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Unbalanced three-phase w. neutral. Finding currents

  1. Aug 21, 2012 #1
    1. The problem statement, all variables and given/known data

    I have to find the currents in the three phases and the neutral.

    I understand that it has got something to do with Kirchoffs law, but how on earth?

    I can simulate it in multisim, and i get the right results for I_rms but i cannot figure out how to calculate.

    N->L = 220V
    L->L = 380V

    2. Relevant equations

    Here is the layout.

    sRcXI.jpg

    I found the I_L3 just by using I=U/R. I found it to be 2.5A
     
  2. jcsd
  3. Aug 23, 2012 #2

    rude man

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    Homework Helper
    Gold Member

    What are V1-1, V1-2 and V1-3 in complex notation? The rest is just cranking thru the KVL or KCL equations, whatever lights your bulb ... :-)
     
  4. Aug 24, 2012 #3
    I found out how to do it with vectors.

    But i also want to learn how to do it with masks.
    I have drawn a new one here:

    http://www.studieportalen.dk/Forums/ShowFile.aspx?id=1225631

    Is that better?

    What do you mean by using KCL and KVL? I know it is Kichhoff current and voltage laws, but do I just have to do all the masks with respect to N?
     
  5. Aug 24, 2012 #4

    gneill

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    Staff: Mentor

    A slightly rearranged schematic may make things more obvious:

    attachment.php?attachmentid=50152&stc=1&d=1345819744.gif

    You should be able to apply either mesh or node equations. Note that it might be worthwhile to recognize that you have the potentials at each end of the load resistors by inspection...

    Va, Vb, Vc are the three-phase line voltages. Write them in complex form and then it's just plug 'n chug.
     

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