Basic Electrical Engineering

Overhead line transmission – Main components used in overhead lines, Transmission line conductors, Properties of conductors

Overhead line transmission

The overhead lines are used to transmit electricity from power plants to consumers. A network of electrical power lines are used to transmit the electricity over a geographic area is called power grid.

Main components used in overhead lines

i. Electric conductors

ii. Poles and towers

iii. Insulators

iv. Cross arm that holds electrical insulation materials

v. Transformer, lightning arrester, blocking barriers to the pole, and circuit breakers

Transmission line conductors

Electric power is transmitted from power plant to the load (consumers) through conductors. Copper, aluminum, steel, Aluminum Conductor with Steel Reinforced (ACSR), and cadmium copper are invariably used for transmission line conductors.

Properties of conductors

i. High electrical conductivity

ii. High tensile strength

iii. Low cost

iv. Less weight

The properties of copper and aluminium conductors are discussed below.

a) Copper

Copper is used to transmit large quantity of electricity from one place to another. Hard-drawn copper is often used for power transmission, because it is twice as strong as soft drawn copper. Hard drawn has a high conductivity. Lesser cross-sectional area of conductor is reduced, because the current density of copper is high. It has low specific resistance. Its life is very long.

b) Aluminium

Aluminium conductor is next to copper in its conductivity. It is cheaper than copper and lighter in weight. But conductivity of aluminium is 60% as that of copper. Its diameter is about 1.27 times thicker than that of copper. The melting point of aluminium conductor is less. Hence it creates short circuit.

c)ACSR (Aluminium Conductor with Steel Reinforced)

An aluminium conductor having a central core of galvanized steel wires is used for high voltage transmission purposes. This conductor is mostly used for power transmission because, it has less sag and high tensile strength of steel and conductivity of aluminium.

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