Hope you are all good and well. 

Today we will discuss about, 

  • What is an insulator?
  • Types of insulator: -
  • Pin type insulator
  • Suspension insulator
  • Strain insulator
  • Shackle insulator
  • Egg or Stay insulator

As we have discussed about various types of line supports in our previous article.  


Now let's go to learn about insulator. 

What is an insulator: -


An insulator is an electrical device which does not conduct the electricity. Means the current will not flow through it. 

The resistance of an insulator is very high.

Why insulator use in transmission and distribution of electrical power?


As we know that the electrical power is transmitted or distributed through overhead conductors which are supported by means of poles or line support. 

So we have to insulate these overhead conductors from the poles so that the current will not flow through the line support to earth. 

To isolate the overhead conductors from the pole, insulators are used. 

As there are different types of insulators used according to the requirement. 

Insulating materials: -


There are various insulating material are there: -

Plastic 
Glass 
Rubber
Mica
Wood etc. 

But there is only some type of material used for the construction of the insulator used in transmission and distribution as given below: -

Porcelain 
Glass 
Polymer

Types of insulators: -


As we have discussed above, there are various types of insulators are used according to the requirements which are discussed below. 

1. Pin type insulator: -


  1. These types of insulators are used up to 33KV. 
  2. It can be used in both means transmission (up to 33KV) and distribution. 
  3. There is a groove at the top of this insulator on which the line conductor is placed. 
  4. The line conductors are tied or bound with the insulator by a piece of the same material of line conductors.  Means if the line conductor is made up of ACSR conductor then the binding piece is also of ACSR conductor. 
  5. Due to the groove at top, the clearance of conductor from ground increase which is an advantage of this insulator. 
Pin type insulator
Fig. Pin type insulator


So a question arises here, why pin type insulators are not used beyond 33KV?


There is no doubt that we can use a pin type insulator beyond 33KV. But due to economical consideration we did not use the pin type insulator beyond 33KV. 

2. Suspension type insulator: -


  • These type of insulators are used above 33KV. 

  • They are used for transmission lines. 

  • These insulators are made up of disc therefore also known as disc insulator. 

suspension type insulator
Fig. disc insulator


  • There are number of disc insulators connected in series with each other for high voltage uses. 

  • Each disc insulator can withstand up to 11KV. 

  • So the number of disc insulators depends upon the line voltage. More the line voltage more will be the disc insulators.  

How to identify the suspension insulator? 


The identification of this type of insulator is that these types of insulators are hung vertically on the cross arm. 

suspension insulator
Fig. suspension insulator


As suspension insulator are hung on the pole with the help of cross arm, therefore the conductor pass from below of cross arm which reduce the ground clearance of the conductor. 

3. Strain insulators: -


  • These are similar to the suspension insulator except that these insulators are used when our transmission line take any sharp turn or at dead end of the transmission line. 

  • These insulators also made up of disc. 

  • Here also the number of discs depends upon the line voltage. 

How to identify strain insulators?


The identification of this type of insulator is that these types of insulators are hung horizontally on the tower. 

Strain insulator
Fig. Strain insulator

Jumper is the conductor which links two different conductors to each others.

4. Shackle insulator: -


  • These types of insulators are used for the distribution purposes. 

  • These are used if there is any turn in the L.T. (low tension) line.

  • Like a pin type insulators they also can be used up to 33KV.

  • The cross arm is fitted with the pole on which shackle insulator is bolted.

  • The low tension line wire pass through this insulator. And insulate the conductor from the pole. 


Shackle insulator
Fig. Shackle insulator


5. Egg or Stay insulator: -


  • These types of  insulators are also used in the distribution system and made up of porcelain material.  

  • As we know that a wire supports the pole in distribution system known as a guy wire. 

  • The egg or stay insulator is placed between the earth and the pole on guy wire so that in any abnormal condition the current will not flow through pole to earth. 

egg or stay insulator
Fig. egg or stay insulator



  • Means let assume the phase wire break and falls on the guy wire then, if the insulator is connected there, no current will flow and if it's not connected, then the current will flow through the guy wire to earth which is dangerous. 

  • So to avoid this, an insulator is connected to guy wire. It is connected 3m above from the ground. 

So this was about, 

Pin type insulator,
Suspension type insulator, 
Strain type insulator,
Shackle type insulator, 
Egg or stay type insulator. 

If you have any doubt then tell me in a comment. 

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Thank you.

Hope the article helps you.