Hawaiian Electric Co. officials were trying to determine what caused three power generating units to shut down Thursday morning, resulting in the loss of electricity for about 45,000 customers around Oahu.
The outage affected Waipahu; portions of central Honolulu; Leeward and Windward Oahu; Aina Haina; and Hawaii Kai.
The company said it isn’t clear which of the system’s three generating units tripped offline first: Applied Energy Services’ 180-megawatt plant in Campbell Industrial Park from which HECO buys electricity; HECO’s 92-megawatt unit at Kahe; or its 92-megawatt facility in Waiau.
"We are conducting an investigation to determine the cause," said Peter Rosegg, Hawaiian Electric spokesman.
Electricity was shut off to some customers briefly as a protective measure to restore balance between the power supply and demand on the Oahu grid and to prevent the chance of a more widespread or longer power failure, HECO said in a written statement.
Hawaiian Electric said it quickly brought additional generators online to restore the balance, and system operators were able to begin restoring power to customers within 25 minutes. Almost all customers had service restored by 10 a.m., with small remaining pockets of customers restored within the hour.
The shutdown knocked out traffic signals throughout the island, slowing traffic near the end of the morning commute.
Jan Miller, Hawaiian Electric spokeswoman, said one of its plants stopped generating power at 8:50 a.m., triggering the shutdown in the other two plants as a safety mechanism tried to balance the load on the electrical distribution grid.
Hawaiian Electric officials began restoring power at 9:15 a.m. to Mililani and Waipahu first, followed by the other parts of the system.
Full electrical power was restored to Hawaii Kai by 9:45 a.m.
"We sincerely apologize for the disruption to our customers," said Lynne Unemori, Hawaiian Electric vice president for corporate relations. "Our employees worked to safely restore power as quickly as possible, and we appreciate our customers’ patience and understanding."
