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Dear Gents,

Need your expertise feedback,

I'm having gas turbine generator which specification as below :

Turbine : GE Frame 5, 5105rpm (2 bearing)

Load gear : GE S-624 (4 bearing)
Generator : 28kVA, 2pole, 3600rpm (1 bearing)

Recently gone for major overhoule ( replace turbine rotor, replace bearing gearbox and generator cleaning, ) previously this unit was detected having high vibration in all axial point vibration in gearbox  up to 0.829 inc/sec. the field analyses was recommended to inspect gear and bearing.

The project was given to well known service , as per request by user the above mention repaired was delivered, during service they found bearing gear on #3 dan #6 were having some burnt part on the housing bearing.

Commisioning was carried out, and somehow similar vibration signal were happening high axial vibration on bearing #3 and #6 and now up to 1.5 in/sec. ( other point vibration all in normal level vibration ) generator 1st order signal was clearly seen on vibration data, balancing were decided to be executed

After 2 x correction, we were managed to lower the vibration level to 0.9 in/sec on those axial gearbox bearing,  the problem is during first 2 hour operation with 15 MW load the vibration were on acceptable level some where around 0.5 - 0.52 in/sec and suddenly rise up  to 0.9 - 1.0 in/sec , oil temperature were also detected rise up .

What could possibly make those high vibration appeared after 2 hours on steady and normal vibration level.

Regards

Dex

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Original Post

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I am guessing that the same 2 bearings (3 and 6) are still showing the high 1x of the generator speed?

What is the phase reading/difference of the 2 bearings (axial with transducer facing the same direction on both bearings or adjusted if in different directions) before and then after the 2 hour increase.

Does the machine have a water type cooling system for the oil?

Thanks

Ralph

Quote:"generator 1st order signal was clearly seen on vibration data,"

I am guessing that the 1x order of the generator is the frequency showing on the #3 and #6 bearing's axial positions, huh?

The #3 and the #6 seem to be at 185 degrees one to the other during both load runs (10MW and 15MW), based on your chart.

Were the transducers mounted facing one to the other (180 degrees opposite) or were they facing in the same direction (0 degrees one to the other)? If in the same direction, the phase would only be 5 degrees.

I noticed you do not have the phase data on the #5 bearing.

John's coupling note is good, especially with a gear type coupling.

Thanks,

Ralph

Quote: "They were opposite to each other ralph,by the way we are using acc sensor to monitor casing vibration of this gearbox using multichannel vibration monitoring that includes reading the phase, the online vibration from HMI only available to monitor overall vibration in vertical direction."

"opposite" as in: Facing each other: with #6 pointing to the right and #3 pointing to the left (in reference to your drawing)? If so, could they be 185 degrees out of phase, or does the multi-channel analyzer correct the 180 degree difference before displaying the phase?

Do you not have the axial phase on #4 and #5 points.

Thanks and Have a Great Day,

Ralph

Edited: Where was the axial data taken on the #7 Bearing, on the bearing housing or at the outer most diameter of the generator housing and in align with the shaft on the inboard of the generator?

Just wondering if the entire generator is moving in phase or out of phase with the gearbox output (#6 bearing).

Last edited by Registered Member

Hi jhon, sorry for late in respond your question. you are correct its double helical, and regarding your question about coupling, before the balancing attempted unit was starting the first time we were having some lubrication problem, pressure drop of lubrication oil, and one of the mechanical activity that  re carried out was re inspecting coupling alignment includes, gear coupling condition, and we were found no problem at all

Is this double helical design the side-by-side arrangement or is it the vertical arrangement of the gear rotors?  Do you know if it has a quill shaft arrangement?  A quill shaft is when the gear has a bore and a shaft is in that bore.  The quill shaft actually connects at the end of the gear away from the generator with the other end of course connected to the generator.

Unless you have reasons not to share, can you post a cross section of the gearbox?

@Registered Member posted:

Is this double helical design the side-by-side arrangement or is it the vertical arrangement of the gear rotors?  Do you know if it has a quill shaft arrangement?  A quill shaft is when the gear has a bore and a shaft is in that bore.  The quill shaft actually connects at the end of the gear away from the generator with the other end of course connected to the generator.

Unless you have reasons not to share, can you post a cross section of the gearbox?

John, if I'm not mistaken, the machine is similar or the same as the link

https://www.slideshare.net/muk...sigitisnaeni/ms-5001

The manufacturer only has speed sensors installed in the vertical orientation, and their alarm limit is 15 mm / s pk and tripping of 25 mm / s pk, these equipments are old 1970, some suppliers offer to improve or update the gearbox like the link

http://www.turboresearch.com/e.../tech-note-july-2009

One of the biggest problems of this machine is the centering of the rotors, the generator moves too much without anything to control this movement and in the end the gear teeth absorb all that axial load



Greetings…

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@Registered Member posted:

Hi Jhon, it's double helical with high speed gear on the above position, unfortunately i really can not share the drawing document ...

This would indicate what is called a high over low design; the pinion is above the gear.  Since you seem confident that the gear coupling on the pinion is OK that would mean the pinion should be free to float.  

Let’s move to a discussion of the low speed shaft...have you identified what I’ve called a quill shaft?  The reason I ask is many people aren’t aware of this type of design unless they look at the drawings.  Also, can you look at your drawings and let me know if you have what appears to be two bearings at the low speed shaft extension.  One of those bearings actually supports the quill shaft relative to the casing; the other supports one end of the gear relative to the casing.

At the β€œblind” or uncoupled end of the low speed shaft there should be the 2nd bearing that supports the gear.  The quill shaft will connect to the gear with essentially 1/2 a gear type coupling.  That 1/2 coupling should be examined to make sure the quill shaft is free to move axially.

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