WASHINGTON -- Voltage shifts, line problems and power plant shutdowns were observed "well before" midday and across several states on the day of the nation's worst blackout, a government task force said Friday.
A time line released by a U.S.-Canadian task force did not provide any new indication on what precisely triggered the Aug. 14 blackout which investigators believe started with power line problems in Ohio.
The blackout began to cascade from Ohio and Michigan into southern Canada and New York state at about 4:11 p.m., investigators have said previously.
"Most of the events that appear to have contributed to the blackout occurred during the period from about noon to about 4:13 p.m.," the task force said Friday.
But "many things happened well before 12 p.m. ... across several states" and some of those problems also "may be relevant in a causal sense to the blackout," the preliminary report issue Friday said.
'Far from complete'
However, it said more work needs to be done before a cause of the massive outage -- and particularly what caused it to spread so widely and so quickly -- can be determined.
"While we are making good progress, this investigation is far from complete," Energy Secretary Spencer Abraham said.
He added, "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, why the collapse took place ... and why the fail-safes in the system were not sufficient."
The blackout, the worst in the nation's history, cascaded across all or parts of eight states from Michigan to southern New England and into southeastern Canada knocked out electricity to 50 million people. At one point more than 100 power generating stations were shut down because of the transmission voltage surges.
"One of the characteristics of the blackout was an apparent voltage collapse" that prevented electricity to move as it should through power lines in northern Ohio and eastern Michigan, the task force said. Adequate transmission voltage is needed to move electric power from generating stations to where it is needed, much like water pressure forces water through a pipe.
But task force investigators said Friday they aren't sure what caused the drop in voltage on the day of the blackout.
The task force said it was looking into whether there may have been an unusual decline in so-called "reactive power" -- a portion of the energy moving through power lines that is essential for keeping proper voltage levels. Reactive power can be consumed by excessive demand resulting in heavily loaded power lines, or by electromagnetic devices that absorb it, technicians said.
"When reactive power is limited, the increased loading will cause a voltage drop along the line," said the task force.
Canadian Natural Resources Minister Herb Dhaliwal, who with Abraham co-chairs the task force, said that the sequence of events released Friday are "only a first step in the process of uncovering what happened."
The timeline generally reflected events previously made public by various investigators as well as FirstEnergy Corp., the company that has been at the center of the investigation because of power line failure in its northern Ohio system during the hour before the blackout.
The task force's timeline noted that American Electric Power's Conesville generating plant in central Ohio shut down at 12:05 p.m. and that two other plants -- Detroit Edison's Greenwood plant north of Detroit and First Energy's Eastlake plant near Cleveland -- shut down between then and 1:31 p.m. EDT.
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 task force said.
Three more transmission lines failed between 3:05 p.m. and 3:41 p.m. in northern Ohio. All belonged to FirstEnergy. These problems, which have been widely reported, became an early focus of the investigation.
The task force said two more lines failed in Ohio between 3:45 p.m. and 4:09 p.m. followed by the failure of three lines between Ohio and Michigan. When these lines failed it blocked a major transmission path from Ohio into eastern Michigan, the task force said.
Twenty power plants along Lake Erie tripped automatically off the power grid in a matter of 40 seconds beginning at 4:10 p.m., causing a loss of 2,174 megawatts of power. This loss of generation increased the power flow into northern Ohio and eastern Michigan on lines that were still open.
Then more power plants disconnected.
"When the transmission 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," the task force described.
That was at 22 seconds before 4:11 p.m. During the next 1 minute and 19 seconds various legs of the power grids that stretched from Michigan, into Canada, through New York states and into parts of New England as well as New Jersey disconnected, according to the task force timeline.
The blackout was in its full force.
Abraham called the timeline of events major step toward learning why the blackout occurred. "The critical first step has been passed," he said. "Now we can focus on to answering the question why."