excitation branch in the equivalent circuit for transformers

Discussion in 'Homework Help' started by Erica, May 18, 2011.

  1. Erica

    Thread Starter New Member

    May 18, 2011
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    1
    I am reading a textbook about transformers. According to the book, the excitation branch in the equivalent circuit of a transformer are two elements (Rc and Xm) in parallel. It says the total excitation admittance is Y = 1/Rc - (1/Xm)j. Any idea why the indutance is minus instead of postive?

    Thanks in advance.
     
  2. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    Because this is talking about admittance (Y) - rather than impedance (Z).
     
  3. jegues

    Well-Known Member

    Sep 13, 2010
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    Ahhh! That makes much more sense!
    So, Z = R_{c} + jX_{m}

    Y = \frac{1}{Z} = \frac{1}{R_{c}} + \frac{1}{jX_{m}} = \frac{1}{R_{c}} - \frac{j}{X_{m}}
     
    Last edited: May 18, 2011
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  4. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    No quite right ....

    Zm=Rc||jXm

    Z_m=\frac{R_c*jX_m}{R_c+jX_m}

    and so on ...
     
  5. Erica

    Thread Starter New Member

    May 18, 2011
    15
    1
    You are right. I just prove that (1/Rc)-(1/Xm)j=1/Z. Thanks so much!
     
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