operating Committee.
The outage of a substation near Baltimore that began early morning on Aug. 11 threatened to spread cascading outages as electricity demand rose in the afternoon. PJM’s actions in coordination with Baltimore Gas & Electric (BGE) averted potential loss of approximately 1,200 MW. The event culminated with a 28-minute limited load shed of about 20 MW.
“In close coordination with BGE, we did everything we could to limit the risk to load and to limit the amount of load that would actually have to be shed,” said Kevin Hatch, PJM Sr. Manager – Dispatch. That action, taken at 3:52 p.m., was required to avert the possibility of widespread outages, he said.
Events began on Monday at about 3:30 a.m. with reports of failing equipment amid heavy, dense fog enveloping the Brandon Shores 230 kV substation near Baltimore, Hatch said.
As the morning progressed, equipment continued to trip offline within the substation, culminating with the loss of the entire Brandon Shores substation around 7:30 a.m.
PJM operators immediately initiated system reliability studies for the projected peak of the day with the equipment out of service to understand how the substation’s loss restricted power flows into Baltimore, and they quickly formed an action plan to maintain overall system reliability. That analysis showed multiple thermal overloads and that approximately 1,200 MW of electricity load would be at risk to potentially trip off the system “in a very, very critical area,” Hatch said.
Such transmission overloads and cascading outages would not have allowed system operators enough time to respond to protect customers and prevent further damage, he said. These reliability studies were run in parallel with analysis performed by BGE, and study results and action plans were coordinated between PJM and BGE.
To mitigate the possibility of such severe system impacts, PJM implemented a series of emergency procedures confined to the BGE transmission zone. Relief also came by starting generation and a call to combustion turbine units to return to service from being out for maintenance.
At 8:45 a.m., PJM began to call for load management, or demand response, of BGE zone resources effective at 10 a.m. Demand response programs pay customers to reduce electricity use in times of system stress. Altogether, these demand response programs from both PJM and BGE reduced load by an estimated 230 MW. That day, BGE also achieved some load reductions via public appeals for all customers to reduce electricity usage voluntarily, PJM said.
At 2 p.m., PJM issued a 5% Voltage Reduction Action and Curtailment of Non-Essential Building Load to further reduce demand on the system between 3 p.m. and 5:15 p.m. This yielded a further estimated 60 MW amount of load relief.
At 3:52 p.m. with system studies indicating need for further load reductions to maintain grid stability, PJM issued a Load Shed Directive to temporarily reduce system load by approximately 20 MW. Equipment started to return to service at the Brandon Shores substation. By 4:20 p.m., PJM studies showed the load shed was no longer needed, and PJM ended the directive, which ultimately impacted an estimated 4,000 customers in Howard County for approximately 30 minutes, according to BGE.
PJM’s ability to direct relatively small load shed compared to the risk of significantly greater system outages was helped in part by recent refinements in coordinated system voltage reduction drills, it said.
Beginning last year, in close coordination with Transmission Owners, PJM initiated twice-yearly voltage reduction tests in both winter and summer conditions to ensure that the critical emergency procedure was ready to be implemented if needed during an emergency. Working closely with Transmission Owners, PJM conducts these drills to help inform PJM operators about the amount of relief a voltage reduction action may actually yield.
The voltage reduction drills help to ensure that system operators are ready to implement the procedure and that equipment is tested, so the procedure can be quickly called upon if needed. BGE’s participation in those PJM voltage reduction tests, “were a result of previous lessons learned, making their voltage reduction very effective,” Hatch said.
Hatch said the demand response and voltage reduction emergency procedures had an impact, lowering the amount of load that was shed and greatly reducing overall risk to the system.
Hatch noted that system awareness is vital for PJM’s operations during conditions like these. As PJM engineers prepared to study how to safely maintain system operations without the critical substation on Aug. 11, they consulted closely with BGE control room operators and leadership to compare study results and analysis on system conditions and impacts.
Shedding load, even at lower levels for short periods, can still mean significant impact to some customers. With that in mind, PJM maintained close contact with city, county and state officials and provided advance notice that load shed was a possibility.
After-the-fact analysis continues with reviews pending by both ReliabilityFirst, which oversees grid reliability in the region on behalf of the North American Electric Reliability Corporation (NERC), and Exelon, BGE’s parent company. PJM’s own teams are reviewing events to create operator training scenarios and simulations, Hatch added.
After-the-fact lessons learned analysis is critical, Hatch said. For example, he said PJM actions taken Aug. 11 are informed by NERC standards and industry practices that evolved from study of the 2003 blackout. That event caused spontaneous cascading outages as far away as New York City and Toronto, affecting 50 million people. Hatch also cited lessons learned that informed NERC standards from the 2011 Southwest blackout, affecting Arizona, California and Mexico.
PJM operators are trained and educated in these scenarios as part of the continual and rigorous training they undergo throughout the year.
“PJM and BGE operators did a nice job and handled the situation well. We took all of the corrective action we could to limit overall risk to the system,” Hatch said. “These events do not happen often, so we want to make sure we are trained and prepared.”
