Reliability Articles

Vibration Analysis Study Case: Bending Rotor Turbine

Vibration Analysis Study Case

Bending Rotor Turbine

Turbine generator on a power generation faced a trip because some breakdown on transmission network. After startup had been redone, turbine generator still faced breakdown because of high vibration which is on speed 900 RPM. Vibration analysis was done to find the root cause of this problem.

Vibration data on startup for each measurement point as below:

Finding:

  • Vibration went up to limit trip along with the increase of rotor rotation
  • High vibration happened a lot to bearing turbine (bearing #1 and bearing #2)

Diagnose:

  • Unbalance
  • Misalignment
  • Run out / bending

Analysis:

  • Unbalance: spectrum pattern and waveform on axial measurement were incorrect on center hung unbalance for this type of rotor on this turbine. This finding was supported by vibration data before turbine trip, which did not indicate an unbalance case.
  • Misalignment: vibration data on generator did not support for misalignment case, because usually misalignment vibration is high on driver or driven.
  • Run out / bending: waveform and spectrum was dominated 1x on every axis measurement on the turbine that was included in this case.

Conclusion:

  • Based on analysis above, it was concluded that the problem was run out / bending on rotor turbine

Recommendation:

  • We recommended for maintenance division to perform a check run out on rotor

Result:

  • Run out rotor 14 mils where the permitted maximum standard is less than 7 mils. Rotor faced bending that was caused by a failed lube oil pump backup when there was a blackout on the plant so rotor was running without lubrication for a while.
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