Hi All,
Any one who knows vibration standard for Axial generator pedestal of GE Frame 5?
The construction of generator is very unusuall:

Generator was only supported on one side(pedestal.

No thrust bearing on generator.

Generator shaft was directly connected by fix coupling to gearbox that consist of helixal gears that generated axial movement.
Load max 25 MW, generator speed 3600 RPM.
Previous problem is unbalance;high on vertical 10 mm/s-pk and after balancing it is 5.4 mm/s-pk. And also horizontal, before balancing 8.3 mm/s-pk become 4.3 mm/s-pk. Axial; 21.4 mm/s-pk become 13.5 mm/s-pk. Altough axial has been reduced, but the level seems still high (13.5 mm/s). Is Axial level still acceptable? Please advice..

Best Regards,

Rahardi
rahardi@gmail.com

There is nothing "very unusual" about the construction of the Frame 5 Generator, they have been the same for decades and work well.
As long as the unit is assembled correctly, taking into account the generator electricl center, the generator will not generate any axial thrust so there is no need for a thrust bearing. The gearbox, if I remember correctly, is a double helix and therefore again is self centering.
Firstly, what frequency is your axial vibration, 1X, 2X??
From what you say about balancing, I presume you have removed the rotor and reinstalled it. If so, did you get the electrical center correct? I'm sure there is a full procedure in the service manuals for doing this.
If not, axial vibration will occur as the rotor tries to locate itself inside the stator.

First of all you should check the quill coupling drop check that is basically the alignment of generattor rotos with the hollow bull gear. Procedurew for this is given in the manual.

Also u cancenter the generator..

The rigid coupling between generator should be checked for runout if rotor had been removed. Also, did you check the rotor before balancing for any physical damage to the windings (short windings or insulations) or previous balance wiehgts.
If these all are correct then just do the alignment checks as others say.

Again, before alignment, what did you do before need for balacing appeared?

Hope to hear details from you.