Experimental and finite element analysis of coupled electro-thermal responses of concrete-encased grounding electrodes under lightning impulses

Grounding systems are critical for maintaining the safety and transient stability of high-voltage and smart-grid infrastructure subjected to lightning-current impulses. This study presents an integrated experimental and three-dimensional finite element method (FEM) investigation of conventional copper-bonded steel rod and concrete-encased grounding electrodes under standardized 8/20 µs impulse-current conditions. Laboratory experiments were conducted using an impulse-current generator with a maximum current capability of 1.5 kA, while a COMSOL Multiphysics model was developed and validated against the experimentally accessible current range and subsequently used to investigate higher-current conditions numerically. Three representative soil types of clay, sandy loam, and gravel were considered to evaluate transient impedance, ground potential rise (GPR), current-density distribution, soil-ionization behavior, and electro-thermal response. Experimentally, the concrete-encased configuration reduced impulse impedance by approximately 33–49% across the investigated soils. FEM analysis showed a reduction in peak current density from 69 to 43 A/m², corresponding to approximately 38%, together with a larger effective current-conduction region. Numerical predictions at higher current levels indicated delayed soil-ionization onset and lower temperature rise for the encased configuration compared with the conventional rod. These high-current results are identified as FEM predictions rather than direct experimental measurements because they exceed the 1.5 kA capability of the laboratory generator. The validated experimental numerical framework demonstrates the potential of conductive concrete encasement to improve impulse-current dispersion and reduce localized electrical and thermal stress in grounding electrodes. Further high-current experimental validation is required to confirm the predicted behavior beyond the laboratory test range.