2. “
”
INTRODUCTION
• Dielectrics arethematerials whichhaving theelectricdipole
moment permanently.
• Adipole isanentityinequalpositive andnegative charges are
separated byasmalldistance…
• Theproductof magnitudeofeither ofthecharges andseparation
distancebetween them iscalledas dipolemoment.
• All dielectricsareelectricalinsulatorsandthey aremainlyused to
store electricalenergy.
• EXAMPLE: Mica,glass,plastic,water, etc.,
3. TYPES OF DIELECTRIC MATERIALS
• Dielectric material can be solid, liquid or gas.
• High vacuum can also be used as a dielectric.
• Solid dielectrics are most commonly used as glass,
rubber, mica, etc.,
• As a liquid dielectric material Transformer oil, cable
oil, vegetable oil can be used.
• Gaseous dielectric materials are used for both as
insulators and cooling agents.
• Example: Air, hydrogen, nitrogen, helium methane,
sulphur dioxide etc.,
4. ELECTRIC POLARIZATION
• The process of producing electric dipoles by an
electric field is called polarization
• The induced dipole moment per unit electric field is
called polarizability
• The induced dipole moment is proportional to the
intensity of the electric field.
5. Properties of a 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 high thermal conductivity.
• It should have low thermal expansion.
• It should have low dielectric loss.
• It should have low water absorption quality.
8. SULPHUR HEXAFLUORIDE
• It is formed by burning of Sulphur in fluorine
atmosphere.
• It has superior cooling properties than air and
nitrogen.
• It is used in the transformers, electrical switches,
voltage stabilizers, and X–ray.
