Genrator Rotor Shaft to ground voltage

[BJ001]

I am looking for typical Generator Rotor Shaft to Ground voltage for a 50MW 3000rpm 11kV Generator to establish if an earthing brush on the alternator rotor shaft will prevent and current flowing through the coupling and down to earth via the prime mover bearings.
Are there any other precautions that need to be taken to protect the prime mover bearings from this problem.

 

[motorman]

A good place to start:

http://www.shaftgrounding.com/techdocs/BDED_pg1.htm

http://www.abb.com/GLOBAL/seapr/SEAPR035.NSF/viewUNID/67BD0B8B45590059412568890037BD7D

http://www.sohreturbo.com/damage.htm

http://www.compsys.com/drknow/aplpa...2f085b6fad75d290852566aa0062720e!OpenDocument

http://www.sohreturbo.com/table.htm

 

[DougMSOE]

There is no standard acceptable standard. I have seen as little as 2 volts and as much as 38 volts. Suggest that you find the cause.
Siemens has a model of the causes of this problem.