MM0704, Lesson 4
Figure 4-14. Section of Solid Iron Core.
This eddy-loss problem is overcome by using thin sheets of core material called laminations (figure 4-15). These are
either varnished or have their surfaces treated to provide insulation. When several of these thin sheet are placed
together, there is no electrical contact between them. A complete transformer core is many of these thin laminations
stacked together providing a large core area and increased electrical resistance to the eddy-currents. There is now a
satisfactory core area with a minimum amount of eddy-current losses.
The second type of iron loss is hysteresis. Hysteresis in an iron core means that the magnetic flux or lines of force lag
behind the magnetizing force that causes them. Recall the phenomena from the study of magnetism. The friction
caused by the little molecular magnets heat up as they try to align themselves with the constantly changing direction of
the current flow in the primary. This heat is wasted energy. Let us briefly review our study of magnetism in order to
get a clearer picture of hysteresis.
Figure 4-15. Laminated Iron Core.
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