HONOLULU -- The Public Utilities Commission has asked Hawaiian Electric Co. for a briefing on what happened on Sunday when all of Oahu lost power and why it took so long to restore power.

Some state senators are calling for a full-blown investigation.

HECO officials will brief the head of the Public Utilities Commission, Gov. Linda Lingle said.

"I want to be clear, we're not seeking an investigation. What he's doing is requesting a briefing and an explanation of what happened. Based on the information he gets, he can open a formal investigation. It's called a docket," Lingle said.

However, state senators in both political parties, including the chairman of the Senate's Energy Committee, called for the PUC to perform an investigation.

"So part of it is to understand how our grid system works -- to understand how our power is generated and to investigate just what happened and why it took so long to come back on," Sen. Kalani English said.

"We will want to see a real explanation why Hawaiian Electric had this catastrophic failure here on this island, especially," Sen. Fred Hemmings said.

HECO said it is doing its own investigation already and will brief state officials about its findings.

"We support an investigation. We want everyone to know, but we also want everyone to know that it's something we would have done anyway," HECO spokesman Jose Dizon said.

The head of the Public Utilities Commission was asked about the chances that a PUC investigation could lead to forcing HECO to compensate people for lost business.

"The odds are slim, but there can be in bad circumstances, but probably not," PUC Chairman Carl Caliboso said.

Someone would have to prove that any negligence on HECO's part rose above the effect of the earthquake, Caliboso said.

KITV asked why much of Oahu had no power all day and Maui and the Big Island were restored to power so much quicker.

"Those systems are smaller. They have quick-starting diesel generators that can get online much more quickly," Dizon said.

Pockets of outages remained throughout the island on Monday morning. These are isolated areas that crews need to deal with on site, according to Dizon.

Many of the areas had blown fuses in the transformers, he said. Crews were dispatched to replace fuses and work on other issues in the outage areas.