VFD Drive – Motor Bearings (Question & Answer)

Question

We recently installed a slurry pump system requiring three, 1100 gpm, centrifugal pumps about 2 miles apart.

The motors are controlled by a VFD drive to match the speed to the flow. We have had bearing failures on

two of the motors and one of the pump barrels. The units ran to failure so most of the evidence is gone. I have

instructed the motor repair shop to save the ODE bearing that didn't fail to check for shaft currents. Are there

special requirements for VFD motors such as shaft brushes, insulated bearings, ceramic bearings, etc?

What's the best?

Answer

Normally above 315 frame (metric) is recommended you use an insulated bearing on the non-drive end. I

would suggest the foil screened motor cable with symetrical earthing, that is to say, one earth next to each

phase is used. Earthing the pump body motor and plinth is also important. This should get rigid of most EDM

issues. If you still have problems after this you can try earth brushes or active filters.