WASHINGTON (AP) – A massive, sudden reduction of electricity going into northern Ohio along the shores of Lake Erie appears to have played a role in the cascading blackout that affected eight states, according to a timeline of events released by investigators.

The U.S.-Canadian task force investigating the Aug. 14 blackout emphasized Friday that it has yet to determine how the sequence of events before the blackout are related or what role any of them might have had in causing the blackout to cascade over such a wide area.

A detailed timeline of events during the roughly four hours leading up to the blackout showed Midwest power systems plagued by a myriad problems from power plants shutting down and high-voltage lines tripping to significant declines in the voltage levels that are needed to push electrons through the transmission lines.

“What we see so far is that a voltage collapse caused plants and power lines to disconnect. But that doesn’t answer why those things happened,” Energy Secretary Spencer Abraham cautioned Friday as the task force he co-chairs issued its first findings.

Although the timeline did little to pinpoint how the problems began, it gave a graphic picture in the minutes before the blackout of a power system struggling to deal with a severe imbalance in electricity supply and demand across northern Ohio and into eastern Michigan.

At one point, seconds after 4:10 p.m. EDT, 20 power plants “tripped off line along Lake Erie” in a matter of 40 seconds as transmission lines began to disconnect and the system showed signs of declining voltage, the task force report said.

With the loss of the plants, power for a brief time rushed into northern Ohio and eastern Michigan from elsewhere. But then a major high-voltage line from western Pennsylvania into Ohio disconnected and “the entire eastern Michigan and northern Ohio load centers had little (power) left available to them,” it said.

That brought even wider problems, the task force documents said.

“When the lines along the southern shore of Lake Erie disconnected, the power that had been flowing along that path immediately reversed direction and began flowing in a giant loop counterclockwise from Pennsylvania to New York to Ontario and into Michigan.”

During the next minute and 19 seconds, various legs of the power systems that ran from Michigan into Canada, through New York state and into parts of New England and New Jersey disconnected. By 4:13 p.m., almost all of a vast area went dark.

Hoff Stauffer, a power transmission expert at Cambridge Energy Research Associates, said investigators need to find out why grid operators were unable to increase power flows to the trouble spots, or promptly reduce demand, to restore the balance needed in the system.

The timeline and comments by task force members made clear that investigators are looking at events far beyond the failures of three FirstEnergy Corp., transmission lines south of Cleveland that occurred during the hour before the blackout.

Still, the failure of those lines between 3:05 p.m. and 3:41 p.m. cannot be dismissed because they forced power onto other lines and “began to overload those lines as well,” the interim report said.

It said most of the events that appeared to have contributed to the blackout occurred between noon and 4:13 p.m. EDT. But it said there also were many events of interest in the Midwest power grid that happened well before that and “across several states.”

These events should not be discounted, said Jimmy Glotfelty, a task force member.

The timeline “acknowledges the importance of looking at all of the events in order to determine how they may be related, ultimately to determine how they may have caused the outages,” said FirstEnergy spokeswoman Ellen Raines.

A power plant in Michigan and two in Ohio shut down between 12:05 p.m. and 1:31 p.m., the first entry in the task force’s timeline. By 2:02 p.m., a transmission line from southwestern Ohio to northern Ohio disconnected from the system “because of a brush fire under a portion of the line.” The three FirstEnergy lines later failed following by a string of other transmission lines tripping in Ohio and eastern Michigan, isolating the northern Ohio grid.

By then “an apparent voltage collapse” was under way that prevented electricity from moving as it should through the system, the task force said. Transmission voltage is what pushes electricity along the lines from generating plant to where it is needed, much like water pressure forces water through a pipe. The caused of the voltage decline remains unclear.

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On the Net:

Department of Energy: www.energy.gov

AP-ES-09-13-03 0255EDT