Faulty wiring installed last week during an equipment overhaul caused a power outage that shut down a South Bay refinery and left about 100,000 customers in the area without electricity, Southern California Edison said Wednesday.
The abrupt loss of power about 5:40 a.m. Tuesday led to flaring at the former Exxon Mobil refinery in Torrance, where city officials urged residents to shelter in place.
Southern California Edison's crews made a wiring error on Friday while upgrading a major substation, part of a multiyear effort to expand the grid's capacity and improve reliability, said Paul Grigaux, the utility's vice president for transmission, substations and operations.
When parts of the substation were "isolated" on Tuesday morning so that upgrades could continue, the increased current automatically triggered a protection device that operated incorrectly because of the wiring mistake and cut off power, Grigaux said.
"We take this event very seriously," Grigaux said in an interview, adding that the company was continuing to investigate the incident. Meanwhile, upgrades have been put on hold while the inquiry proceeds, the company said.
"We have discovered what led to the outage but we want to understand what led to the wiring error in the first place," Grigaux said.
The slip-up occurred at a high-voltage substation that serves about 20 lower-voltage stations, which distribute power to customers across the South Bay, including Westmont, Hawthorne, Gardena, Torrance, Manhattan Beach and Redondo Beach.
The vast majority of customers had power restored by 7 a.m., Grigaux said.
At the 750-acre refinery — which was sold this summer by Exxon Mobil to New Jersey-based PBF Energy — large flames shot from tall flare stacks.
The flames are generated when the plant sends excess hydrocarbon products to the stacks to be burned off. The facility produces gasoline, diesel fuel, jet fuel and liquefied petroleum gases.
Torrance city officials warned residents about 6:40 a.m. to remain in their homes, shut doors and windows and turn off air conditioners. The shelter-in-place warning was lifted about 7:30 a.m.
PBF Energy said the refinery's safety systems operated properly.
Grigaux said the outage underscored how susceptible refineries are to even slight fluctuations in power voltage, which the average customer may not notice. The refinery in Torrance does not have its own dedicated power service, which Grigaux called "unusual."
Modifying the power supply configuration, he said, "is something we are discussing with current owners."
The energy company said Tuesday it had begun to resume operations, a multi-day process that can entail some planned flaring. The refinery has more than 600 employees, as well as some 400 contractors who work there on a daily basis, according to PBF Energy.
Fine-particle air pollution spiked to elevated levels in a residential area near the refinery early Tuesday, according to readings collected by the Coalition for Clean Air, an environmental group.
Air pollution monitors at the facility showed a one-hour increase in levels of fine particles, "but they did not exceed short-term unhealthy levels," Sam Atwood, a spokesman for the South Coast Air Quality Management District, said.
Grigaux said the company was taking steps to prevent such an outage from happening again.