Why High-Voltage Cables (220 kV and Above) Are on Towers, Not Underground

 Why High-Voltage Cables (220 kV and Above) Are on Towers, Not Underground

High-voltage transmission towers and lines near Celilo Converter Station, Oregon. Image by Stefan Andrej Shambora, licensed under CC BY 2.0.

When you look around cities and highways, you’ll often notice tall towers carrying thick electricity cables across long distances. These are high-voltage transmission lines, usually 220 kV and above. A common question people ask is: why don’t we just put them underground like regular power cables?

The answer comes down to safety, cost, and practicality.

1. Safety and Insulation

High-voltage electricity needs very strong insulation to prevent leakage and accidents. For smaller cables (like the ones powering your home), underground insulation is easy and affordable. But for 220 kV or 400 kV lines, the insulation would need to be massive and extremely costly. Towers keep these lines high above the ground, naturally ensuring safety.

2. Heat Dissipation

Whenever electricity flows, it generates heat. Overhead cables can release this heat into the open air. Underground, the soil traps heat, which can overheat the cable. To prevent this, buried high-voltage lines would need special cooling systems, making them more complicated and expensive.

3. Cost of Installation

Building transmission towers may look expensive, but it’s actually much cheaper than digging hundreds of kilometers of trenches, adding insulation, and protecting underground cables from water and damage. For high voltages, overhead lines are far more economical.

4. Maintenance and Repair

If an overhead line breaks during a storm, engineers can quickly locate the problem and fix it. With underground cables, finding the fault is difficult, and repairs take much longer and cost much more. That’s a big reason why power companies avoid burying such high-voltage lines.

5. Terrain and Flexibility

Overhead towers can easily cross rivers, mountains, highways, and farmland. Underground cables, on the other hand, require continuous trenches, which can be nearly impossible in certain terrains.

What About Lower Voltage Cables?

For smaller voltages like 11 kV or 33 kV (used within cities), cables are often buried underground. That’s because:

They’re safer for people and animals in crowded areas.

They don’t need as much insulation as very high voltages.

They are easier to manage in short distances within urban areas.

Conclusion

Overhead towers may not look pretty, but they are the safest, cheapest, and most practical way to carry massive amounts of electricity across long distances. Underground systems work well for lower voltages in cities, but for 220 kV and above, towers will continue to be the preferred solution.