A private power provider generating nearly one-fourth of Oahu’s electricity went off­line Tuesday morning, resulting in a 40-minute power outage for as many as 75,000 Hawaiian Electric customers in Central, West and Windward Oahu.

Hawaiian Electric Co. said it implemented the temporary outage as a precaution after a 180-megawatt generating station owned by independent power provider AES unexpectedly shut down at about 10:30 a.m., HECO spokes­man Darren Pai said.

"It was a precautionary measure to prevent potential damage to the system, and it’s part of an automatic process that’s built into the way the system is operated," he said. The action helps re-balance the supply and demand for power on the grid and prevent a potentially larger and longer outage for customers, HECO said.

The AES unit, at Campbell Industrial Park, is the largest individual power-generating unit on Oahu, Pai said. It was supplying about 23 percent of the island’s power at the time the generator shut down. The cause of the generator outage was being investigated.

HECO estimated that as many as 75,000 customers were affected. Power was restored to circuits by 11:09 a.m., with the exception of a few small pockets of customers who had power restored shortly thereafter, HECO said.

"We began restoring power as quickly as possible while still ensuring safety," Pai said. "We sincerely apologize to our customers for the disruption."