Design Of Grounding Grids Corrosion Detection Device Based On Electric Network Theory

The grounding grid is an important device that is buried underground to ensure the safe production and personnel safety in the plant or station,and has the function of discharging current and reducing the ground step voltage in the event of a fault.The grounding grid is exposed to the harsh soil environment,and after a period of operation,it is prone to corrosion,which will seriously endanger the safety of production.Therefore,periodic inspection of the integrity of the grounding grid is very important for reliable production.The electric network theory is a method of introducing the parameter identification method in the analog circuit fault identification into the corrosion judgment of the grounding grid.In this method,the grounding network is equivalent to a pure resistance network,and the accessible node is connected to inject an excitation source into the port and the port resistance value is obtained according to the output response.Finally,the resistance value of each branch can be calculated.The original parameters and topological structure of the grounding grid are known.By comparing the initial nominal resistance value of each branch with the calculated value,the corrosion condition of each branch can be judged.This paper designs a set of device to detect the corrosion of the grounding grid based on the principle of electrical network.This system consists of 5 parts: excitation source module,matrix switch,data acquisition unit,MCU control module and host computer.The device is designed with 16 channels and can be connected to 16 reachable nodes of the grounding grid.The system controls the conduction of any two channels through matrix switch to form a detection port,and adopts a rotation of the excitation source to realize sequential injection of excitation and detection output response to the network port.The matrix switch adopts a working mode based on the "four-terminal electrode method",which can effectively eliminate voltage collection errors caused by lines and switch contacts.Aiming at the complex environmental interference on the substation site,the host computer software in this paper uses a digital orthogonal algorithm to extract the weak signal of the specified frequency.Cooperating with the strategy of zone measurement and multiple approximation measurements,the location of corrosion faults is finally completed.After multiple measurements and comparisons,the device runs stably and meets the design requirement that the resistance value error of multiple measurements on the same port is within 0.1mΩ.Finally,the design parameters and working effects of the device were verified in this paper through the laboratory test and the field experiment in the Renzhuang substation.Corrosion detection and diagnosis of the grounding grid of Renzhuang station proved the engineering application value and reliability of the grounding grid corrosion detection device in this paper.