Xcel Energy said Wednesday it has completed repairs to its giant Sherco unit 3 coal-fired generator, which has been offline since a catastrophic accident in November 2011.

The 900-megawatt unit in Becker, Minn., is expected to be back in service after a few weeks of testing, the company said in a regulatory filing.

Xcel and its 1.2 million Minnesota electric customers will benefit from the return to service. During the shutdown, Xcel said it has spent $64 million to replace the power, which was added to customers’ bills via the fuel adjustment line.

The Southern Minnesota Municipal Power Association (SMMPA), which owns 41 percent of the Sherco unit, also was forced to buy replacement power, but it absorbed the extra cost, said spokesman Dan Hayes. The full cost of the outage hasn’t been calculated, he said, but the association’s 2012 financial statements reported that it cost SMMPA $14 million that year.

The association supplies power to 18 city-owned utilities across Minnesota, including Austin, Owatonna, Princeton and Rochester.

“It is a critical resource for SMMPA and its members, typically supplying 80 to 85 percent of our members’ energy needs,” Hayes said of the Sherco 3 unit in an e-mail.

Xcel operates the plant and two wholly owned adjacent units that weren’t damaged. The company disclosed that repairs were completed in a filing with the Minnesota Public Utilities Commission.

The massive project required rebuilding the unit’s turbine, generator and other components. In March, Xcel said it had spent $146 million on the repairs, much of which will be covered by insurance.

Xcel has said that an investigation found extensive cracking in one row of turbine blades at their attachment points. The utility’s report attributed the cracks to “stress corrosion” and said the problem was “a function of the original design,” not how the plant had been operated. The blades had been in use since 1999. No one was hurt in the accident.