Transformer Question

Discussion in 'Homework Help' started by quixote, Nov 22, 2012.

  1. quixote

    Thread Starter Member

    Jan 15, 2007
    12
    0
    A transformer used in an electronic power supply has a nominal rating of 120/12 volts and is connected to a 120-Vac source. Its equivalent impedance as seen from the primary is 10 + j10 Ohm.

    Q1. What is the magnitude of the load voltage if the load is 5 ohms resistive?
    Q2. Determine the regulation.

    Q1. My steps:
    1. ZL = 5 Ohm
    2. Turns Ratio, n = 120/12 = 10
    3. Reflected Load Impedance Zeq = n^2 * ZL = 500
    4. Total impedance, Ztot = 10 + j10 + 500 = 510 + j10 = 510.1, phase 1.123º
    5. Reflected Load Voltage, VeqL = (500/Ztot)*120 = 117.624V, phase -1.123º
    6. Load Voltage = VeqL/n = 11.76V, phase -1.123º

    Q2.
    Vnl is Secondary Voltage at No Load = 120V/n = 12V
    Vfl is Secondary Voltage at Full Load = 11.76V
    Regulation = (Vnl-Vfl)/Vfl% = (12-11.76)/11.76% = 2%

    The book says the right answer is 1.8V with 2% regulation but this seems clearly wrong (or am I going mad?)

    Can anybody please confirm this?
     
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    4,979
    744
    this should be in the homework section...
     
  3. RamaD

    Active Member

    Dec 4, 2009
    254
    33
    Sounds ok to me, 1.8V in the book could be just a typo for 11.8V which is approx. equal to your 11.76V !
     
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