Hi,

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!

 

You need to solve Rc and Lm.

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

 

Okay, I have solved this now. I was thinking about it from a circuit analysis perspective too much! Formula used to separate the losses can be referenced here http://www.nptel.iitm.ac.in/courses...l Technology/pdf/L-22(TB)(ET) ((EE)NPTEL).pdf
See the attached for my written solution.