AC power calculations:

Discussion in 'Homework Help' started by whynotsneeze?, Nov 9, 2009.

  1. whynotsneeze?

    Thread Starter New Member

    Nov 6, 2009
    2
    0
    Hi, im a bit lost with AC circuits on the whole and could use some dumbed down explanation on the matter.

    Taking an example from course material:

    (Components connected in parallel. "Ladder connection")

    ------
    l l l l l
    J C L R
    l l l l l
    ------

    Where
    J = 1 (30 degrees) currentsource driving current in the clockwise direction
    C = 0.05 F capacitor
    L = 0,2 H inductor
    w = 10 rad/s

    If im asked to find the real and reactive powers for each component how would i go about solving these?
    I could also use a clarification on the difference between real and reactive powers.

    Thanks.

    ps: sory for the dingy "diagram"
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Find the current through each component according to their impedance which for C and L depends on the current source frequency. C and L have only reactive power, use their impedance value and calculate it like the power in a resistor. The only real power is dissipated in the resistor. This is if the L, C, R and J are ideal.
     
  3. Thav

    Member

    Oct 13, 2009
    82
    0
    I started to explain this but it is very difficult to explain concisely. To solve your problem you will have to know about complex impedances and AC analysis. (hint here: the complex impedance of the L and C are functions of j (the imaginary number), w and L and C respectively). You will also find phasor notation of complex numbers helpful.

    Some reading:
    http://www.allaboutcircuits.com/vol_2/index.html
    Chapters 2-5 should be most of what you need to know.
     
  4. Thav

    Member

    Oct 13, 2009
    82
    0
    Also in response to mik3, it's not a given that the current source J will not deliver any reactive power, it just happens to be so in this case.
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Complex impedance maybe be the easiest way to solve it but if he feels better with differential equations, that is fine. :cool:
     
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