Method Research Of Arrangement Mode Of Spark Thorn To Reducing Impulse Ground Impedance Of Line Structures

In order to effectively reduce impulse ground impedance of the tower,this paper put forward to the calculation method of impulse ground impedance considering the effect of spark thorn,By changing the partial structure of line tower grounding device,A variety of grounding models with spark thorn structures are established for simulation calculation,and the influence of the installation Angle,branch position and number of spark thorn arrangement on impulse ground impedance is analyzed.The simulation results show that the addition of needle-like short conductor can effectively reduce the impulse ground impedance and realize the effective suppression of the impulse ground impedance of the tower ground network.(1)In this paper,the impact characteristics of the grounding resistance are analyzed,and the equivalent model of grounding body discharging is obtained.Based on this equivalent model,the simulation model of the impulse ground impedance is established,and the calculation method of the impulse ground impedance considering the spark effect is obtained by using the radius iteration method.The simulation results show that if the spark effect is not taken into account,the calculation error of impact grounding resistance is significantly large.Therefore,it is necessary to consider spark effect in the calculation of impulse ground impedance.(2)The effects of soil resistivity,grounding material length and lightning current amplitude on the impulse ground impedance of line structures were discussed respectively.Firstly,the higher the resistivity of soil is,the more obvious improvement effect of spark discharge effect of grounding material on impact grounding impedance.Secondly,the impulse ground impedance of single elongated grounding material has a saturation value,so there is an effective length under different soil resistivity for different single elongated grounding materials.When the saturation value of grounding material is reached,the effect of spark discharge is lower than the inductance effect,and with the increase of grounding material,the effect of spark effect is weakened.Finally,with the increase of amplitude of impulse current,the impact of spark discharge effect is greater than that of inductance effect,and the impulse ground impedance of grounding materials decreases with the increase of the amplitude of impulse current.(3)The effect of adding spark thorn on reducing the impulse ground impedance is discussed.The simulation results show that adding spark thorn can effectively enhance the spark effect and reduce the impulse ground impedance.When a needle-like short grounding element is added on the unilateral side of the horizontal grounding element,the best resistance reduction effect is achieved by adding a short grounding element at the position of d=6m to 27.22%.Moreover,the best resistance reduction effect is achieved by adding a needle-like short grounding element with the length of 6m,which reaches 26.23%;besides,the best resistance reduction effect can be achieved by adding a short needle-shaped element at the current injection end when added at both sides of the horizontal earthing body.The effect of resistance reduction reached 19.85%,and the longer the length of bilateral needle-like short element was added,the better the effect of resistance was reduced.When tree-shaped spark spurs were added to the end of a single vertical grounding element,the resistance reduction effect of impulse ground impedance showed a trend of fluctuation with the increase of branching Angle.When the branching Angle was α=60°,adding short grounding element had the best resistance reduction effect,and the resistance reduction effect reached 20.82%.At the same time,the reduction effect becomes more and more obvious with the increase of the length of the tree-shaped spark thorn.