increasing Vibrations
increasing Vibrations
(OP)
We recently refurbished a 1750hp motor as part of Preventative Maintenance. After the installation of motor the vibs increased from 0.2ips to 0.63ips over 7 hour period. The problem was assiciated with the insulation plate. After fixing the insulation plate the uncoupled motor vibs were 0.065ips with no change over 2 hour period. After coupling the motor to a nine stage pump the vibs increased from 0.2ips to 0.42ips over 4 hour period. Before the refurbishment there was no problem with the motor and pump. Any ideas what is the problem? Thanks.





RE: increasing Vibrations
thermal growth causing misalignment
thermal bow of the rotor.
What is the frequency/frequencies? Is the vibration at running speed? Are pole-pass frequency sidebands visible? Horizontal or vertical motor? Uniform in both radial directions? Any axial vibration? Axial phase shift? Temperature of the fluid? Any indication of significant temperature change? What does the base look like?
My gut feel would be thermal bow of the rotor but you need to methodically work through it.
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RE: increasing Vibrations
RE: increasing Vibrations
RE: increasing Vibrations
RE: increasing Vibrations
BK
RE: increasing Vibrations
Good luck
JFB
RE: increasing Vibrations
My personal opinion is still thermal bow of the motor most likely.
Yes, the motor ran ok uncoupled, but the motor does not run as hot during uncoupled run as during running loaded/coupled.
How to test it. One possibility of we want to narrow down to the motor would be to run the motor uncoupled, with ventilation intake choked off. Monitor stator winding rtd temperatures to ensure they are within limits - let's say less than 120C for class B insualtion. I have has Siemens recommend this to me and assure me it was safe. One issue is that vibration occuring during the test proves it's the motor, but lack of vibration does not disprove it 100%... the heating pattern of the rotor by reduced ventilation is not identical to the heating pattern of the rotor due to mechanical load on the motor.
Another possibility to check for thermal bow is to attempt to measure runout of the shaft exiting the motor during motor coastdown after it has been running loaded with high vib. Would require you set up near the motor ahead of time and give careful consideration to personnel safety.
Now that I am thinking of it: rotor problems within the motor (either thermal bow or rotor bar) should show up with pole pass frequency sidebands around 1x in vibration and around 2*LF in current. Use high resolution spectrum to look for these would be a logical first step if you haven't already done it.
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RE: increasing Vibrations
RE: increasing Vibrations
Just for our info, can you clarify: have you restarted after tightening spoolpiece bolts and vibration went away?
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RE: increasing Vibrations
Please let us know the outcome.
RE: increasing Vibrations
So far all we have done is ran the motor with the spool piece (after re-aligning) and vibs are reduced to 0.05ips. THe real test with coupled to the pump and loaded will be run in few days. I will keep you guys posted. By then please post your ideas. Thank you.
RE: increasing Vibrations