Question

Describe the method by which the separation of core losses of a transformer is achieved.

Answer 1

Hysteresis loss and eddy current loss are the components of the core losses. For the applied flux density B to the core, we have

Hysteresis loss = Af

and Eddy current loss = Bf²

The core loss can be expressed as

W=Af+Bf²  

Hence ,

W/f = A + Bf

Which is the equation of a straight line with slope B and intercept on y axis as A

Now during the test the transformer is supplied from a variable frequency alternator. A wattmeter is connected across the transformer. The secondary side of the transformer is opened so that copper loss is zero and the wattmeter reading indicates the total core loss.

For constant E/f, the flux density in the transformer remains constant. To achieve this, the frequency of the alternator emf is varied so that E/f remains constant. The necessary f can be adjusted to vary E so that E/f is kept constant. For different values of frequencies above and below the rated value, the reading of wattmeter (W) is noted. The graph W/f and f is drawn to get the constants A and B. After getting the value of A and B, the hysteresis loss and eddy current loss is obtained.