More information about dielectrics

1. Mechanical engineering
PHYSICS
DIELECTRICS

2. DIELECTRICS
Insulating materials are also called “DIELECTRICS”.
: : : TYPES OF DIELECTRIC MATERIALS : : :
Dielectric materials can be SOLID , LIQUID , GASES.
 A high vacuum can also be used as a dielectric even
though its relative dielectric constant is only unity.

3.  SOLID DIELECTRICS are the most commonly used in electrical
engineering ; these are very good insulators.
Examples : Porcelain , glass , rubber , mica.
 LIQUID DIELECTRICS are basically of 3 different types , which
includes (i) mineral insulating oils , (ii) synthetic insulating oils ,
and (iii) miscellaneous insulating oils.
The function of insulating liquid is to provide electrical
insulation and to dissipate heat.
Examples : Transformer oil , cable oil , vegetable oil ,
silicon liquids.
 GASEOUS DIELECTRIC materials are used both as an insulator and
as cooling agents.
Examples : Air, Hydrogen , Nitrogen , Helium , propane

4. MICA
Mica is an inorganic material, made of the silicate of
aluminium with silicates of soda, potash and magnesia.
 It is crystalline in natural and can be divided into very thin
flat sheets.
 It is rigid, tough and strong.
 It has high dielectric strength and low dielectric loss.
 It is not affected by moisture.
Mica is widely used in electric irons, hot plates and toasters
for insulation purpose.
Mica paper is used as insulation in armature and field coils of
rotating machines.
Mica is also used as a dielectric material in high frequency
applications.

5. MICA

6. GLASS
Glass is an inorganic material made by the fusion of different
oxides
 like SiO2, ZnO and MgO.
Glass is brittle and hard.
 It has good mechanical strength and has low dielectric loss.
 It is insoluble in water and is highly chemical resistant to most
corrosive agents.
 It is used as a dielectric in capacitors.
 It is used in radio

7. GLASS

8. Asbestos
Asbestos is a naturally occurring material of fibrous
nature. It generally consists of magnesium silicate. It has
high dielectric loss and low dielectric strength.
It can withstand very high temperature.
It is used as dielectric or insulating material to prevent
current flow in the outer body of electrical appliances
like electric iron box, oven etc. it is widely used in the
form of paper tape ,cloth and board.

9. Asbestos
Asbestos
(raw material)
Asbestos
(fibrous material)

10. Rubber
Rubber is an organic polymer ,it may be natural or
synthetic . Synthetic rubbers are produced by
copolymerization of isobutylene and isoprene.
Rubber has good electrical and thermal properties. It
possesses high tensile strength.
Rubber is used in the construction of the storage batteries
housings. It is used as insulating materials for electric
wires,tapes,transformers,motor windings etc.

11. Rubber
Natural rubber Synthetic rubber

12. Ceramics
Ceramics are generally non metallic inorganic compounds
such as silicates, aluminates, oxides, carbides,
 borides, nitrides and hydroxides. Ceramics are also called
potter`s earth or clay . Ceramics can be classified as clay
products , refractories and glasses .
Ceramics are hard , strong and dense. They have excellent
dielectric and mechanical properties . They are not affected
by moisture and by chemical agents except with strong acids
and alkalis. They are completely stable at high temperatures.
Ceramics are widely used as insulators for switches , plug
holders, cathode heaters etc.
 They are also used in electric stoves and kettles. They are also
used as dielectrics in capacitors.

13. Ceramics
Ceramics switches Copper cathode heaters

14. …Liquid Dielectrics…
There are 3 types of Liquid dielectrics………
1) Mineral insulting oils: These oils are
obtained from crude petroleum by distillation.
These oils possess high oxidation resistance and have
good thermal stability. These oils are used in
transformers and capacitors.
 Example : Transformer oil , Cable oil and Capacitor
oil.

15. 2) Synthetic insulating oils : This oils are very much
resistant to oxidation and to fire hazards. They are used
as coolant and insulators High Voltage (H.V.)
transformers.
 Example- Aroclors, Sovol , Askarels and Sovtol.
.

16. 3) Miscellaneous insulating oils : The dielectric of this
oils is same as that of mineral oils. This oils are also used
in H.V. Transformers.
 Examples-Vaseline, Vegetable oils and Silicon oils.

17. Gaseous Dielectrics
Gaseous Dielectrics includes :
AIR
NITROGEN
SULPHUR HEXAFLUORIDE
INERT GASES

18. AIR
Air is naturally available dielectric material.
It is the most important insulating material.
The Dielectric loss is practically zero.
The dielectric constant of increases linearly with
increase in pressure.
It is used as a dielectric in condensers.
It can be used as insulation only in low voltage
application.

19. NITROGEN
Nitrogen is an important gaseous dielectric.
It is chemically inert.
It prevents oxidation and reduces rate of deterioration.
In oil filled transformers, it is used to replace oxidizing
atmosphere.
It is also used in capacitor and in cables under pressure.

20. SULPHUR HEXAFLUORIDE
It is formed by burning of sulphur in fluorine
atmosphere.
It has superior cooling properties than that of Air &
Nitrogen.
It has high chemical stability up to 1000 C.
It is used in transformers, electric switches , van de
Graff generator , voltage stabilizer & X-rays
apparatus .

21. van de
Graff
generator

22. INERT GASES
Inert Gases are used in Electronic Tubes and Discharge
Tubes as Insulators.

23. Application of Dielectrics

24. Specific Application
The dielectric materials based on their nature of state
have a variety of application in electric engineering field.
We will learn about two application.
 Capacitors
 Transformers

25. Capacitors
Dielectric materials in capacitors is to store electrical
energy.
Based on the nature of the dielectric material used, the
capacitors fall into different groups.
There are four groups of Capacitors.

26. Capacitors with Vacuum, air &
gases

27. Capacitors with mineral oil

28. Capacitors with combination of
solid & liquid

29. Capacitors with only solid

31. GroupMembers