High Vibration of large motor
High Vibration of large motor
(OP)
We have high vibrations on a 1000hp motor and the motor shaft is moving back and forth with very high resonance and the pump shaft is steady not moving at all. Any ideas as to what could be causing the motor shaft to move back and forth?





RE: High Vibration of large motor
But, start with the easy answers and work to the harder ones. Verify that you have a good alignment in hot, running condition s. Verify that the DBSE is set correctly including allowance for axial growth of the running shafts. A certain about of cold pre-stretch may be needed to achieve a proper DBSE on the running machine train.
Johnny Pellin
RE: High Vibration of large motor
In our case it occurs only at low pump flow. It looks like about 1/8" of movement.
I picture the system as follows. Pump acts like ground (very little clearance in thrust bearing). Coupling acts like spring. Motor acts like mass. You have a simple single degree of freedom system with a low stiffness and high mass giving low resonant frequency on the order of 1hz.
The excitation that I imagine must be broadband axial thrust variation which occurs only at low flow and causes slight movement within the pump thrust bearing clearance.. the broadband excitation excites the resonant frequency.
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