hen an overheating electrical transmission line sagged into a tree just outside Cleveland at 3:32 p.m. on Aug. 14, the events that would lead to the greatest power failure in North American history began their furious avalanche, according to the most extensive analysis of the blackout yet.
The failure of that transmission line was crucial, because it put enormous strain on other lines in Ohio. Soon a utility that serves southern Ohio, with its overloaded lines close to burning up, sealed itself off, creating in very real terms an electrical barrier between the southern part of the state and the northern.
What happened next, by this account, was almost inevitable:To the north, Cleveland, starving for electricity, began to drain huge, unsustainable amounts of power from Michigan and then Ontario, knocking out more lines and power plants and pushing the crisis to the borders of northwestern New York.
First the New York system, acting to protect itself, sealed the state's border with Canada, the analysis found. But that only created a different, devastating problem: New York power plants, without anywhere to quickly send electricity not needed within the state, overloaded their own system. That in turn quickly led to a general shutdown the last stage in the largest blackout in the nation's history.
That picture, based on large amounts of data from the utilities involved, was presented yesterday by Cambridge Energy Research Associates, a private energy consulting firm based in Cambridge, Mass. Two researchers at Cambridge Energy, Hoff Stauffer and Lawrence Makovich, presented the analysis at a conference in which federal energy officials, industry representatives and reporters participated by telephone and on the Web.
The Federal Energy Regulatory Commission was represented by its chairman, Pat Wood III, who would not comment on whether he thought the specifics of the theory were correct.
Both Mr. Wood and the Cambridge Energy experts were unequivocal, though, on one emerging aspect of what went wrong last week: the system for communication among the people and organizations that operate that part of the nation's electrical grid was inadequate.
When problems soar around the grid in seconds, as they did that day, Mr. Wood said, "you need to make sure that the communication between the different regions can move similarly fast." That cannot happen in the current setup, in which the various oversight organizations are fragmented and often connected only by phone lines, he said.
Ellen P. Vancko, a spokeswoman for the North American Electric Reliability Council, the industry group charged with preventing grid problems, said the organization had not seen the Cambridge Energy analysis and could not comment.
Michael Holstein, vice president and chief financial officer at the Midwest Independent Transmission System Operator, which helps manage electrical flows on the grid for certain companies in the region where the blackout began, called the analysis "an interesting hypothesis." But he rejected any suggestion that a lack of communication had contributed to the problems.
"At a certain point in time, things happened so fast that human intervention was not possible," Mr. Holstein said.
That assessment was echoed by the organization that carries out day-to-day management of the grid in New York. Ken Klapp, a spokesman for that organization, the New York Independent System Operator, said events had moved too quickly for humans to react and keep the state from going dark.
Mr. Klapp said a federal investigation just begun by the Department of Energy would give definitive answers about the blackout's cause. "Our position is that the facts will come out," he said. "Eventually it will all be there."
In the days since power went off in eight states and southern Ontario and left tens of millions of people without lights and other necessities, some of the companies involved have made public their partial timelines of events and sometimes their theories about what led to what.
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