Latest indications - Problems stared in Ohio at 3:06 pm
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The earliest known failure on a major high-voltage line began around 3:06 p.m. south of Cleveland, the North American Electric Reliability Council said. Power diverted because of the failure probably caused a nearby line to overheat, sag and short circuit 26 minutes later, David Hilt, the council's director of compliance, said in an interview. By about 4:11 p.m., the failure had spread to New York, Detroit, and Toronto.
``We are at this time fairly certain that this disturbance started in Ohio,'' Michehl Gent, the council's chief executive, said on a conference call. ``We are now trying to determine why this situation was not brought under control after the first three transmission lines'' were shut down automatically.
The group has reported at least four transmission-line failures in Ohio before blackouts hit other states. Engineers will analyze more than 10,000 pages of data, including records from the control rooms of power plants and transmission-system operators, Gent said.
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Engineers don't know why the first line failed, and can't yet explain how the successive failure of at least three more transmission lines south of Cleveland might have triggered the massive blackout, Hilt said.
There were no thunderstorms or lightning strikes reported in northern Ohio at the time, he said.
Circuit breakers dropped power plants from the grid after massive swings in the direction of electricity on lines bordering Lake Erie and Lake Ontario, Hilt said. The action was automatic, to protect equipment from improper voltage.
``Power was sloshing back and forth,'' he said. ``Operators were seeing swings bigger than 800 megawatts, which is a rare event. That puts incredible stress on the system.'' On average, 800 megawatts is enough power for 640,000 U.S. homes.
Power Swings
Transmission or plant failures in other regions may have contributed to the unusual power flow, Hilt said. Earlier on Thursday, power had been flowing from Michigan into Ontario and across Ohio and Pennsylvania to New York to meet demand, Hilt said.
The Midwest System Operator reported power swings at 4:08 p.m., about two minutes before the first reported plant dropped from the grid in Michigan, and just three minutes before ``significant'' power failures hit Canada and the Northeastern U.S.
``There was essentially no human operator intervention into this thing that we're aware of,'' Hilt said. ``This thing didn't leave time for operators to really take any action.''
Cheers,
Scott.