Study On The Characteristics Of The Impact And Dissipation Of The Three-dimensional Tower Grounding Device

In order to ensure the safe operation of the power system equipment,a lower grounding resistance is required during the operation of the system.The main function of transmission line tower grounding is to diffuse and drain the lightning current in the earth after the line is hit by lightning,so as to ensure that the line has a certain level of lightning resistance.Generally speaking,reducing the impulse grounding resistance of transmission lines is the most effective way to improve the lightning resistance level of transmission lines and maintain the safe and stable operation of power grid.In order to ensure the safe and reliable operation of the power system and the personal safety of the power workers,we should study the impact characteristics of the tower grounding device systematically.In the case of geographical location and limited floor area,the three-dimensional tower grounding device with horizontal and vertical common current can better disperse the incoming current caused by short circuit,reduce the impact grounding resistance of the grounding device,so as to ensure the safe and stable operation of the system.However,the effects of different types of three-dimensional tower grounding devices on the characteristics of impulse current are not detailed,which can not effectively guide the grounding design.Based on the theoretical analysis method and experimental study of the impact characteristics of grounding devices at home and abroad,this paper makes clear the three-dimensional tower grounding device with the common flow in the horizontal and vertical directions,and deeply studies the influence of the vertical and horizontal grounding electrodes,the horizontal layered soil and the impact current amplitude on the impact characteristics of the three-dimensional grounding device.Through modeling and simulation analysis,it is concluded that in uniform soil,the impact grounding resistance of three-dimensional grounding device will increase with the increase of soil resistivity;it will decrease with the increase of impact current amplitude and reach saturation;in horizontal layered soil,the impact grounding resistance of three-dimensional tower grounding device basically depends on the upper soil resistivity.By comparing the electric field distribution of the soil around the typical grounding electrode and the three-dimensional grounding electrode under the impact of lightning current,the principle that the three-dimensional tower grounding device reduces the impact grounding resistance by increasing the field strength in the ground,promoting the soil ionization breakdown and expanding the spark discharge is explained.Through the simulation test of the vertical grounding device,the rationality and feasibility of the three-dimensional grounding device are proved.The electromagnetic simulation software CDEGS is used to model two kinds of different grounding devices.The results show that adding different number and length of vertical and horizontal grounding electrodes can significantly change the distribution of impulse current of grounding device,and the three-dimensional grounding device can effectively reduce the impulse grounding resistance of grounding system.In horizontal layered soil,if the resistivity of the underlying soil is low,the advantage of reducing the impact grounding resistance by adding vertical grounding electrode to the three-dimensional tower grounding device will be more obvious.In the project,when the later grounding transformation is carried out,the influence of adding the vertical grounding electrode length should be considered at the place where the leakage current of the grounding device is weak,and then the appropriate number should be added according to the influence range of the corresponding length of the grounding electrode to obtain the best resistance reduction effect.In view of the problems existing in the prefabricated steel barrel pile grounding anchor bolt of steel tube tower,the solution of adding horizontal ray type grounding electrode is given,which provides method guidance for the design of the grounding device of steel tube tower.