LCC Quick Notes, Turbine Vibration Monitor


    Almost without modern rival, steam and gas turbine vibration monitoring systems are notoriously misapplied.  Most systems neither warn operators of pending disasters nor contribute much in the way machinery condition knowledge.  The culprit error in most systems is the use of anti-friction (ball, roller) bearing technology on journal (sleeve or tilting pad) bearing machines coupled with a misunderstanding of turbine rotor dynamics.  With respect to vibration characteristics, turbines do not behave at all like electric motors which are the design target for all popular vibration monitoring systems.  Important specification issues are:

 

 

◘    X-Y Proximity Probe arrangements at or near bearing locations are useless for detecting rotor bows and unbalance, the two vibration causes most likely to damage the turbine.

◘    Modified X-Y Proximity Probe arrangements with "Absolute" velocity probe mounts are also useless for detecting rotor bows and unbalance.

◘    An effective turbine vibration monitor must have sensors located far enough from bearing nodal points to detect the characteristic deflection patterns of the rotor.

◘    Ideally, the turbine vibration monitor should calculate real time rotor deflections and compare them to internal clearances over the rotor span, alerting operators to pending contact and damage.

◘    Most conventional X-Y Proximity Probe installations cannot be calibrated to required accuracy even when properly located.

 

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