Study On The Electrical-thermal-damage Characteristics Of Conductive Concrete Materials Under Lightning Current Impulse

With the expansion of power grid scale,transmission lines are forced to be located in barren and barren areas with high resistivity,and the construction conditions are harsh,which makes transmission line grounding face new challenges.As a new type of composite material,conductive concrete has a good application prospect in power system grounding.The grounding device of the transmission line must often bear the impact of lightning current.When the lightning current leaks into the earth through the conductive concrete material,it will be accompanied by a strong electrothermal effect,resulting in gradient stress,which will cause damage and deterioration of the grounding device,and affect the working state and service life of the grounding device.Studying the electrical-thermal-damage characteristics of conductive concrete materials under lightning current impact has important engineering guiding significance for the design,construction and maintenance of conductive concrete materials in power system grounding.In this paper,based on the theory of multi-field coupling,the static electricity and transient heat of the conductive concrete material under the impact of lightning current are analyzed,the electric and thermal coupling model inside the conductive concrete material is established,and the electrothermal distribution characteristics of the conductive concrete material under the impact of lightning current are studied;on this basis,the temperature gradient distribution and the corresponding thermal stress distribution inside the conductive concrete are analyzed;then based on the strain field distribution of the conductive concrete material,the possible damage of the conductive concrete material is analyzed.Firstly,a multi-physics coupling model of the electrical-thermal-mechanical of conductive concrete materials was established.Based on the law of conservation of charge,the electrothermal coupling characteristics in the conductive concrete material under the impact of lightning current were analyzed,the heat conduction law in the conductive concrete material was studied,and the thermal stress damage of the conductive concrete material was theoretically analyzed.Secondly,the electrothermal characteristics of the conductive concrete module under the impact of lightning current were studied.The method to determine the electrothermal parameters of the conductive concrete material mixed with multiple materials was analyzed,and the COMSOL simulation model of lightning impulse of the conductive concrete module was built.The electrothermal distribution characteristics of the conductive concrete module under lightning impulse were simulated and analyzed,and compared with that of the ordinary concrete grounding module and soil-covered grounding electrode.The simulation results show that the electric heating distribution of the conductive concrete module is more uniform,and the current density,potential,temperature and temperature gradient are smaller,which has better electrothermal characteristics.Finally,the thermal stress damage of the conductive concrete foundation was analyzed.Based on the electro-thermal coupling model,the electro-thermal-mechanical coupling model of the conductive concrete tower foundation was further established,and the distribution of electric potential field,temperature field and stress field inside the conductive concrete foundation under the impact of lightning current was analyzed.On the basis,the distribution of deformation displacement field and strain field was obtained.According to the distribution of the strain field,the damage degree was analyzed and compared with that of the ordinary concrete foundation of the transmission line.The simulation results show that the conductive concrete foundation under the impact of lightning current has a better effect of dissipating current,less damage,and is beneficial to delaying the service life.The research results show that as a new type of grounding material,conductive concrete has good electrothermal characteristics,good current dispersion effect during grounding,and less damage under lightning current impact.The research results provide theoretical support for the application of conductive concrete in tower foundation grounding.