axial vibrations in generator
axial vibrations in generator
(OP)
Hello guys, i posted this thread in the vibration section as well, but was suggested to post it here too.
I am looking for a source of axial vibrations occurring in the bearing support of a diesel driven marine generator. The vibrations occurs at 4x the running speed. We have not identified a mechanical source, but we are suspecting an electrical one, since it occurs at twice line speed. We have encountered this problem in 2 different lay-outs of installations. One is direct driven by a 16 cyl engine (with soft elastic coupling in between), and the other through a PTO of a marine gearbox and by a 9 cylinder engine.
My main question is: can a generator cause axial excitation at 4x operating speed?
I am looking for a source of axial vibrations occurring in the bearing support of a diesel driven marine generator. The vibrations occurs at 4x the running speed. We have not identified a mechanical source, but we are suspecting an electrical one, since it occurs at twice line speed. We have encountered this problem in 2 different lay-outs of installations. One is direct driven by a 16 cyl engine (with soft elastic coupling in between), and the other through a PTO of a marine gearbox and by a 9 cylinder engine.
My main question is: can a generator cause axial excitation at 4x operating speed?





RE: axial vibrations in generator
Muthu
www.edison.co.in
RE: axial vibrations in generator
RE: axial vibrations in generator
Muthu
www.edison.co.in
RE: axial vibrations in generator
RE: axial vibrations in generator
Can you post some pictures of the generator rotor and the overall installation here ?
Muthu
www.edison.co.in
RE: axial vibrations in generator
Sorry but i can't post pictures.
The problem seems to be that the procuced axial vibrations cause resonance of the bearing shields, leading to severe and rapid bearing cage wear, which in turn causes the balls to slip and the bearings to overheat. We were looking for mechanical causes at first, since we were dealing with a installation directly driven by a 16 cylinder engine (which prodcues 4th order vibrations). We now also have installations where this 4th engine order is not present, and mechanical sources for the vibration are not clearly present. Like i said, electricity isn't my field of expertise.
Is the above uneven air gap something that can be checked in the field? I assume this is something like a mis-alignement between center line of the stator and the shaft?
RE: axial vibrations in generator
Muthu
www.edison.co.in
RE: axial vibrations in generator
RE: axial vibrations in generator
In a two ball bearing arrangement, the non-locating bearing (usually the ODE) should be free to move axially inside the housing to accommodate thermal growth. The grease retainer plate/cup should not touch this bearing outer race at both sides.
Look at the fig 9 in this SKF page
http://www
Check if this arrangement is present.
Muthu
www.edison.co.in
RE: axial vibrations in generator
RE: axial vibrations in generator
RE: axial vibrations in generator
RE: axial vibrations in generator
Muthu
www.edison.co.in
RE: axial vibrations in generator
Rotor shorts, at least in my experience with the size machines I'm familiar, show up as linear vibration similar to out of balance, and to some degree get worse as load goes up.
Axial vibration problems with gen sets I've usually seen are the result of improper initial setup in alginment and coupling, where the generator magnetic center was not correctly aligned. Or, more likely in your case since you state you have one fixed and one floating bearing, that you're not centered on your crank thrust.
When installing the generator do you measure crankshaft end float before and then after install to assure you aren't pulling or pushing on the crank thrust surface? If the adjustment is off slightly, the axial vibration is usually the result, if it's way off your usually burn the thurst bearing. This is especially the case if the generator coupling is the flex plate style, but I have also seen this in rubber element torsional couplings as well. A properly installed generator should not change the crankshaft end play clearence, would also preform this check both hot and cold to assure thermal growth isn't playing a part.
Hope that helps.
RE: axial vibrations in generator
RE: axial vibrations in generator
Over here we tend to see NDE as an abbreviation for Non-Drive End
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If we learn from our mistakes I'm getting a great education!
RE: axial vibrations in generator
And I suppose you don't like "counterclockwise" either?
Actually I think NDE is probably more common, even here in the colonies.
RE: axial vibrations in generator