What is a Pin Type Insulator : Construction, Causes & Applications

It is clear that if transmission lines are not correctly insulated from the support of towers or poles, then the flow of current will be in the direction of the ground through the tower so that it will become dangerous. Certainly, the transmission lines are always supported by insulators which are placed on the poles. The insulators which are used on the towers must have these properties like high mechanical strength, high electrical resistance, high relative permittivity, etc. The material of the insulator used in the transmission lines is porcelain but based on the requirement, steatite or glass type is also used. There are different kinds of insulators available in transmission lines like pin type insulator, suspension, strain, stay and shackle. The insulators like pin, strain, and shackle are applicable in medium to high voltage systems whereas shackle and stay are applicable in low voltage applications.

What is the Pin Type Insulator?

Definition: An insulator that is used to isolate a wire from physical support such as a pin on a utility pole or tower is known as pin type insulator. This type of insulator is used within 33kV power distribution systems. As the name suggests, it is arranged on a pin where the conductor connected to it. These insulators are made with glass otherwise porcelain. The pin type insulator diagram is shown below.


These insulators are still used in 33 kV power distribution systems. These insulators are available in different parts like 1 part, 2 parts or 3 parts type based on the voltage of application. One part type is used in an 11 kV power distribution system where the entire insulator is a porcelain/glass shaped piece.

If the leakage path of this insulator is at the surface, it is required to enhance the length of the surface area vertically to increase leakage lane.

Construction of Pin Type Insulator

The internal diagram of pin type insulator is shown below. It includes two main parts namely porcelain as well as galvanized steel bolt. This bolt is connected at the base through cementing. There are a variety of techniques for protecting insulator toward the bolts.

Causes of Insulator Failure

The designing of an insulator must be done properly to overcome the electrical and mechanical stresses on the insulator. Electrical stress on insulators mainly depends on the line voltage, and therefore, appropriate insulators have to utilized based on the line voltage. Surplus electrical pressure can damage the insulator either by puncture or flash-over.



The puncture of an insulator can be occurred due to the electrical discharge from the conductor to pin throughout the insulator. Enough thickness of insulator material must be used to evade a puncture. When such type of puncture occurs then the insulator will be damaged permanently.


The flashover of an insulator can be occurred because of the electrical discharge by designing an arc among the pin of an insulator & line conductor.

Safety Factor

It is defined as the ratio of puncture potency to flash overvoltage. It requires high safety factor value so that a flash-over occurs once before the pin type insulator gets punctured. For this kind of insulator, the safety factor value is approximately 10.

Safety factor = Puncture Strength/Flash Over Voltage

Design Considerations

The conductor is connected on top of the insulator and the base of the insulator can be connected for supporting earth potential structure.

The insulator has to endure from the potential stresses which occur between the earth & conductor. The distance between earth & conductor, insulator surrounding, and electrical discharge through the air is called flashover distance.


Once the insulator gets wet, then its external surface will become almost conducting. Therefore the flashover distance will be decreased in an insulator.

So the design of the upper insulator looks like an umbrella to protect the inner parts from the rain. The upper face of the top petticoat is inclined to maintain the highest flashover voltage while raining. The designing of rain sheds for insulators can be done to protect the voltage distribution from disturbances.

Advantages of Pin Type Insulator

The advantages are

  • The mechanical strength of this insulator is high.
  • It is not expensive
  • It has a good creepage distance.
  • It is applicable to a high voltage transmission line.
  • The designing of this insulator is simple
  • Easy maintenance
  • It is used vertically & horizontally

Disadvantages of Pin Type Insulator

The disadvantages are

  • It is applicable for only transmission lines
  • It must be used by the spindle.
  • The voltage rating is up to 36kV.
  • The insulator pin can damage the thread of an insulator.
  • For above 50KV, these insulators will become uneconomical and bulky.


The applications are

  • This insulator is used in power transmission lines for up to 33kV.
  • These insulators are used on intermediate poles on a straight run
  • Instead of using two suspension type insulators, pin type insulator is used.


1). Why pin insulators are not used above 33kv?

As they become too large and uneconomical.

2). Why is the wavy structure of pin insulators used?

To increase the flash overvoltage

3). Why do we need insulators?

Insulators work as protectors to protect from sound, heat & the flow of electricity.

4). Which insulator is used in the transmission line?

Power line insulator is used in transmission line

5). Are high voltage lines insulated?

Initially, high voltage lines are insulated. The air works as an insulator among the line conductors and normal string insulators to provide insulation among line wire & ground at support points.

Thus, this is all about an overview of pin type insulators. It offers simple, the most economic, efficient technique of conductor. Modern insulators are extremely consistent & inherent breaks within porcelain are extremely rare. The life span of these insulators is relatively long and these types of insulators are obtainable for up to 50 kV. Here is a question for you, what is the function of the insulator?