Associated Press

COLUMBUS- Ohio's section of the power grid experienced at least 64 glitches in the four hours before the nation's worst blackout, according to a draft timeline the state's utility regulator sent Gov. Bob Taft this week.

The timeline by the Public Utilities Commission of Ohio shows that most problems involved power plants and major transmission lines that tripped off momentarily or went down completely.

The Aug. 14 outage affected eight states and parts of Canada. The blackout affected 50 million people, shut down more than 100 power plants and knocked Cleveland's water supply off line.

American and Canadian investigators are focusing on failures of a power plant and lines owned by Akron-based FirstEnergy Corp.

PUCO's draft timeline is consistent with those released earlier by power companies and the joint U.S.-Canadian task force.

For example, the timeline includes the 12:05 p.m. trip of circuit breakers at a unit of American Electric Power's plant in Conesville in eastern Ohio. The U.S./Canada Power Outage Task Force identified the same problem almost two weeks ago.

The PUCO report pinpoints problems - some considered minor, like a small line tripping off for a few seconds - on Ohio's portion of the grid that connects four major Ohio power companies.

An AEP line in Findlay, for example, tripped and closed in half a second at 3:51 p.m., the timeline shows.

Such brief line trips happen constantly, caused by anything from a bird or a tree limb hitting a line, AEP spokesman Pat Hemlepp said Friday. The ability of a line to trip and then immediately reset is a normal function of the power grid, he said.

"When that becomes unusual is when you have a whole series of events on a variety of lines, which was what was encountered that day," Hemlepp said.