| Nowadays,transmission lines span a wide range of areas,and towers are often erected in plains,mountains,lakes and plateaus.The complex terrain will affect the laying of the extension lead.In the strong acid and alkali area,the extension lead is also prone to fracture due to natural corrosion and external force.When the transmission line tower is struck by lightning,it will affect the safe and stable operation of the power system.The reliability and effectiveness of transmission line tower grounding electrode play an important role in improving the lightning withstand level of transmission lines and reducing lightning accidents.Therefore,this paper proposes a suspended grounding method for the transmission line tower grounding electrode near the road,the extension fracture and the steep slope,so as to improve the structure of the extension lead under special circumstances.The main research contents are as follows :(1)The calculation model of transmission line tower grounding electrode under the condition of horizontal and slope soil is established,and the influence of the length,direction and number of extension leads on grounding resistance,resistance reduction efficiency and leakage current density is calculated and analyzed.The simulation results show that the increase of the extension lead length under the condition of horizontal soil can increase the drag reduction efficiency and reduce the dispersion pressure of the square grounding grid.The four-direction epitaxy has the highest resistance reduction efficiency,and the ground scalar potential is symmetrical.Under the condition of slope soil,the one-way extension should be laid down along the slope,and the four-way extension has better grounding performance when the extension is the same.(2)The model of epitaxial lead crossing the road is established,and the influence of soil resistivity and ground current frequency on the shunt coefficient and step voltage of grounding electrode under different suspended length and suspended position is studied and analyzed.The simulation results show that the peak value of the step voltage of the road surface is reduced after adding the insulation coating.Under different soil resistivity and ground current frequency,the difference of shunt coefficient is about 5% when the suspended length of the epitaxial lead is 5 m and 25 m.The influence of the change of the suspended position on the shunt coefficient is related to the soil resistivity and the frequency of the ground current.When the extension lead is connected to the steel mesh in the road,the step voltage or the affected area of the road surface will be increased.(3)The model of square epitaxial fracture and suspended continuation was established to calculate the grounding characteristics of square epitaxial fracture with different structural factors and environmental factors,and to study the effect of fracture location on grounding resistance before and after suspended continuation.The simulation results show that when the fracture length increases from 0.02 m to 0.1 m,the grounding resistance only increases by 0.042 Ω.The closer the fracture position is to the square grounding grid,the greater the rise rate of grounding resistance is.With the increase of soil resistivity,the ground resistance of the square epitaxial fracture increases linearly.With the increase of the frequency of the ground current,the ground resistance of the square extension with fracture increases but the trend is slow.The shorter the distance between the fracture and the square grounding grid,the better the resistance reduction effect after suspension continuation.(4)The calculation model of extension lead commutation and suspension continuation under the condition of slope soil is established,and the influence of surface soil resistivity and ground current frequency on the grounding characteristics of different suspension length and suspension position is studied and analyzed.The simulation results show that the peak value of stepping voltage near the suspended section will be reduced by 72.38%after adding insulating coating,and the peak value of stepping voltage will be reduced again by 2.18 k V when the flexible graphite grounding material is further used.Under low surface soil resistivity,the change of suspension length and suspension position does not have too much influence on grounding resistance.When the suspension length increases from 5 m to 25 m,the increase of grounding resistance decreases with the increase of ground current frequency.When the number of steep slopes is small,the grounding performance of the suspended one-way downward extension is the best.Based on the actual project,the feasibility of the suspended grounding technology in mountainous areas is verified. |
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