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Homework Help: 3 Phase Y Connected Generator

  1. Nov 25, 2012 #1
    1. The problem statement, all variables and given/known data

    A Y connected, 400V (line), 100KVA rated, stand alone generator is operating at 80kW at rated current with a lagging power factor and rated terminal voltage. The synchronous reactance is 2Ω.

    Draw the per phase equivalent circuit and calculate:

    (i) The Phase Current (Iph)
    (ii) The Power Factor
    (iii) The Reactive Power
    (iv) The Voltage drop across the Synchronous Reactance (VXS)

    2. Relevant equations

    [itex]V_{ph} = V_{line}/√3[/itex]
    [itex]P = IV[/itex]
    [itex]P = IVcosθ[/itex]
    [itex]Q = Ssinθ[/itex]
    [itex]S_{ph} = S/√3[/itex]
    [itex]V_{xs} = I_{ph} * jXs[/itex]

    3. The attempt at a solution
    [itex]V_{ph} = 400/√3 = 230.9V[/itex]
    [itex]S_{ph} = 57735W[/itex]
    [itex]S = IV[/itex]
    [itex]I = S/V = 57735/230.9 = 250A[/itex]

    [itex]P = IVcosθ[/itex]
    [itex]cosθ = 0.8[/itex]

    [itex]Q = Ssinθ = 60VAr[/itex]

    [itex]V_{xs} = jXs * I_{ph} = 500V[/itex]

    Not sure where I go wrong but I'm assuming I can't have a voltage drop of 500V over a component when I only have 230.9V of phase voltage!
  2. jcsd
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