# VFD Motor bearing issues Shaft grounding brushes



## Southeast Power

I posted here over the last month or so concerning a motor bearing issue related to the VFD.
Very simply stated, due to improper motor application, the VFD controlled motors have begun to present a high pitched rattling sound associated with fluting or washboarding of the outer race caused by current circulating through the shaft bearings.
Initially one motor was replaced but quickly presented the same damaged bearing sound.
The remediation suggested was the motors be replaced with those with a factory installed AEGIS shaft grounding brush.
It appears to have addressed the problem. 

Question:
Has anyone here installed a ground brush on an in service motor?
If so, is it expected that the brush will only arrest the damage or is it expected that the bearings, without the damaging circulating current will polish out the fluting damage to the outer race?

Im trying to understand why there is a market for field installed ground brush kits. Its been my observation that the bearings present fluting after only 300 or so hours in service.

All comments are appreciated.


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## frenchelectrican

Suncoast Power said:


> I posted here over the last month or so concerning a motor bearing issue related to the VFD.
> Very simply stated, due to improper motor application, the VFD controlled motors have begun to present a high pitched rattling sound associated with fluting or washboarding of the outer race caused by current circulating through the shaft bearings.
> Initially one motor was replaced but quickly presented the same damaged bearing sound.
> The remediation suggested was the motors be replaced with those with a factory installed AEGIS shaft grounding brush.
> It appears to have addressed the problem.
> 
> Question:
> Has anyone here installed a ground brush on an in service motor?
> If so, is it expected that the brush will only arrest the damage or is it expected that the bearings, without the damaging circulating current will polish out the fluting damage to the outer race?
> 
> Im trying to understand why there is a market for field installed ground brush kits. Its been my observation that the bearings present fluting after only 300 or so hours in service.
> 
> All comments are appreciated.


I have one installed a field installed shaft grounding ring on 75 Kw motor and that motor did not even hit a full 100 hours on running time. 

but for other types of motors I have installed few and seems it cure most of it as I mention in other posting the only issue is the brush life during normal useage. 

That part I just can't prediect how long it going last. maybe almost same life as conventail non vsd motor bearing life. 

I know couple other motor gurus will chime in here too fill in their options too.


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## Cow

I've only heard of the bearing issue on these internet forums, I've never seen it happen in real life, nor have I ever installed a grounding brush on a shaft or seen one used?

I'm around VFD's a fair amount too.


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## glen1971

They just installed a new 5,000 hp motor on a compressor and put grounding brushed on the compressor shaft. They said there was a grounding issue and it was causing arcing on the bearings. There is no VFD on the motor and the compressor shaft is turning about 13,500 rpm. I'm not sure if it was successful in stopping the arcing. 

FWIW..One millwright I talked to said he's used ceramic bearings with more success than the brushes..


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## Southeast Power

I understand that the bearing insulation or the lack of it is the root of this problem.
I found quite a bit about the science of it all on the videos and literature on this site:
http://www.est-aegis.com/video.php


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## micromind

Cow said:


> I've only heard of the bearing issue on these internet forums, I've never seen it happen in real life, nor have I ever installed a grounding brush on a shaft or seen one used?
> 
> I'm around VFD's a fair amount too.


Same here, I don't doubt that the issue exists, I've yet to see it in real life. 

I'm not sure but it seems to me that if proper bearing greasing procedures are followed, this type of bearing failure would be minimized.


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## JRaef

Keep in mind, we are _electrical _guys. A lot of people see the problem, but assume it is related to bad bearings, bad greasing, other mechanical issues. Very few of them make the leap into discovering that there is a connection to it being run from a VFD, so there wouldn't be a reason to show it to their electricians. I went to one pharmaceutical facility last year and mentioned it to one guy, he spread the word around and I got called back into the Mtc Mrg's office. He opened a big drawer in the bottom of his file cabinet, it was filled with destroyed bearings, all of them showing the tell tale signs. He had never heard of this before and had been replacing the bearings right and left. He kept the dead bodies in the drawer because he was constantly changing bearing suppliers and would show their salesmen why they were losing the business. Funny thing to me was, apparently none of the bearing salesmen knew about it either! They just accepted their losses. This week, I went to a different building at the same place, and their electrician had never heard of it either. He mentioned it to the millwright, I got a call today asking if I could come back out and train them on what to look for. These guys are literally less than 1,000ft from the place I went to last year, they never talk to each other.


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## Southeast Power

I received a call back from an Aegis rep.
One of his jobs is to travel to facilities and motor shops and present what they know about these bearing failures.
I have a pile of 2 hp motors and the consensus is that they are just throw aways.


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## micromind

Suncoast Power said:


> I received a call back from an Aegis rep.
> One of his jobs is to travel to facilities and motor shops and present what they know about these bearing failures.
> I have a pile of 2 hp motors and the consensus is that they are just throw aways.


If the only issue with them is bearings, it doesn't take much time to replace them.


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## Southeast Power

micromind said:


> If the only issue with them is bearings, it doesn't take much time to replace them.


I think I might go ahead and change the bearings on a couple of them and see how long it takes. I have a RFP in at a couple of shops and they haven't even called me back. I'm not going to beg them to take my work.

If I go for it, I'll cut one of the bearings open and post a pic if the fluting is visible.


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## Southeast Power

I picked op one of the motors and pulled the bearings.
I cut open the outer race of the output shaft.
Interestingly, the frosting was only on half of the bearing race, the other half still shines like a mirror.


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## micromind

Suncoast Power said:


> I picked op one of the motors and pulled the bearings.
> I cut open the outer race of the output shaft.
> Interestingly, the frosting was only on half of the bearing race, the other half still shines like a mirror.


Now all you need to do is polish it up a bit, put the balls back in, weld it up and you've got a new bearing!


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## Southeast Power

micromind said:


> Now all you need to do is polish it up a bit, put the balls back in, weld it up and you've got a new bearing!


Yup, save myself 6 bucks.
I was looking around for these particular bearings and they seem to be very common for snow mobiles.


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## micromind

They're very likely 6203 or 6205. Very common in a lot of stuff.


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## Southeast Power

micromind said:


> They're very likely 6203 or 6205. Very common in a lot of stuff.


6203 Z is the 17mmx 40mm X 12 mm on the fan side
6205 Z is the 25mm X 52mm X 15 mm on the output shaft

The Chinese brands are about 10 for $15

Eastern European and domestic are about four times the price or about $6.50 each


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