Study On Experiments And Simulation On The Current Dispersing And Impulse Grounding Resistance Law Of Tower Grounding Devices

With the deepening of the national UHV and large power grid strategy, it is increasingly serious to protect the overhead transmission lines. The lightning trip-out accident of transmission lines is one of the most common faults in the power system. The impulse current dispersing characteristics and impulse grounding resistance laws of tower grounding devices are different from the power frequency characteristics, which performs more complexly. Therefore, it can't simply use the power frequency characteristics to deduce the impulse characteristics. However, there are little previous literatures which analyze the impulse current dispersing characteristics and the regulations of impulse grounding resistance combined with current dispersing characteristics on the grounding devices.After summing up the theoretical analysis and experimental research in the impulse grounding characteristics of domestic and foreign researchers, a simulation test circuit is designed and built in this paper in the laboratory. The impulse current dispersing characteristics and the regulations of impulse grounding resistance of several typical tower grounding devices under various different factors comprehensively are analyzed via a similar principle. And then, based on the finite element method, this paper simulates and analyzes several typical tower grounding devices which considers the soil non-linear properties and soil ionization breakdown dynamics characteristic at high amplitude value and high frequency of the lightning current Thus, the contents of this paper are as follows:1?A simulation test circuit is built based on the similar principle. Many experiments on several typical grounding devices are done, from which axial current waveforms through a plurality of Rogowski coils at different positions of various grounding devices are measured. The influences of grounding device structure types, the amplitudes of the impulse current, different impulse current injection points and the number of injection points on impulse dispersing characteristics of grounding devices are analyzed in this paper.2?During the simulation test, the waveforms of impulse current and the potential around the injection point at different current amplitudes and ways of current injecting onseveral typical grounding devices are measured, and then the impulse grounding resistances are acquired. The regulation of impulse grounding resistance is analyzed theoretically combined with the impulse current dispersing characteristics.3?In the finite element simulation software calculation, the soil conductivity value is set as a function expression of the soil electric field strength, taking a full account of the soil nonlinear characteristics and ionization breakdown dynamic characteristics, which can make the simulation more in line with the actual process and optimize the simulation results.With this calculation method, a horizontal single grounding electrode whose current is injected from different locations is taken into consideration. By analyzing the current density, potential, soil field strength and other physical quantities on the grounding electrode, we find the end effect in the process of impulse current dispersing into the soil intuitively. The electrode structure also has an influence on the efficiency of the current diffusion similarly.In this paper, the simulation test research and finite element simulation method are used to explore the impulse characteristics of the transmission line tower grounding devices.These results are of important practical significance for the optimization and improvement of grounding devices, reducing the impulse grounding resistance and improving the lightning withstand level of the transmission lines.