Engr. Abbas Abbasi
Behavior of Ferromagnetic MaterialsSaturation and Hysteresis
Ferromagnetic Material A material whose permeability is very much larger than 1 (from 60 to several
thousand times ), and which exhibits hysteresis phenomena
Material that acquires strong magnetism when placed in an external magnetic field. Examples are iron, cobalt, nickel, and their alloys.
MMF (DC ) Vs Flux Curve
If MMF (Ni) is increased flux also increases There comes a stage when increase in MMF does not produce corresponding
increase in flux The plot above is known as “Magnetization curve” of the core
Saturation
Saturation Region
Unsaturated region
cF Hl F H
BA B
B-H Curve
cF Hl F H
BA B
B-H Curve and Permeability (µ)
Permeability is the slope of the “Magnetization curve”
Constant permeability
Low and unstable permeability
MMF (AC ) Vs Flux Curve
F
φ
Hysteresis Loop
Magnetic Domains (Reason for hysteresis) Within the metals there are very small regions called domains In each domain atoms are aligned, with their magnetic fields pointing in the
same direction (acting like a small magnet) These tiny domains are oriented randomly in the metal
When external fields are applied, energy is required to align these domains in the direction of the main field
These energy losses are called hysteresis losses (core losses) When all the domain have been aligned, the stage is called saturation
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