Cranston, RI (Feb 12, 2014) On Oct. 21, 2013-Xcel Energy submitted a long-promised Root Cause Analysis Report to the Minnesota Public Utilities Commission about the primary cause of the catastrophic outage that occurred in November 2011, at the coal-fired Sherburne County Unit 3 (Sherco 3).(click here to view full press release)

Thielsch Engineering, Inc. was commissioned in late 2011 by Xcel Energy to conduct a root cause analysis and found that the Unit 3 steam turbine generator event on November 17, 2011 was initiated by the fracture of multiple finger pinned blade attachments in the Low Pressure Turbine “B” turbine end L-1 stage disk rim. The fractures resulted in liberation of portions of the finger pinned blade attachments and associated L-1 blades.

The loss of mass, due to the liberation of these blades and disk sections, created a significant imbalance at the affected stage, resulting in high amplitude vibration throughout the steam turbine generator train. This vibration was responsible for the fracture of the generator shaft, fractures of the exciter shaft at three locations, and extensive additional damage to the steam turbine generator train and other plant equipment.

As a result of the findings per Thielsch’s highly detailed analysis, Xcel Energy Inc. and the co-owner and insurers of the Sherco 3 electric generator in Becker, Minn., have sued turbine maker General Electric Co., alleging that the manufacturer fraudulently concealed a known equipment defect for years. This incident is recognized as one of Minnesota’s most expensive industrial accidents and has initiated a legal battle over a 22-month repair job costing over $200 million.
For more information about Thielsch’s Root Cause Investigations and Professional Engineering Services, please contact Peter Kennefick, VP, Thielsch Engineering, Inc. at (401) 467-6454 or via email at pkennefick@thielsch.com. You may also visit Thielsch Engineering, Inc. on the web at www.thielsch.com.