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Phasor transformation

Discussion in 'Electronics Homework Help' started by Joe Bachi, Sep 21, 2013.

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  1. Joe Bachi

    Joe Bachi

    Feb 3, 2013
    Hey guys,
    I attempted to solve the following exercise but i'm pretty sure i messed up somewhere because my answers just don't seem to add up
    Can you please check my work?
    Hope the pictures are clear enough
    Photo Sep 21, 8 18 46 PM.jpg

    Photo Sep 21, 8 18 58 PM.jpg
    1) Express L, using R, C, and w so that R(equivalent) of AC is a pure resistor
    2) Knowing that E(0)=180V, Find the amplitude of the main current I(0)
    3) Find the amplitudes of U(AB) and U(BC)

    Thank you in advance for your help :)
  2. Harald Kapp

    Harald Kapp Moderator Moderator

    Nov 17, 2011
    Your error is in the first line of computing the parallel circuit of R and C.
    Two impedances in parallel are calculated as

    1/Ztotal = 1/Z1 + 1/Z2 where Z1, Z2 are the impedances of the resistor and the capacitor.

    The impedance of a capacitor is Zc = 1/jwC

    1/Ztotal = 1/R + jwC

    With that in mind, do your calculations again. If they still don't add up, show us the new results.
  3. Joe Bachi

    Joe Bachi

    Feb 3, 2013
    Zc=1/jwC which is the equivalent to Zc=-j/Cw (by multiplying by j)
  4. Laplace


    Apr 4, 2010
    I arrived at the same expression for L as you did so you seem to be on the right track.

    Attached Files:

  5. Joe Bachi

    Joe Bachi

    Feb 3, 2013
    I did the Fresnel representation of the circuit and my answers turned out to be the same, so i think it was right all along
    Thank you all for taking the time to help :)
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