Northern States Power d/b/a Xcel Energy (NYSE: XEL) told the Minnesota Public Utilities Commission on Aug. 14 that restoration activities at the coal-fired Sherburne County (Sherco) Unit 3 are still due for completion in early September.
The unit was forced into an extended shutdown by mechanical failures and a fire in November 2011. Early September has been the expected on-line time in the last several restoration updates.
“We continue to make good progress on our restoration efforts and expect Unit 3 to return to service in early September,” said the latest of the company’s updates on unit restoration. “As noted previously, once the unit is returned to service, there will be a short period of testing (likely a couple of weeks) to complete testing, tuning, and ramping before releasing the unit for dispatch by MISO.”
The 884-MW Unit 3 went off-line in November 2011 while being restarted after a repair shutdown. During the testing procedure after unit restart, specifically the overspeed test, the turbine and generator instrumentation showed vibration levels significantly above normal, and the unit was shut down. The vibration damaged many of the steam, oil, and hydrogen seals in the turbines and generator, and caused a fire.
Sherco is a three-unit, 2,400-MW plant. It burns low-sulfur Western coal from mines in Montana and Wyoming. The plant normally burns more than 9 million tons of coal a year. Notable is that Northern States Power, after doing a life-cycle study of Sherco Units 1-2, recently said these units are viable for the long-term future.