Bearings of motors powered through VFD

[npower0073]

On site we have 3 400V motors 200kW , spupplied via ABB ACS 800 inverters. he motor bearings are nit special insulated bearings , for applications that use inverters, they are typical nearings. The frame of the motor and the driven fan are grounded, the motor cbles are special shielded power cables. Is it possible for us to change the bearings with other tyoes, special insualted?

 

[Skogsgurra]

Hello,

not quite sure what you ask.

Do you have standard (not insulated) bearings and want to put in insulated (Insocoat) bearings?

That would usually not be a problem (except that Insocoat may run a little hotter if coating is on outer rim).

Why do you want to change bearing types?

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[ravensfan]

I've had problems with this in the past myself and we corected the problem by installing a grounding device on the shaft of the motor. Your problem is shaft currents...

 

[whycliffrussell]

depending on the length of the run you may have a commom mode voltage problem. this may be resolved by putting a common mode filter on the leads from the inverter to the motor.

 

[ozmosis]

npower0073
Do you have a problem with your bearings or do you think you might have a problem with your bearings?
If you have a problem then first be sure it is related to the inverter before going further otherwise its an expensive process and you may be back to square one. The type of bearing failure is quite specific if it is.

 

[petronila]

Hello npower0073,

If the motors are running fine then you don´t have nothing to alarm. But I think the best you can before take some action about the bearings is to do a question for your motor´s dealer or to the manufacturer about the motor´s design.

Normally you could find two typical designs for inverter´s motors, one with insulated or hibrids bearings and other with standard bearings and OD shaft insulated, I think the last could be your case.

Regards

Carlos

 

[ravensfan]

you can find out for sure if your problem is shaft currents by replacing the bearings and cutting the old bearings in half to examine the internal surfaces--if you see an 'etched look' that is a sure sign of shaft currents. good luck..

 

[ozmosis]

ravensfan
that's quite a major undertaking on 3 x 200kW just to see if there is a problem!

There is a device coming onto or already on the market called BEPPE Bearing predictor developed by one of Eng-Tips regular tipsters Skogsgurra. Try

http://www.gke.org/beppe/files/Bearing currents on one page 1.pdf

At the moment there is nothing really on the market to predict if EDM is causing premature bearing failure other than setting up an oscilliscope and knowing what to look for.
BTW, I have no commercial interest in BEPPE. I wish I did as it is a great little device!