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3-Phase Transformer Model

Discussion in 'System Modeling and Calculations' started by RJohnson, Jul 28, 2010.

  1. RJohnson New Member

    If I have a 300 kVA utility transformer bank made up of 3 single phase 100 kVA transformers each with an impedance of 1.9%, is the equivalent impedance of the 300 kVA transformer simply 3 x 1.9, or is it the square root of 3 times 1.9?
    RJohnson, Jul 28, 2010
    #1

  2. jghrist Well-Known Member

    1.9%. The impedance is a per phase value.
    jghrist, Jul 29, 2010
    #2

  3. stevenal Well-Known Member

    How are the transformers connected? Wye or delta?
    stevenal, Jul 30, 2010
    #3

  4. RJohnson New Member

    Connected delta-wye.
    RJohnson, Jul 31, 2010
    #4

  5. stevenal Well-Known Member

    Edited: Sorry I misremembered. Connections make no difference. 1.9% using 100 kVA and line to neutral voltage to get ohms secondary equates to 1.9% using 300 kVA and line to line voltage.
    stevenal, Aug 2, 2010
    #5

  6. J.T New Member

    No matter how the 3 single phase transformer connected, the impedance should be the same as the single phase tested value
    J.T, Aug 3, 2010
    #6

  7. LarryJo New Member

    What is one of the transformers has a different nameplate impedance?
    LarryJo, Jun 7, 2011
    #7

  8. stevenal Well-Known Member

    Then there is no equivalent three phase impedance.
    stevenal, Jun 10, 2011
    #8

  9. J.T New Member

    Can 3 single phase transformers with different IZ% be connected to a transformer bank?
    J.T, Jun 12, 2011
    #9

  10. glen1971 Well-Known Member

    It is my understanding that they can be, but they still have to be within a very tight range..
    glen1971, Jun 12, 2011
    #10

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