This objective can be achieved only if the transmission and distribution system is so designed and constructed that it is an efficient, technically sound and reliable system.
The line should have sufficient current-carrying capacity so as to transmit the required power over a given distance without an excessive voltage drop and overheating.
The line losses should be small and insulation of the line should be adequate to cope with the system voltage. The line should have sufficient mechanical strength to cope with the worst probable (not worst possible)* weather conditions and provide satisfactory service over a long period of time without the necessity of too much maintenance.
The main components of an overhead line are enlisted, as below
1. Supports. Poles or towers depending upon the working voltage and the region where these are used. The function of the line support is obviously to support the conductors so as to keep them at a suitable level above the ground.
2. Cross arms and Clamps. These are either of wood or steel angle section and are used on pole structures to support the insulators and conductors.
3. Insulators. Pin, strain or suspension types, as the case may be, for supporting the conductors and taking strainer suspending the conductors respectively.
4. Conductors. Copper, aluminium or ACSR or of any other composition depending upon the current to be carried and the span of the line.
5. Guys and Stays. Braces or cables are fastened to the pole at the termination or angle poles to resist lateral forces.
6. Lightning Arrestors to discharge excessive voltages built upon the line, to earth, due to lightning.
7. Fuses and Isolating Switches to isolate different parts of the overhead system.
8. Continuous Earth Wire is run on the top of the towers to protect the line against lightning discharges.
9. Vee Guards are often provided below bare overhead lines running along or across public streets to make the line safe if it should break.
10. Guard Wires are provided above or below power lines while crossing telephone or telegraph lines. The guard wires and steel structures are solidly connected to the earth.
11. Phase Plates in order to distinguish the various phases.
12. Bird Guards. A stick of ebonite with a rounded top is fixed near the insulator on the cross arm to prevent flashover due to birds pecking on the conductors (on lines with pin insulators).
13. Danger Plate. It is provided on each pole, as a warning measure indicating the working voltage of the line and the word “danger". It is provided at a height of 2.5 m from the ground.
14. Barbed Wire. Barbed wire is wrapped on a pole at a height of about 2.5 m from the ground for at least 1 metre. This prevents climbing by unauthorized persons.
15. Miscellaneous Items such as vibration-dampers, top hampers, beads for jumpers etc.