LONDON, July 15 -- Rio Tinto PLC (RTP, RIO.LN) said Wednesday it has repaired one of the transformers at its Laterriere Works aluminum smelter in Quebec after a power failure last week, allowing it to stabilize one of the facility's two potlines.

Two of three transformers feeding electricity to the smelter failed on July 6--the first power failure of its kind at the Laterriere operations.

"We have repaired one of the transformers that failed onsite," Rio spokesman Bryan Tucker told Dow Jones Newswires on Wednesday. "This transformer coming back online has allowed us to stabilize the line that is still in operation."

The second potline remains suspended, he said.

"We are still working to provide reliable energy source for the suspended line," Tucker added. "Once we are able to secure a reliable current to this line, it will take three to six months to restart the line."

Following the power failure last week, he warned the loss of electricity to a potline makes it technically difficult to resume full production quickly, as the smelting pots in the potline can harden.

The cause of the incident is still under investigation.

Laterriere's annualized capacity is 250,000 metric tons of aluminum metal.