A study on the instantaneous and dynamic characteristics of impulse grounding resistance in grounding grids for artificially triggered lightning

The impulse grounding resistance is a critical parameter for evaluating performance of lightning protection devices, and effectively reducing this resistance remains a major challenge in lightning protection or electrical engineering. While most previous studies have focused on single-pulse characteristics within a triggered lightning process, comparative analyses on the characteristics of instantaneous impulse grounding resistance across multiple distinct discharge pulses in an entire triggered lightning process are scarce, and research on the dynamic variation characteristics of this resistance is even more limited. This study addresses these research gaps. Based on field-measurements and artificially triggered lightning experiments, this study measures lightning current and the corresponding ground potential rise generated after the current is injected into the grounding grid. The results show that the instantaneous impulse grounding resistance is lower than the power frequency grounding resistance for M components, 95.5% of return strokes (RS), and initial continuous current pulse (ICCP) (with lightning discharge current values around 1 kA). The instantaneous impulse grounding resistances of ICCP and the M components decrease with increasing current peak, whereas no significant correlation with the current peak is observed for RS. The instantaneous impulse grounding resistance of M components superimposed on the falling edge of the RS exhibits an exponential-like decay trend with its own current peak, background current value and preceding RS current peak. Using SPSS, a collinearity diagnosis was conducted on the three independent variables. The results show severe multicollinearity between the current peak of the Type b M component and the background current peak. The spark effect becomes prominent on the falling edge of the RS currents, causing the impulse grounding resistance to decrease rapidly. When the current peak of RS is small, the duration of low resistance state is short, with an average of 0.16 ms. Conversely, when both the current peak of the RS and half-peak width are large, the soil continuously undergoes ionization, maintaining the low resistance state for a longer duration. If the current falling edge is further superimposed with multiple large-current M components, it provides more substantial energy for soil ionization, thereby significantly prolonging the duration of the soil ionization spark effect. The findings offer valuable insights for lightning protection design, grounding device installation, and optimization of laboratory simulation models.