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Main Components of Overhead Transmission and distribution lines

Main components of overhead Transmission lines

The main Components of an overhead Transmission line are enlisted, as below: 



Overhead Transmission line
Overhead Transmission line


Supports :- 

Poles or towers depending upon the Working Voltage and the region Where these are used. The function of the line Support is obviously so Support the conductors so as to keep them at suitable level above the ground.

Cross arms and clamps :- 

These are eighter of wood or steel angle section and are used on pole structures to Support the Insulators and Conductors.

Insulators :- 

Pin, strain or suspension types, as the case may be, for supporting the Conductors and taking strain or suspending the Conductors respectively. 

Conductors :

Cooper, aluminum or ACSR or of any other composition depending upon the current to be carried and the span of the line.

Guys and stays :- 

Braces or cables are fastened to the pole at the termination or angle poles to resist lateral forces.

Lighting Arrestors :-

Lighting arrestors To discharge excessive Voltages built upon the line, to earth, due to lighting.

Fuses and isolating switches :-

Fuses and isolating switches to isolate different parts of the overhead System.

Continuous Earth wire :- 

Is run on the top of the towers to protect the line against lightning discharges.

Vee- Guards :- 

Vee - Guards are often provide below bare overhead lines running along and across public streets to make the line safe if it should break.

Guards Wires :- 

Guards wires are provided above or below power lines while crossing telephone or telegraph lines. The guard wires and steel structure are solidly Connected to earth.

Phase plates :- 

Phase plates in order to distinguish the various phases.

Bird guards :-

A Stick of ebonite with rounded top is fixed near the Insulator on the cross arm to prevent flash - over due to birds pecking on the Conductors (on lines with pin Insulators). 

Danger plate :- 

It is provided to each pole, as a warning measure indicating the working Voltage of the line and the word "danger". It is provided at a height of 2.5m from the ground.

Barbed wire :- 

Barbed wire is wrapped on a pole at a height of about 2.5m from the ground for At least 1 meter. This prevents climbing by unauthorized persons.

Miscellaneous items :- 

Such as Vibration dampers, top hampers, beads for jumpers etc. 


Points to be Considered at the time of erection of overhead Transmission lines


1. Continuous ground wire Earthed at the substations should be provided. Every 4th span of the pole and first and last pole should be properly earthed and wires should be joined properly to the continuous Earth wire.

2. The clearance of Conductor from the ground and adjoining should be according to IER 77, 78, 79 and 80.

3. All metallic parts, Line components (except the main line Conductor) should be Earthed properly according to IER 90. 

4. Permissible spacing between the Conductors should be maintained throughout the lines. 

5. Anti - climbing device and danger plate
( or caution notice ) should be fixed on each pole.

6. One - sixth on the pole length should be properly buried and rammed in the soil.

7. The joints of the conductor should be mechanically Strong and in proper sleeves.

8. The conductor should be tightened on the Insulator properly with binding wires.

9. Guard wire should be provided where essential.

10. Pole steps should be provided in the towers for the lineman to climb the pole.

11. Proper jumper should be used whenever Required.

The points to be kept in view in the design of an overhead line are... 

1) The line should be able to meet desired load demands Efficiently.

2) The line should be able to withstand adverse Atmospheric conditions.

3) The Voltage drop along the lines should be within prescribed limits (IER 54).

4) The cost of the overhead line should be tolerable.

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