Research on cylinder Flexible Graphite Earth Electrode (FGEE) used to reduce tower earth resistance

Abstract The excellent performance of earth electrodes is the key to stable and safe operation of transmission lines. However, corroded earth electrodes in practical cases can increase the tower earth resistance. In this paper new Flexible Graphite Earth Electrodes (FGEE) are introduced to address the corrosion problem and its new wrapping method is proposed to reduce the tower earth resistance. The proposed earth resistance reduction method is effective by theoretical analyses. Lots of simulation work is conducted to analyze the effect of factors on both single-pile and multi-pile tower earth resistance. Comparisons are conducted on five commonly used types of tower earth-electrode network, including sole tower foundation, tower foundation with ring earth conductor or FGEE, tower foundation with both ring earth conductor and FGEE, and tower foundation with ring earth conductor and horizontal radial electrode of 20 m on four directions.. Besides, grounding tests on scaled foundation earth electrodes are carried out to verify the validity of the proposed method. Simulation results show that the tower earth resistance is reduced by 15~60% in 500~3000 Ω•m soil. For single-pile tower foundation, the lower the wrapping position, the smaller the earth resistance, and the earth resistance is negatively related to the wrapping radius, while down lead wire connection types have little influence on earth resistance; besides, all the three factors above have impacts on current density. For multi-pile tower foundation, earth resistance is negatively related to the distance between two piles and separate wrapping is a preferred type of wrapping. Moreover, among the proposed five commonly used grounding types, Type V is preferred. Finally, scaled laboratory test results indicate that the cylinder FGEE can effectively reduce the tower earth resistance.