Blackout '03: Lights Out

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That said, even the experts were surprised by the speed and breadth of last week's failure. It began, according to Gent, with an immense buckle in the system, when a still mysterious event--three transmission lines near Cleveland failing--began pulling down parts of the grid. A broken alarm at First Energy, a northern Ohio utility, may have allowed too much to go wrong before technicians noticed. The loss in power soon forced as much as 5,000 megawatts--almost enough to power Nevada for a day--that had been moving west to east to suddenly change direction. The reversal happened so fast that operators did not have time to react, and within about 10 seconds, vast sections of the grid were overwhelmed. The failed lines in Ohio started a cascade that was able to crash more than 100 power plants, including 22 nuclear plants in the U.S. and Canada, despite a structure designed specifically with such a danger in mind. "There are so many systems in place to prevent this kind of thing from happening," says Maria Zazzera, a former utility manager who worked for the New York Power Authority for 21 years. "I know people whose whole lives are dedicated to the reliability of this system. They do drills. They have procedures in place."

Those procedures were meant to isolate problems and keep them from spreading. Because supply and demand need to match up for the system to work, relay mechanisms throughout the grid continuously monitor the flow of power. If there is a sudden failure for some reason, like a lightning strike on a transmission tower, circuit breakers open, and the sector unhinges itself from the grid. This process is called islanding; the goal is to contain the glitch by sealing it off from the rest of the network.

When that happens, it creates a hole; the network is programmed to quickly either pick up power from other sources or shed load, meaning purposely shut off power in one part of the grid to protect the rest of it. That's one reason suburbs are more likely than urban centers to suffer brownouts: to protect commerce and hospitals in the most densely populated areas. But to work, any shift has to happen very fast, in real time, says Zazzera, "and nobody likes to drop load. You never want it to go black because you have to report it to your regulatory commission. You get in trouble; it's difficult to start up again." In this case, there may never have been time to make a decision. In past blackouts, there was a window of as much as 45 minutes to try to adjust to a deviation. This one moved across hundreds of miles in seconds.

The fallout could have been worse. If you lived in Vermont, you could even say that the system worked. By quickly unplugging itself from power feeds from New York, the state was spared the same fate. Down in Chattanooga, Tenn., when engineers at the Tennessee Valley Authority operations center saw transmission flows spike, they managed to program their generators to slow down and stabilize the flow of electricity; that and a system of circuit breakers in Ohio stopped the crash from spreading south.