The suspension insulator separates the line conductors and supports them electrically. It consists the number of porcelain insulator units connected with each other by metal links to form a flexible string. The conductor is connected at the bottom of the string.
The suspension insulator is shown below.
Advantages of Suspension Type Insulator
The suspension type insulator has the following advantages.
- Each unit operates the voltage of about 11kV and hence depending upon the voltage the appropriate number of discs are connected in series with the string.
- If one of the units is damaged, then it is replaced by the new one and hence no need of replacing the whole string.
- The string is free to swing in any direction and, therefore, great flexibility is provided to the transmission line.
- The conductors are placed below the suspension insulators and hence it partly protects the conductor from lightning.
Types of Suspension Insulator
The suspension insulator is mainly classified into two types.
- Cap and Pin Type
- Hewlett or Interlink Type
The detail explanation of the cap and pin and Hewlett type insulator are explained below.
1.Cap-and-pin type Insulator
A galvanised cast iron or forged steel cap and a galvanised forged-steel pin are connected to porcelain in the cap-and-pin type construction.The unit is joined either by ball and socket or clevis-pin connections.
2. Interlink Type Insulator
The interlink type unit employs porcelain having two curved channels with planes at the right angle to each other. U-shaped levelled covered steel links passed through these channels and served to connect the unit.
The Interlink type insulators are mechanically stronger than the cad-and-pin type unit. The metallic link continues to support the line if the porcelain between the link breaks. Thus the supply is not interrupted.
The only disadvantage of Hewlett type insulator is that it suffers from the disadvantages that the porcelain between the links is highly stressed electrically and, therefore its puncture stress is less as compared to other types.