Generator NDE Bearing Axial Vibration High


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Dear all.

I am Vivek mechanical engineer. I found this website as I am facing a problem.
I have a 105 bar back presser gas turbine
12.5 MW -11 kv generator

Here I start from beginning that we done a turbine overhauling and then start turbine

Now what happen after baring and rolling we move to rated rpm at 7029 rpm. But as increase rpm from 1000 to 7029 in between near about 4000 rpm it will trip. So it is earth pole problem.

After that we changed diode then this problem was no more.

There are 8 bearings. of which 7th & 8th are Gen Brg.
Here problem is related to 8th brg. Which is generator NDE

what happens that at rated 7029 rpm there is no vibration on pedestal cover at 8th in axial direction as soon as 11kv voltage given the vibration at 8th in axial is 13.1 mm/s and after taking 2MW load vibration is 13.1 mm/s

And one thing i note that when we remove cover from generator winding at 11kv the axial vibration is 3.8 mm/s and as cover fitted on generator vib. in axial direction become 12.0 mm/s