Xcel was testing the Unit 3 turbine on Nov. 17, 2011 after a planned outage when the spinning turbine began to vibrate. Pieces of metal were hurled across the turbine room. The turbine erupted in flames, damaging more equipment. No one was injured.
Repairs took 22 months and cost Xcel and unit co-owner Southern Minnesota Municipal Power Agency (SMMPA) $200 million, of which $65 million was spent on replacement power.
Thielsch Engineering Inc. was commissioned in late-2011 to conduct a root cause analysis into the event and found that stress corrosion cracks had developed where the turbine blades attach to the rotor.
The report said the cracks may have developed a few years before the accident, and that GE and its service affiliates knew about the defect for decades and had documented previous failures and even developed and patented an improved design. But GE did not tell Xcel about the problem before the accident.
The lawsuit also alleges that GE held meetings with Xcel officials prior to the turbine being serviced and said inspections of the part that failed were unnecessary “unless abnormal events or operational anomalies occur.” The suit alleges that if GE or its service affiliates had performed or recommended inspections, the problem would have been found sooner.
GE said in a statement that the accusations are not true.
“The Northern States Power Company’s and the Southern Minnesota Municipal Power Agency’s claim that GE concealed a defect in our steam turbines is simply false," according to the statement. "There are 271 of these steam turbines operating under the same stresses of the NSP/SMMPA unit. Of the 271 steam turbines, many of which had been operating for more than 30 years, the NSP/SMMPA unit is the only unit to have suffered a catastrophic failure. This is typically indicative of a unit that has been operating outside of recommended inspection and maintenance requirements; this is supported by evidence within the NSP’s/SMMPA’s own investigative findings.”
The root cause analysis was submitted to the Minnesota Public Utilities Commission in October 2013. That same month, the lawsuit says GE issued a letter to customers who are using the units, warning of the problem and recommending inspections. It accuses GE of fraudulent concealment, negligence and failure to warn, but doesn’t specify damages.
In a separate lawsuit, Westmoreland Coal Co., whose Absaloka mine in Montana supplies coal to Sherco 3, is seeking $36.7 million from GE in lost business while repairs were made. GE asked a county district judge to dismiss the case.