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Thevenin voltage and impedance

  1. Jan 28, 2016 #1
    1. The problem statement, all variables and given/known data
    Find the maximum power on a impedance Z.

    2. Relevant equations


    3. The attempt at a solution
    I got as Thevenin impedance Zt=4+j4 and Ut= 32 V, but since my solution for power is wrong, something is wrong with either impedance or voltage (or both).
    If point A is above Z, and point B is under Z, looking from A to B I get for impedance:
    First j4 , then since I have current source in of the branches, I ignore impedances in that branch and get j4+(j4-j4+4) and since there is voltage source I ignore 2-j12.
    For Thevenin voltage, I tried with superposition, and if potential of B=0, I get that for A:
    $$ \varphi_A= 16 \angle 0 + 4 \angle 0 \cdot 4 + 4 \angle 0 \cdot j4 + 4 \angle 0 \cdot (-j4)=32 $$
     

    Attached Files:

  2. jcsd
  3. Jan 28, 2016 #2

    gneill

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    Staff: Mentor

    Your Thevenin values look okay. How did you calculate the maximum power?
     
  4. Jan 29, 2016 #3
    I=Ut/(Z+Zt)=2-j2 , P=I^2 Z = 32-32i = 32 sqrt(2) , And the solution says 64.
     
  5. Jan 29, 2016 #4

    gneill

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    Staff: Mentor

    What value did you give to the load impedance Z?
     
  6. Jan 29, 2016 #5
    Z=Zt=4+j4
     
  7. Jan 29, 2016 #6

    gneill

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    Staff: Mentor

    Check the maximum power theorem for complex impedance. I think you'll find that the imaginary part of the load should nullify the source impedance's imaginary component.
     
  8. Jan 29, 2016 #7
    You're right. I now get P=64-j64, do I now just take real part to get P=64?
     
  9. Jan 29, 2016 #8

    gneill

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    Staff: Mentor

    Yup.
     
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