Dielectrics and High Voltage Insulators
Air acts as a principal dielectric in the overhead power lines made of aluminium or aluminium with steel core wires, hence it can be said that Air is an excellent high voltage insulator. But, these wires need to be serviced and extend to great distances and need to be supported – generally this is done with cross-armed pylons made of metal – we all know metals are good conductors of electricity hence the live wires need to be covered with other kinds of high voltage insulator materials like Teflon, plastic, ceramics, or other dielectrics, which can withstand mechanical, electrical and environmental stresses. The porcelain pin type insulators were initially used for telephone poles and lightning conductors, and are now adapted for power lines, Cap and pin insulators are made up of porcelain and glass. Post-type and line post insulators mainly used at substations. The porcelain long rod insulators are lighter, slimmer and post insulators. Bushings, composite polymeric insulators and cyclo-aliphatic epoxy resin insulators are also used on many occasions too.