Improving the Measurement Accuracy of HVDC Grounding Impedance Under Multilayer Soil Uncertainty for Energy Engineering Applications

This study examines model based interpretation of HVDC grounding responses in horizontally layered soil. Grounding impedance denotes the real voltage to current ratio in the steady state DC conduction model. A finite element forward model is combined with a surrogate assisted constrained robust optimization framework, denoted SACRO, to fit equivalent soil parameter combinations subject to physical bounds and prior information. The observation model distinguishes response fitting from the separate identification of layer resistivities and thicknesses. For a fixed geometry, varying current amplitude in the linear model does not create independent normalized observations; consequently, a small impedance residual alone does not establish unique soil parameter recovery. The ten reported response pairs have relative errors of 1.56% to 1.62% and an arithmetic mean of approximately 1.59%, calculated directly from the displayed values. For SACRO, the results showed 415 FEM evaluations, a runtime of 98.2 min and a post-perturbation mean response error of 2.55%. The algorithm and perturbation summaries are interpreted as case specific descriptive results. The framework supports layered soil response analysis and the interpretation of grounding measurements within the stated model assumptions.