Why is the Ground Wire Always Positioned Above the Overhead Power Lines?

Ground Wire in Overhead Transmission Lines

The ground wire (also called earth wire or OPGW) installed above phase lines in overhead transmission lines acts as a key protective and safety component. It provides lightning protection, ground fault defense, and helps prevent electrical system disruptions.

In overhead transmission lines, positioning the ground wire above phase lines serves specific safety and performance purposes. Referred to as a "shield wire" or "static wire," this configuration has several critical functions:

1. Lightning Protection

The primary role of installing ground wires above phase conductors in overhead transmission lines is to shield the system from lightning strikes. Lightning, a natural phenomenon, often targets tall structures like transmission towers. By positioning the earth wire above the phase lines, it acts as a physical barrier to intercept lightning and safely channel its high-energy currents to the ground through tower grounding systems. This mechanism diverts lightning away from phase conductors, significantly reducing the risk of equipment damage or power outages caused by transient overvoltages.

2. Ground Fault Protection

Ground wires, which are periodically grounded along the line, maintain electrical system integrity by providing a low-resistance fault current path. During ground faults (e.g., phase conductors contacting towers or vegetation), this configuration quickly diverts fault currents to the ground, enabling protective relays to detect and clear faults faster. By minimizing the impedance of the return path, the overhead ground wire reduces the likelihood of phase-to-ground faults that could disrupt grid stability.

3. Wildlife Contact Prevention

Overhead lines face risks from wildlife interfering with conductors. The elevated ground wire acts as a physical deterrent for birds and other animals, discouraging them from landing on or perching above phase lines. This reduces the probability of faults caused by animal contact—such as short circuits from birds spanning phase conductors or squirrels climbing towers—thereby improving system reliability.

4. Visual Marking for Aviation Safety

Ground wires, often painted in bright, high-visibility colors, serve as critical visual markers for aircraft. This feature helps pilots identify transmission line corridors, particularly in low-visibility conditions, and prevents accidental collisions with overhead infrastructure. In regions with frequent air traffic, such as urban areas or near airports, this function is essential for ensuring both aviation safety and uninterrupted power supply.

5. Dual Function as Optical Ground Wire (OPGW)

Notably, modern ground wires often integrate optical fiber technology, forming an Optical Ground Wire (OPGW). This composite structure serves a dual purpose:

Communication: The embedded optical fibers enable high-speed data transmission for SCADA systems, remote monitoring, and grid automation.
Grounding: The metallic structure maintains its role as a lightning protection and fault current conductor.

Conclusion

In Vietnam’s 220kV and 500kV networks, OPGW has become standard, allowing real-time grid management while enhancing lightning resilience in overhead lines spanning mountainous or thunderstorm-prone regions.

The strategic placement of ground wires above phase conductors in overhead transmission lines embodies a blend of safety, reliability, and technological innovation. From shielding against lightning and fault currents to enabling smart grid communications, these components are indispensable for modern power systems—especially in countries like Vietnam, where diverse topography and climatic conditions demand robust overhead line designs. As grids evolve toward smarter infrastructure, OPGW will continue to integrate protection and connectivity, driving the next generation of resilient power distribution.