by Kathiann M. Kowalski
On August 14, 2003, all the rides at Cedar Point Amusement Park in Ohio suddenly stopped. The day was steamy, and so was Chris; he'd wanted to plunge into cold water on a ride called Snake River Falls. Michelle, a friend who was visiting from Alabama, still hadn't ridden Millennium Force by the time the power went out. And Chris's sister Laura wanted to ride Top Thrill Dragster. Frustrated, the three friends headed back to Cleveland. The trip only added to their frustration. With no traffic lights working, cars crawled.
Last August's blackout was the biggest ever in U.S. history. From New York to Michigan and into Canada, 100 power plants shut down. Work halted in offices, malls, supermarkets, and restaurants. Trains and subways stopped running. With no electric pumping stations working, water pressure dropped and some areas lost running water. Food spoiled as temperatures climbed.
The August 14 blackout underscored how much North Americans rely on electricity—and lots of it! Just what happened?
Electricity and magnetism are different aspects of the same thing—electromagnetism. Electricity is the force produced when one electron from each of billions of atoms jumps to the next atom in a circuit. Magnetism is like the flip side of the coin. It's the force produced when a material's magnetic domains all line up the same way. Magnetic domains are groups of millions of atoms whose electrons orbit the nuclei in the same direction. Think of magnetic domains as arrow-tipped pick-up sticks. Only when the “sticks” all point the same way does something become magnetic.
You can use electricity to make an electromagnet—a magnet that “works” while current flows. You can also use a moving magnet to generate electricity in a wire. Most electric generators work by combining these concepts.
In a typical generating plant, pressurized steam powers a turbine. The turbine spins a magnet (usually an electromagnet) inside wire coils. The magnet makes electricity flow through the wire.
The spinning magnet alternately exposes the wire to its north and south poles. Thus, each half spin changes the current's direction. Turbines in North America's generating plants rotate 3,600 times per minute. Thus, their alternating current (AC) switches direction back and forth 60 times per second.
To get from the generator to where it's used, electricity travels along wires. Power from an electric line is voltage times the current, measured in units called amperes, or amps. Voltage is basically the pressure of the electricity, while current is its flow rate.
“If we can keep the voltage very high, we keep the current low to transmit the same amount of power,” says Don Benjamin at the North American Electric Reliability Council (NERC). That reduces heating on wires and makes the system more efficient. To do that, step-up transformers just outside the generator boost the voltage from 12,000 to 25,000 volts up to anywhere from 69,000 to 765,000 volts. Power travels along transmission lines at nearly the speed of light.
Step-down transformers at substations lower the voltage for delivery within service areas, and more step-down transformers finally reduce voltage to 120 or 220 volts. Voilá! Your toaster, TV, computer, and lights can turn on.
Going with the Grid
Throughout North America, electric transmission systems connect to each other in a network called “the grid.” The Eastern Interconnection serves most of the United States and Canada east of the Rocky Mountains. The Western Interconnection serves most of Canada and the United States west of the Rockies (except Alaska and Hawaii). Texas has its own interconnection.
“The grid provides many different paths for electricity to get from the generators to the customers,” says Benjamin. “You cannot map a particular customer back to a generator.”
The setup provides backup sources of power. If one generator or transmission wire goes down, electricity can flow in from elsewhere. The grid also lets companies sell each other electricity. Sometimes it's cheaper to buy 100 megawatts of power from another company than to run a less-efficient plant during peak demand times.
Because wires link everything, all generator turbines in an interconnection must spin in sync with each other. Otherwise, they could disrupt power flows and cause shutdowns.
Meeting demand is tricky, too. Electric companies can't readily store power. “It has to be generated at the instant that it's used,” says Benjamin, “so we're constantly chasing the demand on the system.” Computerized control centers constantly monitor power flows into and out of about 140 areas, using NERC standards.
“There has to be a perfect balance,” stresses Jim Owen at the Edison Electric Institute, an industry organization. Otherwise, lines could overheat and cause fires. Or, variations could change the frequency of the whole grid and affect the speed of generator turbines.
“The steam turbines are designed to run within a narrow band,” says Benjamin. “If they run too fast or too slow, there are automatic controls that will take those generators off-line to protect them.” Otherwise, instead of being down for several hours or days, generators could be out of service for months.
So, What Happened?
Hours before the lights went out on August 14, things started going wrong. Between noon and 1:35 p.m., several generators in Ohio and Michigan tripped, or shut down temporarily. Around 2:00, a brushfire disconnected a transmission line in southwestern Ohio. Seven more transmission lines in Ohio disconnected between 3:05 and 4:10 p.m. A generating unit in Michigan shut down, too.
Power flows changed through the grid. Northern Ohio had less and less ability to deliver power. Voltage dropped, and the Eastern Interconnection alternating current frequency rose slightly. Around 4:10, more generators and transmission connections in Michigan and Ohio went out.
With transmission along Lake Erie's south shore out, the power flow reversed between Michigan and Ontario. In a quick cascade, more lines disconnected in Ohio, Pennsylvania, New York, northern Ontario, New England, and New Jersey. Fifty million people lost power.
Getting the lights back on takes much more than just throwing a switch. Generators must be restarted. Customers must be added little by little to balance generation and load. And all generators put back on the grid must be in sync. “That's why it takes 30 hours,” says Benjamin. “It's just a very methodical process.
As ODYSSEY goes to press, an interim report suggests that FirstEnergy in Ohio should have cut power to certain areas to keep the grid going. California utilities did that when they couldn't meet demand in 2001. “Rolling blackouts” temporarily cut power to different areas so that the whole region doesn't lose power.
An open question is whether the system can meet today's energy needs. The grid should withstand random failures. Is more equipment or a different control system needed?
“There is no way to 100-percent ensure that we never have any power outage,” says Owen. But investigators hope that they can learn from the August 14 blackout. After all, says Owen, “Electricity touches almost every part of our lives. It's the lifeblood of our economy.
- Think about the nature of electricity. Why do you think it is difficult for electric companies to store electricity?
- This article quotes Don Benjamin as saying, “We're constantly chasing demand on the system.” What does Benjamin mean?
- What are some situations that might cause an unexpected demand on a power system? Remember that a power grid is not necessarily affected by a single home or business.