Why in the Overhead Transmission Lines, the Ground Wire is above the Phase Line?

Why in the Overhead Transmission Lines, the Ground Wire is above the Phase Line?

The ground wire, sometimes referred to as the shield wire, guard wire, or earth wire, is positioned above the phase conductors and the wires that carry the electrical current - in overhead transmission lines for a number of significant reasons:

  • Lightning Protection
  • Shielding Effect
  • Electrostatic Charge Dissipation
  • Mechanical Protection
  • Grounding Reference

Lightning Protection

The ground wire’s main function is to create a low-resistance path that allows lightning strikes to safely travel to the earth. Since the ground wire is the highest point in this scenario, lightning usually strikes it there. The ground wire keeps lightning from striking and harming phase conductors, insulators, (or) supporting towers by providing a direct passage to the ground.

Shielding Effect

When adjacent lightning strikes (or) other electromagnetic disturbances occur, the ground wire serves as a shield against induced voltages and currents. It lessens the possibility of insulation failure or flashovers by minimizing the electromagnetic coupling across the phase conductors & surrounding objects.

Electrostatic Charge Dissipation

In the case that electrical phenomena or environmental conditions cause electrostatic charges to accumulate on phase conductors (or) supporting structures, the ground wire facilitates in their dissipation. By doing this, high voltage accumulation that can cause arcing or insulation failure is avoided.

Mechanical Protection

In particular conditions, the ground wire can also act as a mechanical barrier, assisting in shielding the phase conductors from unintentional contact with foreign objects like trees or airplanes or falling objects.

Grounding Reference

The ground wire serves as a point of reference for the transmission line’s grounding system, enabling the correct operation of protective relays & other devices meant to identify abnormalities or failures.

The ground wire must be positioned above the phase conductors in order to accomplish these objectives. By positioning it to be the highest point in the transmission line design, it maximizes shielding for the phase conductors below and increases its likelihood of being struck by lightning.

To properly dissipate any currents or charges to the earth, it is crucial to ensure that the ground wire is firmly grounded at regular intervals along the transmission line route. Typically, this is done by grounding rods or counterpoise devices.