“While the vast majority of customers power has been restored, the risk of intermittent power outages may occur as complex process of full restoration proceeds,” the utility said.
The outage began as an island-wide blackout that closed schools and courts for days and caused other interruptions for the US territory’s 3.2 million residents.
Still, the power company urged customers to conserve electricity when possible to help reduce demand and assist full restoration.
The massive outage began around 8:45 p.m. Wednesday when an unspecified failure led to a fire at the Costa Sur Substation, said Kevin Acevedo, vice president of LUMA Energy. Firefighters have since extinguished the flames at the facility outside the town of Guayanilla on the southwest coast.
Initially, all customers lost power “because all the generating units went offline,” according to Josué Colón, the island’s lead telecommunications and infrastructure engineer.
Schools across the island also canceled classes for students on Thursday and Friday, though principals, custodians and school cafeteria employees were told to report to work Friday, the island’s education department said.
By Thursday afternoon, all hospitals were operational either through power restoration or generators, Secretary of the Interior Noelia García Bardales said.
Cause of fire is under investigation
As the lights are turning on in the remaining homes and businesses, little is known about what caused the fire that plunged the island into darkness.
“Every single (piece of) equipment (at the plant’s switchyard) needs to be inspected and tested to make sure that when it’s back in service, we can restore power for customers reliably and safely,” Shay Bahramirad, LUMA Energy’s senior vice president of engineering and asset management, told reporters Friday in San Juan.
The utility said Thursday the “massive island-wide blackout” might have been “caused by a circuit breaker failure” at the Costa Sur plant.
Acevedo, LUMA’s vice president, said the cause of the fire remains under investigation, noting that the equipment was up to date on maintenance inspections.
Replacement parts for the power plant have been ordered, and cleanup efforts were underway, Acevedo added.
CNN’s Jason Hanna, Rafy Rivera and Michelle Watson contributed to this report.