What are insulators and types of insulators used in transmission lines

What are insulators

Insulators are materials which will prevent the flow of electrons through them. Insulators are used in transmission and distribution system, it is also used in household appliances and portable tools one of them is electrical hand drilling appliances. Electrical protective insulation is effective in protection from electrical shocks

Why should we use insulators in a transmission system

Insulators are used in transmission lines to separate or support electrical conductors on high voltage electricity supply networks, insulators provide insulation to the power conductor from the ground

Insulators are connected to the cross arm of the supporting structure and the power conductor passes through the clamp of the overhead line insulators

What are the properties of an insulator

  • Insulators in overhead lines have both electrical and mechanical strength. Highly insulative materials are used it has watershed fins which will resist the conductive water path during rain.
  • It must have the high mechanical strength to bear the conductor load under the worst loading condition
  • It must have high resistance to temperature changes to reduce damages to power flashover
  • It must not be porous and it should be impervious to gases in the atmosphere and it must be free from impurity and cracks which could lower the permittivity

What are the types of insulators used in overhead lines

  • Pin type
  • Suspension type
  • Strain type

Pin type insulator

This type of insulator is used in the cross arm of the pole, these insulators are used in voltage range up to 33kv beyond that it would become too bulky

Pin type insulators are secured with steel or lead bolts onto transmission poles they are mostly used for straight running transmission lines

Suspension type insulator

These type of insulators are used in high voltage range, these insulators are suspended from the cross arm and the line conductor is fastened to the cross arm. This insulator will suspend and support high voltage transmission lines. It is cost-effective for high voltage transmission

Strain type insulator

This insulator will look similar to the suspension type but it can hold heavier physical loads. Strain type insulators are used to relieve the tension of the line whenever there is a corner or sharp curve

These are horizontally suspended suspension insulator, it can handle mechanical stresses and it can take the pressure of a conductor at the end of the transmission line it is mostly used for higher voltage transmission

How insulators can be damaged

Excessive voltage can create an electrical breakdown of an insulator

  • Puncture voltage – it is the voltage across the insulator which could cause a breakdown and conduction through the interior of the insulator
  • Flashover voltage – it is the voltage which can cause the air around or along the surface of the insulator to break down and conduct thus causing a flashover arc along the outside of the insulator

What is string efficiency and how can it be improved

It is a measure of utilization of the material in the string and it is defined as a flash- overvoltage voltage of a string

Improving string efficiency

Use of long cross arm – string efficiency can be improved by reduction in stray capacitance to ground

Capacitance grading – By assembling the string with units of different capacitance with the appropriate voltage, the voltage distribution can be equalized

Guard rings – it is the most efficient way to equalize the voltage distribution by fitting rings, it will increase the stray capacitance to the line and decreases stray capacitance to the earth


post-graduate in Electronics & communication.

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