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#130574 - 07/24/06 03:03 PM Double tapped secondary.
VAElec Offline
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Registered: 07/26/05
Posts: 49
Loc: Sterling, Virginia, US
Found a new transformer today. 480-208Y/120 with two sets of taps on the secondary, thirty degrees out of phase (0 degrees X1,120 X2,240 X3, XO then 30 X5,150 X6,270 X7, XO). Anyone seen this? From what I can figure it is supposed to cancel harmonics and reduce the need for an oversized neutral conductor. 1/0 with 3/0 neutral on the secondary, which differs from the size A mcm a,b,c size 2xA neutral for a K-rated transformer.

Anyone have an idea on how the coils are tapped? No namplate diagram.

(edited for coil question)

[This message has been edited by VAElec (edited 07-24-2006).]
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#130575 - 07/24/06 07:49 PM Re: Double tapped secondary.
LarryC Offline
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Registered: 07/05/04
Posts: 780
Loc: Winchester, NH, US
Is this for using a 3 phase primary to create a single phase secondary?

Just like wiring a 12 lead 3 phase genny to get a single phase output at 2/3 of the rated output.

http://electrical-contractor.net/ubb/Forum15/HTML/000091.html

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#130576 - 07/24/06 10:34 PM Re: Double tapped secondary.
Scott35 Offline

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Registered: 10/19/00
Posts: 2707
Loc: Anaheim, CA. USA
Does it look anything like this:



This is a "Rectifier Transformer" - part of an elaborate UPS System.

Although the one shown in the drawing does not have a 4 wire Wye Secondary scheme, all that is needed to make the Wye section a 4 Wire type is to tap into the "Common Jumper" which connects the left sides of each coil on the Wye side, and extend that tapped point with a suitable sized Conductor.

This is the way that _ALL_ 4 Wire Wyes are done.

The Delta winding is used for cancelling Harmonics. It is likely connected to some external load.

Need to refresh myself, by grabbing the Electrical Engineering Handbooks!


Here's another type of Rectifier Transformer I have run across:



This has Three (3) 3 Phase Secondaries - resulting in a 9 Phase Secondary Transformer.

These drawings are from the Technical Reference section, and may be found under the topic:

6 and 9 Phase Transformers

I thought I had uploaded some pictures of these Transformers, but not sure where and when - if at all!
Plan to make a new topic in the Technical Reference section tonight, which will have pictures of these "Specialty Transformers" I have come across. Once this is done, will reply to this thread with link(s).

Scott35
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#130577 - 07/30/06 04:15 AM Re: Double tapped secondary.
Scott35 Offline

Broom Pusher and
Member
Registered: 10/19/00
Posts: 2707
Loc: Anaheim, CA. USA
***BUMP***

Scott35
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#130578 - 08/03/06 05:16 PM Re: Double tapped secondary.
VAElec Offline
Member
Registered: 07/26/05
Posts: 49
Loc: Sterling, Virginia, US
This is a 3 phase primary, 3 phase (times two with 30 degree shift) secondary. It is delta/wye-wye. I think that it must look very much like the first image posted, but can't say for sure as the nameplate has info. The main thing I can think of is that both sets of secondary taps are 3P/4W wye.

I know almost enough about this type of transformer to give me problems.
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