This is an excerpt from EERE Network News, a weekly electronic newsletter.

October 31, 2007

Wildfires Create Transmission Emergency in Southern California

The southern California wildfires that burned many homes and caused half a million people to evacuate in late October also had dire impacts on the state's electrical transmission system. The trouble started on Sunday, October 21st, when the Acton Fire caused the Southwest Powerlink to go out of service. On Monday, October 22nd, the state's electrical grid operator—the California Independent Systems Operator (ISO)—declared an emergency when the Santiago Fire in Orange County caused two more high-voltage transmission lines to trip off-line. To reduce stress on the power grid, the California ISO asked two utilities—Southern California Edison (SCE)and the San Diego Gas and Electric Company (SDG&E)—to reduce their electrical load by a total of 500 megawatts.

By Tuesday, October 23rd, the fires had knocked out multiple transmission lines in the San Diego area, causing the California ISO to request voluntary energy conservation in San Diego. Over the course of that week, more than two dozen transmission lines were knocked out of service, and on Wednesday, San Diego was being served by only one 230-kilovolt transmission line. (Of course, the evacuations probably helped to dramatically reduce the load on that line.) As one example of the tenuous situation, the California ISO notes that over the course of 24 hours, several lines that connect SCE and SDG&E at the San Onofre nuclear power plant tripped in and out of service at least 25 times. A complete loss of off-site power would have caused the nuclear plant itself to automatically trip off-line. See the California ISO press releases.

By Friday, October 26th, the emergency had passed, and utility crews were completing their repairs to the transmission lines, but the electrical distribution system in San Diego was still under repair. SDG&E says that nearly 80,000 of its customers lost power, but by October 27th, power had been restored to all but 6,700 customers. Over the weekend, the utility expected to restore power to 97% of those affected, leaving only 2,400 without power. The utility estimates that more than 1,000 of its utility poles burned in the fires and at least 35 miles of overhead wire were damaged. See the SDG&E press release.

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