In this paper, application of multi-conductor transmission line model (MTL) in transient analysis of grounding grids buried in soils with frequency-dependent electrical parameters (dispersive soil) is investigated. In this modeling approach, each set of parallel conductors in the grounding grid is considered as a multi-conductor transmission line (MTL). Then, a two-port network for each set of parallel conductors in the grid is then defined. Finally, the two-port networks are interconnected depending upon the pattern of connections in the grid and its representative equations are then reduced. Via solving these simplified equations, the transient analyses of grounding grids is efficiently carried out. With the aim of validity, a number of examples previously published in literature are selected. The comparison of simulation results based on the MTL shows good agreement with numerical and experimental results. Moreover, in despite of numerical methods computational efficiency is considerably increased.
In this paper, an approximate modeling approach called simplified multiconductor transmission line model (simplified MTL) is proposed for transient analyses of multiple grounding electrodes. Since this approach is in the frequency domain, the effect of soil dispersion (frequency variation of soil electrical parameters) is easily incorporated. In addition, the soil ionization effect is treated as gradually increasing radius of the electrode. With the use of this approach, predicting formulae for effective length of multiple grounding electrodes considering both ionization and dispersion are proposed for the first time. Finally, combining the extracted formulae with the apparent resistivity in two‐layer soils, effective length in such soils is easily predicted.
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.
Purpose
The purpose of this paper is to investigate the ionization and dispersion effects in combination with the inhomogeneity of soil simultaneously on the effective lengths of counterpoise wires.
Design/methodology/approach
Improved multi-conductor transmission line model is used for computing effective length of counterpoise wires considering all aspects of soils.
Findings
The simulation results show that the ionization and dispersion effects simultaneously results in placing the effective length between situations where only one effect is considered. Also, predicting formulae for effective length of counterpoise wires considering all effects are proposed.
Originality/value
A sensitivity analysis on the effective lengths of counterpoise wires considering all aspects of soils is carried out.
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