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How do you know if pf (power factor) is leading or lagging

  1. May 17, 2013 #1
    1. The problem statement, all variables and given/known data

    power factor leading or lagging

    v(t)=3.5cos(600t-120)
    i(t)=2.3sin(600t+45)

    2. Relevant equations

    pf=cos(Vθ-Iθ)


    3. The attempt at a solution

    pf=cos(-75)
    =.25881905

    I get confused, How do we figure out whether it leads or lags.
     
  2. jcsd
  3. May 17, 2013 #2

    verty

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    Homework Helper

  4. May 20, 2013 #3

    NascentOxygen

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    Staff: Mentor

    You draw the phasor diagram. :smile:

    The phasors rotate counter-clockwise. Consider a pair rotating together, and differing by an angle ≤ 90°. Whichever passes over an axis first is the leading phasor of that pair.
     
  5. May 22, 2013 #4

    rude man

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    Gold Member

    First, change the cos voltage to a sin function. Use sin(x) = cos(x - 90 deg).
    Then, you get V = sin(wt + ψ1) and i = sin(wt + ψ2).

    V leads i if ψ1 > ψ2 or ψ1 - ψ2 > 0.
     
    Last edited: May 22, 2013
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