Shaft Grounding

[lukin1977]

We just installed a VFD Yaskawa AC Drive-A100 on a wire drawing machine

I´ve read that we need to ground the shaft to avoide damage to the bearings cause by leaking currents through them

My question is: Isnt the shaft already grounded through the gear train? The shaft has a steel gear directly couple to it and the machine structure is already grounded

 

[MikeHalloran]

No. Gear teeth and bearing balls both are normally separated from mating surfaces by a hydrodynamic oil film, which is thin, but insulating.



Mike Halloran
Pembroke Pines, FL, USA

 

[Skogsgurra]

As Mike says. And it is when capacitively and inductively coupled voltages discharge through those insulating films that you get EDM (Electric Discharge Machining) in your bearings.

There is no cure-all for this. You have to find out if the situation is bad or not and then what the dominant coupling mechanism is. After that, you can decide if you need to do anything about it and also what to do.

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[petronila]

Hello Lukin1977

Use a proper motor with insulated bearing or install a brush for shaft earthing. The VFD applications requieres an Inverter duty motor usually this kind of motor are prepared for it and some one have an insulated bearing in N.D.E, could be good you consult with your motor dealer.

Regards

Carlos

 

[lukin1977]

The VFD was intalled on and old machine and the motors are old too. So they are not inverter duty motors.

Skogs: Are you saying that grounding the shaft it is not always necessary and it depends on case study? Sorry my english is not very good

 

[Skogsgurra]

Yes. There are four distinct failure mechanisms and many different mitigation techniques. See

http://www.gke.org/presentationer/files/EDM Physics and Reality 1.pdf

for an introduction.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.