Dear All,

This is a 30 MW T.G.Set coupled with Gearbox & Generator. Turbine rpm is 7500 and Generator rpm is 1500.

* The slow speed Gear-Rear, Generator Front & Generator Rear indicating high shaft vibration of 170Microns, 110 Microns, 166 Microns respectively. Predominant vibration frequency is 1 x rpm (1500 cpm).

* Generator balancing attempts were made by adding 2.1kg at Gen. Front & 2.9 kg at Generator Rear which resulted in the vibration amplitudes as follows:

Gearbox slow speed rear - 171 Microns (No change)
Generator Front - 122 Microns
Generator Rear - 80 Microns.

From the above there is absolutely no change at Gearbox vibration & Generator Front but reduction could be observed at Generator Rear bearing. Still tbe balancing calculation suggests to add another 2 kg to Gen-Rear side.

* My query is whether 5 kg of correction mass for Generator is acceptable for a "Newly Installed" Machine"?

* What is the reason for high 1 x component at Slow speed Gear - Rear. Even after adding weight at Generator Front no influence is occurring. Whether any resonance problem? Coupling problem?

* Bearing "casing vibration" at Slow speed Gear is only 0.5 mm/sec RMS. Is there any problem with the Proximity probes? or is there any references/standard to compare "Casing vibration" Vs. "Shaft vibratin"? i.e., how to rely on the validity of the Shaft vibration indicated?

Valuable Machine Doctor's comments to alleviate the sickness of the machine, highly appreciated.

Regards,

Deepak

quote:

My query is whether 5 kg of correction mass for Generator is acceptable for a "Newly Installed" Machine"?

Could be - what does newly installed mean? is this a brand new machine (in which case, the need to add 5 kg is really poor) or a machine that has been reworked? How was the rotor balanced before installation?

quote:

Bearing "casing vibration" at Slow speed Gear is only 0.5 mm/sec RMS. Is there any problem with the Proximity probes? or is there any references/standard to compare "Casing vibration" Vs. "Shaft vibratin"? i.e., how to rely on the validity of the Shaft vibration indicated?

Are you trying to balance out a scratches on the shaft surfaces - check for runout/glitch?

Yes, this is a newly installed machine. Balancing details before installation right now not know. I will let u know.

Regarding Balancing, attempts are made only on the Generator rotor. By adding correction mass, casing vibration at Generator is coming down from 0.7 mm/sec to 0.3 mm/sec. whereas no change is observed at the Gearbox side casing vibration in-spite of 2 kg mass at the Generator Front side.

Runout/Glitch I will verify and let u know.

Thanks for your response.

Tell us a bit about what type couplings are in this machine train. For instance, is the coupling between the gearbox and generator two rigid flanges bolted up? If so you need to pay careful attention to concentricity between the two rigid flanges.

John from PA

Hi Deepak,

i regularly carry out on-site balancing of the TG sets at various sites. even i go for only trim balancing where the correction will be in terms of gms and not in kgs as you had mentioned. 5 Kg is too much of mass. do not attempt with such a high mass.

recently i had a simillar experience on one of the TG set. but in this case the gen vibs came down (only casing) and no change in the gearbox side bearings vibs. in my case the casing vibs came down and the shaft vibs remained same. i will try and post you that case study if you are interested.

have you checked with the critical speeds of the gearbox. i observed this phenomena for a quill shaft gearbox design. for balancing activity which reference did you take shaft or casing... if casing then why can't you try once by taking shaft vib as the reference. i got good results by taking shaft vibs as reference but casing went up.

cheers
madhu