11-01-2013, 03:44 PM
INSULATORS
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INTRODUCTION
An electrical insulator is a material whose internal electric charges do not flow freely, and which therefore does not conduct an electric current, under the influence of an electric field.
A perfect insulator does not exist, but some materials such as GLASS, PAPER and TEFLON, which have high resistivity, are very good electrical insulators.
Insulators are used in electrical equipment to support and separate electrical conductors without allowing current through themselves.
MATERIAL
Insulators used for high-voltage power transmission are made from glass, porcelain or composite polymer materials.
Porcelain has a dielectric strength of about 4–10 KV/mm.
Glass has a higher dielectric strength, but it attracts condensation and the thick irregular shapes needed for insulators are difficult to cast without internal strains.
Different Types Of INSULATORS
There are mainly three types of insulators:
PIN INSULATOR
SUSPENSION INSULATOR
STRAIN INSULATOR
PIN TYPE INSULATOR
For lower voltages pin type insulators are used but for higher voltages two or more units are cemented together to provide sufficient thickness.
Pin type insulators are used to a limit of 66kV and thereafter suspension insulators are used for higher voltage work.