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Aluminium production at Rio Tinto's Tiwai Point smelter at Bluff has been cut by the equivalent of about 280 tonnes per day due to equipment failure, the company says.
The smelter has capacity to produce up to 350,000 tonnes of aluminium annually but was already operating at a reduced rate of 315,000 tonnes prior to the failure of an electrical transformer late on Sunday, a spokeswoman told the Reuters news agency.
"We have shut one of the potlines and are currently assessing the degree of damage to the transformer," she said, adding it was too early to determine the duration of the curtailment.
Lost production was estimated at around 8500 tonnes on a monthly basis while the potline was inoperable, according to the spokeswoman.
The smelter has been running below capacity since May to help reduce demand on New Zealand's national electricity grid.
