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Transformer Efficiency Problems

  1. Apr 12, 2016 #1

    My friend designs a special transformer, believing that its efficiency will rise and voltage regulation will fall compared to an ordinary one . He did a test with the same resistive load and got results below:

    T1(ordinary) Vp=220V 50Hz AC Vs(nl) = 99.8V Vs(fl) = 92.8V Pin = 129W Pout =92.8W
    T2(special) Vp=220V 50Hz AC Vs(nl) = 99.8V Vs(fl) = 96.7V Pin = 130W Pout = 96.7W

    Vp: Primary voltage
    Vs: Secondary voltage
    Pin: Input power from a 220V source. (household outlet)
    Pout: Output power at a load
    All voltages are in RMS

    He expected that the input complex power(Sin) of the special transformer should be 100VA with an efficiency of 90%.
    However, the Sin is actually 130VA and the efficiency is about 74.38%. What is the cause of this event?

    Thank you
  2. jcsd
  3. Apr 12, 2016 #2

    jim hardy

    User Avatar
    Science Advisor
    Gold Member

    A question well stated is half answered.
    You're asking us to guess .
    Okay -
    Excerpting from your post -
    Sin and Pin should differ by magnetizing VA. So,
    My guess is somebody doesn't know the difference between a volt-amp and a watt.

    I cannot can figure out your riddle from what you've given us.
  4. Apr 12, 2016 #3


    Staff: Mentor

  5. Apr 13, 2016 #4
    Hardy, I agree with you. The current source should supply core loss resistance with a real power, magnetizing inductance with a reactive power, and a leakage inductance with a reactive power also. I mean even without a resistive load, there should be both real and reactive.

    The experiment of my friend is strange. The 130VA of a voltage source is purely from a wattage. I ask him twice before posting this.

    Also,Neumaier, thank you for the information. I will tell my friend to read this carefully.
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