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Friday, 10 January 2020

Transmission Line Components- Conductor, Support, Insulator, Cross arm, Stay wire, V-guards, Bordered wire.

Transmission Line Components


Introduction:

  • Transmission and distribution are essential links between generating stations and costumers for transmission of power. 
  • Because of tremendous growth of industries the requirement of power has increases hence it become important that transmission and distribution of power carried out with minimum losses and disturbance. 
  • This is achieved by designing transmission and distribution system effectually, technically, strong and reliable which require low maintenance. 

Main Components Of Overhead Line:

Conductor- Conductors carry current from sending end to receiving end.

Support- Support which may pole or tower keeps the conductor at suitable level above the ground.

Insulator- Insulator which insulate conductor from the ground. 

Cross arm- Cross arm provide support to insulator. 

Stay wire- It is connected to the pole at some angle to resist literal forces or stress.

V-guards- It is provided below  bare overhead line running along or crosses public streets to make the line safe if it should break. 

Bordered wire- It is wrapped on a pole at a height 2.5 m from ground at least for 1 m. This prevents the claiming the to unauthorized person.

Overhead Conductors-

  • The conductor is one of important item of transmission system.  The most of the capital cost is invested for it. 
  • Therefore proper choice of material and size of the conductor it is very important. 
  • The conducting material  is use for transmission and distribution  should have following 
Properties
  • High electric conductivity.
  • High tensile strength in order to with stand mechanical stress. 
  • Low specific gravity so weight of conductor reduce. 
  • Low cost so that it can be use for long distance. 
  • It should be easily available. 
  • Copper Conductor
  • Aluminium Conductor 
  • Stranded Conductor 
  • ACSR Conductor (Aluminium Conductor Steel Reinforced)
  • AAAC Conductor (All Alloy Aluminium Conductor)

Line Support-

Requirement Of Line Support-
  • High mechanical strength to with stand the weight of conductor, insulator and wind.
  • Light in weight but without loss in mechanical strength.
  • It should have longer life.
  • It should be economical.
  • Easy accessibility for maintenance, transportation etc.   
Types of line support-
  • Wooden pole 
  • Steel pole 
  • RCC pole 
  • Steel tower

Insulators-

  • The overhead lines are supported by using different poles or towers 
  • The supporting structure in a such a way that  current from the conductor do not flow to the earth i.e line conductor must be properly insulated from the support this is achieved by securing line conductor from the support with the help of insulator.
Properties of Insulators-

1) It should have high mechanical strength in order to with stand weight of conductor and wind.

2) It should have high electric resistivity to avoid flow of leakage current.

3) It should have high relative permeability. In order to high dielectric strength.

4) The insulator material should be non porous, free from impurity and cracks otherwise permeability will be decreases. 



  • Pin type insulator
  • Suspension type insulator
  • Stay insulator
  • Strain insulator
  • Shackle insulator 
Causes Of Insulation Failure-

1) Poor mechanical strength-
Due to reduction of strength of insulation it may causes to failure.

2) Porosity-
The material used for insulator are made up of porcelain, glass such a materials has porosity property due to this it can be absorb moisture from atmosphere.

3)Internal Impurity- 
Due to this breakdown strength may get reduced of insulator.

4) Ageing-
Continues operation of insulator for long time periods may causes to increase flow of leakage current.

5)Lightning- 
Due to lightning extra high voltage is appear across transmission  line if such voltage is more than its dielectric strength of insulator it may be permanently failed.

6) Uneven expansion and contraction- 
Insulator are manufactured by using different materials the coefficient of expansion and contraction is different due to this there will be possibility of cracking of insulator.

7) Wrong selection-
If 11Kv insulator are used for 22Kv or more then it cause to damage the insulator therefore insulator should be select according to voltage capacity.

8) Rough handling-
Due to rough handling of insulators during transportation and erection of line etc.



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