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Old 07-29-2013, 12:00 AM
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racer-john racer-john is offline
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Default Bearing failure due to transient voltages from VFD's

Don't know if any of you using VFD's have experienced bearing failure, but
thought I would throw this in.

VFD's problem, causing stray electrical current thru
bearings resulting in bearing failure.

Quote

Virtually all VFD-driven motors are vulnerable to
bearing damage. To make the savings generated by VFDs
sustainable, an effective long-term method of shaft
grounding is essential. Although an AEGIS ring safely
bleeds damaging currents to ground...
end Quote

John
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Old 07-29-2013, 02:09 AM
metal manny metal manny is offline
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Hi John

This is a 'news' to me. We use VFD's in all types of applications and to date, I haven't noticed any adverse effects.

This discussion might be terminated by the administrators as it may be considered 'outside of metalshaping'.

Would you please furnish the source of your quotation (you can PM me) as I am very interested in researching this further.

Thanks
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Old 07-29-2013, 06:25 AM
RockHillWill RockHillWill is offline
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I too, am interested in the source of this information and the date of its publication. I am beginning to use mine more and want to prepare accordingly. Thanks.
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Last edited by RockHillWill; 07-29-2013 at 06:31 AM.
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Old 07-29-2013, 08:29 AM
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I have several machines with VFD's. The 5hp motor on my lathe has started to make noise. I will have to check into that
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Old 07-29-2013, 09:20 AM
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When I rebuilt my Nibbler, it went under water in Hurricane Katrina, so all of the electrics needed to be replaced. I contacted SEW Euro Drive and told them what I needed and asked them to design a complete drive system for the machine.
Here are the specs that I gave them:
220 volt single phase input
motor speed requirements 300 to 3600 rpm.

The original motor on the Nibbler was 1.2 hp two speed, 1200 and 2400 rpm

They recommended and supplied:
3 hp three phase motor rated for VFD use.
VFD unit
Choke, it is an isolation transformer that isolates the VFD unit from all other electrical components on the machine that are feed from the incoming power cable.

If you are going to use other electrical devices, lights or whatever then you need to have the input wiring 4 wires, two power leads, neutral and a separate ground. I don't have anything on the machine that is power off the incoming power feed so I have a three wire feed.

The motor supplied has a higher class of insulation to withstand the additional heat generated when running at low rpm. By going to a 3 hp motor there is more iron and copper in the motor to dissipate heat and have no loss in required power at lower speeds, compared to the original motor. The fan in the motor is also rated for VFD use.

Not an inexpensive package but it has worked perfect and has never given any problems at all. All of the components were built in Texas at one of their US plants.

Most of the problems that I have heard about are heat related because the motor is not VFD rated.

This is an OFF TOPIC subject for this site.
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Old 07-29-2013, 09:34 AM
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Here is a link to Baldor motor supplier that talks about it.
http://www.vfds.com/aegis-shaft-grounding-rings
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Old 07-29-2013, 01:33 PM
bobadame bobadame is offline
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Maybe a grounded, spring loaded carbon brush against the end of the armature shaft would solve this.
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Old 07-29-2013, 01:50 PM
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This really is nothing new or isolated to VFDs. Since the beginning of the use of bearings and electricity any stray voltage due to a short, ground or any other electrical malfunction might possibly find a path to ground through a shaft and bearing.

If you have not concerned yourself with this problem before, I wouldn't spend any time worrying about it now or in the future. Probably a many times greater risk due to heart failure than bearing failure. And a motor bearing failure won't kill you.
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Old 07-29-2013, 07:34 PM
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Default Bearing failur e due to transient VFD's

Manny, Richard K. has given a source that you could check.
Unfortunately I lost the source of my info.
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Old 07-29-2013, 07:40 PM
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I'd be amazed if this was a problem on anything unless it is in an industrial environment running 24/7 or close thereto.

The cost of the solution is greater than the cost of a new motor.

Not a EE and never played on on TV just my opinion.
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