Transformer Open Circuit Frequency and Losses

Discussion in 'Homework Help' started by BlackSuede, Nov 13, 2013.

  1. BlackSuede

    Thread Starter New Member

    May 8, 2013

    I have an exam prep question which I cannot figure out. I tried creating a thread but the website will not allow me for some reason - so I have hijacked this thread;

    The open circuit tests on a single-phase 10 kVA, 3300V / 240V, 50 Hz transformer at different voltage and frequencies give the following:

    Test 1, 135V, 30Hz, 105W of losses
    Test 2, 270V, 60Hz, 300W of losses

    Determine for rated voltage and frequency of 240V and 50Hz;
    a) Hysteresis Losses
    b) Eddy Current Losses
    c) Total Losses
    d) If maximum efficiency occurs at full load with lagging PF of 0.8 find this efficiency

    I am quite lost on how to solve this. I have attached the equivalent circuit for the OC test and I have deduced that the change in frequency will linearly change the core inductance which will in turn change the current in the core. The resistance will remain constant.

    Any help in methods to tackle this problem would be appreciated!
  2. jegues

    Well-Known Member

    Sep 13, 2010
    You need to solve Rc and Lm.

    Solve for them using the two equations you get from the two open circuit tests.
  3. BlackSuede

    Thread Starter New Member

    May 8, 2013