WASHINGTON - The failure of three transmission lines in northern Ohio was the likely trigger of the nation's biggest power blackout, a leading investigator said Saturday.
Experts are working to understand why the disruption spread throughout the Northeast and Midwest and into Canada, and was not contained.
"We are fairly certain" that the problem started in Ohio, said Michehl Gent, head of the North American Electric Reliability Council. "We are now trying to determine why the situation was not brought under control."
Gent said the transmission system was designed to isolate problems such as those apparently involving the three lines in the Cleveland area.
"The system has been designed and rules have been created to prevent this escalation and cascading. It should have stopped, we think, after the first three" line failures, Gent said in a telephone news conference at which he did not take questions.
His organization is a nonprofit, industry-sponsored group that is supposed to oversee power line reliability. The council earlier had released documents showing four transmission line problems in the Cleveland area in the hour before the blackout spread Thursday afternoon across eight states from New England to Michigan.
The transmission system in northern Ohio is operated by FirstEnergy Corp. Company officials have declined to discuss details of their investigation into the blackout.
Council investigators were examining more than 10,000 pages of data, including automatically generated logs on power flows over transmission lines, Gent said.
The investigation has become more difficult because at the time of the power breakdown, "events were coming in so fast and furious that (some) ... weren't even being logged in a timely way," Gent said.
Nonetheless, Gent said he is convinced that no data was lost and whatever was not recorded will be recovered.
"We will get to the bottom of this," he said.
A federal task force of U.S. and Canadian officials was forming to investigate the outages that spread within seconds, affecting millions of people from New York City to Michigan.
The preliminary investigation focused on an electrical transmission loop that encircles Lake Erie.
Investigators since Friday had been intrigued by a series of interruptions on a number of power lines in the Cleveland area during the hour before the massive blackout began.
Two minutes after the last of the Cleveland-area line problems there were "power swings noted in Canada and the eastern U.S.," said a document made public late Friday by the council.
The United States and Canada have agreed on a task force to identify the cause of the blackout and correct whatever shortcomings caused it. The investigation will be headed by Energy Secretary Spencer Abraham and Canadian Natural Resources Minister Herb Dhaliwal.
Congressional hearings also are planned in September, and federal regulators were reviewing the power grid breakdown.
Abraham, who met Saturday with the governors of New York and New Jersey in Albany, N.Y., said the task force would not prejudge what might have happened.
More than 100 power plants, including 22 nuclear reactors in the United States and in Canada, shut down, most of them automatically to protect themselves against power surges, officials said.