Electrical Engineering ⇒ Topic : B-H Curve
The B-H curve (or magnetisation curve) indicates the manner in which the flux density (B) varies with the magnetising force (H).
(1) For non-magnetic materials. For non-magnetic materials (e.g. air, copper, rubber, wood etc.), the relation between B and H is given by
Hence, the B-H curve of a non-magnetic material is a straight line passing through the origin as shown in Fig. (a). Two things are worth noting.
First, the curve never saturates no matter how great the flux density may be. Secondly, a large m.m.f. is required to produce a given flux in the nonmagnetic material e.g. air.
(2) For magnetic materials. For magnetic materials (e.g. iron, steel etc.), the relation between B and H is given by ;
B = μ0μrH
Unfortunately, μris not constant but varies with the flux density. Consequently, the B-H curve of a magnetic material is not linear. Fig. a (i) shows the general *shape of B-H curve of a magnetic material. The non-linearity of the curve indicates that relative permeability μr,(B/μ0H) of a material is not constant but depends upon the flux density. Fi (ii) shows how relative permeability of a magnetic material (cast steel) ,varies with flux density.
While carrying out magnetic calculations, it should be ensured that the values of μr, and H are taken at the working flux density. For this purpose, the B-H curve of the material in question may be very helpful. In fact, the use of B-H curves permits the calculations of magnetic circuits with a fair degree of ease
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