spectrum gas motor 4 strokes vibration on generator 1

[uhpo]

Hi there

I upload this spectrum of a generator, on the spectrum you´ll see on your left drive end and on your right hand non drive end, and i have vibrations on 5,5X, 4,5X, and i wonder if this means a loose bearing...but i´m not sure, cause most of vibrations are axial, so i can´t understand why i have most vibrations on axial than radial... and also the vibration is on drive end and non drive end....maybe some torsion....

this group is syncronized with net on cogeneration an it´s a 4 stroke machine, with 4.6 MW output generator..... this generator carries two NJ1044 MP bearing (one in drive end and other in non drive end together with a ball bearing without adjustement on radial, just for axial centering of the stator....the speed is 1000 rpm...

i would appreciate all the help

 

[GregLocock]

The plots are unreadable.

what configuration is the crankshaft?



Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[electricpete]

If you look at the behavior of a single cylinder within a 4-stroke engine, the period over which it repeats is TWO revolutions. So the fundamental frequency is 0.5 times running speed and (given the nature of the waveforms), we also have harmonics of that fundamental frequency... i.e. 0.5x, 1x, 1.5x, 2x, 2.5x etc where x indicates multiple of running speed. As far as total force and torque from sum of all the cyclinders, that is more complicated and sometimes we expect portions to cancel, but all the 4-stroke machine spectra I have seen have those frequencies present, similar to your posted spectra. I would not be inclined to suspect looseness from the spectrum (it would be hard to detect looseness becauswe harmonics and half-order-harmonics are typically present in the "normal" spectrum). Also your magnitudes don't look tremendously high. Unless there is some history of lower magnitudes previously, or some other data you haven't shared, I'd have a hard time seeing any problem with this data.

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(2B)+(2B)' ?

 

[uhpo]

electricpetter, thanks a lot, you talked about magnitudes... do you have some number to refer to standard, in the way that for this type of unit... a vibration of 11 mm/s is not too high or something like this.. cause generator normally is manufacturate to 20 mm/s.... thaks

 

[uhpo]

also do you have some paper where i could read about this subject???