Conductors and Insulator
InsulatorsThe insulators are provide to conductors proper insulation and also provide necessary clearances between conductor and metal work.
The insulator must provide proper insulation and necessary clearance against the highest voltage in worst atmospheric condition in transmission line. Which the line is likely to be subjected.
The insulator also prevents short-circuiting between the different phase conductors and provides necessary mechanical support for the line conductors. Thus insulator is undoubtedly one of the most important and vulnerable links in transmission and distribution practice and, therefore, proper selection is of utmost importance for the successful operation of overhead transmission and distribution system.
The important properties of insulator
High mechanical strength so as to bear the load dew to the weight of line conductors, wind force and ice loading if any. In transmission and distribution line.
High relative permittivity so as to provide high dielectric strength .
High insulation resistance in order to prevent leakage of currents to earth.
High ratio of rupture strength to flash-over voltage.
Ability to withstand large temperature variations, it should not crack when subjected to high temperature during summer and low temperature during winter .the dielectric strength should remain unaffected under different conditions of temperature and pressure.
The material most commonly used for overhead line conductors is porcelain but toughened glass, steatite and special composition materials are also used to a limited extent.
PorcelainIt is produced by firing at a controlled temperature a mixture of kaolin, feldspar and quartz.
It is mechanically stronger than other. It gives less trouble from leakage, and is less usceptible to temperature variations and its surface is not affected by dirt deposits.
It is cheaper than porcelain in the simpler shapes and if properly toughened annealed gives high resistivity and dielectric strength (14KV per mm of thickness of the material). Owing to high dielectric strength , the glass insulator have simpler design and even one piece design can be used glass is quite homogeneous material and can with stand higher compressive stresses as compared to porcelain .
SteatiteIt is a naturally occurring magnesium silicate, usually found combined with oxides in varying proportions. It has a much higher tensile and bending stress than porcelain.
In electrical engineering, a conductor is a material that allows the flow of electrical current in one or more directions. For example a wire is an electrical conductor that can carry electricity along its length.
In metals such as copper or aluminum, the movable charged particles are electrons.
Property of conductors
High electric conductivity
Low specific resistance
High tensile strength in order to withstand the mechanical stresses.
Low specific gravity in order to give low weight per unit volume.
Low cost in order to be used over long distances usually involved in transmission lines.
Should not be brittle.