VFD's

[mpparent]

Hey All,

Wanted to know if anyone on the forum has run across motor bearings pitting because of bearing currents caused by common mode voltages from VFD's. I've a situation at my plant where this phenomenon is occurring. We've decided on shaft grounding kits to alleviate this problem. Any others w/ similar problems?

Mike

 

[busbar]

Some discussion at thread237-30937

 

[purplepete]

I appreciate the circulating bearing currents could come from a number of sources. In turn this can pit the bearings leading to premature failure. One I saw in a 398-amp 50 Hz 415 volt motor was caused by nothing more than the ground conductor being run neatly alongside the same phase conductor (they were single-core double-insulated conductors) over the route length of about 100 metres. Current measured in the ground conductor was 90 amps. I think the drive end bearing lasted just over two years. Separating the ground by about 300 mm from the trefoil of the phases reduced the current to just a couple of amps.

 

[NavyPower]

You should check out the Sept/Oct issue of IEEE Industry Applications Magazine which contains an article on motor bearing fluting. There have also been numerous technical papers written over the past few years regarding this problem and means to mitigate it.