Vibrations on a shaft generator

[pankajrao]

This 1800 RPM/ 1000 KW/440V/60Hz generator driven off a marine engine through a gear box started vibrating after 5 years in operation. Runs perfectly well on a test bench , the engine and gear box too work well without being connected to the generator. But as soon as the shaft generator is connected the vibrations are in excess of 100mm/s.
Since this is a floating vessel other changes on the deck , for example heavy loads added and removed at intervals do continue.
Suggestions welcome. Thanks

 

[Tmoose]

What is the frequency of the 100 mm/sec ( rms? peak ? ) vibration.
Or is that an overall reading of some kind?

 

[Strong]

Is the vibration present with generator at rated speed but without excitation? Is generator vibrations affected by excitation and varying/increasing load?

Walt

 

[pankajrao]

Good Day,

The frequency is 100mm/s RMS.

The Generator vibrates without any excitation at rated speed.

The vibrations increase on loading the generator.

Could an earlier botched up alignment and chocking job be the reason. This job was later done by professionals but this never worked?

 

[rob768]

The frequency is NOT 100 m/s RMS, this is the level of vibration. A frequency is given in Hz and will tell you where the vibration is related to (such as unbalance, misalignment, or other)

 

[Tmoose]

Hi pankajrao,

"The frequency is 100mm/s RMS."

Do your vibration measurements include the frequency of the vibration?
Maybe spectra/fft etc.
That is, Is the 100 mm/s amplitude you describe at a single frequency, like 1X shaft rpm of one of the components in the train?

Please post an example.

 

[MikeHalloran]

Could you provide some photos of the installation please?


Mike Halloran
Pembroke Pines, FL, USA

 

[pankajrao]

Sorry for the delay due to internet problems.
Please find vibration reports attached.

 

[Tmoose]

Hi pankajrao,

There are No attachments/uploads

 

[pankajrao]

Sorry folks .
After many a trials it was finally found that the rubber coupling between the gear box and the shaft generator was the problem. Though it did not show any signs of wear , aging or damage.
The coupling from another engine was swapped to this engine and the system is performing well.
Thanks for your help.

 

[rob768]

very strange story...