Method of Tower Grounding | Electrical Transmission Line

What is the purpose of a tower grounding?

Not only is tower grounding, but it is also fundamental and essential in an electrical system for both the safety and reliability of the system. 

The most important part of grounding is to protect people, structures, and equipment since damage can cause outages or malfunction and result in economic losses of great value. 

The installation of a proper grounding must ensure a safe and controlled power flow with minimum losses. A perfect grounding of a system also limits the voltage stress on cables and equipment and extends the lifetime of the installations.

What Should be the Tower Grounding Resistance?

Tower grounding is used to reduce earth wire potential and stress on insulators at the time of stroke, and also for safety.

Typically, tower grounding resistance needs to be maintained as follows:

1. Tower footing resistance will be 10Ω and should not be more than 20 Ω under any condition throughout the year.
2. Earth resistance depends upon soil resistivity (generally 100 Ω-m).

The tower grounding resistance of a ground electrode depends on the resistance of-

1. electrode material;
2. the contact resistance of the electrode to the soil;
3. The resistivity of the soil.

Soil resistivity is defined as the resistivity of a 1 m3 sized cube between the two opposite sides and is measured in ohmmeter or ohm centimetres. 

Tower Ground Resistance Good Value

For transmission towers, a good ground resistance value is typically 1–5 Ω, with ≤1 Ω preferred for substations and lightning protection systems. Values above 5 Ω are generally considered inadequate for reliable safety and fault current dissipation.

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Recommended Ground Resistance Values

Application	Good Value (Ω)	Notes
Transmission substations	≤1 Ω	Ensures safe fault current dissipation and lightning protection.
Distribution substations	≤5 Ω (ideally 1 Ω)	Acceptable for most utility-grade installations.
Telecom towers	≤5 Ω	Industry standard for central offices and tower grounding.
Lightning arresters	≤1 Ω	Critical for effective surge protection.
General industrial sites	≤5 Ω	Often achievable with parallel rods or grounding grids.

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Key Considerations for Tower Grounding

• Soil resistivity: The most significant factor influencing tower ground resistance. Sandy or rocky soils often yield higher resistance values. 
• Grounding system design: Parallel rods, deep-driven rods, counterpoise conductors, and buried plates can reduce resistance.
• Tower footing resistance: Impacts fault current distribution and relay protection sensitivity. High footing resistance can reduce fault current detection reliability. 
• Maintenance: Corrosion, soil drying, and mechanical damage can increase resistance over time. Regular testing is essential.

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Practical Guidelines for Site

• Target ≤5 Ω for transmission towers, but strive for ≤1 Ω where lightning protection is critical.
• Soil in Dhaka (clay-rich, high moisture) generally allows lower resistance values, making ≤1 Ω achievable with proper grounding grids.
• Recommended practices:
  • Use multiple ground rods in parallel.
  • Apply soil treatment (bentonite, conductive concrete) to reduce resistivity.
  • Connect tower steel reinforcement to the grounding system for added conductivity.

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Risks of Poor Tower Ground Resistance

• High resistance (>10 Ω) can cause:
  • Ineffective lightning dissipation → equipment damage.
  • Reduced fault current detection → relay misoperation.
  • Increased risk of step and touch potential hazards for personnel.

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What is the Method of Tower Grounding?

In tower grounding, different methods are used for connection to the ground depending on the facility and its function, but all connections are called ground electrodes.

Buried Conductor

One or more conductors are connected to tower lags and buried in a backfilled tower foundation. Buried conductor-type tower grounding is used where the soil resistivity is low.

Counterpoise Wire

A length of wire or a strip of around 50m is buried horizontally at a depth of around 0.5m below the ground, and this wire is connected to tower legs. Counterpoise wire tower grounding is used when earth resistance is very high and soil conductivity is

mostly confined to the upper layer.

Rod Pipe
A pipe or Rod of around 3 to 4 m is driven into the ground near the tower, and the top of the rod is connected to the tower by a suitable wire or strip. This rod pipe tower grounding is used where ground conductivity increases with the depth of soil.

Treated Earth Pits

Pipes or Rods of around 3 to 4m are buried in treated earth pits, and the top of the rod is connected to a tower by a suitable wire or strip. The treated earth pit-type tower grounding is used in very high resistivity soil near the tower.