HONOLULU -- Hawaiian Electric Co. crews restored power to most of Oahu by Saturday afternoon, officials said.

HECO reported that power had been restored to most of its 295,000 residential customers.

Areas still without power include neighborhoods of East Honolulu, HECO officials said. HECO officials said crews may be able to restore power to many areas before nightfall. However, they said some pockets may not be restored until Sunday.

HECO officials said there is still much they do not know about why Oahu lost power in the first place.

There was a thunderstorm happening when four major transmission lines tripped off at about 6:35 p.m. on Friday. At a briefing on Saturday afternoon, HECO said the lines showed no sign of lightning fires.

"We found that there was not any significant damage so we were able to restore those lines into service," HECO spokesman Darren Pai said.

A lightning bolt's near miss could have put enough excess electricity into the line to trip the breakers, but the failure of the system happened after the lines tripped, while engineers failed in an effort to balance the amount of power being generated to the number of customers needing electricity.

"It was just trying to maintain that delicate balance and unfortunately it didn't happen and those units tripped back off line," Pai said.

One factor may have been the timing of the problem. It was right at the peak hour for electrical usage, which meant tons of electronics and appliances demanding power when the generators came on. The company was also reluctant to use the tripped lines until they were inspected at daylight.

"It doesn't matter how much you spend, how much you invest in the system, there is no way to guarantee this will never happen again," Pai said.

Residents who have their power restored should conserve electricity in order to avoid overloading the system, HECO said.

HECO sent a power generator to the home where President-elect Barack Obama is spending his vacation in Kailua. However, an Obama aide said it was not used. (Read more about the Obama family's night.)

Lingle Praises Emergency Teams

Gov. Linda Lingle praised the state's first responders for acting swiftly to maintain normalcy during the outage.

In a conference call to news organizations, the governor credited police officers, many whom were called to duty, for keeping traffic flowing at major intersections.

The lessons learned after the 2006 earthquake had public agencies prepared, Lingle said.

She was particularly pleased with communications within the tourism industry and airport operations. An "after-action analysis" will go one step further to improving emergency response systems, Lingle said.