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Homework Help: Power system analysis, per unit system help

  1. Feb 13, 2015 #1
    1. The problem statement, all variables and given/known data
    https://dl.dropboxusercontent.com/u/88040310/powerhw3.png [Broken]
    1. Draw the reactance diagram.
    2. Calculate the per unit impedances
    3. If bms #1 is operating at 30 kV, find the current
    Assume base of 100 MVA, 300 kV on the generator side.
    2. Relevant equations
    P = VI
    s = p +jq
    Apparent power = (reactive power^2 + real power^2)^(1/2)

    per phase equations, tap transformer equations
    3. The attempt at a solution
    Starting it slowly, is this how you draw the reactance diagram?
    https://dl.dropboxusercontent.com/u/88040310/hw3xdiagram1.png [Broken]
    Last edited by a moderator: May 7, 2017
  2. jcsd
  3. Feb 16, 2015 #2


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    Gold Member

    At the risk of being called a heretic, I suggest that the best thing you can do is abandon the "per unit" system. Work with actual quantities, so that your equations make sense and are dimensionally correct. Per unit is useful only in that for certain system classes, it enables estimates of parameters before the actual values are know. Thereafter, it is simply a confusion factor (and a large one at that!).
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