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XFMR test question - wye-delta TTR

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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?
    Your Answer: 15:1

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

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    Quote Originally Posted by dbryce89 View Post
    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?
    Your Answer: 15:1

    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 Im doing the math in my head and on my cell phone.

    Hope this helps

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    Quote Originally Posted by dbryce89 View Post
    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?
    Your Answer: 15:1

    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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    Quote Originally Posted by JtotheJ View Post
    I did the same thing. Is the first reply right? Anyone?
    First reply is correct. 4160/480=8.66667

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    Quote Originally Posted by ElectricalTestTech View Post
    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 Im 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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    Quote Originally Posted by dbryce89 View Post
    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?
    Your Answer: 15:1

    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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    Quote Originally Posted by dbryce89 View Post
    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?
    Your Answer: 15:1

    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
    so your ratio is 25.99:1

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    Quote Originally Posted by dbryce89 View Post
    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?
    Your Answer: 15:1

    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 =

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    Kalbi_Rob is offline Member Pro Subscriber
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    Quote Originally Posted by dbryce89 View Post
    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?
    Your Answer: 15:1

    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).

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    Wanderer20001us is offline Junior Member Pro Subscriber
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    Quote Originally Posted by Kalbi_Rob View Post
    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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