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Which of the following grounding methods is used to reduce the tower footing resistance where earth resistance is low?
Single driven rod
Multiple rod
Counterpoise
Plates
Single driven rod
In areas where the soil resistivity is naturally low, a single driven rod is the most efficient and cost-effective method to provide a low-impedance path to the earth for transmission tower footings. It minimizes material usage while providing sufficient contact with the conductive soil layer.
In areas where the soil resistivity is naturally low, a single driven rod is the most efficient and cost-effective method to provide a low-impedance path to the earth for transmission tower footings. It minimizes material usage while providing sufficient contact with the conductive soil layer.
R=2╧АL╧БтАЛln(d4LтАЛ) тАФ Resistance of a single vertical driven rod of length L and diameter d in soil with resistivity ╧Б
The grounding electrode acts as a low-resistance path for fault currents and lightning surges to dissipate into the earth. When soil resistivity (╧Б) is low, the resistance of a vertical rod is inversely proportional to the soil resistivity and length of the rod. By driving a single rod, we create a direct connection to the moisture-rich soil, ensuring efficient discharge.
Grounding is essential for personnel safety and equipment protection against transient overvoltages.
Soil resistivity varies significantly with moisture, temperature, and mineral content.
A single rod is sufficient in low resistivity soil; however, counterpoise wires are preferred in high resistivity soil or rocky terrain.
Low installation cost
Minimal excavation required
High structural simplicity
Ineffective in high soil resistivity environments
Prone to corrosion over long periods
Limited current discharge capacity compared to counterpoise systems
Transmission line tower footings in conductive clay or loam
Distribution pole grounding
Telecommunication mast earthing
Counterpoise systems (Option C) are specifically used in high-resistance soil to provide a large surface area contact, whereas single rods are sufficient for low-resistance scenarios.
For lightning protection, the grounding resistance is ideally maintained below 10тБ╗┬▓тБ░ ohms.
A is correct тАФ A single driven rod provides an adequate, economical low-impedance ground path when the surrounding soil resistivity is already inherently low.
Always relate grounding method selection to the soil resistivity (╧Б); low ╧Б favors simple rods, while high ╧Б necessitates extensive counterpoise or chemical electrodes.