# Separation Of Core (Or Iron) Losses In A Transformer

Hysteresis loss and eddy current loss are the components of the iron losses. For the applied fl ux density *B _{max}* to the core, we have

Hysteresis loss = *Af*

and Eddy current loss = *Bf*^{2}

The no load loss can be expressed as

*W _{c}*=

*A*+

_{f}*B*

_{f}^{2}(1.36)

where

*A*and

*B*are constants.

Therefore,

Figure 1.38 shows the graph, which is a straight line when and

*f*are plotted along the

*y*-axis and

*x*-axis, respectively. The intercept on the

*y*-axis gives the value of A, whereas the slope of the line gives the value of

*B*. Now the hysteresis and eddy current loss can be determined at any desired frequency.

The experimental circuit arrangement for determining and

*f*is shown in Figure 1.39.

In Figure 1.39, a variable frequency alternator supplies to the transformer under the test, which is driven by DC shunt motor whose speed can be varied over a wide range. The switches

*S*

_{1}and

*S*

_{2}are opened and the alternator is started with the help of the DC shunt motor. The speed is adjusted to the

**Figure 1.38** Plot of and f

**Figure 1.39** Experimental Circuit for Determining and *f *value of the required frequency. The excitation of the field coil (X-XX) is varied until the voltmeter on the secondary side of the transformer achieves the rated value. If *E*_{2} is the transformer emf on the secondary, we have

*E*_{2}=4.44*Φ _{m}*

*fN*

i.e.

For constant , the flux density in the transformer remains constant. To achieve this, the frequency of the alternator emf is varied so that remains constant. The necessary

*f*can be adjusted to vary

*E*

_{2}so that is kept constant. For different values of frequencies above and below the rated value, the reading of wattmeter (W) is noted. The graph 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.