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Single phase transformer question

  1. Apr 26, 2016 #1
    1. The problem statement, all variables and given/known data
    A 100 kVA, 2300/230V, single phase transformer has the following parameters: Rp = 0.30Ω, Rs = 0.0030Ω, Rc = 4.5 kΩ, Xp = 0.65Ω, Xs = 0.0065Ω, Xm = 1.0 kΩ The transformer delivers 75 kW at 230 V at 0.85 power factor lagging, find:
    a) The input current.
    b) The input voltage.

    2. Relevant equations


    3. The attempt at a solution

    Referred to primary
    IMG_20160427_002407.jpg

    I'm confused with the part where the transformer delivers 75kW. Then will the secondary current be 0.75*Israted ?
     
  2. jcsd
  3. Apr 26, 2016 #2

    NascentOxygen

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    Staff: Mentor

    You know the power and the PF so you can determine the secondary's VA output.
     
  4. Apr 27, 2016 #3
    So,
    cos(∅) = P/S
    S = P/cos(∅)
    = 75/0.85
    = 88.24 kVA

    So would the secondary current be
    Is = 88.24/230 = 383.65A ?
     
  5. Apr 27, 2016 #4

    NascentOxygen

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    Staff: Mentor

    That should be right.
     
  6. Apr 27, 2016 #5
    Ok, so to find the input current, Ip, would this be right ?

    From my schematic:

    Ip = Io + Is/a..................1

    Io = 2300(1/4.5k + 1/1k)

    Is/a = 383.65∠-31.79 / 10
    = 38.365∠-31.79

    Therefore,

    Ip = 2300(1/4.5k + 1/1kj) + 38.365∠-31.79
    = 40.05∠-34.2
     
  7. Apr 27, 2016 #6

    NascentOxygen

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    Staff: Mentor

    That looks right.
     
  8. Apr 30, 2016 #7
    Thanks
     
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