Hello All

Im currently having a machine (engine & Alternantor) running on a skid/beam supported by 3 (yes 3!) spring damperner.

Previously i witness the alignment (cold & hot) and passed the 3 days endurance test. But later after 10 days the coupling shims were broken.

I had a survey during 2nd endurance test (after realignment & new shims replaced) but the horizzontal vibration on most measurement points is around 4-5mm/s rms. Vertical and axial around 2-3 mm/s rms. DOMINANT peak is on 2x rpm (1004 engine RPM - direct couple)

Im not happy with horizontal vibration, afraid coupling shims damage again. THen i took skid/beam vibration. The result is ~ higher vibration on the skid up to 20 mm/s rms (2x dominant = 19mm/s on engine nde beam).

IS THIS RESONANCE???

You said it was within alignment specifications? What's a 3 day test? Is the unit in the sun? And, what was the alignment and with a shim pack coupling are you sure it's the right model.

With a poorly designed skid and deflection and/or twisting you could encounter very bad alignment conditions with alignment exciting resonance or poor design. Three supports for the skid? Three footed engine?

Hello RBM

If you think it is resonance you have to do some measurements about it.
- bump test at standstil
- run-up or run-down
- working at variabel frequency.
You make the diagram amplitude versus frequency and the patern of resonance will show up (perhaps).
Silvain

Sam & Depauws,

Thanks for the input.

The alignment is as low as 0.05mm and we have standard of 3 days (72hours) endurance test to handover to operation (site). The shim pack coupling im not sure whether it is the right model but supplied by the contractor.

The bump test is ideal on the machine or the skid? What i can see it is resonance on the horizontal axis only. The genset is fix running at 1000rpm and its a good idea running at diff speed ~ i'll request to run at 1200rpm/800rpm if have the opportunity.

Im using CSI 2130 with speed vue but not sure of getting run up / coast down amplitude & phase. I asked in other disscussion already.

Attached you can find my report and the finding plus machine drawings (showing the machine support)

Lgast_Generator_Skid_Spectrum.pdf (235 Kb, 66 downloads)

Additional info

Did the cross phase analysis on the machine (Eng DE Hori & Alternator DE Hori = 164 deg)
while Eng DE Hori & Alternator NDE Hori = 176 deg)

So it is closed to 180 deg which mean out of phase. Confirm misalignment? or Resonance effect?

Lgast_Gen.xls (26 Kb, 45 downloads)

Mr CBM
180˚ out of fase is same as in opposite, when the one of the machines goes left, the other end goes right.
This causes some misaligment, and when that misalignment is amplified with a resonance the misalignment becomes that big that the sims break.

You only have to proof that there is an resonance at 2 * RPM.
Silvain

Mr Depauws

Thanks for your input.

I'll do the bump test (machine & skid) and also run up or coast down with phase if possible.

From the i hope can get the exact natural frequency, based from the output

Thanks!

Dear Sifu,

I'm going to the site once again. Will carryout several tests.

Bump test 2)Check vibration isolator/dampener 3)check beam/skid flatness 4)engine solo run 5) REALIGNMENT

So guys, where should i hit(bump) it as the beam so huge and long?

Run up/coast down method could be ideal but unlucky i dont have tachometer. Only Speedvue (CSI Speed Sensor).

I tried to use it with CSI2130 but lack of info on tacho setup i.e CSI showing TACHO TIMEOUT

CBM Analyst,

Thailoh....Your spectral profiles indicates a classic case of mechanical looseness I've seen before, which will explain your resonance suspicion, damaged coupling shim, etc.
Rather then performing bump tests, I'd be looking for signs loose/broken anchor bolts, weld cracks, damaged dampeners; around the Engine and Alternator. Ensure all anchors bolts are torqued to spec.

Good Luck...Rajan

The other clue can be in type of shim damage. Depends where the breakage happened it could provide some additional info.

Guys,

As per attached diagram, you can see there is only 3 vib isolator/dampener. This only 3 spring mount holding the overall beam/skid plus gas engine and alternator. The plant is more than 10 years now. I suspect than the isolator weaken.

Alignment had been done more than 3 times. The best achievement after doing hot alignment but 2 weeks later coupling shim CRACK. Im afraid the same will be happen again.

I'll check on the vibration dampener tomorrow. (only visualize) and REALIGN. Hopefully the vib would be less than 3mm/s than im happy.

Alex,

The shim crack on the engine side. What clue we have here?

The beam vibrate more at engine NDE

Thanks

Hello CBM Analyst,

I'm interested in learning about your findings so far and/or any resolutions you have proposed/instigated.
Kindly share so that we all may learn.

Cheers...Rajan

hi everyone,

latest update.

Vibration of the skid which max 22mm/s previously had reduced to 11mm/s and casing vibration also reduced to max 3mm/s.

We jus adjust the level of the adjustable dampener and live vibration show reduce in overall vib.

Thanks