(Reuters) - Xcel Energy Inc's 860-megawatt Unit 3 at the Sherburne County coal-fired power plant in Minnesota has returned to service after a nearly two-year outage, the company said on Monday.
The unit shut in November 2011 during turbine testing as it was restarted after a maintenance outage. The failure caused extensive damage to the turbine, generator and associated plant systems, Xcel said.
"An investigation by external experts found extensive cracking in one row of turbine blades due to stress corrosion. The problem was a function of the original design and was not related to how the plant has been operated or maintained," Xcel said.
The utility expects much of $200 million repair bill to be reimbursed by insurance.
"Restoration following such a significant event on such a large unit was extremely complex," said Dave Sparby, president of Xcel's Northern States Power-Minnesota.
The three-unit plant, called Sherco, is Xcel Energy's largest Midwest power plant, generating 2,400 MW to serve more than 2 million Minnesota homes and businesses.
Sherco 3 is jointly owned by Xcel Energy and Southern Minnesota Municipal Power Agency, which holds a 41 percent stake.
(Reporting by Eileen O'Grady in Houston)