Response Of Grounding Systems Research Articles

Experimental analysis of horizontal grounding wires buried in high-resistivity soils subjected to impulse currents

• Experimental response of grounding wires in high-resistivity soils is presented. • Grounding impulse impedance is lower than resistance for higher resistivities. • Experiments show relevant influence of frequency dependence of soil parameters. • Influence of increasing the front-time on impedance depends on electrode length. This paper presents experimental results of the ground potential rise (GPR) developed by grounding wires buried in high-resistivity soils and subjected to impulse currents. A large experimental dataset is presented, comprising grounding wire lengths ranging from 10 m to 50 m, buried in soils of resistivities between around 1100 Ωm to 1600 Ωm, and subjected to impulse currents with front-time ranging from around 1.2 μs to 7 μs. The experimental results further confirmed some important aspects regarding the lightning response of grounding electrodes buried in high-resistivity soils, namely the influence of the frequency dependence of soil parameters and the value of impulse impedance lower than the grounding resistance for electrodes shorter than effective length. Comparison between experimental and simulated results reinforces the need to consider the frequency-dependence of soil parameters for obtaining accurate results of the lightning response of grounding systems buried in poor conducting soils.

A study on the response characteristics of adjacent grounding grids under artificially triggered lightning strokes

Previous studies regarding the transient response of grounding systems have mainly focused on grounding grids with injected current, while there are few studies on adjacent unconnected grids. An "active-passive" grounding grid model was set up based on the artificially triggered lightning experiment, and the GPR data from 39 return strokes were measured. The results show the peak ratio of GPR between the two grounding grids caused by return strokes ranges from 9.6% to 17.3%, and the GPR decreases rapidly after reaching the peak and forms a subpeak. In addition, the 10–90% rise time and the time to half value of the passive grid are longer than those of the active grid. There is a good linear fitting relationship between the GPR peaks of the two grids and the injected current peaks. This shows that, under the joint action of soil dispersion and the resistance component of the active grid, the transfer potential of the passive grid becomes smoother and the amplitude decreases significantly, due to the attenuation of the high-frequency components. It shows there is a long-time difference between the GPR peak values of the two grounding grids, which is not affected by the injected current, and is almost unchanged.

High frequency response of grounding electrodes: effect of soil dielectric constant

paper is a postprint of a paper submitted to and accepted for publication in IET Generation, Transmission & Distibution (GTD) and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at the IET Digital Library.Abstract:Grounding electrodes have an important role in electric power transmission and distribution systems. They are used to prevent excessive hazardous voltages between metallic structures and ground in the case of system faults or lightning surges. It is important that they provide a low impedance path for the current in to the ground. The electrical properties of soil, which vary substantially with geographical location and time of year, affect the process considerably along with the properties of the grounding electrode itself, such as its dimensions.In order to have an accurate estimation of the developed overvoltages and the backflashover rate of the transmission lines due to a lightning strike, one has to take into account the effect of the value of the soil electrical parameters, such as the electrical conductivity and dielectric constant.This paper investigates the high frequency behavior of the grounding electrodes by solving a full-wave electromagnetic problem using the Finite Element Method (FEM). The focus is on taking into account the effect of the variation of soil relative permittivity which has been neglected in the previous studies of the grounding systems. This allows an evaluation of the response of grounding systems due to seasonal changes and specifically change of the water content of the soil, which would cause its electrical properties to vary significantly. This studydemonstrates the importance of considering the variation of relative permittivity of the soil especially in the modeling of electrodes buried in highly resistive soil.

Analysis of Lightning-Related Stress in Transmission Lines Considering Ionization and Frequency-Dependent Properties of the Soil in Grounding Systems

This article analyzes the performance of grounding systems buried in the ionized soil during the lightning discharge. To this aim, at first, a method to simultaneously analyze the transient response of grounding system considering the time-dependent nonlinear behavior arising from soil ionization and frequency dependence of soil electrical parameters related to the frequency content of the lightning surge is presented. The proposed method is performed by a combination of the harmonic balance method and the method of moment, which is aimed at representing an equivalent circuit to model the grounding system during the lightning discharge. The proposed model is validated by comparing the associated results with the published measurement and the numerical data for different grounding systems. Finally, an application of the proposed method is presented and the generated overvoltages across the insulator string caused by lightning strokes, the outage rates of transmission lines, and the lifetime of surge arresters are discussed.

Analysis of Transient Performance of Grounding System Considering Frequency-Dependent Soil Parameters and Ionization

Frequency-domain approaches are usually used to study the impact of the frequency dependence of soil electrical parameters on the lightning response of grounding systems. On the other hand, time-domain simulations are required to study nonlinear soil ionization behavior. A time-domain frequency-dependent simulation is needed to incorporate both effects simultaneously. Based on dynamic harmonic domain (DHD) concept and transmission-line method, this paper derives a new approach for simulating the grounding system surge behavior that includes both time-dependent ionization and frequency-dependent effects of the soil. The DHD permits to decouple harmonic contents of each variable state during transients in time-domain simulation. The simulation results are validated against measured and simulated published results from other researchers. The comparison of experimental results and those provided by this model denoted its consistency.

