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CASPER, Wyo. -- A power outage Sunday damaged the Sinclair refinery in Evansville, decreasing its capacity while repairs are completed.

The plant belched thick black smoke and flared excess gas Monday night, but it wasn't yet clear if the smoke was connected to the damage suffered from the short power outage the previous night.

The refinery suffered a "complete power loss" for about three minutes about 7:30 p.m. Sunday, forcing crews to shut down several refinery units, according to a statement issued by Sinclair Oil.

There were no injuries or off-site impacts caused by the outage, but the facility's fluid catalytic cracking unit was damaged, company officials said.

The refinery will operate at 75 percent capacity until repairs are made, probably by the end of the week, according to the statement.

Rocky Mountain Power, which supplies power to the refinery, experienced a "momentary interruption" in service Sunday, according to spokeswoman Margaret Oler.

Oler said Rocky Mountain Power is aware of the refinery outage. The company is conducting an investigation to determine the cause.

Sunday's outage is the second at a Sinclair-owned Wyoming refinery in three weeks. An Aug. 17 outage at the company's refinery in Sinclair forced workers to engage emergency shutdown procedures.

Four fires have been reported at the company's Sinclair refinery since May. Two fires that month burned six workers, three severely.

An Aug. 5 fire caused minor injuries to one worker. No injuries were reported following a fire Aug. 24.

The Evansville refinery was built in 1923. It produces more than one million gallons of product every day.