Hawaiian Electric Co. had enough excess power to keep O'ahu lit after earthquakes caused two generators to fail Sunday morning, but when a third, much larger, turbine crashed minutes later, it took the entire island with it.

"If only two units went down, we wouldn't be having this conversation," said HECO spokesman Jose Dizon last night. "The system would have stayed up."

HECO is investigating the cause of the blackout, which left most of O'ahu without power for more than 12 hours Sunday.

O'ahu residents have questioned why the failure of two generators — which only supply 12 percent of the island's electrical needs — could cause the entire system to crash. The two turbines — a 90-megawatt turbine at Kahe Point and a 55-megawatt unit at Aloha Tower — went down at 7:09 a.m. Sunday, or about two minutes after the first earthquake.

HECO said yesterday that its power reserves are typically equivalent to about 15 percent of its total capacity. Had the earthquake only caused the two generators to go offline, the excess capacity would have been enough to keep O'ahu running.

SYSTEM OVERWHELMED

The failure of the third generator — a 142-megawatt unit at the Kahe Point power plant — meant that about 25 percent of the power supply was lost. That overwhelmed the system, triggering the automatic shutdown of electricity to HECO's 291,000 O'ahu customers, Dizon said.

The third generator shut down three minutes after the first two at 7:12 a.m. Sunday because of shaking from the first earthquake, a 6.7-magnitude temblor off the coast of the Big Island.

HECO has begun an internal investigation into the blackout.

The state Public Utilities Commission will begin questioning HECO officials in the next few days over the causes of the outage. State lawmakers are calling for a full investigation by the PUC that could result in fines and penalties should HECO be found at fault.

LONGER BLACKOUT

HECO officials said the shutdown of the islandwide system was necessary once the third generator came down to avoid permanent damage to the operating generators. If one of the other generators had been damaged, it could have led to blackouts lasting days or weeks and not hours.

"It could easily take months" to repair a damaged generator, said Dan Williamson, HECO president from 1990 to 1995. "They would have to get (a new generator) from a Mainland manufacturer or borrow one from another utility on the Mainland and would have to have it dismantled and reconfigured for use here."

Reach Rick Daysog at rdaysog@honoluluadvertiser.com.