Study On Safety Performance Of Substation Grounding System

The substation grounding system is the fundamental guarantee and important facility for maintaining the safe and reliable operation of the power system and ensuring the safety of power equipments and operating personnels.With the emergence of large-capacity and long-distance EHV and UHV power grids,the grounding short-circuit current of the power system has been increased greatly,and the ground potential rise of the substation grounding grid is getting higher and higher,which puts forward more stringent requirements for substation grounding system to protect human beings,primary equipment and electronic monitoring devices with low anti-interference ability.Therefore,the study on the safety performance of grounding system is of great significance to ensure the safe and stable operation of substation.In this paper,the grounding parameters numerical calculation method of grounding system is studied based on the two-layer soil structure model,and according to the established model,the program for unequal potential of grounding system is compiled,which takes into account the resistance,the self inductance and the mutual inductance of the ground conductor of steel grounding grid.The program can calculate the grounding related safety indicators when short circuit fault occur,and draw the potential distribution curve of the specified direction.Comparing with the grounding software CDEGS through the examples,the correctness of the program is verified.For substations in regions with high soil resistivity,it is difficult to effectively reduce the grounding resistance,so it is important to balance the distribution of surface potentials.In order to ensure the safety of human beings,the touch voltage and step voltage should be limited within the allowable value of human safety to increase the safety level of the substation grounding grid.In this paper,the safety of grounding grid under the optimal design based on two-layer soil model is analyzed,the optimal layout rule of the grounding conductor is studied,and the optimal compression ratio is calculated when optimizing the layout.Combined with examples,the influencing factors are analyzed.The variation regularity of the relevant ground safety indicators under the equal spacing and unequal spacing arrangement is analyzed,and the influence of laying vertical grounding electrodes on the optimization rule is studied.Finally,the maximum touch voltage of the large grounding grid is discussed.Modern substations use a large number of microcomputer protection devices and microcomputer-based integrated automation equipments These devices mainly use cables for signal transmission and control.Control cables connect primary and secondary devices,and their safety performance affects the stability of the secondary system.In order to reduce the interference voltage level of secondary equipments,the two ends of the cable shield are usually grounded.In this paper,based on potential nodal analytical method,a grounding parameters calculation model with two-end grounded cable is built.The potential difference between the core and sheath of cable is calculated by programming,and the safety performance and influence factors are analyzed.Finally,the measure to reduce the potential difference of the core and sheath is proposed and applied in combination with specific engineering example.