California's electric grid operator expected to have sufficient electricity on Tuesday afternoon as increasing generation and conservation efforts averted the potential for a blackout, the agency said.

A number of generators were able to restart power plants that shut unexpectedly Tuesday morning while power consumption in the state fell below earlier forecasts even as 100-degree-plus temperatures boosted the need for air conditioning across the state and the entire western U.S.

NRG Energy Inc. was working to restart several units at its Encina power station that tripped about 5:30 a.m., said spokesman David Knox. "We expect to have all but one of the units that tripped off online later today and the last unit online by Thursday," Knox said. The Encina unit can produce 965 megawatts of power. In California, one megawatt can supply about 700 homes.

While the state escaped power disruptions on Tuesday, the grid agency remains concerned about tight supply conditions on Thursday when offices and industrial plants reopen after the July 4th holiday.

"Thursday is looking to be a difficult day," said Gregg Fishman, spokesman for the California Independent System Operator. "Temperatures across the western U.S. will be at triple digits."

The regional heat wave "will tax the whole system," Fishman said. "We are encouraging people to think about what they can do to conserve power."

The California ISO said Thursday's peak-hour demand will reach 47,000 megawatts, up from about 43,500 MW on Tuesday and 42,600 MW on Wednesday, according to a release.

While NRG and Sempra Energy's San Diego Gas & Electric utility were working to restart generators on Tuesday, transmission damage caused by a small plane crash north of San Diego will not be fixed quickly, the ISO said.

The plane clipped two high-voltage lines before crashing, the ISO said. In addition, about 1,900 MW of generation tripped overnight due to transmission issues unrelated to the plane crash.

"Currently there is no estimated time of return for the transmission capacity," the agency said in a release. "Reducing demand through voluntary conservation is the prudent thing to do, especially with a significant heat wave due in California this week."

Thursday's peak will fall short of the 2006 summer peak which exceeded 50,200 megawatts during a late July heat wave.

Earlier Tuesday, the ISO ordered power-plant owners in the state to restrict maintenance activity, an initial step in the grid operator's emergency procedures to avoid blackouts.

Wholesale power prices in California jumped to more than $300 for Thursday delivery, traders said, compared to $60-$70 per megawatt-hour normally, according to Reuters data.