ELECTROMAGNETISM – PART – 04 – B-H CURVE, MAGNETIC LEAKAGE AND FRINGING

The ampere is defined as the current, which when flowing in each of the two infinitely long parallel conductors of negligible, cross-section and placed one meter apart in a vacuum produces on each conductor a force of 2 x 10 ^-7 newton per metre length.

INTENSITY OF MAGNETISATION

The Intensity of magnetization is the measure of the extent to which the force, the material is magnetized. It is denoted as ‘I’ and It is defined as the magnetic moment developed per unit volume of the material.

Intensity of magnetization (I) = M/V

Where M is the magnetic moment developed in the material and V is the volume of the material.

If m is the pole strength developed, a is the cross   area of the material and 2l is the length then

Intensity of magnetization = (m * 2l) /(a * 2l) = m/a

Intensity of magnetization = Ampere x metre^2) / (metre^2)

The unit of I is A/m

MAGNETIC SUSCEPTIBILITY

It indicates the how easily the material can be magnetized.

Magnetic susceptibility is denoted as Χ_m

Χ_m = Intensity of magnetization/ magnetic field intensity

Χ_m is a number. Χ_m is also called volume susceptibility of the material.

B-H CURVE

B-H curve shows that the permeability μ_r of magnetic material changes with the flux density B.

MAGNETIC LEAKAGE AND FRINGING

The part of the total magnetic flux which has its path wholly within the magnetic circuit is called useful flux.

The magnetic flux having its path partly in the magnetic circuit and partly in an air is called leakage magnetic flux.

Leakage factor = Total flux produced / useful flux

The leakage factor is assumed to be 1.15 to 1.25

FRINGING

When the flux lines cross the air gap, they tend to bulge out across the edges of the air gap. This effect is called fringing.

This increase depends on the length of the air gap.

Longer the air gap, greater is the fringing.

Generally, the increase in cross-sectional area of an air gap due to fringing is assumed to be about 10%.