Definition
Retentivity and coercivity
The value of B at H = 0 is called retentivity or remanence. The value of H at c is called coercivity.
Definition
Hysteresis loss
Hysteresis loss is due to the reversal of magnetization of transformer core whenever it is subjected to alternating nature of magnetizing force .Whenever the core is subjected to an alternating magnetic field, the domain present in the material will change their orientation after every half cycle. The power consumed by the magnetic domains for changing the orientation after every half cycle is called Hysteresis loss.
Definition
Selection of magnetic materials for a specific purpose
Permanent magnets:
Desired properties:
1. High retentivity for increasing strength of the magnet
2. High coercivity for sustaining magnetisation for a longer time.
Example: steel, cobalt steel etc.
Electromagnets:
Desired properties:
1. High permeability (or susceptibility) to increase the magnetic field strength in the core.
2. Low retentivity to quickly kill the magnetic effect on the removal of excitation current.
Example: soft iron
Transformer cores and Telephone diaphragms: Materials goes through continuous complete cycles of magnetisation continuously.
Desired properties:
1. Low hysteresis loss to reduce loss of energy.
2. High permeability (or susceptibility) to obtain large flux density
3. High resistivity to reduce eddy-current losses.
Example:
Soft iron, permalloys, etc
Desired properties:
1. High retentivity for increasing strength of the magnet
2. High coercivity for sustaining magnetisation for a longer time.
Example: steel, cobalt steel etc.
Electromagnets:
Desired properties:
1. High permeability (or susceptibility) to increase the magnetic field strength in the core.
2. Low retentivity to quickly kill the magnetic effect on the removal of excitation current.
Example: soft iron
Transformer cores and Telephone diaphragms: Materials goes through continuous complete cycles of magnetisation continuously.
Desired properties:
1. Low hysteresis loss to reduce loss of energy.
2. High permeability (or susceptibility) to obtain large flux density
3. High resistivity to reduce eddy-current losses.
Example:
Soft iron, permalloys, etc
Definition
Hard and soft ferromagnetic materials
- Materials which have high values of the coercive field strength are called magnetically hard whereas materials those with low values of the coercive field strength are magnetically soft.
- A soft magnetic material does not make a good permanent magnet, because its remanant magnetization after switching off the magnetic field is small. On the contrary, a hard magnetic material will make a good permanent magnet because its remanant magnetization is large.
- Hard magnetic materials have large hysteresis loss due to large hysteresis loop area whereas soft magnetic materials have low hysteresis loss due to small hysteresis area.
- Susceptibility and permeability are low for hard magnetic materials whereas they are low for soft magnetic materials.
- The eddy current loss is high for hard magnetic materials whereas it is low in case for soft magnetic materials.
Definition
Soft iron andnSteel
Iron gets magnetized faster but loses its magnetism as soon as the inducing magnet is removed. Hence soft iron is said to have high susceptibility but low retentivity. This property of soft iron is very useful in making temporary electromagnets where we need strong but temporary magnets. If the magnets used in these devices were to retain their magnetism for a longer period, the devices would not function properly.
Steel is slow to be magnetized but retains the acquired magnetism for a long time. Steel is said to have low susceptibility but high retentivity. Steel is used for making magnets.
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