Research On Lightning Characteristic Of Transmission Tower And Resistance Reduction Effect Of Grounding Device

Lightning protection level is a key factor to influence the operation safety and reliability of transmission line. On the one hand, the lightning may lead to high step voltage and touch voltage on the ground which could endanger personal safety. On the other hand, the grounding device with high resistance may cause lightning counterattack and line tripping.In order to study the transient electromagnetic characteristic of transmission tower after being struck by lightning, we are based on the CDEGS software, researching on the modeling method of lightning current and the distribution of electric field and magnetic field on the ground. Further, combined with MATLAB software, we analyse the variation between the grounding device, amplitude of lightning current, soil resistivity and the maximum step voltage on the ground and the maximum contact voltage at the bottom of the tower. Finally, we discuss the safety of tower being struck by lightning.In order to study the resistance reduction effect of grounding device in different types of soil, we choose three kinds of soil types which are homogeneous type, horizontal layered type and vertical layered type. Then, we establish horizontal epitaxial and vertical and horizontal grounding device models and calculate the resistance reduction effect of extending the length of radiation lead wire, changing the number of vertical grounding body, adjusting the direction of radiation lead wire and other measures. Results show that in homogeneous soil with high resistivity, the grounding resistance decreases as the length of radiation lead wire increases. While the length reaches a certain value, the trend of decreasing is slower and the resistance reducing effect tends to saturation; In the soil type which has high resistivity in upper layer of soil and low resistivity in lower layer of soil, the resistance reduction effect of adding vertical grounding body is obvious; In vertical layered soil, the grounding resistance can be effectively reduced by adjusting the direction of radiation lead wire of grounding device reasonably.Finally, combined with the actual data of 220kV Jin-dong A line and the knowledge of the structure of grounding device and soil layered structure of transmission tower, we can calculate the grounding resistance of tower and put forward reasonable improvement measures by the results of simulation and the actual situation of transmission line. The results show that no matter how complex the tower structure of soil is, the grounding device can be calculated and set with better resistance reduction effect by using CDEGS simulation platform and we can put forward reasonable design and retrofit scheme of grounding device. The research has higher engineering practical value.