In this article we will discuss about the magnetization curve and cycle magnetization.
Magnetization Curve:
Magnetization curve is the relationship between changing magnetic field H and its influence on the magnetic flux density B. This curve has three regions.
In the first region OA, the curve rises up. The second region AC has almost a constant slope which starts bending near C.
The third region CD has a decreasing slope, and becomes almost horizontal at D. At this part the material has reached to a saturation flux density B. If H is enhanced further, there will be no useful increase in the value of flux density.
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The slopes of the first and second regions are known as initial permeability and maximum permeability respectively.
Magnetic Hysteresis Loop (Or Cycle Magnetization):
Remanence:
The changes in magnetization in a ferromagnetic material lag behind the variations of the magnetic field applied on it.
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In figure, when the magnetic field is decreased and brought back to zero, the curve assumes DE path. Even at H = 0, the magnitude of magnetic flux is equal to OE = Br.
This is residual magnetic flux density, and is also known as retentivity or remanence of ferromagnetic material. Higher this value, better is the quality of ferromagnetic material.
Coercive force- When direction of the field H is reversed, the curve follows EF path of indicates demagnetization force or coercive force.
It means that a ferromagnetic material requires magnetic field of H = -Hc to bring down its flux density to zero. A strong ferromagnetic material will need a higher value of -Hc.
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On further increasing the magnetic field, the curve follows FG path and reaches to saturation flux density -Bs in the opposite direction. Thus one cycle is complete.
Now the magnetic field is applied again on the ferromagnetic material. This time the B-H curve follows HJD path. The curve does not take on the original OACD path. The curve DEFGHJD is called magnetic hysteresis loop. OBs = -OBs, OF = OJ, and OE = OH = Br.
The enclosed area OACDJO is called hysteresis loss.
Comparison of properties of eddy current and hysteresis losses. These are:
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i. Eddy current loss is proportional to the square of the frequency, while the hysteresis loss is directly proportional to the frequency.
ii. Eddy current loss is proportional to the square of the peak flux density, while the hysteresis loss is usually proportional to the 1.6th power of the peak flux density.
iii. Eddy current loss is proportional to the square of the thickness of the laminations, while the hysteresis loss does not depend on thickness of laminations.
iv. Eddy current loss is dependent on the resistivity of the material, while the hysteresis loss is dependent on the Steinmetz constant of the material.