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For reducing tower footing resistance it is better to use
Chemical and ground rods only
Chemical and counterpoise only
Ground rod and counterpoise only
Chemical, ground rods and counterpoise
Ground rod and counterpoise only
Tower footing resistance refers to the resistance offered by the grounding system of a transmission tower to the flow of lightning or fault current into the earth. Reducing this resistance is critical for preventing flashovers during lightning strikes and is effectively achieved by using ground rods and counterpoise wires to increase the contact surface area with the soil.
Tower footing resistance refers to the resistance offered by the grounding system of a transmission tower to the flow of lightning or fault current into the earth. Reducing this resistance is critical for preventing flashovers during lightning strikes and is effectively achieved by using ground rods and counterpoise wires to increase the contact surface area with the soil.
R=╧БALтАЛ тАФ Basic resistance formula where reducing resistivity or increasing cross-sectional area lowers resistance
ZimpulseтАЛ<RstaticтАЛ тАФ Impulse impedance is typically lower than static resistance due to soil ionization at high current densities
A ground rod provides a low-resistance path to deeper, moister soil layers. A counterpoise, which consists of one or more buried wires connected to the tower base and extending radially, increases the effective area of the grounding electrode system. Together, they lower the impulse impedance of the tower footing, dissipating transient surges more effectively into the ground.
Grounding is essential to maintain tower potential near earth potential during surges.
Counterpoise wires are highly effective in high-resistivity soil conditions (e.g., rocky or sandy soil).
Chemical grounding is used in specific high-resistance scenarios but requires maintenance, unlike rods and counterpoise.
IS codes typically recommend a maximum footing resistance of 10┬а╬й for transmission lines.
Lowering impulse impedance reduces the probability of back-flashover across insulators.
Counterpoise provides a distributed ground path, improving transient current dissipation.
High initial installation cost for long counterpoise conductors.
Corrosion of buried copper or galvanized steel components over time.
EHV and UHV transmission line towers.
Substation grounding grids.
Communication tower grounding.
Option D is often technically viable, but 'Chemical' rods require periodic refilling of electrolytes, making ground rods and counterpoise the more standard and preferred passive combination for permanent tower footing applications.
Soil resistivity (╧Б) is the dominant factor in footing resistance.
C is correct тАФ Ground rods and counterpoise wires are the standard, maintenance-free, and effective combination for reducing the impulse impedance of transmission tower footings.
Always remember that during lightning strikes, the impulse impedance is more relevant than the low-frequency static resistance measured by a standard earth tester.