In practice, most dielectric materials are solid. Examples include porcelain (ceramic), mica, glass, plastics, and the oxides of various metals. Some liquids and gases can serve as good dielectric materials. Dry air is an excellent dielectric, and is used in variable capacitors and some types of transmission lines.

1. Dielectrics Materials

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3. 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 either of the charges
and the separation between them is called electric 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

4. dipole

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

6. 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.
• Polarizability is a constant

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

8. 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

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

10. 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..

11. 1) Solid Dielectric
Materials

12. 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.

13. 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.

14. 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.

15. IV) Rubber
• It is organic polymer
. It may benatural 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.

16. 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

17. 2) Liquid Dielectric
Materials

18. 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.

19. 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.

20. 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.

21. 3) Gaseous Dielectric
Material

22. 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.

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

24. 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.

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

26. 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.

27. Applications of
Dielectrics

28. Capacitors

29. 2.Transformers

30. 3.Polymeric film

31. 4.Electrolytic