Cast Coil versus VPI Dry Transformer

[brupp]

Years ago I attended a Square D presentation where they sang the praises of cast coil or cast resin transformers. It was even stated that they have been successfully operated underwater in the ocean, showing how wonderful the insulation system is for wet or dirty environments. I know one company had a lot of units fail to meet their expected force-cooled ratings but I'm not aware of any real "failures" of cast coil transformers.

Now I'm in a situation where I have to replace a failed VPI dry type transformer (2000 kVA, 13800-480V, 3-phase, outdoor) and I am seriously considering cast coil. I have requested quotes for both VPI and cast coil.

I would appreciate any feedback for or against cast coil transformers in this general size and voltage range.

I would have expected to see this previously in the forum but my review of 400 topics didn't uncover any and the search function is inoperative.

 

[DanDel]

Have you considered liquid filled, usually the best for outdoor applications?
I am aware of several installations of outdoor cast-coil transformers (one WW plant with upwards of 20) for close to 10 years with no problems.

 

[brupp]

In retrospect it may have been best to use oil-filled. But since this is an existing installation I don't want to have to build new foundations and deal with oil catch basins & oil water separators. So I have ruled out oil-filled.

 

[dpc]

You will get varying opinions on this, but I'm a big fan of cast-coil transformers, especially in dirty and/or poorly maintained installations. We specified dozens of these for wastewater plants, but generally indoors.

They can be placed outdoors (but must be specified as such)and I think they would perform better outdoors than a VPI unit.

Keep in mind that there are various types of cast-coil transformers and that the secondary windings are often done differently.

With regards to oil-filled, you could look at the new vegetable oil that Cooper is marketing. This eliminates a lot of environmental and fire hazard issues.

 

[seanmcc]

dpc

Iam interested to know more about your comment on vegetable oil for transformers. We use both mineral oil and midel insulating fluid for our transformers at present. Do cooper have a web site and is the product type tested?

Thanks
seanmcc

 

[DanDel]

The Cooper fluid is called Envirotemp FR3, and is 'a non-toxic, fire-resistant, bio-based natural ester dielectric fluid. Check out this link:

http://www.cooperpower.com/news/article.asp?status=Current&id=62

We used this fluid for a retrofill on an existing transformer about 2-1/2 years ago, and have been very satisfied with the results. There are some differences as far as typical test results. This fluid can safely hold more water than mineral oil, and there are different limits for insulation tests.

 

[RJF]

ABB also makes a seed (vegetable) oil (BioTemp) transformer oil that competes with Cooper's Envirotemp Fluid. Both would be considered less flammable per the current NEC.

In the 80's and early 90's we put in a lot of VPI and VPE outdoor dry's (13.8 KV primary, 1000-2500KVA AA with Fans). Due to the last few failures we are going back to silicon liquid or seed oil liquid outdoor units. Still using VPI dry for indoor. We have looked at resin-block and cast coil for outdoor but have not bought any. They still have bus connections, taps and other exposed conductors. Wind driven rain and dirt can get in most fo the outdoor enclosures. Any dry type outdoor unit will require cleaning. If you need to stay with dry dues to liquid containment issues - consider at least going to a VPE and then on to cast.

 

[jbartos]

Suggestion: Visit

http://www.dynapower.com/Products/Cast_Coil/ultracast.htm

etc. for Ultracast(TM) Transformers

 

[kidlat]

Try the Square-D web site (

http://www.squared.com)

and go their technical library. Subject: Key Features of Liquid-Filled, Dry Type and Cast-Resin Transformers


Document Number: 7300PD9203
Publication Type: DB
Class: 7300
Date of Publication: 02/92
Language(s): English
File Size: 1966 Kb

This product data bulletin provides feature/benefit information for Class 7300 Liquid-Filled, Dry Type and Cast-Resin Transformers.