arc welding on Generator bearing 1

[MAH82]

hi
during the erection of our Generator we got arc welding on the bearings and due to it the surfase of bearing(babbit) was damaged.we are considering the earth system but please in this regard if any body has an idea or similar experience present to me.

 

[byrdj]

I'm going to assume you mean electrolisis arcing in the bearng during operation. If you actually mean by welding during construction, never mind. Welding around rotating eqiupment needs to have a dedicated welding ground and not assume station steel as ground

I'm familair with steam turbine driven generators. the outboard generator bearing (and adjancent oil deflector and seal)is insulated from the frame (stator), thus breaking the current loop through frame, inboard bearing, rotor, at the outboard bearing. The inboard bearing has a grounding braided copper strip on the rotor.
Failure of the inboard ground strap will allow rotor voltage to increase and damage the inboard bearing.
Failure of the outboard insulation will allow a current loop and damage the outboard bearing. The quality of ground can be verified by measuring rotor voltage with a carbon brush on a stick. It should be near 0 volts

If the insulation at the outboard is double, there should be a test terminal to let you know both layers are clean. If one layer should fail, or if the unit is built with only one layer, the voltage at the out board rotor can be measured and the nominal trended (dependsonunit normally 50VAC)