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Homework Help: 3 Phase unbalanced load AC electronics question.

  1. Nov 16, 2009 #1
    1. The problem statement, all variables and given/known data
    http://img196.imageshack.us/img196/1295/40343374.png [Broken]
    This is a past exam questions which I am doing as revision, now I am confused about how to calculate the answers.

    3. The attempt at a solution
    I have tried using millmans theorem which is
    Vsn = (Van/Za + Vbn/Zb + Vcn/Zc) / (1/Za + 1/Zb + 1/Zc)

    Assuming the following:
    Van = 240v @ 0 degrees
    Vbn = 240v @ 120 degrees
    Vcn = 240v @ -120 degrees

    As complex impedances:
    Van = 240
    Vbn = 195 + 139i
    Vcn = 195 - 139i
    Za = 10
    Zb = 15
    Zc = -20i

    Vsn = 273 +32i
    Vsn = 275v @ 6.6degrees

    Now I feel like I am really guessing here and have no idea if what I have done is correct (I don't think it is) so any help would be greatly appreciated

    For the currents it is just Ia = Van/Za = 240/10 etc which is easy and then you can easily construct the phasor diagram as well from these. Either way I don't think my values for Van, Vbn, Vcn or my method for calculating Vsn is correct.
    Last edited by a moderator: May 4, 2017
  2. jcsd
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