Study On The Grounding Characteristics Of The Flexible Graphite-Copper Composite Grounding Material

Lightning strikes have always been the primary factor threatening the stability of transmission lines,while the low-resistance,long-term and stable grounding device is an important guarantee for the safe and stable operation of transmission lines.Graphite flexible grounding materials have superior corrosion resistance,which can fundamentally solve the problem of corrosion of steel type grounding materials,but the temperature resistance of the internal adhesives and fibers of the graphite flexible grounding material is poor.It has a weak thermal stability when it is subjected to a short-time and large power frequency current.In order to make the graphite flexible grounding material can withstand the short-time and large current and increase its thermal stability,this paper was devoted to the study a flexible graphite-copper composite grounding material.Simulation and experimental research were carried out to provide theoretical support for its practical engineering applications.Firstly,a 500 kV transmission line model was established.The related factors affecting the short-circuit current of the tower scattering into the ground were analyzed.The short-circuit current through the tower into the ground was determined to be 1kA¹0kA.In order to improve the thermal stability of the graphite flexible grounding material,a flexible graphite-copper composite grounding material was adopted.Taking the temperature rise not exceeding120°C as the index,the cross-sectional structure layout was optimized from the aspects of reducing skin effect and temperature rise effect,and the optimal cross-section structure design method was determined.The design reference values of the diameter and quantity of copper wire required for the flexible graphite-copper composite grounding material under1kA/1s¹0kA/1s power frequency current were given.The corrosion resistance,short-time power frequency and high current withstand capability,high and low temperature resistance and tensile properties of the flexible graphite-copper composite grounding material were tested.The bulk resistivity and the connection resistance of the flexible graphite-copper composite grounding material sample were measured by the quadrupole method.The resistivity was on the order of 10^-7Ω·m,and the connection resistance at the joint was less than 4 mΩ.Corrosion resistance was analyzed by actual cyclic alkali,acid and brine medium corrosion tests.There was no obvious structural damage such as broken strands on the surface of the sample.The bulk resistivity test increased before and after the test increased by about 3%,it has good corrosion resistance.A 10 kA/1 s power-frequency short-time high-current withstand test was conducted on the typical designed sample of flexible graphite-copper composite grounding material.The bulk resistivity of the sample was increased by less than 3%before and after the test,and the highest temperature was less than 60°C.It has good thermal stability.The high and low temperature tolerance test and tensile test were carried out on the flexible graphite-copper composite grounding material samples.The samples were subjected to high temperature of 120°C for 2 h and low temperature of-60°C for 2 h,and maintained for 10 s by 5 kN.After the test,the samples did not show obvious breakage,and its bulk resistivity changed less than 5%.Taking a single long vertical grounding electrode as an example,the dispersion characteristic of the flexible graphite-copper composite grounding material under different current frequencies were analyzed.The temperature rise distribution of grounding materials under soil environmental conditions was also analyzed.The application of the flexible graphite-copper composite grounding material in typical tower grounding grids was analyzed.Providing theoretical support for its practical engineering applications...