Soil Impulse Current Density Measurement And Influence Of Karst Landform On Current Scattering

The safe operation of the power system is closely related to the tower impulsegrounding resistance. Under the effect of the impulse current, the tower groundingsystem has the spark effect and inductive effect, and the impact of the reduction of thesoil near the grounding electrode on the impulse grounding resistance is significant;therefore, it is necessary to carry out further study of it. However, there is no directstudy of the reduction principle of the soil near the grounding electrode at home andabroad.In view of the above situation, this paper designed a test device based on theimpulse reduction principle of grounding electrode of the current sensor and drainageneedle, measured the current density of the soil near the grounding electrodes ofdifferent structures by using the prepared test platform for impulse reduction principle,and comprehensively analyzed the reduction principle of the soil near the groundingelectrode. According to the characteristics of Karst landform, through the analysis of thereduction principle in the soil with the cavity near the grounding electrode in case oflarge grounding current upon the test, and combined the simulation calculation to putforward the grounding electrode type suitable for the Karst area. Major studyconclusions are reached as follows:â‘ Because of the existence of spark discharge area near the grounding electrodeunder the effect of impulse current96A, the current density of soil about1cm from theground electrode is significantly greater than that outside this area. For the horizontalgrounding electrode of the drainage at the terminal, the ratio of the distance to theboundary of effective reduction area to the length of grounding electrode is0.85. Underthe same conditions, the ratio of the size of the midpoint of the horizontal groundingelectrode of the reduction at the terminal and the reduction area at the end to the lengthof grounding electrode is0.75. When the impulse current amplitude decreases, in thecase that6A current is injected, the ratio of the effective reduction area of the groundingelectrode to the length of grounding electrode is0.65. The ratio of the size of effectivereduction area vertical to the grounding electrode to the length of vertical groundingelectrode is0.7, slightly smaller than that compared with the horizontal groundingelectrode.â‘¡Under the effect of impulse current, the current density of the measuring point of the grounding electrode near the upper surface of the cavity close to the horizontalgrounding electrode is slightly lower than that at the corresponding point on the lowersurface. When the current continues to flow along the surface of cavity from the near tothe distant, the current density on the lower surface decays faster.â‘¢The blocking effect of the big cavity on the reduction in the soil near thegrounding electrode is stronger, reducing the reduction area of grounding electrodelargely. More distant the grounding electrode is, the impact of the cavity on its reductiondistribution is smaller. Under the effect of large-amplitude impulse current, the impactof cavity on reduction of the soil near the grounding electrode is little. It can be found atthe same time that the impact of the cavity on the cross-shaped grounding electrode isminimal, and its grounding resistance is minimal in case of different injected currentamplitudes. Therefore, it is necessary to avoid the simple structure of the groundingdevice when selecting the grounding device in the Karst area, and try to increase theconductor branches as many as possible.