MAGNETIC CIRCUIT
Md. Manjurul Gani, Lecturer, EEE, CUET
MAGNETIC
FIELD
Surrounding a magnet there exists a magnetic
field, represented by flux line.
Radiate from the north pole to the south pole,
returning to the north pole through the metallic
bar.
No origins or terminating points
Flux Distribution
Flux distribution
for unlike poles
Flux distribution
for like poles
RIGHT HAND RULE
If the fingers of the right hand are placed
in the direction of current flow around the
core, then the thumb will then point in the
direction of the north pole of the induced
magnetic flux.
FLUX DENSITY
The number of
flux lines per unit
area is called the
flux density
Permeability
?
It is measure of how easily magnetic flux
lines can be established in the material.
Materials in which flux lines can readily be set up are
said to be magnetic and to have high permeability.
It is similar to conductivity in electric circuits.
Paramagnetic
Permeability slightly
greater than that of
free space
Diamagnetic
Ferromagnetic
Have very high
permeability
Material
Permeability slightly
less than that of
free space
Relative permeability:
It is the ratio of the
permeability
of
a
material to that of
free space
The permeability of free space:
Electromagnetic Shielding
RELUCTANCE
It is the property of a material that oppose the
setting up of magnetic flux lines through the material.
Similar to the resistance given by:
OHM’S LAW FOR MAGNETIC CIRCUITS
The magnetomotive
force is proportional
to the product of the
number of turns
around the core and
the current through
the turns of wire.
MAGNETIZING FORCE
The magnetomotive force per unit length is called
the magnetizing force (H).
HYSTERESIS
Setup for finding B-H curve
B-H curve: A curve of
the flux density B versus
the magnetizing force H
If the current I is increases, the magnetizing force H will also
increase.
The flux φ and the flux density B (φ /A) will also
increase with the current I (or H). If the material
has no residual magnetism, B will start from 0
B-H CURVE
BR :Residual flux density
-Hd :Coercive force
The Greek hysterein, meaning “to lag behind.” The flux
density B lagged behind the magnetizing force H during
the entire plotting of the curve.
AMPÈRE’S CIRCUITAL LAW
Algebraic sum of the mmf rises and the mmf drops around a
closed loop of a magnetic circuit is equal to zero.
We know
KCL FOR MAGNETIC CIRCUITS
The sum of the fluxes entering a junction is equal to
the sum of the fluxes leaving a junction
Math
Air Gap
Loop 1
Loop 2
Thank
You