1 Worker's Mistake Caused Power Failure, SDG&E Chief Says

he head of San Diego Gas & Electric said Friday that a single worker in Arizona started the

The subsequent electromechanical failures that rippled throughout Southern California, Arizona and northern Baja, Mexico, are still under examination, however.

Meanwhile, federal regulators said they will  launch their own investigation into the cause of the outage, which left more than 1 million customers without power and caused the shutdown of the San Onofre nuclear plant.

“This inquiry is an effective way for us to protect consumers and ensure the reliability of the bulk power system,” said Jon Wellinghoff, chairman of the the Federal Energy Regulatory Commission, in a news release.

SDG&E President and CEO Michael Niggli, when asked to explain how a single maintenance employee changing out a capacitor could have cut power to a huge swath of the Southwest, said the utility can’t prepare for every contingency.

Niggli pointed to an outage several years ago that started in Ohio and plunged seven states and several Canadian provinces—40 to 50 million people—into darkness.

“And that one started with a tree branch,” he said.

Niggli did explain, however, that the electrical grid has systems of circuit breakers that cut power to whole sections in instant response to changes in voltage.

When a transmission line goes offline, voltage is rerouted around the broken circuit. In this case, the tripped transmission line was extremely important for importing power to Southern California, Niggli said. The subsequent loss of voltage reached lines going into San Onofre Nuclear Generating Station, which automatically shut down to protect itself, as it was designed to do.

Gil Alexander, a San Onofre spokesman, said in a statement Friday morning that the

“San Onofre personnel are conducting the routine inspection of plant equipment that follows a shutdown, plus reviewing restart issues,” he said. “Meanwhile, the plant continues in a safe, stable shutdown condition.”

Alexander said the plant generates so much electricity that its stopping and starting affects wholesale electricity prices in the state. For that reason, the plant doesn’t share the exact start-up times.

The power station—which is operated and maintained by Southern California Edison and 40 percent owned by SDG&E—should be back generating power within 24 to 48 hours, Niggli said.

The utility operators have access to data about the system down to the sub-second, so the several operators involved will be combing that information to find out exactly what happened, Niggli said.

“We’ll be looking at all that data very carefully,” he said.