We have been having bearing fluting problems with some of our VFD driven motors. We had an engineer from the drive manufacturer come in to test and inspect our installation. One of his recommendations was an insulated bearing on the NDE of the motor. A sales rep from the bearing manufacturer is pushing a hybrid bearing with ceramic balls, which he said was more reliable and slightly cheaper than the ceramic coated model. Has anyone had experience with the different types of insulated bearings on the market and can make a recommendation?

You should search the vibes forum for "fluting" and see the recomendations from people who have fought the problem, and won (at least they say they did). I think you'll find the proper cabling (High Freq. grounding mesh) is the first step (check the kind you have against what has been recommended in the forum), then try the bearings if you still need it.
After thinking about it again however, if you don't have the proper cabling, and have to retrofit, the cost may be prohibitive up front to the managers who are clueless. Then you can fool around with bearings, grounding brushes, etc.
By the way, do not necessarily depend on the factory rep telling it like it is. The question from you, if you find you do not have the right type supply cable, is "why did I not know this up front?"

D

Thanks for your reply Dave. The engineer from the drive manufacturer did extensive testing and inspection of our system and is reputed to be their top guy on this problem. He found our cabling to be good. His recommendations include a shaft grounding brush, an insulated bearing on the motor NDE, and installing a non-conductive type of coupling between the motor and Fan. All this is on an installation less than two years old.

I still say search the vibes forum for "Fluting", or click on Ron Brook and view his posts. Ron worked for Rockwell, Reliance for years, and did a lot of work with the VFD's. I think you may need to read the posts and look at the cabling for yourself.

Edit: Here is the link
http://maintenanceforums.com/e...631064293#6631064293
D

I second Dave's recommendation.

Thanks guys for your responses. I have read most of the posts about fluting on these boards in the past and participated in some on them. I used the knowledge I gained to convince management that I had a real problem and the result was getting the drive engineer down to our plant. We have decided to implement his recommendations as our course of action. One of the recommendations is to inspect the cabling and grounding of each installation as we come to it.
Management here thinks if the shaft brush and insulated bearing stops the damage it will be cheaper than running new cable. We do have the proper type of cable but the armor was not run all the way down to the motor. The installer said that the transitions from flex to hard conduit was done with a special grounding fitting but I am not sure if it was checked after we found we had a problem. Our installation is armored flex cable from the drive to hard conduit about 15 feet above the motor and then flex again about 3 feet from the motor. I guess that leaves 2 extra places that have to be properly grounded. Do you have any advice about checking the transitions for proper grounding or the whole circuit?

If the flex you are refering to is Seal Tite type, then no, you probably do not have 360 deg. grounding. The ABB attachment that Bruce Shepard put up in the discussion on the link above explains it very well. Even has some nice pictures
You really want to try and shield it as the Europeans do in the pdf.

Dave