| Popis: |
We present a study of the causality of dispersive soil models for exact prediction of the effective length of grounding electrodes in single and two-layer soils. The causal and non-causal models of dispersive soil are applied to the analysis of grounding electrodes subject to two typical first and subsequent return-strokes. For computations, we adopt the computationally efficient multi-conductor transmission line method. The simulation results show that the causality plays an important role on the effective length so that under causal assumption it can be less or greater than that of the non-causal counterpart, depending on the low-frequency resistivity of lossy soil and current waveform. The difference between causal and non-causal models for predicting the effective length is more pronounced for subsequent return current, whereas for first stroke current it is ignorable. Moreover, the simulation results show that the burial depth effect in causal and non-causal-dispersive soils should be considered for subsequent stroke current. The mentioned facts are observable in two-layer dispersive soils as well when the upper layer is denser than the lower one. After then, causal-based formulae for predicting effective lengths of grounding electrodes buried in dispersive soils are proposed. Finally, the impact of causal and non-causal-based effective lengths on the touch and step voltages for both single and two-layer soils is investigated. |
