Transmission Tower Earthing Design for Lightning Condition in Malaysia’s Power Grid

The transmission tower earthing design is installed under the ground to protect nearby personnel and equipment, as well as to improve the line lightning performance. The previous tower earthing design in Malaysia’s grid system was tailored for normal power frequency fault, which are low-frequency in nature. This tower earthing design was not suitable during lightning fault, which is of higher frequency. The previous earthing design practice involves installing radial counterpoises up to 120 meters horizontally from each tower legs to get the tower footing resistance (TFR) reading of 10 Ω or less. This practice is proven to be ineffective in lowering the resistance at higher frequency i.e. lightning strike. This paper discusses a new compact earthing design that has low impedance value at low and high-frequency. The performance of this new earthing design were simulated at various soil resistivity values over a frequency range, and were compared to the performance of previous tower earthing design. The new earthing design were also installed on a number 500kV, 275kV and 132kV towers and their TFR were measured using both low and high-frequency TFR meters. The proposed concentrated earthing design was shown to have low impedance value at both low and high-frequency domain.

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