Editor's Note: This story was originally published in the May 2007 issue of Scientific American.

August 14, 2003, was a typical warm day in the Midwest. But shortly after 2:00 P.M. several power lines in northern Ohio, sagging under the high current they were carrying, brushed against some overgrown trees and shut down. Such a disturbance usually sets off alarms in a local utility’s control room, where human operators work with controllers in neighboring regions to reroute power flows around the injury site.

On this day, however, the alarm software failed, leaving local operators unaware of the problem. Other controllers who were relaying, or “wheeling,” large amounts of power hundreds of miles across Ohio, Michigan, the northeastern U.S. and Ontario, Canada, were oblivious, too. Transmission lines surrounding the failure spot, already fully taxed, were forced to shoulder more than their safe quota of electricity.

To make matters worse, utilities were not generating enough “reactive power”—an attribute of the magnetic and electric fields that move current along a wire. Without sufficient reactive power to support the suddenly shifting flows, overburdened lines in Ohio cut out by 4:05 P.M. In response, a power plant shut down, destabilizing the system’s equilibrium. More lines and more plants dropped out. The cascade continued, faster than operators could track with the decades-old monitoring equipment that dots most of the North American power grid, and certainly much faster than they could control. Within eight minutes 50 million people across eight states and two Canadian provinces had been blacked out. The event was the largest power loss in North American history.

The 2003 disaster was a harbinger, too. Within two months, major blackouts occurred in the U.K., Denmark, Sweden and Italy. In September 2003 some 57 million Italians were left in the dark because of complications in transmitting power from France into Switzerland and then into Italy. In the U.S., the annual number of outages affecting 50,000 or more customers has risen for more than a decade.

In addition to inconvenience, blackouts are causing major economic losses. The troubles will get worse until the entire transmission system that moves power from generating plants to neighborhood substations is overhauled. More high-voltage lines must be built to catch up with the rising demand imposed by ever more air conditioners, computers and rechargeable gadgets.

But perhaps even more important, the power grid must be made smarter. Most of the equipment that minds the flow of electricity dates back to the 1970s. This control system is not good enough to track disturbances in real time—as they happen— or to respond automatically to isolate problems before they snowball. Every node in the power grid should be awake, responsive and in communication with every other node. Furthermore, the information that operators receive at central control stations is sparse and at least 30 seconds old, making it impossible for them to react fast enough to stop the large cascades that do start. A self-healing smart grid—one that is aware of nascent trouble and can reconfigure itself to resolve the problem—could reduce blackouts dramatically, as well as contain the chaos that could be triggered by terrorist sabotage. It would also allow more efficient wheeling of power, saving utilities and their customers millions of dollars during routine operation. The technology to build this smart grid largely exists, and recent demonstration projects are proving its worth.

Overwhelmed by Progress
The transmission system has become vulnerable to blackouts because of a century-long effort to reduce power losses. As power moves through a wire, some of it is wasted in the form of heat. The loss is proportional to the amount of current being carried, so utilities keep the current low and compensate by raising the voltage. They have also built progressively longer, higher-voltage lines to more efficiently deliver power from generation plants to customers located far away. These high-voltage lines also allow neighboring utilities to link their grids, thereby helping one another sustain a critical balance between generation supply and customer demand.

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