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# XFMR test question - wye-delta TTR

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1. Junior Member
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## XFMR test question - wye-delta TTR

A wye-delta transformer has a primary line voltage of 7200 V and a secondary line voltage of 480 V. What is the turns ratio?

Not sure what I did wrong on this question. They are both line voltages so I thought it was a simple division question.

2. Originally Posted by dbryce89
A wye-delta transformer has a primary line voltage of 7200 V and a secondary line voltage of 480 V. What is the turns ratio?

Not sure what I did wrong on this question. They are both line voltages so I thought it was a simple division question.

It is not a simple division. You have to pay attention to the Wye and Delta. Any winding that is Wye, you have to use phase to ground voltage. 7200/1.732. Delta windings use phase to phase.

7200/1.732= 4160ish / 480 = ?

Sorry I’m doing the math in my head and on my cell phone.

Hope this helps

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Originally Posted by dbryce89
A wye-delta transformer has a primary line voltage of 7200 V and a secondary line voltage of 480 V. What is the turns ratio?

Not sure what I did wrong on this question. They are both line voltages so I thought it was a simple division question.
I did the same thing. Is the first reply right? Anyone?

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Originally Posted by JtotheJ
I did the same thing. Is the first reply right? Anyone?

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Originally Posted by ElectricalTestTech
It is not a simple division. You have to pay attention to the Wye and Delta. Any winding that is Wye, you have to use phase to ground voltage. 7200/1.732. Delta windings use phase to phase.

7200/1.732= 4160ish / 480 = ?

Sorry I’m doing the math in my head and on my cell phone.

Hope this helps
Thank you that cleared up this question for me.

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Originally Posted by dbryce89
A wye-delta transformer has a primary line voltage of 7200 V and a secondary line voltage of 480 V. What is the turns ratio?

Not sure what I did wrong on this question. They are both line voltages so I thought it was a simple division question.
divided 7200/480(square root 3)= 8.66
thats because its a 3 phase wye-delta, in a delta-wye I would do in 480(square root 3)/208 in a normal commercial transformer which in fact its 4 as most of us know. correct me if I'm wrong.

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Originally Posted by dbryce89
A wye-delta transformer has a primary line voltage of 7200 V and a secondary line voltage of 480 V. What is the turns ratio?

Not sure what I did wrong on this question. They are both line voltages so I thought it was a simple division question.
you need to find the phase voltage on the secondary which is 277 or 480/square root 3

then do the math ie 7200/277 answer =25.99

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Originally Posted by dbryce89
A wye-delta transformer has a primary line voltage of 7200 V and a secondary line voltage of 480 V. What is the turns ratio?

Not sure what I did wrong on this question. They are both line voltages so I thought it was a simple division question.
For a Wye / Delta the formula is Vh÷(Vx×√3)= with the numbers above it should be 8.660

For a Delta / Delta it's Vh ÷Vx =

9. Originally Posted by dbryce89
A wye-delta transformer has a primary line voltage of 7200 V and a secondary line voltage of 480 V. What is the turns ratio?

Not sure what I did wrong on this question. They are both line voltages so I thought it was a simple division question.
WI | DE

So, easy way to remember how to perform turns ratio is to start with the acronym WIDE where WI stands for Wye where current is equal between phase and line, and DE stands for Delta where E (electromotive force which also defines voltage) or voltage is equal between phase and line.
So, on the Wye side of the transformer you need to take the voltage (assume to be phase voltage if not otherwise noted) and divide by square root of 3 (or ~1.73). So the equation is
(7200V/(sqrt(3))/480V = 4156.9V/480V = 8.66 so the TTR = 8.66:1

Turns ratio is only taken on single phases of a transformer, so all values need to be reduced to individual line values to represent each single phase. This is also why you see a 12kV/480 delta/wye transformer with voltage values of 12kV - 480Y/277V.
If for whatever reason you needed to convert current values from phase to line on a Delta Xfmr, then you take phase current and divide by sqrt(3).

10. Originally Posted by Kalbi_Rob
WI | DE

So, easy way to remember how to perform turns ratio is to start with the acronym WIDE where WI stands for Wye where current is equal between phase and line, and DE stands for Delta where E (electromotive force which also defines voltage) or voltage is equal between phase and line.
So, on the Wye side of the transformer you need to take the voltage (assume to be phase voltage if not otherwise noted) and divide by square root of 3 (or ~1.73). So the equation is
(7200V/(sqrt(3))/480V = 4156.9V/480V = 8.66 so the TTR = 8.66:1

Turns ratio is only taken on single phases of a transformer, so all values need to be reduced to individual line values to represent each single phase. This is also why you see a 12kV/480 delta/wye transformer with voltage values of 12kV - 480Y/277V.
If for whatever reason you needed to convert current values from phase to line on a Delta Xfmr, then you take phase current and divide by sqrt(3).
Thanks for this memory tool.

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