A "nearly fatal" power outage at Alcoa's Portland smelter at the weekend has prompted calls for work to be done to stabilise the state's electricity grid.
Australian Workers Union south-west Victoria union organiser Rob Saunders said workers came in on days off to help save the plant.
"It was nearly fatal, there's no two ways about it," Mr Saunders said.
"To lose power to a potline for as long as they did, it's pretty well unheard of to be able to save it from that.
"It sounded like they were bending physics to achieve this because they probably shouldn't have been able to do it, but they managed to make it work.
"It's a huge success story."
Mr Saunders said the first potline was offline for about four hours after a network fault, which caused the Heywood interconnector to trip, just after 7pm on Saturday. A second potline was out for about eight hours before power could be restored.
"At the moment the plant's in pretty good shape," he said.
"For them to save that potline in those circumstances was genuinely heroic.
"They had plenty of workers come in on their days off to help out because they know it's just terrible trying to work in those conditions.
"It takes a huge effort. It was an all-in, shoulder-to-the-wheel sort of commitment. It was great."
Mr Saunders said there would be plenty of "unstable pots" over the next few days but so far the signs were "very, very good".
"They're working hard to get those unstable pots under control," he said.
"They're having more success than loss so they're fairly confident that they've got things under control."
He said they had to cut the flow of current to about five or six pots.
Mr Saunders said problems with the state's electricity network was putting jobs at risk.
He said the smelter directly employed about 500 people and provided work to hundreds more outside the plant.
"It shows that we need to do more work on our electricity grid because it puts a lot of jobs at risk," he said.
He said the Portland site had learnt a lot from previous power outages. In 2016, a five-and-a-half hour power outage caused molten aluminium at the smelter to solidify, crippling the site for months.
"They've now learnt a lot from that that they've been able to save the whole plant with an even longer outage," he said.
Mr Saunders said Saturday's outage would have tested the limits of the plant, "but essentially they've found a way to reach a new limit".
He said the plant had already been putting in place preventative measures to deal with expected calls to shed power during peak times over summer.
"They can put some measures in place to prepare the potlines and they were doing that anyway, fortunately," he said.
Mr Saunders said everyone onsite, from the operators to management, rolled up their sleeves to save the plant.
He said there had been question marks over the future of the Portland plant in recent months and "those question marks will remain until we get a solid power deal I imagine".
Mr Saunders said everyone was "fighting as hard as they can" to keep the plant going.
"The AWU motto is stronger together and what we saw on the weekend was that in action and it saved hundreds and hundreds of jobs," he said.
Ausnet Services said it was still investigating the cause of the fault.
Alcoa said it was working to safely stabilise the plant and reinstate normal operations.
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