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#130398 - 04/03/06 12:35 PM Dry Type Distribution Transformer
rhpope Offline
Member
Registered: 02/23/06
Posts: 18
Loc: North Carolina
Ihave a dry type 3-phase distribution tranformer with the following specs:

45 KVA
HV: 208Delta V
LV: 220Y/127 V

How do you get 208V Delta? Is this just the three phases of 208Y/120 V brought in without the neutral? What would be the typical application of such a small voltage increase? Would this be considered an isolation transformer?


[This message has been edited by rhpope (edited 04-03-2006).]
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#130399 - 04/03/06 12:56 PM Re: Dry Type Distribution Transformer
Larry Fine Offline
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Registered: 02/18/05
Posts: 693
Loc: Richmond, VA
"Is this just the three phases of 208Y/120 V brought in without the neutral?"

That would be the result; 208v line-to-line.


"Would this be considered an isolation transformer?"

More likely a neutral-deriving device. Here's why I say that: (208/220)*127 = 120

It seems that the function of this transformer is to restore a "lost" neutral, or perhaps a way to provide an isolated (floating) neutral.
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#130400 - 04/03/06 01:13 PM Re: Dry Type Distribution Transformer
Larry Fine Offline
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Registered: 02/18/05
Posts: 693
Loc: Richmond, VA
Thinking further, it could be a 208-to-220v step-up, instead of using buck-boosts.
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Fine Electric Co.
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#130401 - 04/03/06 04:42 PM Re: Dry Type Distribution Transformer
Dnkldorf Offline
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Registered: 12/12/04
Posts: 1064
Loc: nowhere usa
Larry, I am guessing a buck-boost right now also...

But don't know without seeing the nameplate..

And if it is, you don't need the nuetral on the Hv side, just the 3 phases..

Never seen a use for a 208-220 3 ph transformer, but I am sure there is one. Is this used on a machine that needs isolation?


Dnk..

[This message has been edited by Dnkldorf (edited 04-03-2006).]
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#130402 - 04/03/06 05:21 PM Re: Dry Type Distribution Transformer
winnie Offline
Member
Registered: 09/15/03
Posts: 649
Loc: boston, ma
I use a 208V delta to 277/480V wye transformer to separately derive a neutral for an isolated system in my lab.

-Jon
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#130403 - 04/04/06 12:40 PM Re: Dry Type Distribution Transformer
Scott35 Offline

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Registered: 10/19/00
Posts: 2707
Loc: Anaheim, CA. USA
Definitely sounds like a Voltage Boosting setup here - in the form of an Isolated Transformer, rather than the more commonly used "Brute Force" approach with Autotransformer connected 1 Ø Transformers.

Quote:

How do you get 208V Delta?


The Primary Windings are connected as a Closed Delta 3 Ø 3 Wire arrangement - as is common with many 3 Phase Low Voltage Dry-Type Transformers.
The Secondaries are connected as a Wye, with provisions to land a Common Conductor to the Star Point via Terminal "X-0"

The Primary Windings of the Transformer mentioned in this thread, are wound for an input Voltage level of 208 VAC nominal, and are simply connected in Parallel to each other - resulting in a Delta configuration.

Scott35
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