Corrosion evaluation of the grounding grid in transformer substation using electrical impedance tomography technology

In order to improve the corrosion maintenance efficiency of grounding grid metal, the corrosion state of underground grounding grid in an 110kV substation was tested and evaluated by the electrical impedance tomography (EIT) technology. Results indicated that the impedance increase ratio of grounding grid branch was in a reasonable range below the warning value, proving the whole ground grid metal had not suffered severe thinning in soil and no breaking had happened in the grounding grid branches. The two-dimension corrosion image of the whole grounding grid was simulated and drawn accurately using the corrosion diagnosis software, with the consideration of the impedance increase ratio of grounding grid branch and the network topology of grounding grid. By realizing the underground grounding grid from the "black-box state" to the "visible state", EIT technology could be used to evaluate and detect the corrosion degree, corrosion area and corrosion failure of grounding grid rapidly and effectively, which could reduce the blindness of corrosion detection for grounding grid, provide guidelines on the corrosion maintenance of grounding grid and improve the fine management ability of grounding apparatus in substation.