The Ohio region where the nation's worst blackout started became a black hole ahead of the outage, sucking electricity from two power companies' generators and threatening to burn transmission lines, the utilities say.

As a result, power lines that were operating above emergency levels disconnected from the system and power plants automatically shut down in eight states and in Ontario, Canada — protecting equipment from permanent damage, but also rapidly spreading darkness across state and national borders.

American and Canadian Investigators are examining the cascade of events to determine what triggered the Aug. 14 crash. The most prominent theory faults the failure of a power plant and lines owned by FirstEnergy Corp. (search) in Ohio, including one transmission line that sagged into a tree. Some 50 million people lost power.

Pat Wood, chairman of the Federal Energy Regulatory Commission, on Friday was presented with details of that Ohio-based theory during a conference call with industry analysts, but he said it's too early to form any conclusions.

Wood said that in the end the root problem of the widespread outages that began in Ohio may have been something as simple as an untrimmed tree. "That's not a really deep policy debate," Wood said, adding that problems are deeper than untrimmed trees.

In the wake of the blackout, Wood said the intricate interconnectivity of the nation's power grid — which makes one region vulnerable to another's problems — makes it imperative to have a market designed in a way so that communication between utilities and system operators flows more smoothly than it did a week ago.

Cambridge Energy Research Associates (search), a private energy consulting firm based in Cambridge, Mass., presented Wood with its outage theory during a telephone conference call that included energy officials, industry representatives and journalists.

According to the chronology provided by Cambridge:

  • The outage of a power plant operated by FirstEnergy in Ohio led to the failure of a single transmission line shortly after 3 p.m. on Aug. 14. "Absent any other difficulties , it wouldn't have been a problem," said Hoff Stauffer, a senior consultant at CERA who specializes in transmission issues. As expected when one path is down, the electricity began to flow on a parallel transmission line. That's when the real trouble started.
  • The second line heated up and sagged into a tree, which should have been trimmed enough to avoid such contact. But it wasn't, and a the conditions were ripe for a blackout. At that point, it was only a matter of how far the problem would spread, Stauffer said.
  • Shortly after, power lines from American Electric Power (searchfeeding into FirstEnergy's system began tripping off automatically and AEP and others in the area managed by PJM Interconnection were able to isolate themselves from the event. AEP and PJM have also provided similar timelines and theories this past week.
  • Some 2,000 megawatts of power that had been going to FirstEnergy's system across AEP's lines was still trying to find a way to get there. It attempted to do this by entering southwest Michigan and in the process knocked out power plants and transmission lines in such a way that isolated eastern Michigan. "Then, eastern Michigan found itself trying to supply all of FirstEnergy and it couldn't do it and so eastern Michigan went out and FirstEnergy went out," Stauffer said.
  • That caused the problem to spread to Ontario, which had been importing power from eastern Michigan.
  • Power plants in New York — which recognized the problem — starting shutting down then as the blackout peaked at 4:11 p.m. "We're told New York actually saw this happening and was able to isolate itself from Ontario but then they found themselves in an overgeneration situation because they had been exporting to Ontario," Stauffer.

Indeed, data released by AEP and by International Transmission Co. (search) of Ann Arbor, Mich., show amounts of power above emergency summer standards moved from their systems to northeast Ohio after FirstEnergy's Eastlake plant tripped off-line at 1:35 p.m.

AEP, which generates the most electricity and owns the most transmission lines in the nation, said its first failure came at 3:45 p.m. in a line it co-owns with FirstEnergy that comes from a Canton substation in northeast Ohio.

The company said it avoided potential widespread outages — only 14,000 of its customers lost power — because automatic control systems detected "abnormal operating conditions" and tripped, or disconnected, from linked FirstEnergy lines.

FirstEnergy would not say if it stopped exporting power to curtail demand or warned the public to cut back on usage after losing electricity generated by the Eastlake plant.

The company also said it detected several tripped plants and lines elsewhere on the grid before the Eastlake plant dropped.

Joseph Welch of ITC said the Michigan system adequately handled the increased demand FirstEnergy's grid was pulling from it.

He said parts of Michigan lost power when the transmission systems in northern and southern Ohio separated from each other. That caused electricity meant to move through FirstEnergy's system to reverse itself and flow over AEP's system through Indiana and into Michigan, then back to FirstEnergy in Ohio.

"Those lines were never designed for that tremendous shot," he said.