# T to T connected transformer



## nolabama (Oct 3, 2007)

Bump


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## stuiec (Sep 25, 2010)

this is for the 9t2f from here: http://static.schneider-electric.us...ral Purpose-Resin Encapsulated/7400CT9601.pdf


View attachment 21079


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## hardworkingstiff (Jan 22, 2007)

You should be getting 208V phase to phase and 120V any phase to X0 (neutral) and if the X0 is properly grounded, then to the ground also.

This is a small transformer, 100% balanced loaded the output is 25A.


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## brian john (Mar 11, 2007)

I have only worked on one T wound transformer, when properly connected the voltage was as noted above 120 A, B, C to Neutral/Ground and 208 phase to phase.

Took me a while to figure out the correct connections as the transformer was a 1950 vintage and all the phase tags/labels had fallen off.


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## hardworkingstiff (Jan 22, 2007)

brian john said:


> Took me a while to figure out the correct connections as the transformer was a 1950 vintage and all the phase tags/labels had fallen off.


Do you remember the methodology you used to figure it out? If so, if you have time, could you walk us through it?

Thanks,


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## brian john (Mar 11, 2007)

The contractor that relocated the transformer could not remember how it was hooked up (and paid for that mistake).

I used a 3 phase variac and back fed the 480 side I think 40 VAC, went to the secondary and measured voltages. THe only reason I used a variac was to get past blowing fuses with transformer inrush from utilizing a 120/208 vac 20 amp source.

I never did understand the advantages of a T connected transformer while it has two coils in lieu of three in a wye/delta, I swear for a 50 kva it weighed more than a 112.5 wey/delta.


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## mnelectrician (Dec 1, 2008)

brian john said:


> The contractor that relocated the transformer could not remember how it was hooked up (and paid for that mistake).
> 
> I used a 3 phase variac and back fed the 480 side I think 40 VAC, went to the secondary and measured voltages. THe only reason I used a variac was to get past blowing fuses with transformer inrush from utilizing a 120/208 vac 20 amp source.
> 
> I never did understand the advantages of a T connected transformer while it has two coils in lieu of three in a wye/delta, I swear for a 50 kva it weighed more than a 112.5 wey/delta.


Welcome back!


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## Lone Crapshooter (Nov 8, 2008)

If you do a Wiki search on Scott T connection there is a very basic explanation of the "T" transformer connection.
LC


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## hardworkingstiff (Jan 22, 2007)

*anyone know?*










Does anyone know why the secondary side of T2 has the X0 drawn in from the end of the coil instead of showing it at the end of the coil? It would seem that that little bit of coil of T2 becomes part of the windings of the 2 sides of T1. 

It just seems strange, and if someone knows why, I sure would like to know.


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## micromind (Aug 11, 2007)

hardworkingstiff said:


> Does anyone know why the secondary side of T2 has the X0 drawn in from the end of the coil instead of showing it at the end of the coil? It would seem that that little bit of coil of T2 becomes part of the windings of the 2 sides of T1.
> 
> It just seems strange, and if someone knows why, I sure would like to know.


A typical ∆ - Y transformer has a 30º phase shift between the primary and secondary. Most of the time, this is not an issue, but occasionally it is important. It looks to me as though the T connection would have no phase shift at all. 

Also, a closed ∆ will tend to balance voltage at the expense of current. This can be an issue when a small transformer is supplied by a large source that isn't balanced. The T connection looks like it doesn't care about voltage balance, it just passes the imbalance through. This is why it would be the connection of choice for small transformers. 

I'm mostly guessing here, none of this is proven fact, so take it with a grain or two of salt......


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## hardworkingstiff (Jan 22, 2007)

micromind said:


> A typical ∆ - Y transformer has a 30º phase shift between the primary and secondary. Most of the time, this is not an issue, but occasionally it is important. It looks to me as though the T connection would have no phase shift at all.
> 
> Also, a closed ∆ will tend to balance voltage at the expense of current. This can be an issue when a small transformer is supplied by a large source that isn't balanced. The T connection looks like it doesn't care about voltage balance, it just passes the imbalance through. This is why it would be the connection of choice for small transformers.
> 
> I'm mostly guessing here, none of this is proven fact, so take it with a grain or two of salt......


Thanks for your response, but I fail to understand how it addresses the question I posted, or, I missed it completely, lol.

Edit: Doing some searching on the internet, it seems it does have to do with phase shift (I think). I'm just going to admit that I'm over my head on these phase shifting formulas I found and move on.


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## CoopElec (May 16, 2011)

*2 Phase ?*

Maybe a relic of the 2 phase days? It would be a good way to use up
back inventory.


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