| 35kV transmission line is widely used in urban and rural power distribution grid, located at the end of power distribution, and closely associated with residential electricity. However,judging from the annual national network report of line operation and maintenance, the lightning protection of 35 kV distribution network is the weakest. Lightning withstand level is the base to evaluate the stability and safety of the power transmission line, hence the study on influencing factors of lightning withstand level of 35 kV transmission line, is of great significance. This dissertation will be based on EMTDC/PSCAD electromagnetic transient simulation software to build the simulation model of lightning striking 35 kV transmission line and study on the influence of tower grounding resistance, lossy ground, lightning arrester and other factors on lightning withstand level of the line, in the case of the direct lightning and induction lightning respectively. Taking the earth resistance value of the soil resistivity in the different regions of the eastern and western of China as examples, the corresponding lightning induced overvoltage and the lightning withstand level of transmission lines under different arrester assembly schemes are calculated, to provide effective advice for the assembly density of arresters in the engineering design and construction of transmission line, according to local conditions.Firstly, the structure functions and parameters of transmission line, tower and arrester in the PSCAD electromagnetic transient simulation software's component library is analyzed in this dissertation, and based on the practical application of the device performance, the insulator and direct lightning model lacked in PSCAD software are custom designed. After all the constructions are completed, the effectiveness of the lightning strike line simulation platform is vertified by the known influence of tower grounding resistance on lightning overvoltage amplitude of lines.Secondly, the back stroke modle, electromagnetic field distribution modle and field coupling model are analyed, which were needed in the process of establishing the mathematical model of lightning induced overvoltage, and the mathematical derivation and parameter setting of MTLE, Cooray-Rubinstein and Agrawal model are completed. Then the linear field coupling model is solved by using the first order and two order FDTD algorithm in MATLA. The programming process and the parameters have been made cleared. By interfacing the MATLAB program to PSCAD, the calculation of lightning induced overvoltage is achieved at last.Finally, according to the different soil resistivity range of China, the effect of lossy ground resistance value on tower grounding resistance is analyed. The tower grounding resistance value and the lightning induced overvoltages are selected under there kinds of earthresistivity, and then imported into the lightning strike line simulation platform built in the previous chapter. The different assembly schemes of line arrester are simulated. So the influence of the arrester assembly on lightning withstand level of the transmission line can be studied in this dissertation. |
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