Fires threaten remaining power link to San Diego

LOS ANGELES (Reuters) - Wildfires threatened to shut down the last remaining major power transmission link to San Diego, which would make the Californian county an electricity "island", susceptible to major blackouts, the manager of the state power grid said Wednesday.

If it is cut off from external electricity supplies, San Diego County would have to rely only on the power its own plants can generate, which would greatly increase the chance of major blackouts, said officials from the California Independent System Operator.

Urgent pleas for conservation need to be heeded or there could be widespread outages without warning for San Diego Gas & Electric Co's 1.3 million business and residential customers.

San Diego Mayor Jerry Sanders implored residents to cut power use.

"You've got to conserve today. You have no choice," Sanders said.

About 20,000 homes and businesses were without power, down from 28,000 on Tuesday, SDG&E said on its Web site.

Four days of wildfires have caused the largest evacuation in California's history and burned at least 2,200 homes, state officials said.

Never before has California faced as many shutdowns on the big power lines that are strung across the state and link it with the rest of the U.S. Western grid, said California Independent System Operator spokeswoman Stephanie McCorkle.

"This is unheard of, to lose this many transmission lines," said McCorkle. "But it is obviously a historic disaster we are dealing with."

SDG&E has two major links to the rest of the U.S. Western power grid, one to the east and Arizona that has been shut since Sunday and one that connects with the grid to the northern of San Diego County. That second line is in peril, said McCorkle.

Power demand in San Diego County was diminished on Tuesday as many homeowners fled to escape advancing fires. Depending on how many get to go back home on Wednesday that may increase the demand on the power supply, McCorkle said.

The link to Arizona, the 500-kilovolt Southwest Powerlink, and 138-KV and 230-KV lines in the SDG&E system have already cut power supplies to the point that if San Diegans don't watch their energy use, a serious emergency could occur, McCorkle said, even without the shutdown of the remaining link to the Western grid.

"The problem is that with winds shifting, the fires can change direction and threaten lines again," McCorkle said. "The situation is still very volatile today."

The power situation in most of the rest of the state appeared to be improving.

Southern California Edison, which serves three times as many power customers as SDG&E, had lowered power outages to about 2,000 customers and reported no problems on its transmission system, nor any of it in danger.