OVERHEAD LINE INSULATOR

 OVERHEAD LINE INSULATOR

The overhead line conductors are supponed over the tower structures by means of line insulators. 

The line insulators provide sufficient mechanical strength as well as insulation between the live conductors and tower structures

In general, the insulators should have the following desirable properties.

✓High mechanical strength in order to withstand conductor load, wind load ese ⚫ High electrical resistance of insulator material in order to avoid leakage currents to earth. 

✓High relative permittivity of insulate material in order that dielectric strength is

high. 

✓The insulator material should be non-porous, free from impurities and cracks otherwise the permittivity will be lowered.

✓High ratio of puncture strength to flashover.

✓The most commonly used material for insulators of overhead line is porcelain but glass, statite and special composition materials are also used to a limited extent. 

✓Porcelain is produced by firing at a high temperature a mixture of kaolin, feldspor and quartz. 

✓It is stronger mechanically than glass, gives less trouble from leakage and is less affected by changes of temperature. 

✓The successful operation of an overhead line depends to a considerable extent upon the proper selection of insulators

There are three types of insulators used in connection with overhead lines

✓ Pin-type

✓ Suspension-type

✓ Strain-type