Is the apparent power calculation in this text...

Discussion in 'General Electronics Chat' started by powersys, Jan 10, 2006.

  1. powersys

    Thread Starter New Member

    Jan 10, 2006
    5
    0
    The attached example was scanned from a textbook. I tried to calculate S1 but the answer I got was different from the one shown in text. Could someone please help me to verify whether the solution provided in the text is CORRECT or WRONG?

    My calculation:

    I
    = (V1 - V2) / Z
    = (240 - 208 - j120) / j10
    = -12-j3.2

    S1
    = V1 x (-I*)
    = 240 x (12-j3.2)
    = 2880-j768

    Question: Why a negative '-' sign in front of I* is required for the calculation of S1? Pls advise.


    S2
    = V2 x (I*)
    = (208+j120) X (-12+j3.2)
    = -2880-j774.4


    [​IMG]
     
  2. chesart1

    Senior Member

    Jan 23, 2006
    269
    1
    Hi

    The asterick indicates a footnote for the -I. What does the footnote say? The negative sign usually indicates that I is flowing in the opposite direction of that assumed in the diagram.

    John
     
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