SAN DIEGO — A blackout that swept across parts of the Southwest and Mexico began with a single utility worker and a minor repair job.
How it then rippled from that worker in the Arizona desert to southern California and across the border, plunging millions of people into darkness, has authorities and experts puzzled, especially because the power grid is built to withstand such blips.
However it spread, the outage Thursday was a reminder that the nation’s transmission lines remain all too vulnerable to cascading power failures.
“There are a lot of critical pieces of equipment on the system, and we have less defense than we think,” said Rich Sedano at the Regulatory Assistance Project, a utility industry think tank based in Montpelier, Vt.
In 2005, Congress required utilities to comply with federal reliability standards for the electricity grid, instead of self-regulation. Layers of safeguards and backups were intended to isolate problems and make sure the power keeps flowing. But that didn’t happen Thursday.
The Arizona Public Service Co. worker was switching out a capacitor, which controls voltage levels, outside Yuma, Ariz., near the California border. Shortly after, a section of a major regional power line failed, spreading trouble farther down in California and later Mexico, officials said.
And the lights began to go out in a border region of roughly 6 million people.
The outage knocked out traffic lights, causing gridlock on the roads. Two reactors at a nuclear power plant along the coast went offline after losing electricity.
More than 2 million gallons of sewage spilled into the water, closing beaches in the nation’s eighth-largest city.
Federal investigators are trying to determine what caused the blackout and how future problems can be prevented.
If regulatory violations are found, the government could issue fines of up to $1 million per day for every violation, officials said.
The line has been “solid, reliable” with no history of problems, said Daniel Froetscher, vice president of energy delivery for Phoenix-based Arizona Public Service Co.
Powerless
2003: A blackout knocked out power to 50 million people in the Midwest and the Northeast.
2005: A major outage struck the Los Angeles area.
Thursday: Two million people lost power in California, Arizona and Mexico.
