We have recently installed vfd's in exixting circuits and now one of the motors has burned out and they are blaming our VFD. The vfd s are not even programmed to do any control as of yet just off and on.
Can it be the VFD the controls company is saying that our VFD's are causing a voltage across the bearings?

What is the motor driving? Is there any chance voltage is getting transferred to the motor shaft?
I really don't see this being a VFD problem.

That isn't logical.

However, blaming the competition for everything from bearings to bad weather is quite normal.

I vaguely remember reading something about this in a trade magazine (maybe EC&M). As I recall, it has to do with current spikes from the VFD's output inducing a voltage on the motor shaft via the windings, and the current arcing across the bearings and burning them.

Here's a paper on the topic:
http://www.aemc.fr/index.php?page=t...mp;file=200710291112-BearingCurrents.pdf

Thanks Albert

Another timely subject! Got a call this afternoon regarding a sewage lift station pump/VFD/panel meltdown, on a 'fairly new' install. That's Mondays problem child. This PDF may be interesting reading.

interesting stuff. Surprised me.

I recall this conversation not too long ago.

Wait For RENO Or Frenchelectrician. I believe they have the skinny on it.

Yes it did have something to do with induction.

I think the real answer is the EMI filter mentioned in the article. I would be surprised that a decent VFD wouldn't have that, just for FCC compliance.

Thanks for the vote of confidence ... but the issue is beyond my experience.

I've only seen bearings damaged by current flow, either through a fault condition, or when someone did some welding on the machine.

Thanks Lee .,

Anyway with the VFD's there is some issue what I heard and I did confirmed and there is pretty wide area to cover for this situation.

typically majorty of the VFD's should have spike filter to reduce the stray voltage/current which it will compound with long conductors.

I know it was disscused in the ECN forum here before and other electrical forum it was discussed also in depth and along the way there is few new info show up however., of my stupidty I did not save the link for the info.

And if the new motor is inverter duty it should work with VFD without any issue at all.

Merci,Marc

http://www.hitachi.us/supportingdoc...nimizing%20Motor%20Bearing%20Current.pdf

I see this bearing pitting sometimes and each time it is the VFD. The solution is insulated bearings. There are other solutions but changing the bearing will eliminate the issue.
It is caused by induced voltage transfered to the motor shaft.

I can't seem to open Alberts attachment. The VFD is a Siemens And the motor is about 50' away.

Do you have a load reactor installed. These reactors can and do prevent unwanted harmonics at the motor. They also clean up the simulated sign wave produced by the VFD.
Do not confuse the load reactor with the line reactor. Both are relatively the same with the exception being that the load reactor is installed close to the drive just like the line reactor but is connected to the output leads of the drive.
However, 50 feet is not considered a great distance to any drive or motor manufacturer. Considerations are usually discussed at lengths exceeding 100 feet.

Well we installed a new motor and now this motor is doing the same thing...screaming, it took a couple of weeks for it to get this loud.This motor is only 45' from VFD.Load test shows two phases 9amps and one 7 amps.I don't know what could be the cause?

The phenomenon is called "bearing fluting" and is similar to EDM (Electric Discharge Machining). A voltage potential builds up between the rotor and the frame and the current flows across the bearing races. But because the bearings are rolling around in the race, the discharge is not continuous so it builds up until it is high enough to "jump the gap" between the bearing and the race. As time goes on, the rate of build-up and discharge becomes repeatable and every time it happens, the race is damaged a tiny bit. But eventually, the damaged areas help facilitate the process so it gets worse and worse.

Reactors and such don't really help much. The true fix is what is called a "grounding bushing" on the motor shaft. There are a few available, but the most widely used one is from a company called Aegis.

http://www.est-aegis.com/

I have seen this happen on several occasions. The only easy fix is to use ceramic bearings. They are insulated so they cannot transfer voltage. I have seen load reactors help to some degree on long runs. The change to insulated bearings will eliminate the issue. I would get the drive and motor manufacturer involved.

The idea mentioned above will work too. It is just much easier to change out the bearings. Not necessarily on your dime either.

ps.....Check the carrier frequency (Hz). Set it as low as possible.