How Pulling the Plug Keeps Most Power On

Rolling a power blackout across a state the size of California requires a delicate balancing act on an enormous scale.

To keep machinery working, appliances operating, traffic signals, burglar alarms and medical equipment all functioning, power engineers must keep electricity flowing within very precise specifications. If there is not enough to go around, they cannot give everyone a little less. Instead, they must drop some customers entirely to make sure that the system as a whole does not crash.

And to make sure that no one neighborhood or part of the state bears the entire burden, the system is designed to spread the outages among many different areas.

A power shortage throws the electricity grid out of balance, explains Jim Detmers, managing director of operations for the agency that runs most of the electricity grid, the California Independent System Operator.

If too little power is generated to meet demand, the frequency of electricity traveling through the wires, which is supposed to be 60 cycles per second, drops. Falling to just 59 or 58 cycles can be big trouble, he suggested. If “the frequency goes down . . . that can damage equipment.”

So attuned to electrical frequency is precision machinery that the slightest change can cause havoc. “A mechanical clock will actually slow down if the frequency drops,” he said.

To prevent that from happening, grid system managers determine how much power must be shut down to maintain balance. And though utilities may know hours ahead of time about an imminent outage, the final word comes generally just 10 minutes or so in advance, largely in response to immediate demand.

Rolling blackouts sometimes arouse concern that poor communities are hit harder than wealthier ones. Utilities deny that charge and say they cut off power here and there across large areas at the same time to disperse the effects.

When word comes down from grid managers that a blackout must be instituted, utilities have to quickly identify blocks of commercial and residential customers whose consumption matches the target power figure and switch off their power.

Pacific Gas & Electric’s more than 13 million electricity customers have been divided into 14 blocks, based on the load of each circuit. Each block, accounting for about 500 megawatts of usage, covers about 200,000 customers in neighborhoods scattered throughout PG&E;’s Northern and Central California service area.

“Your neighbor may or may not be on your circuit,” said Staci Homrig, a company spokeswoman.

Sometimes, blackouts may be needed far away from the actual area of shortage. Thursday, for example, grid managers feared that to keep Northern and Southern California in balance, they would have to black out parts of San Diego to cope with shortages in the Bay Area.

For Southern California Edison, the first customers denied power are those linked to automated substations, said Ron Nunnally, Southern California Edison director of federal regulation and contracts.

Automated circuits handle about 3,500 megawatts of peak winter load--about 25% of the normal winter peak of nearly 14,000 megawatts consumed by Edison’s 11 million electricity customers

“Once we have rotated through as many automated circuits as we can, we would have to manually open the switches” until the need for blackouts is over, Nunnally said. Automated switches are spread throughout Edison’s 50,000-square-mile territory, so no one community would be completely in the dark, he said.

Generally, police, firefighters, large hospitals and some other essential users of electricity are spared the blackouts.

People at home who depend on electricity to survive, such as patients on respirators, are supposed to have registered with their utility company as special users.

“Every year, regardless of this current crisis, we notify them” by mail of the need to have backup power sources, said Suzanne Middleburg, Southern California Edison’s manager of customer satisfaction. “My sense is, these folks have backup plans, because their lives depend on it.”

PG&E; keeps the names of such customers in a database and tries to notify them of a coming blackout, a representative said.

Medical suppliers like Wishing Well Inc. of Santa Monica provide backup power to their clients. “We give them tanks that are typically good for five hours, which is normally good enough for us to get to them,” said Don Albrecht Jr., who helps run his family’s business. Those backup tanks, he said, “run on compressed air so they don’t require electricity.”

And when things go really wrong, utilities can be held legally responsible for damages resulting from electricity outages.

After an accident at a PG&E; substation in 1998 cut power to a million people in the Bay Area for nearly a day, the city and school system sued the utility, settling for more than $1 million, said San Francisco City Atty. Louise Renne.

“Patients were on the operating table at the time and the hospitals had to bring in emergency generators,” said Renne. “There was spoiled food in restaurants. Schools closed.”

All told, the utility received 16,000 claims and paid $10 million in damages, said PG&E; spokesman John Tremayne, adding that the utility’s liability depends heavily on the cause of an outage.

“If it is an act of God, it is beyond our control,” he said. “But if it is a misstep on our part, we can be held responsible.”

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Times staff writers Nancy Rivera Brooks, Tim Reiterman, John Glionna and Christine Hanley and researcher Maloy Moore contributed to this story.