Impulse Grounding Characteristics Of Nonmetallic Grounding Materials Considering Spark Discharge Effect

The long-term effectiveness of power system grounding device is the premise to ensure the safe and stable operation of power equipment,which plays an extremely important role in improving the lightning resistance level of transmission lines and reducing lightning accidents.The grounding devices are mainly made of metal materials such as copper,steel and their alloys.In actual operation,there are often problems such as corrosion,theft and construction difficulties.However,the non-metallic graphite composite grounding material,which has appeared in recent years,is of great significance in saving costs and improving the safe and stable operation of power systems.At present,the impulse grounding characteristics of graphite composite grounding materials have not considered the spark discharge effect,which is still a big error from the real results.This article analyzes the impulse grounding characteristics and application of graphite composite grounding materials.The research contents are as follows:(1)Programming with MATLAB software,and modeling and simulating the lightning impulse divergent process of the grounding electrode without considering the spark discharge effect through frequency domain electrical network analysis.The simulation results are compared with those of CDEGS.Based on this,an iterative algorithm of equivalent radius is proposed to simulate the spark discharge process caused by soil breakdown.The results are compared with the experimental results,which verifies the accuracy and validity of the algorithm.(2)The grounding device will be accompanied by physical phenomena of spark discharge effect,inductance effect,capacitance effect and skin effect during the process of stray lightning impulse current.The impulse grounding characteristics of copper,steel metal materials and non-metallic graphite composite grounding materials are compared by simulation,and the impact of four physical effects on the impulse grounding characteristics of different materials is analyzed.The results show that the influence of skin effect and inductance effect on graphite composite grounding material is very small.Considering the effect of spark discharge,the influence of spark discharge effect on graphite composite grounding material is slightly weaker than that of metal grounding material.However,due to the advantages of skin effect and inductance effect,its impulse grounding characteristics is better than that of metal grounding material.(3)Under the influence of different soil parameters and lightning current parameters,the impulse grounding characteristics of non-metallic graphite composite grounding materials are simulated,and the impulse grounding characteristics of graphite composite grounding materials under various factors are analyzed.The results show that the soil parameters will affect the strength of the spark discharge effect,the lightning current wavefront time will cause the inductance effect to change significantly,and its amplitude is not sensitive to the inductance effect,but the spark discharge effect is more significant.Through the selection of three typical lightning impulse currents with different specifications for simulation,the optimal selection range of the length of the graphite composite grounding electrode in practical engineering applications is summarized.(4)The structure transformation of non-metallic solid graphite composite grounding material was carried out.The impulse grounding characteristics of the expanded graphite composite grounding electrode after structural optimization are simulated and analyzed.The results are compared with the calculation results of the solid graphite composite grounding electrode.The simulation results show that the spreading characteristics of the expanded graphite composite grounding electrodes are better than the solid graphite composite grounding electrodes at power frequency,and the impulse grounding characteristics of the longer length expanded graphite composite grounding electrodes are better.Finally,the practical engineering application example of the graphite composite grounding material in the 220 k V transmission line tower grounding device is used to illustrate the feasibility and practicality of the lightning protection application of the non-metallic grounding material proposed in this thesis in the tower grid.The research methods and achievements of this thesis in the application of non-metallic grounding can provide a certain reference for the design and transformation of grounding engineering for transmission lines and towers.