Suspension Insulator

The main function of a suspension insulator is to separate the line conductors and support them electrically. It comprises several porcelain insulator units connected by metal links to form a flexible string. The conductor is usually connected to the bottom of the string.

The suspension insulator is shown in the image below.


Advantages of Suspension Type Insulator

The suspension-type insulator offers the following advantages

  1. Depending on the voltage, the appropriate number of discs are connected in series with the string, with each unit operating at about 11kV.
  2. If one unit is damaged, it can be replaced instead of the entire string.
  3. The transmission line provides great flexibility as the string can swing freely in any direction.
  4. The suspension insulators are placed above the conductors, and thus, they provide partial lightning protection.

Types of Suspension Insulators

There are two main types of suspension insulators

  1. Cap and Pin Type
  2. Hewlett or Interlink Type

Below is a detailed explanation of the cap, pin, and Hewlett-type insulator.

1. Cap-and-pin type Suspension Insulator

A porcelain cap-and-pin unit is connected by either a ball and socket or clevis-pin to a galvanized cast iron or forged steel cap and a galvanized forged steel pin.

2. Interlink Type Insulator

The unit uses porcelain with two curved channels intersecting at right angles. U-shaped covered steel links pass through these channels to connect the unit. This type of insulator is known as the Hewlett insulator.

The interlink-type insulators are mechanically stronger than the cad-and-pin type units. The metallic link continues to support the line even if the porcelain between the links breaks; thus, the supply is not interrupted.

The Hewlett-type insulator has one major disadvantage: the porcelain between the links is highly electrically stressed, causing its puncture stress to be less than that of other types.


In conclusion, suspension insulators play a vital role in overhead power transmission. They offer robust support and reliable insulation for conductors. The Cap and Pin and Composite Suspension Insulators have advantages like high mechanical strength and resistance to environmental factors.


  1. Pin Insulator

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