Stabbed in the BackBy Mel Duvall | Posted 2003-11-01 Email Print
The Ohio utility's systems protected its 4.9 million customers during the Aug. 14 blackout. But did they knock out power to 50 million people in the process?
Stabbed in the Back
That's AEP's assessment. But experts are now debating whether AEP's automated systems acted too quickly or self-servingly, preventing the grid from healing itself by redistributing power. The relays' digital smarts may have, in fact, done something very stupid.
"It's a double-edged sword," says Hoff Stauffer, a senior analyst with Cambridge Energy Research Associates (CERA) in Boston. "We give AEP credit for saving itselfwhich it did. But in the process, it stabbed Michigan in the back. There was nothing Michigan could do; and that, in turn, led to the cascading blackout."
Investigators say events on Aug. 14 unfolded in this sequence:
12:05 p.m. AEP's 375-megawatt Unit 5 in Conesville, Ohio, shuts down. An hour later, Detroit Edison's 785 MW Greenwood power plant in the Detroit area shuts down. At 1:31 p.m., FirstEnergy's 597 MW Eastlake Unit in northern Ohio goes out. The events are unrelated but begin to destabilize transmission flows.
2:02 p.m. A brush fire in southwestern Ohio downs a transmission line. The flow of electricity in the region is diverted around the disruption.
3:32 p.m. A transmission line jointly owned by FirstEnergy and AEP sags, likely from overheating, touching a tree and shorting out.
3:45 p.m. AEP's automatic relays, detecting instability in the voltage on the lines it shares with FirstEnergy, begin turning off power to FirstEnergy's network in Northern Ohio.
4:08 p.m. With transmission lines cut to FirstEnergy, the system looks for an alternate way to reach equilibrium. A huge wave of electricity rushes from AEP's system along a high-voltage line into Indiana and then through southeast Michigan attempting to get back to FirstEnergy. That surge shuts down lines and power plants along the way. Detroit Edison actually goes black before FirstEnergy, although only by seconds.
4:10 p.m. "At this point, the coffin is basically nailed," says Stauffer. Ontario's electricity system had been importing power from Michigan. Now, it suddenly finds itself struggling to supply both itself and Michigan with power. Ontario pulls power from New York and Pennsylvania, but the surge in demand trips lines conducting electricity across national borders. After struggling for 90 seconds to rebalance loads, Canada's most populous province goes black. By 4:13 p.m., New York and parts of New England and New Jersey are added to the casualty list.
Relays owned by ISO New England shut down lines flowing between New York and New England, preventing the blackout from spreading further north. Relays also isolated PJM Interconnection, a regional transmission organization serving parts of Pennsylvania, New Jersey, Maryland, Virginia and West Virginia. This protected the company's own power generation and transmission systems. But, in the process, New York was starved for power.
"Those automatic relays cut both ways, and that's one of the things the investigation will have to wrestle with," says Stauffer.
One critical question, says AEP's Draper, is why relays at other utility and transmission companies didn't behave in the same manner as those at AEP.
If each region had been able to isolate itself from the troubles at FirstEnergy, the blackout would have only impacted thousands, instead of millions. Draper told the House Committee on Energy and Commerce in September that Consumers Energy, a subsidiary of CMS Energy Corp., serving Michigan regions west of Detroit, was able to protect itself and maintain power to most of its 1.7 million customers. "I don't know why all systems didn't perform in a similar manner," he told the committee.
AEP has been more aggressive in its deployment of digital relays than some counterparts. Chuck Evans, president of Newton-Evans Research Company, of Ellicott City, Md., estimates as few as 35% of relays in place today use microprocessors to route power, even though such relays have been available since 1982. The vast majority are electromechanical, with some dating back as much as 40 years.
Utilities have been slow to replace the electromechanical relays because of cost and other factors, says Dave Dolezilek, technology director for Schweitzer Engineering Laboratories, of Pullman, Wash. The price of a new digital relay ranges from about $1,000 to $7,000. However, installation can hike the cost as much as tenfold. That means upgrades are hugely expensive. Any given utility has thousands of relays in its networks. One substation alone might include as many as 150 relays.
"There's not much of an incentive to replace the [electromechanical] devices that are out there in the field," says Dolezilek. "But people are realizing that attitude has to change."
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