An electrical transformer that supplies power to the Shell Oil refinery in St. James Parish caught fire Tuesday night, leading to an uncontrolled shutdown that refinery workers had to scramble to control, parish officials said.

St. James Parish Sheriff Willy Martin Jr. said the Entergy substation where the transformer is located is the main power supply to the 227,500-barrel oil refinery in Convent. The transformer's loss cut power to portions of the huge complex along the Mississippi River and at the parish line, he said. 

The transformer fire started about 8 p.m. and was extinguished later Tuesday night, parish officials added. 

Shell said in a statement that after the fire started, it "initiated its emergency response plan, which included immediately deploying personnel to respond to the incident."

Francis Hymel, St. James Parish homeland security director, said plant officials assured the parish Tuesday night that they were trying to get the plant back online.

Martin said there were no offsite impacts. Shell said that all its personnel were accounted for and no injuries occurred. 

Hymel said the substation where the fire happened is outside the plant in Ascension Parish. Michael Burns, Entergy spokesman, said that while the substation is Entergy's, Shell owns the transformer that burned.

The refinery, previously part of Shell's Motiva joint venture with Saudi Aramco, went fully under Shell's ownership earlier this year in a planned break-up of Motiva. But the refinery has sustained other fires in the last 13 months, including a dramatic one inside its H-Oil unit in August 2016 that knocked the unit out for months.

Sheriff Martin said that flames and smoke continued to come from the refinery and were periodically brightening and dimming in the night sky around the plant, though that diminished by 10 p.m. 

Hymel said the refinery was doing a lot of flaring and other activity while plant workers tried to get additional electrical power to the plant.

"They have a state readiness right now until they get back online," Hymel said.

He said it was too early say what caused the electrical outage. Burns, the Entergy spokesman, said the utility will be working with Shell "to conduct a root cause analysis" of the incident.

Video posted on social media show large flames and smoke near the facility.

Not seeing the video below? Click here. (NOTE: Contains some graphic language.)

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Follow David J. Mitchell on Twitter, @NewsieDave.