Discuss applications of dielectrics.
Application of dielectrics:
For various applications various properties of dielectric materials are required as: electrical, mechanical, chemical and thermal. Electrically the insulating material must have high resistivity to decrease the leakage current and high dielectric strength to enable this to withstand higher voltage without being punctured. Additionally, the insulator must have small dielectric loss. Because the insulators are used on the basis of volume and not weight, a low density is chosen.
Liquid and gaseous insulators are also used as coolants. For illustration: transformer oil, hydrogen and helium are used both for cooling and insulation purpose. For these materials good thermal conductivity is a selected property.
Materials with huge electronic and ionic polariability and so large permittivity are used for making dielectric capacitors. Titanium oxide that has a permittivity of around 100 is a good example of this material.
Some of the significant dielectric materials and applications are as follows:
Mica: These sheets are used for insulating leaves among commutator segments.
Porcelain: This is used for high voltages transmission line insulators, high voltage switch parts and conductor rail support on railways.
Bakelite: This is used for small moulded parts as lamp holder, switch covers and terminal blocks.
Polyvinyl Chloride: Cables with PVC insulation are not influenced by oil and petrol and are thus widely used in aircraft and factories.
Cotton and silk: Cotton covered wire is widely used for the winding of small magnet coils, armature winding of small and medium sized machines, small transformer coil choke etc. silk is more costly than cotton but takes up less space and therefore is used for winding in fractional horsepower machines.