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Joined: Feb 2003
Posts: 939
F
Member
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


Pas de problme,il marche n'est-ce pas?"(No problem, it works doesn't it?)

Joined: Jul 2004
Posts: 3
H
New Member

Joined: Jun 2007
Posts: 301
J
Member
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.

Joined: Oct 2003
Posts: 172
G
Member
I can't seem to open Alberts attachment. The VFD is a Siemens And the motor is about 50' away.

Joined: Jun 2007
Posts: 301
J
Member
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.

Joined: Oct 2003
Posts: 172
G
Member
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?

Joined: Jul 2004
Posts: 101
J
Member
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/

Last edited by jraef; 01/09/09 03:18 AM.

JRaef
Joined: Jun 2007
Posts: 301
J
Member
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.

Last edited by JValdes; 01/09/09 02:40 PM.
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