| The reliability and effectiveness of the grounding device of the transmission line tower plays an important role in improving the lightning resistance level of the transmission line and reducing lightning accidents.The flexible graphite grounding body is widely used in the grounding project of the transmission line tower to achieve compact grounding,save land resources,and is of great significance to improve the safety margin of the transmission line corridor.With the application of flexible graphite grounding bodies,the corrosion problem of the galvanized steel down conductor and its connection has attracted more and more attention.This paper analyzes the problems encountered by flexible graphite composite grounding materials in the grounding engineering of transmission line towers.The research contents are as follows:(1)Establish a finite element model for the external application of the single-pile concrete pile foundation,calculate and analyze the influence of the external application form,conductor density,and external application length on the grounding characteristics and resistance reduction efficiency of the single-pile foundation.The calculation results show that when the pile foundation height is 9m,when the number of cage-wrapped conductor warps is 4,the resistance-reducing characteristics and the amount of grounding conductor are optimal;when the number of spiral-wrapped turns is 15,the resistance-reducing characteristics and conductors The amount is optimized;for the cast piles in large excavation foundation pits,the spiral wrapping is more material-saving than the cage wrapping.(2)Establish a finite element model for the external application of the four-pile concrete pile foundation,study the grounding characteristics of the four-pile foundation-distance wrapping scheme,take the cage external application and spiral external application in the optimal scheme as the experimental group,and use the best method to reduce the resistance of the existing pole-tower pile foundation.Extensive horizontal epitaxial grounding was used as a control group for comparative analysis.The simulation shows that under the condition of soil resistivity of 50～1200Ω·m,the national standard limit of grounding resistance can be achieved by using short-distance external application;when the soil resistivity exceeds 1200Ω·m,a combination of short-distance external application and horizontal extension is required The grounding resistance can reach the national standard limit.The grounding construction of poles and towers for different soil conditions should be adapted to local conditions.Both schemes effectively save the use of construction land and effectively improve the safety margin of the transmission line corridor.(3)The corrosion problem of the connection between the pole tower galvanized steel ground down conductor and the flexible graphite grounding body is studied by simulation and experiment,and the corresponding anti-corrosion measures are proposed.Using the electrochemical corrosion module in COMSOL Multiphysics,the electrochemical corrosion model of the connection between the pole tower galvanized steel ground down conductor and the flexible graphite grounding body was established,and the electrochemical corrosion strength of the connection before and after the thermoplastic layer was compared and analyzed,and The design test verifies the protective effect of the thermoplastic coating on the joint corrosion.Simulations and tests show that the use of the thermoplastic coating for the ground down conductor of the tower can effectively inhibit the corrosion of the galvanized steel conductor.The research conclusions of this paper can save the area of cultivated land occupied by transmission line corridors,improve the efficiency of tower grounding construction,and reduce the life cycle cost of tower grounding grids,and provide a reference for the design and construction of transmission line tower grounding engineering. |
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