Analysis of the Impact of Complex Soil Structure and River Flow Velocity on Impulse Current Dispersion in Grounding Devices for River-Crossing Transmission Towers

The lightning withstand performance of transmission lines is critically affected by grounding impulse characteristics, particularly for river-crossing towers where soil conditions are complex. This study develops a coupled seepage–electric field model to evaluate these characteristics under dynamic hydrological influences. A complex soil model is constructed integrating Bernoulli’s laminar flow equation with Richards’ equation for unsaturated seepage; long-term finite-element iterations simulate seepage dynamics, yielding distributed soil conductivity parameters that vary with river flow velocity, water depth, and impermeable layers. These parameters are then coupled with an electroquasistatic Maxwell framework to model impulse current dispersion. Validation against experimental data confirms the model’s accuracy. Results show that seepage increases moisture and lowers resistivity. Increasing flow from static to 10 m/s reduces riverbed pressure from 5.61 × 10 4 Pa to 1.86 × 10 4 Pa, shifting the 0 Pa isobar downward by 5.1 m, weakening seepage and raising impulse resistance. A shallower impermeable layer deflects seepage laterally, reducing nearby resistivity. Raising water depth from 5 m to 10 m increases pressure from 1.96 × 10 4 Pa to 5.61 × 10 4 Pa, enhancing seepage and lowering resistivity. These findings indicate that grounding design must holistically account for flow velocity, water depth, and subsurface barriers to ensure reliable lightning current dissipation and stable grid operation.