Dielectric materials

Topic-Dielectric Materials
Prepared
By :-
RUSHIT

Introduction
• Dielectrics are the materials having electric dipole moment
permantly.
• Dipole: A dipole is an entity in which equal positive and negative
charges are separated by a small distance..
• DIPOLE moment (µele ):The product of magnitude of either of the
charges and separation distance b/w them is called Dipole moment.
µe = q . x  coul – m
-q
x
• All dielectrics are electrical insulators and they are mainly used to
store electrical energy.
• Ex: Mica, glass, plastic, water & polar molecules
q
…

Dielectric Constant
Dielectric Constant is the ratio between the
permittivity of the medium to the permittivity of
free space.
The characteristics of a dielectric material are
determined by the dielectric constant and it has no
units.

Electric Polarization
The process of producing electric dipoles by an electric field is
called polarization in dielectrics.
Polarizability:
• The induced dipole moment per unit electric field is called
Polarizability.
• The induced dipole moment is proportional to the intensity of
the electric field.
• Is a Polarizability constant

Polarization vector:
The dipole moment per unit volume of the
dielectric material is called polarization vector.

• Electric flux Density (D):
• It is defined as the flux passing per unit area of a
section , held normal to the direction of flux.
• Electric flux density D at a point in a free space or
air in terms of Electric field strength is
• At the same point in a medium is given by

Electric susceptibility:
The polarization vector P is proportional to the total
electric flux density and direction of electric field.
Therefore the polarization vector can be written

TYPES OF DIELECTRIC MATERIAL
• Dielectric material can be solid, liquid or gas.
• High vacuum can also be used as a dielectric.
• Solid dielectrics are most commonly use like glass,
rubber, mica etc..
• As a liquid dielectric material Transformer oil, cable
oil, Capacitor oil, Vegetable oil etc can be used.
• Gaseous dielectric materials are used for both as
insulators and
also as a cooling agents.
For example: Air, Hydrogen, nitrogen, Helium,
Sulphur- dioxide, Propen, methane etc..

I) Mica
• It is inorganic mineral material made up of
silicate of aluminium with silicate of soda,
potash and magnesia.
• It is rigid, tough and strong. It has high
dielectric strength and is not affected by
moisture.
• It is widely used in irons, hot plates and
toasters.

II) Glass
• It is inorganic material made by the fusion of
different oxides like SiO2, ZnO and MgO.
• It is Brittle and hard material and has good
dielectric strength
• It is mostly used in the capacitors. Also used
as dielectric tubes in radios and television.

III) Asbestos
• It is naturally occurring material. In general it
consist of magnesium silicate.
• It has low dielectric strength. It is used as
insulating material to prevent current flow in
the outer body.
• It is widely used in the form of the paper, tap,
cloth etc.

IV) Rubber
• It is organic polymer. It may be natural or
synthetic.
• It has good electrical and thermal properties
and also it has good tensile strength.
• It is used for the insulating materials on
electrical wires.

V) Ceramics
• They are generally non-metalic inorganic compounds
such as silicates, aluminates, oxides, carbides, borides
etc.
• Ceramics can be classified as:
clay products, refractories, and glasses.
• Ceramics are hard, strong and dense. They have exellent
dielectric and mechanical properties.
• They widely used as insulators in switches, plug holders
etc.
• They are also used as dielectric in capacitors

2) Liquid Dielectric Materials

1. Mineral Insulating Oil
• These oils are obtained from crude
petroleum.
• These have good thermal stability.
• They are used in Transformers as cooling and
insulating material and also in Capacitors.
• Transformer oil, cable oil and capacitor oil
belong to the category of mineral insulating
oil.

2.Synthetic Insulating Oil
• Askarels, aroclors, sovol and savtol are a few
synthetic oils that are widely used.
• They are very much resistant to fire hazards.
• Due to longer life and safety in operating
condition, these oils are used as coolants and
insulators in high voltage transformers in
place of Transformer oil.

3.Miscellaneous Insulating Oil
• Vaseline, vegetable oils and silicon liquid
belongs to these category. Silicon liquids has
thermal stability upto 200 C and are very
costly.
• The dielectric strength of these oils are same
as mineral oils so they are also used in the
H.V transformers.

3) Gaseous Dielectric Material

1.Air
• It is naturally available dielectric material.
• Dielectric loss is practically zero.
• The dielectric constant of air linearly increase with
increase in pressure.
• It is used as dielectrics in air condensers.
• It can be used as an insulator only in low voltage
applications.

2.Nitrogen
• It is important gaseous dielectric material. It
prevent oxidation.
• It is used in cables and capacitors under
pressure.

3.Sulphure Hexafluoride
• It is formed by burning of Sulphure in
fluorine atmosphere.
• It has superior cooling properties than air
and nitrogen.
• It is used in the transformers, electrical
switches, voltage stabilizer and X-ray
apparatus.

4.Inert Gases
• They are used in electronic tubes and
discharge tubes as insulators.

Properties of Good Dielectric Material
 It should have high resistivity to reduce the leakage current.
 It should have high dielectric strength.
 It should have high mechanical strength.
 It should have high fire resistance.
 It should have low thermal expansion.
 It should have high thermal conductivity.
 It should have low dielectric loss.
 It should have low water absorption quality.

Dielectric materials

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