Impact Characteristic Analysis of Tower Foundation Under Concealed Conductive Paths with Grounding Grid Based on a Scaled Model

Concealed conductive connections between a transmission tower’s grounding grid and its foundation can cause a portion of the lightning strike current to enter the foundation and concentrate at the concealed conduction locations, thereby increasing the risk of foundation deterioration. To investigate the impact characteristics of such currents on the foundation under this operating condition, this study first establishes an electro-thermal-mechanical coupled finite-element model of the tower foundation that incorporates a subsurface concealed conductive loop, and compares the foundation’s temperature rise and mechanical characteristics under lightning currents and under power-frequency follow currents. The results indicate that power-frequency follow current poses a substantially greater hazard to the foundation than lightning current. Based on similarity theory, scaling laws for the foundation subjected to the impacts of power-frequency follow current are then derived. Considering that the intrinsic electro-thermal properties of the foundation cannot be altered in the scaled model, a parameter correction method is proposed according to quasi-similarity criteria. The corrected scaled-model results are compared with those of the prototype in simulation, and principal indicators exhibit deviations within 3%. A physical scaled model was subsequently designed and fabricated for impact testing, and ultrasonic inspection was used to assess potential damage in the concealed conduction region. The results show that under the action of power-frequency follow currents, the maximum temperature at the concealed conductive region reaches 124 °C, with deviations of 2.83% from the prototype simulation and 3.58% from the scaled-model simulation. The tower foundation was subjected to 20 power-frequency follow current impacts. After each impact and subsequent cooling, ultrasonic measurements of wave propagation velocity at the concealed conduction center decreased from 3.797 km/s to 3.571 km/s. The observed reduction in wave speed indicates a loss of local concrete structural integrity and suggests the risk of performance degradation and initiation of microcracks. These findings provide a reference basis for assessing the safety of tower foundations under concealed conduction conditions.