Transient Behavior Of Grounding Systems Research Articles

Analysis of grounding system transient with consideration of soil ionization and mutual coupling effect

The grounding system of an electrical substation provides safety to both operator and equipment. The lightning current waveform has a major influence on the dynamic performance of ground electrodes. If lightning current is large enough, soil will be ionized, which will have a great effect on the transient performance of the grounding system. Many numerical models have been developed to evaluate the transient performance of grounding system, still it is a challenging task to analyze the impulse behavior of grounding system efficiently. In this paper, the transient behavior of grounding systems with consideration of nonlinear and dynamic effects of soil ionization is presented. Grounding systems such as vertical rod, horizontal conductor and grounding grid buried in the homogeneous soil are considered as case study. Proposed model is the combination of circuit theory approach and method of moment with consideration of frequency-dependent impedance and mutual coupling effect between the conductor segments. Self and mutual component of inductance and resistance are considered in the analysis. Initially, transient performance of grounding system is analyzed for single vertical rod, horizontal and square grounding electrodes, further it is extended for vertical rod (more than one), horizontal conductor and grounding grids with different configurations. The analysis of grounding system with the consideration of mutual coupling effect is compared with devoid of mutual coupling, and differences between them are evaluated. For validating the developed method, simulated results are compared with the results reported in the literature, and good agreements are found. Analysis shows that the grounding impulse impedance decreased with increasing the magnitude of injected current. Developed method will help to improve the modeling of simple as well as complex grounding system buried in homogeneous soil.

A simplified numerical modeling of the transient behavior of grounding systems considering soil ionization

The analysis of the transient performances of grounding systems during a lightning discharge is proposed in the literature by modeling in time or in frequency domain. The frequency modeling makes it generaly possible to take into account the electromagnetic effects observed during the rise time of the pulse while temporal modelling makes it possible to introduce the nonlinear phenomenon (soil ionization) observed following an injection of a very high intensity lightning strike. In this work we propose a modeling with a simplified implementation which takes into account the various electromagnetic couplings which arise after spatial discretization of the grounding system as well as the ionization of the soil. This new formalism is developed from the equations of nonuniform Transmission Lines (nuTL) and the Finite-Difference Time-Domain (FDTD) method. This simplified modeling is carried out solely by spatial discretization of the grounding system conductors, is done without loss of precision and with very low calculation times. Our calculation results are compared to those already published and carried out by simulation or by the measurements.

Realistic modeling of the grounding system transient behavior with frequency dependence

For better protection of electrical networks, modeling the transient behavior of grounding systems is now fundamental before the realization step. In this work we propose a new modeling approach which permits a quick and efficient analysis of the grounding systems.In the proposed approach we solve the transmission lines equations using the Finites Differences (FD) taking into account the different electromagnetic couplings that occur during the spatial discretization of the grounding electrodes. To achieve this objective we complete the general transmission lines equations by introducing the coupling terms between the different parts of the grounding system and we calculate the self and mutual per-unit length parameters according to the geometrical position of the elements (cells). We therefore use rather the term non-uniform Transmission Lines (nuTL). This new modeling offers the advantages of calculating in a single step the currents and voltages at all the points of a grounding system, also taking into account the frequency dependence. Compared to already existing full-wave electromagnetic models our modeling is realistic because its numerical implementation is simple, retains good precision and the calculation times are much reduced.

Investigation of Horizontal Ground Electrode's Effective Length Under Impulse Current

This paper discusses the impulse analysis of horizontal ground electrode buried in uniform and two-layer soils, describing applications of a recently developed model based on transmission line approach for the analysis of high frequency and transient behavior of grounding systems. Simulations were carried out to compute the ground electrode' potential and the impulse impedance. A practical method to estimate the effective length of horizontal ground electrodes is presented. The results have been successfully compared with those computed using formulas reported in the literature and only developed for uniform soils. The proposed method is intended for estimation of the effective length of horizontal electrodes buried in soils having a two-layer stratification, which has not yet been considered so far. Based on this method, parametric analysis carried out has shown that the parameters influencing the effective length are mainly the soil resistivity and the rise time of the injected current for uniform soils or associated with the upper layer depth and the refection factor for two-layer soils. Using a genetic algorithm, mathematical expressions for the effective length of horizontal ground electrodes are proposed in terms of these parameters.

Transient Behaviour of Grounding System in a Two-Layer Soil Using the Transmission Line Theory

The present work deals with modeling of the transient behavior of grounding systems in the presence of layered media. A simple and efficient Transmission Line (TL) model featuring the use of the Finite Difference Time Domain (FDTD) is proposed. The proposed approach easily accounts for the influence of semi-infinite media (soil or air) and imposes conditions at the interfaces. The TL model is verified through the direct solution of the Maxwell's equations in the time domain by means of the FDTD method. Some illustrative computational examples addressing some engineering applications stemming from industry are given in the paper.

The Effect of Frequency Dependence of Soil Electrical Parameters on the Lightning Performance of Grounding Systems

A rigorous full-wave approach based upon the finite-element method (FEM) is used for the analysis of grounding systems taking the frequency dependence of soil electrical parameters into account. The method uses minimum approximations to model the transient behavior of grounding systems. In this analysis, frequency dependence of the soil conductivity and relative permittivity is represented using available analytical formulae obtained from experimental data. It is shown that there are cases in which the frequency dependence of the soil conductivity and relative permittivity can affect the transient behavior of grounding systems. Our simulation results show that the effect of frequency dependence is more pronounced for grounding systems buried in low conductive soils in contrast with those buried in highly conductive soils and especially when these systems are subjected to lightning subsequent return stroke currents. In practice, it seems legitimate to disregard the frequency dependence of the soil conductivity and relative permittivity for grounding systems buried in highly conductive soils subjected to lightning first return stroke currents. Within this context, it is shown that the soil conductivity, length of grounding electrode, and the frequency content of the injected current are the main factors contributing to the beneficial effect of the frequency dependence of soil electrical parameters.

Calculating the transient behavior of grounding systems using inverse Laplace transform

This paper deals with a unified and novel approach for analyzing the frequency and time domain performance of grounding systems. The proposed procedure is based on solving the full set of Maxwell’s equations in the frequency domain, and enables the exact computation of very near fields at the surface of the grounding grid, as well as far fields, by simple and accurate closed-form expressions for solving Sommerfeld integrals. In addition, the soil ionization is easily considered in the proposed method. The frequency domain responses are converted to the time domain by fast inverse Laplace transform. The results are validated and have shown acceptable accuracy.

Transient Analysis of Grounding Systems Associated to Substation Structures under Lightning Strokes

In this paper we propose a new formalism for analyzing the transient behavior of grounding systems associated to substation structures (Faraday-cage) under lightning strokesin unsettled regime. The protective device to study is formed of a guard filet connected to a grounding grid by simple conductors called down conductors. Our formalism is based on the resolution of the propagation equation in potential on 3D. The purpose of our proposition is the direct analyzing in time domain and simple implementation. We compare the results obtained by this new approach to results published in literature.