The 884-MW Unit 3 at Xcel Energy’s (NYSE:XEL) Sherburne County (Sherco) plant in Minnesota has returned to service following completion of repairs after a catastrophic failure nearly two years ago.
“Restoration following such a significant event on such a large unit was extremely complex,” said Dave Sparby, president and CEO of Northern States Power Co.-Minnesota, an Xcel company, in an Oct. 21 statment. “Plant employees, contractors and vendors worked thousands of hours to safely and efficiently return the 884 megawatt unit to service. We implemented repairs that ensure Sherco Unit 3 returned to operation with the highest integrity and reliability.”
The three-unit Sherco plant is Xcel’s largest power generator in the Midwest, providing 2,400 MW. The Minnesota Public Utilities Commission has lately been taking public comment on a life cycle study that Xcel did that says the older Units 1 and 2 at Sherco should remain viable for the long-term future.
Sherco Unit 3 is jointly owned by Xcel and the Southern Minnesota Municipal Power Agency. The agency, comprised of 18 municipally-owned electric utilities, owns 41% of the unit.
The failure at Unit 3 occurred on Nov. 19, 2011, during turbine testing as Unit 3 was being returned to service following a maintenance outage. The event caused extensive damage to the turbine, generator and associated plant systems. The company on Oct. 21 filed a report on the causes of the failure at the Minnesota commission.
That 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. Repair costs are estimated to be in excess of $200m. It is expected that most of the costs will be reimbursed by insurance proceeds.
The Sherco facility is located in Becker, Minn. Units 1 and 2 have a production capability of 750 MW each. U.S. Energy Information Administration data shows that coal suppliers to the plant earlier this year were the Absaloka mine in Montana of Westmoreland Coal and the Black Thunder mine in Wyoming of Arch Coal.