A power outage that affected 7 million people last month in the Southwest U.S. and part of Mexico was not solely caused by a utility worker doing a minor repair job, as originally thought, utility officials said Wednesday.
Federal officials and executives from California and Arizona utility companies said they still don't know exactly what happened the afternoon of Sept. 8, when power was knocked out for up to 12 hours from Arizona to southern California and into the northern part of Mexico's Baja California.
While the utility employee's work on a transmission line at an Arizona substation was the first action in the chain of events, it should not have triggered a massive blackout because the system is built to quickly compensate for such glitches, utility officials said.
Investigators have discovered that at least 20 events took place within an 11-minute period, said Stephen Berberich, president and CEO of the California Independent System Operator, or ISO, which operates the state's wholesale power system.
"This blackout should not have happened," Berberich said Wednesday during an oversight hearing of the California State Assembly Committee on Utilities and Commerce, and of the Joint Legislative Committee on Emergency Management, held in San Diego.
Donald Robinson, president and chief operating officer of Arizona Public Service Co., said it was wrong to pin the blame solely on a utility worker at his company's substation.
"There are still many things we do not know that happened on those days," he said.
But the nearly two-month probe has revealed one fact, Robinson said: "This event was not caused by the actions of a single utility worker. That is an unfortunate perception that came out early in the process. The system is built to withstand an event like that."
The utility companies involved, under ISO's direction, have formed a voluntary joint task force to investigate. Berberich said it could take up to a year before they find the exact cause.
The Federal Energy Regulatory Commission and the North American Electric Reliabilty Corp. also have opened a joint inquiry into the outage.
The outage knocked out traffic lights, causing gridlock on the roads in the San Diego area. Two reactors at a nuclear power plant up the California coast went offline after losing electricity. Nearly 3.5 million gallons of sewage spilled into the water off San Diego, closing beaches in the eighth-largest U.S. city.
The National University System Institute for Policy Research has estimated the outage cost the San Diego-area economy more than $100 million.
Many people on both sides of the U.S-Mexico border had to spend the night struggling to fall asleep in high temperatures, which reached up to 115 degrees in the desert areas.
There were no reported deaths or injuries related to the outage.
The blackout was another reminder that U.S. transmission lines remain vulnerable to cascading power failures.
In 2003, a blackout knocked out power to 50 million people in the Midwest and the Northeast. And in 2005, a major outage struck the Los Angeles metropolitan area.
That same year, Congress required utilities to comply with federal reliability standards for the electric grid instead of self-regulation. Layers of safeguards and backups were intended to isolate problems and make sure power keeps flowing.
Berberich said some of the safeguards helped curb the problem.
As the lines were knocked out, power flows jumped to levels that were at or exceeded safety standards and triggered the San Onofre Nuclear Generation Station to be taken offline, as it is supposed to do, Berberich said. That kept the outage from spreading to Los Angeles.
Mexico also took power plants offline to contain the blackout.
Utility companies used Twitter and email to communicate with the public and learn of breakdowns in backup systems at hospitals, the airport and other critical customers, so officials could focus on restoring power to them first.
The companies are communicating more often with each other, Berberich said. ISO is putting in place operating procedures that monitor the transmission flows on the south line of the San Onofre Nuclear Generation Station, he said. That way, when power reaches certain levels officials will take immediate action, such as bringing up additional generation to alleviate a potential overload before a blackout occurs.
But the companies say pinpointing the cause is crucial.
"We think that the only way that we get better is if we understand exactly what took place and put in place steps that we can to prevent it from happening in the future," Robinson said.
If regulatory violations are found, the government could issue fines of up to $1 million per day for every violation, officials said.