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#130398 - 04/03/06 03:35 PM Dry Type Distribution Transformer  
rhpope  Offline
Member
Joined: Feb 2006
Posts: 18
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 03:56 PM Re: Dry Type Distribution Transformer  
Larry Fine  Offline
Member
Joined: Feb 2005
Posts: 693
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.


Larry Fine
Fine Electric Co.
fineelectricco.com

#130400 - 04/03/06 04:13 PM Re: Dry Type Distribution Transformer  
Larry Fine  Offline
Member
Joined: Feb 2005
Posts: 693
Richmond, VA
Thinking further, it could be a 208-to-220v step-up, instead of using buck-boosts.


Larry Fine
Fine Electric Co.
fineelectricco.com

#130401 - 04/03/06 07:42 PM Re: Dry Type Distribution Transformer  
Dnkldorf  Offline
Member
Joined: Dec 2004
Posts: 1,064
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).]


#130402 - 04/03/06 08:21 PM Re: Dry Type Distribution Transformer  
winnie  Offline
Member
Joined: Sep 2003
Posts: 649
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


#130403 - 04/04/06 03:40 PM Re: Dry Type Distribution Transformer  
Scott35  Offline

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Member
Joined: Oct 2000
Posts: 2,707
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


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!


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