Basic Electrical Theory
MAGNETIC CIRCUITS
Example:
A coil has an mmf of 600 At, and a reluctance of 3 x 106 At/Wb.
Find the total flux F.
Solution:
F
mmf
R
F
600At
3 x 106 At/Wb
200 x 106 Wb
200µWb
BH Magnetization Curve
The BH Magnetization Curve (Figure 27) shows how much flux density (B) results from
increasing the flux intensity (H). The curves in Figure 27 are for two types of soft iron cores
plotted for typical values. The curve for soft iron 1 shows that flux density B increases rapidly
with an increase in flux intensity H, before the core saturates, or develops a "knee." Thereafter,
an increase in flux intensity H has little or no effect on flux density B. Soft iron 2 needs a much
larger increase in flux intensity H before it reaches its saturation level at H = 5000 At/m, B =
0.3 T.
Air, which is nonmagnetic, has a very low BH profile, as shown in Figure 27.
Figure 27 Typical BH Curve for Two Types of Soft Iron
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