Dry Type Transformer Type

[k0412d]

Hello all,

I've been studying lately dry type transformer and I realized it was a little more complex than I thought

After searching in a book 4 types of dry transformers exist:

Cast coil :
The winding is reinforced or placed in a mold and cast in a resin under vacuum pressure. Lower sound levels are realized as the winding is encased in solid insulation. Filling the winding with resin under vacuum pressure eliminates voids that can cause corona. With a solid insulation system, the winding has superior mechanical and short-circuit strength and is impervious to moisture and contaminants.

Vacuum-pressure encapsulated (VPE):
The winding is embedded in a resin under vacuum pressure.
Encapsulating the winding with resin under vacuum pressure eliminates voids that can cause corona. The winding has excellent mechanical and short-circuit strength and provides protection against moisture and contaminants.

Vacuum-pressure impregnated (VPI):
The winding is permeated in a varnish under vacuum pressure.
An impregnated winding provides protection against moisture and contaminants.

Coated:
The winding is dipped in a varnish or resin. A coated winding provides some protection against moisture and contaminants for application in moderate environments.

Here are my questions:
Is Coated = Cast resin?, if not what is cast resin?

Is the order given show the transformer type from best to worst?
I guess no since some manufacturer gives some type with new manufacturing process as the utmost in transformer quality (eg ABB RESIBLOC)

To sum up, could someone give me a clear picture on the subject because obviously I'm still struggling to get one.

Thank you very much for your help.

 

[dpc]

Coated is not the same as cast resin. Plenty of on-line references on cast coil:

http://www.abb.com/product/db0003db004283/c12573e700330462852568cc0055df16.aspx

What is "best" is dependent on the application. Pretty safe to say that cast coil will be the most expensive.

 

[rbulsara]

From the description it appears that coated would be just that , no vacuum-pressure treatment or casting. Perhaps small or control transformers fall in this category.

Cast coil is considered better than VPI or VPE.

I am not sure of the difference between VPE and VPI but they would be comparable.

Your best bet it to contact a vendor like ABB or Cooper Industries and talk to them or request your local rep to find a knowledgeable factory engineer.


Rafiq Bulsara

http://www.srengineersct.com

 

[prc]

You are right .The order goes best to worst .Cost also moves the same way.Based on environment of use and criticality of application,one may decide.RESIBLOCK is ABB TM for VPE type transformer.

 

[k0412d]

Thanks for the feedback.

 

[DamnYankee1]

Resibloc TM is actually a cast type transformer. The Hv windings are wet wound with epoxy and fiberglass strands and is mechanically stonger than conventional vacuum cast trasnformers. VPE = Vacuum Pressure Encapsulated and uses a silicone varnish. VPI = Vacuum Pressure Impregnated using a polyester based varnish.