Bearing shield insulating procedure 2

[dule00]

Hello!

I have to insulate bearing shield on NDE of 1000 kW induction motor. So far, I didn't have any experience with this type of work.

Could somebody suggest and explain the procedure of getting this work done, what are the materials (polymer materials or ceramic powder or something like that) that I need, and so on... Could you maybe also suggest some materials manufacturers, so that I don't wander to much.

Thank you, I really appreciate all the help!

 

[Skogsgurra]

There are several ways of doing it. For a relatively large motor like this, it is important to use material that is strong and rigid enough so you don't lose center when putting the rotor in place and running the machine.

It is also important to keep capacitance low. The reason that you want to insulate the shield instead of using an Insocoat bearing is mainly to keep capacitance low. A typical Insocoat bearing for a machine this size will have more than 10 nF capacitance and a good insulation can be as low as a couple of nanofarads.
(This is important if you are running the machine off a PWM inverter, frequency components up to MHz are present).

You can use a washer (gasket) between motor frame and end shield, but that requires insulating the bolts with washers and sleeves and more often than not, there will be a problem with one of the many parts needed to insulate six bolts.

The other method is to water cut a circle in the shield and then fill it with a strong two-component resin. Glass-fiber is good for strength, but do not use carbon fiber. It conducts.

Be very careful when putting everything in place again. Regrease piping, transducer cables (shielded) and the like will short-circuit the insulation if you are not careful.
I have a few photographs of insulated shields and will make them available here soon.

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.

 

[dule00]

Thanks, Skogsgurra,

It would be great if you could put here a few photographs of insulated bearing shields.

 

[rhatcher]

Good answer Skogsgurra (lps). In my experience, the most common method is to insulate the circumference of the bearing housing with a glass fiber resin compound and to use insulating gaskets to insulate the bearing sides from the bearing caps.

 

[Skogsgurra]

Here's one of the pictures:

http://www.gke.org/pub/files/Insulated NDE bearing 1.jpg

I wasn't present when this was done. I do not know if laser or water jet cut. Running in a 700 kW test rig for diesel engines.

Gunnar Englund

http://www.gke.org

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

 

[Skogsgurra]

This is another method. A steel ring has been manufactured and inserted together with insulating material after the end-shield bore has been turned wider.

http://www.gke.org/pub/files/Insulated NDE bearing 2.jpg

Gunnar Englund

http://www.gke.org

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

 

[electricpete]

dule00 - can you clarify if you are talking about rolling bearing machine or sleeve bearing machine?

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(2B)+(2B)' ?

 

[rhatcher]

Skogsgurra,
That is not what I imagined that you were describing but, a picture is worth a thousand words and this picture does make sense of your reference to laser or water cutting. If I am interpreting this correctly, you are cutting the bearing housing away from the end bracket, insulating the cut, and then somehow attaching it back to the end bracket. Is this correct?

What I am describing is boring the inside diameter of bearing housing to a slightly larger size, lining the inside diameter with an insulating glass fiber resin compound, curing the resin compound, and then machining the insulating 'sleeve' to match the original bearing housing diameter. I have also seen this done with newer, ceramic based, compounds. This work can be done in a standard machine shop using a regular lathe.

Another approach is to purchase a pre-manufactured insulating sleeve as shown in the links below. The principle is the same. The bearing housing is bored oversize, the sleeve is installed, and then the inside diameter of the sleeve is finish bored to match the original bearing housing diameter. This method is preferred (quicker and easier) if the bearing size matches an available pre-manufactured sleeve. Again, this method only requires a standard lathe and the skills that are normally found in a standard motor shop machinist.

In both cases, an insulating gasket is required to prevent the bearing sides from contacting the bearing caps. This can be easily manufactured (cut out) from a sheet of nomex-mylar laminate that is typically found in a motor shop.

Note that the first link includes "[1].pdf" at the end. The posting preview function shows that this link may not post correctly.

http://www.eis-inc.com/files/pdf/EM_Quick_Sleeve

[1].pdf (page 10)

http://www.shaverkudell.ca/steel_insul_sleeves.html

http://www.eis-inc.com/suppliers/arlon.asp?showcase_no=13770

(nomex-mylar laminate)

 

[Skogsgurra]

rhatcher
You may not have seen my second post. It shows the method you are describing (with the steel ring).
I did not know about the Eze-Sleeve, but it makes sense. The insulation is rather thin (.2 mm) and that may result in a high capacitance, which lets lots of HF current through. But better than the Insocoat with its .05 mm alumina coat.

BTW, it's not eddy currents that cause the "arcing". Arcing is also a rather careless way of putting it.


Gunnar Englund

http://www.gke.org

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

 

[rhatcher]

Skogsgurra,
You are right, I did not see your second post. I began my post shortly after you posted the first picture. However, I got distracted several times and enough time elapsed for you to make your second post before I finished.

 

[dule00]

Thank you all for sharing your experiences with me.

Electricpete, this is a rolling bearing machine. Vertically mounted, 1485 rpm, more then 20 years old. It is DOL driven, so I'm not sure why does the customer want to insulate bearing shield on a 20 years old motor, I suppose that they are doing some preparation work to be able to drive it over frequency converter in the future.