axial vibrations in generator

[rob768]

Hi all,

is it possible that electrical problems in a generator cause high levels of axial vibrations at a frequency of 2x line speed? Any reference to articles or books would be highly appreciated. I am examining a case in which high axial vibratios seem to cause the roller bearing cages to wera out rapidly, introducing failure of the sets without prior warning (other than smoke coming from the seized bearing). (sets are rated 2300 kW, running at 1800 rpm)

 

[rob768]

We don't have a cause yet, just some suspicions (my favorite suspicion is cage whirling).
Vibration levels on the shields are all lowered to within specs (some weren't, which was one the suspect causes, but not mine) and the customer and the manufacturer figured that was enough. I hope they are right..

A generator does not need an thrust bearing, as axial forces are low.

 

[dicer]

Thrust bearing, yeah but you said "axial vibrations" so there must be a force component acting axially. Is the rotor ridgedly connected to the engine crankshaft?
If not how is it connected?

 

[rob768]

the axial vibrations are measured on the bearing shield, which vibrates in what we call an umbrella shape (largest deflection near the bearing, less to zero along the edge). We also measured shaft displacement. The shaft is not vibration in axial direction at all. The frame on which the set is positioned is also not vibration in axial direction, and level at vibrations measured on the frame are actually quite low compared to other similar installations.