Study On Impulse Characteristics While Lightning Strikes The Transmission Tower And Grounding Experiment For Dispersed Current

It is a complex transient process that lightning current flows through the grounding device in the ground.On the one hand,the impulse characteristics of the grounding device directly determine its lightning protection performance,and the dynamic ionization process of the soil is an important factor affecting the impulse characteristics of the grounding device;on the other hand,the complex diffuse environment caused by the lightning dispersing in the ground will also bring hidden dangers to the safety of people,equipment and organisms around the grounding device.Therefore,it is urgent to carry out related researches about impulse characteristics of the tower grounding device and dispersed current in the ground.In this paper,a test platform for soil impulse characteristics is firstly established,and the dynamic ionization process of soil is studied by using parallel plate electrodes and concentric hemispherical electrodes.The test results show that the critical breakdown field strengths of different types of soils are different,and the soil with larger particles is more prone to spark effect;the critical breakdown field strength of soil decreases with the increase of water content,and the smaller the soil particle size is,the smaller the impulse resistivity will be affected by water content;in addition,the electrical properties of the soil will change after impulse lightning,and the change in electrical properties can be recovered,but the recovery speed is different.Then,a calculation model of impulse grounding parameters considering the ring return electrode is established and solved by the self-written program.The influence of ring return electrode on field impulse test is studied and appropriate layout of ring return electrode is determined efficiently quickly in the test planning stage.The results show that the existence of the ring return electrode actually reduces the potential rise of the grounding device and causes the current density near the return electrode to be distorted.The compensation of the potential rise of the grounding device can be realized by calculating the compensation coefficient k corresponding to the radius of the ring return electrode.By calculating the maximum effective measurement distance d at different reference error rates?₀,the optimal radius of the return electrode can be determined,and the influence of the current density distortion caused by the ring return electrode can be reduced.Subsequently,the divergence acquisition module with a flat-type structure is designed and the ground dispersed current measurement system is developed,which effectively captures and measures the dispersed current in the ground.Finally,a field test scheme is designed,and the suitable radius of the ring return electrode,the potential compensation coefficient and the size of the divergence acquisition module are determined according to the test target.The field test is carried out in a 220 kV transmission line tower.The relative error of the field test results is less than 10%,which can be used to guide the optimization design and protection transformation of the grounding device.