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Homework Help: Fundamentals ofElectric circuits

  1. Aug 18, 2009 #1
    1. The problem statement, all variables and given/known data

    The load in Fig. 11.44 draws 10 kVA at PF =0.8
    lagging. If |IL |=40 A rms, what must be the value of C
    to cause the source to operate at PF =0.9 lagging?

    2. Relevant equations

    P(apparent power VA)= |I| |V| cos@
    @ = @V - @I
    cos@= p.f
    X= Xrms*(2)^0.5
    S(complex power)= 0.5 * I * V (cos@ - j sin@)

    3. The attempt at a solution
    I just face a difficulty in knwoing the face of IL
    I will be thankful if you solved the wole problem.

    Attached Files:

  2. jcsd
  3. Aug 24, 2009 #2
    First, there is no capacitor. And, you have 10 kVA at 0.8 so 8 kW.

    You add a capacitor and you get 10 kVA at 0.9 and 8KW

    Find the reduction in the reactive power required to make the pf equal to 0.9. To find the capacitor value now you have its reactive power and you need voltage which is equal to the voltage across the source.

    You can find the voltage across the source using the initial condition when there is no capacitor.
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