Behind the hum of a power-grid: human choices

Last Thursday, as Adams was sitting in his office, the nearby power grids started to be swamped. To stabilize themselves, they apparently tried to suck power in from outside sources, including Vermont.

To switch metaphors, it's as if the other systems became black holes, pulling all available energy toward them. Since electricity travels at virtually the speed of light, no human could have reacted quickly enough. But Vermont's sensors instantly rebelled, walling off the state.

The sensors' action was a godsend. But it also left no outside power flowing into the state. That sent voltage levels - a key measurement of the system's stability - falling fast. Like an airplane losing speed, Vermont's grid risked stalling and crashing. Now the humans had to stabilize things.

Adams and the other engineers knew they had to get in quick contact with Vermont's other utilities. Fortunately, the control room has several "bat phones," including a red instant hotline to the Vermont Electric Power Company, which runs the state's big transmission lines.

Adams knew his counterparts there would want extra power to boost voltage. He knew he could fire up a nearby gas-turbine generator quickly. "Do you want it?" he barked into the red phone. "Yep," came the reply. Done.

Such communication and coordination is key. In fact, a report prepared in May by the national industry watchdog targeted the Midwest as especially susceptible to lack of cooperation.

"There is a continuing need for the reliability coordinators, transmission planners and operators to communicate and coordinate their actions to preserve the continued reliability of the [Midwest] system," said the report by the North American Electric Reliability Council. It continued, ominously, "As long as transmission limitations are identified and available operating procedures are implemented ... no cascading events are anticipated." Then just such an event occurred.

Now communication is a central focus of the probe. Some Ohio operators reportedly may have known of troubles in the system for at least an hour before the ultimate crash. If they did - and had alerted other nearby operators - it may have prevented the blackout.

One other key difference: Regional power coordinators in the Eastern US have more authority to demand cooperation between local utilities than their Midwestern counterparts. More centralized authority may help those systems have tighter response times.

In Vermont, Adams and others drew on everything they had. They cranked up power generators, including a dam. It helped that three weeks of steady rain had raised reservoir levels. But just to be sure, they sent operators to each plant and substation - ready to manually operate them if needed.

The crowning moment came as they watched the voltage creep back up. "We've got 108 volts," Adams counted, "112 volts, 116 volts...." It meant that Vermont had avoided - if just barely - the great blackout of 2003.

• Amanda Paulson contributed.

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