INSULATORS

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HISTORY


Early history centers around what today we would consider very low DC voltages
Basically grew out of the needs of the telegraph industry – starting in the late 1700s, early 1800s

Glass plates used to insulate telegraph line

Gradually technical needs increased as AC voltages grew with the development of the electric power industry


DIELECTRIC STRENGTH


The dielectric strength of an insulating material is defined as maximum dielectric stress which the material can withstand without any conduction.

The electric stress to which an insulating material is subjected is numerically equal to voltage gradient and which is equal to electric field intensity.

Voltage at which current starts flowing through the dielectric is known as breakdown voltage.

LIQUID INSULATOR


Liquids are usually 103 times denser than gases.

So, they possess much higher dielectric strength of the order of 107 V/cm.

Petroleum oils are the commonest insulating liquids


ELECTRICAL BREAKDOWN


gaseous dielectric
ionization leads to breakdown of gases.
Ionization may occur due to….
A) collision
B)photo ionization
C)thermal ionization

liquids dielectrics
Presence of any solid impurity lead to breakdown
Formation of gaseous product


Fluorocarbons ,silicones, esters are also used as insulating oil.