MSI conducted vibration testing of a rerated medium power steam turbine in US-Mideast.  The main purpose of the testing was to evaluate a potentially resonant bladed disk vibration of the control stage within a specified speed range. 

Continuous Monitoring: Accelerometers along plane of stage circumferentially mounted

MSI performed specialized vibration testing that included experimental modal analysis (EMA), continuous monitoring, and operating deflection shape (ODS) characterization.  This testing indicated that harmful vibration from resonance of the control stage (energized by nozzle pass excitation) was transmitted to the turbine casing.  To temporarily address the issue, the lower boundary of the no-run zone was extended and no significant evidence that operation above a certain rpm provided any significant reliability problem for the turbine.

  • Work Performed
    • Methods: EMA, ODS, Condition Monitoring
  • Results/ Solution
    • Findings: Vibration from resonance of the control stage (energized by nozzle pass excitation)
    • Impact: No-run zone was extended & operation above a certain rpm did not provide a significant reliability problem

Acceleration data filtered at Nozzle Pass Frequency

FFT of an accelerometer on the turbine casing

Operating Deflection Shape at 172 Hz (1xN)

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