Terre (électricité)

Résumé

En électricité, la terre est un concept qui représente le sol (la masse terreuse, d'où son nom) en le considérant comme parfaitement conducteur et, par convention, au potentiel . Cette dernière hypothèse peut être invalidée si le sol est peu conducteur, par exemple dans le cas du sable dans le désert ou du granit peu fissuré. Définition juridique La définition juridique française est : Cette définition repose sur l'hypothèse que la terre est parfaitement conductrice et que son potentiel est le même en tout point. Ceci peut être contredit :

localement: pour les sols très secs (cas du Sahara par exemple) ou certains types de sol ;
temporairement: en période de sécheresse prolongée ou si la nappe phréatique est très profonde ;
ponctuellement: par exemple lors d'un coup de foudre en un point précis. Pendant cette période, certes très courte, le potentiel du sol n'est plus homogène et localement il n'est pas au potentiel moyen du globe. Il s'agit donc d'une conventi

Source officielle

https://fr.wikipedia.org/wiki/Terre_(%C3%A9lectricit%C3%A9)

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We present a review and comparison of different models representing the frequency dependence of the soil electrical parameters (conductivity and permittivity). These models are expressed in terms of curve-fit expressions for the soil conductivity and relative permittivity, which are based on experimental data. Six availablemodels/expressions are discussed and compared-making reference to two sets of experimental data. It is shown that the soil models by Scott, Smith-Longmire, Messier, and Visacro-Alipio predict overall similar results, which are in reasonable agreement with both sets of experimental data. Differences between the soil models are found to be more significant at high frequencies and for low-resistivity soils. The causality of the considered models is tested using the Kramers-Kronig relationships. It is shown that the models/expressions of Smith-Longmire, Messier, and Portela satisfy the Kramers-Kronig relationships and thus provide causal results. The soil models are applied to the analysis of grounding systems subject to a lightning current. A full-wave computational model is adopted for the analysis. The analysis is performed considering two cases: 1) a simple horizontal grounding electrode, and 2) a realistic grounding system of a wind turbine. Two current waveforms associated with typical first and subsequent return strokes are adopted for the representation of the incident lightning current. In agreement with recent studies, simulations show that the frequency dependence of the soil parameters results in a decrease of the potential of the grounding electrode, with respect to the case where the parameters are assumed to be constant. It is found that the models/expressions by Scott, Smith-Longmire, Messier, and Visacro-Alipio predict similar levels of decrease, which vary from about 2% (rho(LF) = 20 Omega.m and first stroke) up to 45% (rho(LF) = 10 000 Omega.m and subsequent stroke). On the other hand, the models of Portela and Visacro-Portela predict significantly larger levels of the decrease, especially for very high resistivity soils. Furthermore, in the case of a high resistivity soil (10 000 Omega.m), the Visacro-Alipio expression predicts a longer risetime for the grounding potential rise, compared to the predictions of Scott, Smith-Longmire, and Messier models.

Ieee-Inst Electrical Electronics Engineers Inc2014

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On the Application of Frequency Dependent Soil Models to the Transient Analysis of Grounding Electrodes

Damir Cavka, Nicolas Mora Parra

2013

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Three-dimensional multilayer concentric bipolar electrodes restrict spatial activation in optic nerve stimulation

Marta Jole Ildelfonsa Airaghi Leccardi, Eleonora Borda, Ricardo Camilo Moreira, Vivien Gaillet, Diego Ghezzi, Elodie Geneviève Zollinger

Objective. Intraneural nerve interfaces often operate in a monopolar configuration with a common and distant ground electrode. This configuration leads to a wide spreading of the electric field. Therefore, this approach is suboptimal for intraneural nerve interfaces when selective stimulation is required. Approach. We designed a multilayer electrode array embedding three-dimensional concentric bipolar (CB) electrodes. First, we validated the higher stimulation selectivity of this new electrode array compared to classical monopolar stimulation using simulations. Next, we compared them in-vivo by intraneural stimulation of the rabbit optic nerve and recording evoked potentials in the primary visual cortex. Main results. Simulations showed that three-dimensional CB electrodes provide a high localisation of the electric field in the tissue so that electrodes are electrically independent even for high electrode density. Experiments in-vivo highlighted that this configuration restricts spatial activation in the visual cortex due to the fewer fibres activated by the electric stimulus in the nerve. Significance. Highly focused electric stimulation is crucial to achieving high selectivity in fibre activation. The multilayer array embedding three-dimensional CB electrodes improves selectivity in optic nerve stimulation. This approach is suitable for other neural applications, including bioelectronic medicine.

IOP Publishing Ltd2022

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Ieee-Inst Electrical Electronics Engineers Inc2014