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Transformer question

  1. Oct 6, 2009 #1
    1. The problem statement, all variables and given/known data
    A single phase 500V/250V transformer that supplies a rated load current of 10 A with a power factor of 0.8 lagging. At no load, the supplied current is 0.25 A with a power factor of 0.10 lagging. I am supposed to find the full-load primary current and express it in polar form. Winding impedance voltage drop can be neglected.


    2. Relevant equations
    I=Io + I2'
    I2'=(N2/N1)*I2
    V2/V1=N2/N1


    3. The attempt at a solution

    Full Load

    500V/250V=N1/N2
    I think that rated load current is = to I2
    therefore, I2'=(250/500)*10 A
    I2'=5 A

    No Load

    Io=0.25 A

    using the equation I=Io + I2'
    I= 5 A + 0.25 A
    I=5.25 A

    The correct answer is supposed to be 5.17 A at an angle of -38.9o
     
  2. jcsd
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