By Mike Boyer
The Cincinnati Enquirer

The good news for electric customers across the region is that the country's electric grid worked the way it was supposed to in the midst of the worst power blackout in the nation's history.

While 50 million customers in northern Ohio, Michigan, Ontario, New York and New Jersey lost power, those in the southern half of Ohio, all of Indiana and Kentucky didn't.

"The grid system is set up so it isolates where there is a problem,'' said Steve Brash, spokesman for Cinergy Corp., which has 1.4 million electric customers in the Tristate.

"It isolated that area and prevented the rest of the state from getting into a cascading outage,'' he said.

Brash said Cinergy was asked to put some of its peaking plants on standby to generate additional power if needed.

Although officials said it's too early to say what triggered the massive blackout, they are focusing on a nine- or 10-second event near Lake Erie Thursday afternoon.

Some 300 megawatts of power moving on transmission lines from Detroit to New York, through Ontario, suddenly reversed to 500 megawatts going the other way, said Michehl R. Gent, president of the North American Electric Reliability Council, a voluntary industry organization overseeing reliability of the nation's wholesale power system.

The power loop around lakes Erie and Ontario has been "a problem for years,'' he said.

Officials don't know what led to that power shift, which may have been the event that caused a dozen or more transmission lines and 100 or so generating plants in the region to switch off.

Cinergy's Brash said the transmission lines and generating plants have automated protection systems so that when problems are sensed, they immediately shut down to prevent further damage.

Bob Burns, senior research specialist at the National Regulatory Research Institute at Ohio State University in Columbus, said transmission lines have both voltage and thermal limits.

The lines literally stretch and sag if there's too much heat buildup, say from too much electrical demand, or if the voltage gets out of predetermined limits.

When that happens, protective devices shut the lines down. Much the same thing happens at power plants when devices sense a problem, Cinergy's Brash said.

Cinergy is a member of the Midwest Independent Transmission System Operator Inc., a Carmel, Ind.-based organization that manages 111,000 miles of high voltage transmission lines in 15 states and one Canadian province.

Spokeswoman Mary Lynn Webster said when system engineers began seeing the problems in the Northeast late Thursday afternoon, they had time to redirect and redistribute power that otherwise could have triggered a wider failure.

E-mail mboyer@enquirer.com