ALCOA is working to stablise its Portland Aluminium smelter after both of the site's potlines lost power for hours at the weekend.
An Alcoa spokeswoman said an issue with the incoming transmission line caused a power outage at 7.06pm on Saturday night.
She said power to the smelter returned at 10pm on Saturday, while power returned to potline one an hour later, and to potline two at 3.50am on Sunday morning.
"The smelter team continues to work to safely stabilise the plant and reinstate normal operations," the spokeswoman said on Sunday night.
It follows a 2016 power outage that caused molten aluminium at the Portland smelter to solidify. The incident crippled the site for months.
South West Coast MP Roma Britnell said she was in contact with Alcoa on Sunday and was "confident" the team had the situation under control.
"I will visit the smelter this week to receive further updates from the team," she said.
"I also call for whatever it takes be done to ensure secure power supply to the smelter to stop these events occurring."
An Australian Energy Market Operator spokesman said a network fault had caused the Heywood interconnector to trip.
The smelter is Victoria's single biggest electricity user, the spokesman confirmed.
"The causes of the fault are still being investigated," he said.
The Heywood interconnector connects Victoria and South Australia, and the spokesman said it was unknown which side of the border the fault originated from.
The fault also caused South Australia to be separated from the national electricity grid.
"At no point throughout the incident did AEMO or ElectraNet direct any load shedding to occur in South Australia or Victoria. Both states had ample supply," AEMO's spokesman said.
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