Page 153 - Electrician - TT (Volume 1)

ELECTRICIAN - CITS

Magnetic saturation

When a piece of steel or iron fails to acquire a higher degree of magnetization however much magnetizing power
is increased is known as magnetic saturation.
According to molecular theory of magnetism ,this would happen only when every molecule in the magnetic
substance is lined up in the magnetic position.
When the B-H curve of a ferromagnetic material is drawn at a certain point the B-H curve levels off and eventually
becomes horizontal line

The horizontal line indicates that there is no increase in flux density(B) for further increase in magnetising force(H).
This behaviour is called magnetic saturation.ie all domains in the core material have become perfectly aligned.
Magnetic induction

The process by which a substance, such as iron or steel, becomes magnetized by a magnetic field. The induced
magnetism is produced by the force of the field radiating from the poles of a magnet. It is the action by which a
magnetic substance acquires a magnetic property by the presence of a magnet without actual contact

Magnetic screening

Magnetic lines can pass through any media because there is no known insulation for them. Whenever it is
required to protect any instrument or device from magnetic effect, they are magnetically screened or shielded.
A space is said to be magnetically screened when the magnetic force at that point is destroyed. This can be done
by placing an iron ring in the magnetic field.
Electromagnetic shielding is the practice of reducing the electromagnetic field in a space by blocking the field with
barriers made of conductive or magnetic materials.
The fig.Shows the influence of a circular ring on the distribution of magnetic lines of force between the two
opposite poles. The lines of force will pass through the iron ring rather than air, and there will be no lines of force
inside the ring. The space which is not effected by magnetic lines of force is known as magnetically screened
space.
Shielding is typically applied to enclosures to isolate electrical devices from the ‘outside world’, and to cables
to isolate from the environment through which the cable runs. Electromagnetic shielding that blocks frequency
electromagnetic is also known as RF shielding.

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CITS : Power - Electrician & Wireman - Lesson 26-29