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Transformer Efficiency Calculations

  1. May 13, 2010 #1
    Hey. Im currently doing a bit of revision for an exam and I am struggling on the following question:

    I understand the whole voltage/current/power/impedance ratio stuff, but cant seem to find any information on calculating efficiencies using the resistances or the transformer core losses. Any Suggestions?
     
  2. jcsd
  3. May 13, 2010 #2
    Hey. Ive found a bit more information regarding copper losses in transformers. It states:

    I would think given the question that the asnwer would be:

    P = VI ∴ I = P/V

    For the primary:
    500/230 = 2.27 Amps

    For the secondary:
    500/24 = 20.83 Amps

    Copper loss for primary:
    2.272 x 0.05 = 0.258 W

    Copper loss for secondary:
    20.832 x 0.01 = 4.34 W

    Total Copper Loss:
    0.258 + 4.34 = 4.598 W

    Total loss including core loss:

    4.598 + 0.07 = 4.668 W

    Total efficiency =
    (500-4.668)/500 = 0.9907 = 99.07% efficient.

    The problem with this is if we were only getting an efficiency of 99.07% the secondary wouldnt be developing 20.83 Amps! Does anyone know how to actually solve this question?
     
  4. May 13, 2010 #3

    Averagesupernova

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    @ Maths:
    I skimmed through this pretty fast but I would say that you should not have 500 watts for both the primary and secondary. With any efficiency of less than 100% you will naturally get you a lower secondary current than 20.83.
     
  5. May 13, 2010 #4
    You are nearly there except for the last bit.

    The 500W refers to the output not the input for transformers so

    input power = output power + total losses = 500 + 4.668 = 504.668.

    efficiency = 1 - losses/input power = 1 - 4.668/504.668 = 99.07% expressed as a percentage.
     
  6. May 13, 2010 #5
    See this is where I am getting confused. If the input power is 504.668W instead of 500W wouldnt that make the current and thus the losses higher on the primary winding??
     
  7. May 13, 2010 #6

    Averagesupernova

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    More power is lost, but more is put in too. The percentage of loss should be the same.
     
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