On a summer day, the grid begins to stir about 6 a.m.
It comes alive as toaster elements burn orange, showers run and coffee makers gurgle.
The interconnected electric network, a continental organism of copper and spark, begins to draw more power as people wake. And it will demand more and more energy as the day heats up.
The technicians who operate the grid know it as a collection of power plants, substations and transmission lines woven over the eastern half of the United States. But they also know it as the embodiment of the collective appetite for electricity, and that appetite increases on hot days–like the ones predicted for the end of this week.
The grid must be fed–precisely the right amount at exactly the right moment–or it can collapse in a flash. And physics dictates that demand, not supply, rules the system.
The electricity dispatchers who sit in “the war room” at Commonwealth Edison’s Bulk Power Operations, a windowless building in the western suburbs that old timers call “the block house,” have had their hands full this summer. To witness them work for a day, monitoring demand and firing up supply, is to see what makes the region light up–and sometimes come close to going dark.
After years of mismanaging its nuclear plants and cutting back on its margins of reserve power, ComEd has been at risk of not having enough electricity to feed into the system when the grid demands it.
Ultimately, if demand outstrips supply, the hunger for power somehow has to be eliminated to stop the grid from frying. That, as almost everyone in Illinois has learned from this summer’s dire warnings, is called a rolling blackout.
“Cut off the hand to save the body,” the electricity dispatchers say.
In the block house, computer stations sit in front of a movie screen-size map of ComEd’s main transmission lines. The computers monitor everything from energy usage to weather–in the summer, air conditioning can account for 40 percent of the power demand–and portions of the giant map blink when a transmission line is in trouble.
Over the course of a recent summer day in the block house, ComEd dispatchers watched and fed their portion of the grid, constantly eyeing the balance between supply and demand–or “load,” as the dispatchers call it.
“Weather is our life,” said John Blazekovich, who trains the dispatchers, “because weather drives the load.”
With the day forecasted to head toward the 90s, the dispatchers were anticipating heavy load.
The appetite for power can nearly double between its low point before sunrise and its high point in mid-afternoon. With eight nuclear units running around the clock, ComEd plans to meet the changes in the load by switching on and off its coal and natural gas plants.
Sometimes a dispatcher calls the plant. Other times it can be done directly from a block house computer.
At 4:05 a.m., knowing the demand could be high, dispatchers fired up a boiler at the Powerton coal plant south of Peoria to get it ready to begin producing power.
About 5 a.m., the demand for power hit its low of about 10,250 megawatts–a measure of how much electricity is flowing through the system.
At 7 a.m., energy use began to soar, and the dispatchers started increasing the steam generated at some plants and pushing up the amount of coal flowing into others.
And the grid kept drawing more power as the day heated up and air conditioners worked to keep homes and businesses cool.
At 9:06 a.m., dispatchers fired up the big, 572-megawatt Collins 1 boiler. At 10:06, Collins 2 was brought up. At 11:14, Collins 5 came on line.
Over those two hours, the dispatchers had added as much electricity to the grid as could be generated in the biggest nuclear power plants.
By noon, it was 85 degrees at O’Hare International Airport, and the grid that stretches out over northern Illinois was demanding 17,019 megawatts of power–almost 7,000 megawatts more than it had been drawing before sunrise.
The grid operated by ComEd is woven into the fabric of the larger grid that covers the U.S. east of the Rocky Mountains. Together, all the utilities connected to the grid have to maintain the balance between supply and demand.
This managed and monitored grid is the result of the Northeast Blackout in 1965.
Utilities had been wiring themselves to their neighbors for decades before that, without fully understanding the consequences. When a power line failed in Canada in 1965, they learned them quickly.
The downed line made 1,700 megawatts of power vanish from the grid. The grid abhors a vacuum–remember, demand runs the system–and the next generator down the line tried to make up for the loss by producing more electricity until it overloaded. One power plant after another went down in a cascading collapse of the system.
On this day, the same physics came roaring into play at 2:35 p.m.
Far to the north, near a hydroelectric plant in Manitoba, Canada, a massive transmission line piping 2,000 megawatts of power toward the United States suddenly went dead.
“We feel any event on the grid if it is big enough, and this was big enough,” said Anthony Jaras, vice president of electric operations for ComEd.
The loss of the 2,000 megawatts caused a vacuum to the north, and electricity from the south rushed to fill it–a “power swing” in the grid.
At virtually the same instant that the transmission line failed in Manitoba, the rush of electricity caused by the power swing overloaded a line leading from the ComEd system north into Iowa.
Losing the line cut off that route for the electricity, and ComEd’s dispatchers watched as 900 megawatts of power pushed north into Wisconsin to fill the void.
Safeguards in the system and operational responses introduced after the Northeast Blackout, including firing up fast-starting generators and calling for “voltage support” from neighbors, maintained the grid.
“Service was maintained even though all these things were going on,” Jaras said. “The customers actually saw nothing.”
Meanwhile, demand was still on the rise as temperatures climbed.
At 5 p.m., it was 89 degrees at O’Hare and all of ComEd’s power plants were running near full power. By 6 p.m., the company also was buying 1,900 megawatts of power from other utilities through the grid.
At the hottest point in the day, ComEd’s 3.4 million customers were demanding almost 19,063 megawatts before demand began to tail off to end the daily cycle.
“We were sitting with capacity of greater than 20,000 megawatts,” Jaras said. “We still had room.”
