Real difference between: Standard, AEGIS grounding, Insulated Bearings, Ceramic Bearings? 1

[mntash]

What are the practical benefits/drawbacks of each type of motor/fan combination?

I know ceramic bearings are often considered "the best" but they are incredible expensive and have long lead times.

This is for mechanical applications, from Air Handlers, Exhaust Fans and even some process equipment.

We have a customer who is pushing for ceramic bearings but the lead time we got from the vendor is about 6 weeks LONGER than the actual project completion time! LOL.

 

[Tmoose]

Are you just being asked to supply the bearings? Are they willing to elaborate on why they want "ceramic" bearings( usually hybrid ceramic with 5210 steel races and ceramic balls).
Are they having issues with bearing damage from shaft currents ? Usually motor are the victims of shaft currents, although I guess if a fan was transporting some turbo-ionic products along with air or a mixer was processing bright yellow golf ball rubber there could be some wicked static charge buildup.

Or, are they unhappy with bearing life of the current design as repaired and maintained by the night shift, and hoping hybrid ceramic tribological advantages are what they need?

According to motor manufacturers Shaft currents come in several different flavors, and technical solutions range from adjusting VFD lead length and position, to providing one shaft ground at a particular end of the shaft, to providing a ground at each end of the shaft, to insulating everything in ( and out of ) sight. A thin layer of ceramic coating on a conventional bearing OD and faces should effectively block hundred of volts. I figure the charge will still have to sneak out somewhere.

Some folks have dabbled with conductive grease to mitigate shaft current problems, but I am not aware of a major bearing manufacturer advocating that solution.

http://www.eis-inc.com/files/enewsletter_pdfs/Insocoat360.pdf

 

[Skogsgurra]

There is a lot to be said about bearing currents. And lots is being said. Many misconceptions out there.

We were invited to GE, Schenectady last year to present our view and the live presentation is available to those who have access to the GE intranet.

Those who can not access it that way should be able to find the presentation by googling GE Bearing Currents



Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[electricpete]

Gunnar (skogsgurra) is our resident expert on that subject.

Here is a link to that file from google

http://www.gke.org/presentationer/files/GE Bearings and their electric environment w O and E.pdf

I was curious about the statement on the last page:

Insulated bearings can be a hazard. Especially ASIMs when an electrical failure occurs inside the machine. Lethal voltage may then be present on the shaft.

Can you elaborate on this? Are you talking about with motor running or secured?


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(2B)+(2B)' ?

 

[electricpete]

ASIM = asynchronous induction motor?

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(2B)+(2B)' ?

 

[Tmoose]

looks like OP Mntash has not been back since Dec 14, so his customer's ceramic bearing expectations are still unknown.

 

[Skogsgurra]

Yes, Pete. That's the presentation I meant.

Quote: Insulated bearings can be a hazard. Especially ASIMs when an electrical failure occurs inside the machine. Lethal voltage may then be present on the shaft. Can you elaborate on this? Are you talking about with motor running or secured?

Answer: One of the fundamental principles when it comes to electric safety is to make sure that no parts that can be touched by man or animal always is at a safe potential. Especially if there is a fault in the system.

Techniques used are bonding and grounding. For an Asynchronous Induction Motor (yes, ASIM) the assumed and hitherto universally accepted rotor grounding method is via the bearings. The well-known ASIM is shown here:

http://www.google.se/imgres?imgurl=...iact=rc&uact=3&dur=2248&page=1&start=0&ndsp=8

It is obvious that there are several ways in which the stator winding can get in electrical contact with the rotor in a fault situation and if the load is connected via a belt or an insulated coupling - or directly driven - then there will be a lethal voltage on the shaft if it were not grounded via the bearings.

Now, if both bearings are insulated, the shaft is a potential death trap to the operator, mechanic or electrician that grabs the shaft to find out why the motor doesn't moving. Not all care about tag and lock out before doing a preliminary check.

That is what the last picture in the presentation is showing.


Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.

 

[electricpete]

Thanks. I understand now better the nature of the concern. I gather the time constants are short enough that there is not much concern for trapped voltage with the machine shut down (which is a more typical time for humans to come in contact with the shaft)

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(2B)+(2B)' ?

 

[Skogsgurra]

I guess that you already guessed that "make sure that no parts that can be touched by man or animal always is at a safe potential" shall read "make sure that parts that can be touched by man or animal always is at a safe potential".

Gunnar Englund

http://www.gke.org

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Half full - Half empty? I don't mind. It's what in it that counts.