What is Insulator ?Its Types

What is Insulator ?It is a material that do not conduct electricity under normal condition.


 It is a material whose internal electric charges does not flow freely .

Paper, plastic, rubber, glass and air are insulating material .Vacuum is also the insulator but it is not a material. To protect and safely flow of electric current ,conductors are covered by insulation.


It is rated in hundreds of volts or hundred thousands of volts when it is used in high transmission and distribution system.

Insulating material






6.Distilled or pure water



Insulating material properties

 The material which is used as a insulator is called insulating material .For successful used and better performance ,an insulating material  should have the following properties .

  1. It should be strong mechanically  so that it can carry tension and weight of conductors.
  2. The material should have high dielectric strength to withstand the stress  voltage in case of high voltage system.
  3. The material should be free from unwanted impurities .
  4. The material should not be porous.
  5. Its should be less effected by the temperature.
  6. There must be an entrance on the surface of it so that the gases or moisture can enter in it

Porcelain insulator

Porcelain are the most commonly used insulating material in the daily life .Its is Aluminum silicate. when  aluminum silicate is mixed with the plastic kaolin, feldspar and quartz ,the porcelain insulator formed

The surface of the insulating material should be glazed so that the water should not kept on it .It should be free from porosity because the porosity is the main cause of deterioration of its dielectric property.

porcelain ins

Properties of Porcelain 

 Dielectric Straingth – 60 KV / cm

Tensile Strength  — 500 Kg / cm2

Compressive Strength- 70,000 Kg / cm2

Glass insulator

Glass type Ins are becoming more popular now a days in transmission and distribution system due to their some properties . Annealed tough glass is used as a insulating purpose.

 Glass insulat0r have many advantage over the porcelain . It has very high dielectric strength as compare to porcelain. The resistivity of glass is very high .Its has very low thermal expansion coefficient.

Glass Insulator

Due to their transparency the impurities and air bubble can easilt detected inside the glass. The glass insulator  has a very long life as compare to other insulators.

Properties of Glass

Dielectric Straingth– 140 KV / cm

Tensile Strength– 35,000 Kg / cm2

Compressive Strength– 10,000 Kg / cm2

Polymer Insulator

It has two parts, one is glass fiber In a polymer insulator has two parts, one is glass fiber reinforced epoxy resin rod shaped core and other is silicone rubber or Ethylene Propylene Diene Monomer (EPDM) made weather sheds. The weather sheds is useful because its protect insulator from outside environment..Due to its two parts it is called composite insulator.

Type of insulator

There are three main types

1.Pin Type

2.suspension type

3-Strain Type

1Pin type Insulator

The pin type insulat0r are mounted on a pin on a cross-arm with the pole .On the upper end of the insulator there is a groove.

The conductor which is passed through the groove and is tied by annealed wire of same material as of conductor. Pin type ins are used in transmission and distribution up to 33V..

Pin ins 01
Pin ins 02

2Suspension type Insulator

It separate the line conductors and support it electrically. This type consist number of porcelain insulat0r units connected with each other by a metal links which is form a string. The conductor is connected at the bottom of the string.

Each unit of the insulator operate the voltage of about 11KV so depending upon the voltage the disc can be increase and decrease in the string .If one unit damaged then it can be replace by a new  without replacing the whole string. The string  which can move in any directions

Suspension insulation
suspension type

3Strain Insulator

When there is dead end or sharp corner in the transmission line ,the line has to sustain a great tensile load of the conductor. To support this load strain insulator are used .It must have mechanical strength as well as necessary electrical insulating properties .

strain insulator

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