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Old 06-12-2016, 09:28 AM   #21
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Originally Posted by Ultrafault View Post
My boss asked me a question, and I could not satisfactorily explain what would happen if you hooked a three phase transformer to a single phase supply. For the sake of this conversation we assumed the transformer would be delta 240 to wye 480 as the suggestion was for step up. I told him it would be horribly inefficent but to be honest I was only using supposition.
Could some of you guys enlighten me about the physics of this situation?
Could you use this setup as a single phase transformer?
What output could you expect at the secondary conductors?
Would a delta delta transformer provide you with different results?
If you connected 240V to H1 H3 , you would need to ground H2
The result on Wye or Delta would be the same, because the vectors are 180˚ apart. You would have 480V on X2 to X0 , and 240 on both X1 and X3 to X0
Although in Delta secondary you would have 480V on X1 to X3 and 240V on X2 to X1 and X3

Made a quick drawing to show it better.

The thing to remember is that the "wye" output is NOT a Y ... ie they are not 120˚ vectors, so they simply add up.

**edit** added dwg ... note, two H1's on primary ... one should be H3
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3 phase transformer single phase supply-240-480-d-y.jpg  

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Last edited by emtnut; 06-12-2016 at 09:34 AM.
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Old 06-12-2016, 11:10 AM   #22
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Originally Posted by emtnut View Post
If you connected 240V to H1 H3 , you would need to ground H2
The result on Wye or Delta would be the same, because the vectors are 180˚ apart. You would have 480V on X2 to X0 , and 240 on both X1 and X3 to X0
Although in Delta secondary you would have 480V on X1 to X3 and 240V on X2 to X1 and X3

Made a quick drawing to show it better.

The thing to remember is that the "wye" output is NOT a Y ... ie they are not 120˚ vectors, so they simply add up.

**edit** added dwg ... note, two H1's on primary ... one should be H3
Since it is a step up transformer, wouldn't the 240 vac go onto X1 and X3, and the 480 would be on the high side?
This might do in a bind, but I'm thinking the correct transformer should be installed as soon as possible....
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Old 06-12-2016, 11:18 AM   #23
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Since it is a step up transformer, wouldn't the 240 vac go onto X1 and X3, and the 480 would be on the high side?
This might do in a bind, but I'm thinking the correct transformer should be installed as soon as possible....

Yes, it should ! I was still on my first coffee
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Old 06-12-2016, 11:35 AM   #24
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Quote:
Originally Posted by emtnut View Post
If you connected 240V to H1 H3 , you would need to ground H2
The result on Wye or Delta would be the same, because the vectors are 180˚ apart. You would have 480V on X2 to X0 , and 240 on both X1 and X3 to X0
Although in Delta secondary you would have 480V on X1 to X3 and 240V on X2 to X1 and X3

Made a quick drawing to show it better.

The thing to remember is that the "wye" output is NOT a Y ... ie they are not 120˚ vectors, so they simply add up.

**edit** added dwg ... note, two H1's on primary ... one should be H3
The X windings on a 240∆ - 277/480Y transformer are 277 volts, not 480. 480 is derived from the Y connected 277 volt windings having 120 of phase shift.
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Old 06-12-2016, 11:47 AM   #25
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The X windings on a 240∆ - 277/480Y transformer are 277 volts, not 480. 480 is derived from the Y connected 277 volt windings having 120 of phase shift.
Yep !

So you would have 277V , and 138.5V for that tx .... think that's what you said in your earlier post
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