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Thread: Phase shift in Delta-Wye transformer

  1. #1
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    Phase shift in Delta-Wye transformer

    I know there is a phase shift between the primary and secondary of a Delta-wye transformer of 30degrees with the voltages of the primary delta leading the voltages of the secondary by 30degrees. But I'm looking to clarify how exactly these voltages are represented with respect to this difference.

    Since the primary is always delta connected do we always take these voltages to be L-L voltages such as Vab@0deg, Vbc@-120deg, and Vca@-240deg? Or do we refer to these primarys as their L-N voltages.

    Sticking with the L-L convention above and referencing the secondary voltages the L-N voltages are all shifted by 30deg with Van@-30, Vbn@-150, and Vca@-270. But what about the L-L voltages of the secondary wye connection. Does Vab on the secondary have the same angle as VAB on the primary. I'm confused weather or not this 30deg shift is in referencing between the L-L primary and L-N secondary voltages, or both the L-L primary and secondary voltages?

    If we took one of the primary phases to neutral would this be in phases or would it be shifted from the seconary to neutral of the same phase?

  2. #2
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    The 30 deg phase shift is from L-L voltage to L-L voltage.

    For instance, on your delta primary with Vab@0deg, Vbc@-120deg, and Vca@-240deg, the wye secondary would see Van@0deg, Vbn*-120deg, and Vcn@-240deg. Solving for Vab on the secondary, Vab= Van-Vbn= Vab@30deg.

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    Quote Originally Posted by david luchini View Post
    The 30 deg phase shift is from L-L voltage to L-L voltage.

    For instance, on your delta primary with Vab@0deg, Vbc@-120deg, and Vca@-240deg, the wye secondary would see Van@0deg, Vbn*-120deg, and Vcn@-240deg. Solving for Vab on the secondary, Vab= Van-Vbn= Vab@30deg.
    Thanks! Great explanation.

    What about for a wye-delta transformer.

    Taking primary to be Van@0deg, Vbn@-120deg, and Vcn@-240deg would the L-L voltages on the seconary be Vab@0deg, Vbc@-120deg and Vca@-240deg with the L-N voltages on secondary being Van@-30deg, Vbn@-150deg and Vcn@-270deg ?

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    Quote Originally Posted by mull982 View Post
    What about for a wye-delta transformer.

    Taking primary to be Van@0deg, Vbn@-120deg, and Vcn@-240deg would the L-L voltages on the seconary be Vab@0deg, Vbc@-120deg and Vca@-240deg
    Yes, that is correct.

    Quote Originally Posted by mull982 View Post
    with the L-N voltages on secondary being Van@-30deg, Vbn@-150deg and Vcn@-270deg ?
    I don't think you'll have any L-N voltages on a DELTA secondary.

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    [QUOTE=mull982;1252559]I know there is a phase shift between the primary and secondary of a Delta-wye transformer of 30degrees with the voltages of the primary delta leading the voltages of the secondary by 30degrees. But I'm looking to clarify how exactly these voltages are represented with respect to this difference.

    There is also a 30 degree shift in the opposite direction with the voltages on the primary lagging the voltages on the secondary. The key is how the delta is configured. A to B, or A to C.

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    Quote Originally Posted by mull982 View Post
    I know there is a phase shift between the primary and secondary of a Delta-wye transformer of 30degrees with the voltages of the primary delta leading the voltages of the secondary by 30degrees.
    Isn't it more correct to say:

    There is always a 30 degree phase shift from primary to secondary in a D-Y or Y-D transformer configuration. ANSI standards specify the high side of the transformer leads the low side, regardless of which side is Y or delta?

    If you had a wye high voltage primary, it would lead the low voltage delta secondary?
    Dennis L. Karst, P.E.

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    What I was saying that if you change the primary delta configuration from A to B to A to C. This happens in from the 138kV/13.8kV distribution substation to the 4.16kV Unit substation. The phase angle shifts from a 30 degree lag at the 138kV/13.8 delta/wye transformer to a 30 degree lead in the 13.8kV/4.16kV delta/wye Unit substation.

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    Quote Originally Posted by richxtlc View Post
    There is also a 30 degree shift in the opposite direction with the voltages on the primary lagging the voltages on the secondary. The key is how the delta is configured. A to B, or A to C.
    Yes so on the Delta primary the L-L AB or AC voltage will lead or lag the A-N voltage with AB leading by 30deg and AC lagging by 30deg.

    Is this what you meant?

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    Yes it is. there are also transformers that can shift the phase angle to lead or lag as needed to move mw in different directions.

  10. #10
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    A phasor diagram is helpful in understanding these phase relationships.
    Don't mess with B+!
    (Signal Corps. Motto)

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