What is the purpose of ground wires in overhead transmission system?

In electrical power system, long distance high voltage 3-phase power transmission requires large transmission towers and transmission lines. These Transmission lines take 3-phase power from generating station to grid.

But have you ever noticed that other than these phase wires, there is also a thin wire connected at top of transmission towers. The thin wire is called the ground wire. In this post we will discuss that what is the purpose of ground wires in overhead transmission system? And Ground wires are made up of which material?

Construction and purpose of Ground wires

The Ground wire is also called shield wire, static wire or overhead earth wire.

Ground wires are bare conductors supported at the top of transmission towers and solidly connected to the ground at each tower.

What is the purpose of ground wires?

The ground wire or shield wire gives protection to the current carrying conductors. They provide protection against lightning stroke.

When lightning occurs then they serve to shield the line and intercepts the stroke before it hits the current carrying conductor below them.

Ground wires do not carry any current and that is why they often made up of galvanized steel which has good mechanical strength.

For single circuit tower, there is only one ground wire but for double circuit towers, there are two ground wires as shown in the figure below.

In power system, ground wire is provided in overhead transmission lines having voltages of 110kV, 132kV or above.

Sometimes, the ground wires are also used as communication lines and they carry signals also.

Note: Do not misunderstand the ground wire with neutral wire, because high voltage transmission system does not carry any neutral wire. Ground wires are merely connected just to protect phase wires from lightning strokes.

I hope I have given sufficient explanation to the question “what is the purpose of ground wires in overhead transmission system?”

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