An Adaptive Chebyshev Approach for Fast Computation of Grounding System Admittance Matrix

The paper proposes an adaptive Chebyshev method for expediting the calculation of grounding system admittance matrix. This facilitates the characterization and the inclusion of the wideband model of the grounding systems into the time-domain electromagnetic transient solvers. In the proposed method, a general electromagnetic approach based on the method of moments (MoM) solution to Maxwell's equations is utilized to obtain the grounding system admittance matrix over the frequency range of interest. Rather than applying the MoM to each distinct frequency obtained from the FFT procedure, the proposed method is utilized to reduce the number of frequency points for which the response of grounding system is calculated. Several simulated case studies are presented to examine the accuracy of the proposed method. It is shown that the selected sampling frequencies are sufficient to generate the exact response of the grounding system over the working frequency interval

Transient behavior of wind towers grounding systems under lightning strikes

Wind turbines, because of their height and localization, are frequently subject to direct lightning strikes. Thus, the investigation on the performance of their grounding system is of paramount interest for the prediction of the potential threats either for people working in (or animals passing through) the wind farm area and for the power and control units installed in close proximity of the turbine towers. In this paper,we perform a comprensive study of the transient behavior of the earthing systems of wind turbines. The analysis is conducted in the frequency domain and an hybrid approach, based on circuit theory and Method of Moments, is adopted to fully account for resistive, inductive and capacitive couplings between elements of the ground system. The actual transient behavior is obtained by means of an Inverse Fourier Transform. The results, computed considering a typical wind turbine grounding system configuration, provide more insight on the nature of the early-time transient response of grounding systems and allow to draw up useful design guidelines.

Accelerating the frequency-domain response calculation of complex grounding system using wavelet based MBPE technique

The transient response of grounding systems is essential for their designs and related electromagnetic compatibility problems in power systems. Although the method of moments (MoM) is a popular way to analyze the responses of grounding systems, it is prohibitively slow. In this paper, the model-based parameter estimation (MBPE) technique and wavelet matrix transform (WMT) are combined and applied to the method of moments (MOM). It is expanded on two-steps technique to accelerate solution of electric field integral equations (EFIE). In a first step, the WMT is used to get a sparse matrix equation in wavelet-domain. Then in a second step, the adaptive model-based parameter estimation is used to reduce the number of frequency-domain calculation points required for the evaluation of space–time current distribution along a grounding grid. The accuracy of the proposed model is confirmed by comparing the simulation results of several case studies with those obtained using the direct MoM method combined with inverse fast Fourier transform (IFFT). It is shown that considerable computation efficiency is achieved in terms of CPU time without losing accuracy.

Numerical and Experimental Investigation of Grounding Electrode Impulse-Current Dispersal Regularity Considering the Transient Ionization Phenomenon

This paper presents a numerical method, combined the finite element method in the spatial domain with the finite difference time domain, to calculate the transient impulse response of grounding systems considering the ionization phenomenon. In this numerical method, space-time variable soil resistivity is used to simulate the soil ionization phenomenon where soil resistivity is controlled according to its relationship with the local instantaneous value of the electric field and no a priori hypothesis on the geometrical shape of the ionized region around the electrodes is necessary. Based on the widely accepted principle of dimensional similarity, this paper makes simulated experimental investigations on the impulse-current dispersal regularity of grounding electrodes with various structures. The proposed numerical scheme is validated by comparing computed results with experimental results and simulation results in literature. Based on the measurement and simulation results, the impulse response regularity of grounding electrodes is discussed and the effect of ionization on human and installations safety is reported.

Grounding transient response of lightning protection GTIERRAS software

A computer program developed in Matlab (GTIERRAS) from an electromagneticbased model is used to assess grounding impedances and the behavior of grounding electrodes of arbitrary shapes under lightning impulses. Impedance, currents and voltages, or other electric variables of the grounding system can be presented as well in frequency or in time domain with the use of Fast Fourier Transform. The generality of the model allows its use for assessing lightning overvoltages, but also for other typical transients associated with electromagnetic compatibility problems. Results show the influence of some variables on the response of grounding system and shed light on some differences that must be taken into account when applying criteria based on low frequency performance to groundings stressed by surges. Calculation examples and comparison with results from other authors are presented and analyzed so as to illustrate some grounding behaviors that by no means are evident. Effects of electrode geometry and soil resistivity, as well as of wave front and number of injection points are also investigated. Results of touch and step potentials are shown. A study of a lightning protection system is presented as an extension of the model application capabilities. Some conclusions useful for grounding system design are derived.

An improved model for soil ionization around grounding system and its application to stratified soil

An improved model for taking into account the effect of the soil ionization around grounding system under lightning strike is proposed in this paper. In this model, the soil ionization region is assumed to retain 7% of its pre-ionization resistivity, which is consistent with the experimental results on soil ionization found in literature (Trans. SA Inst. Electr. Eng. (1988) 63; AIEE Trans. 61 (1942) 349; Proc. IEE 121(2) (1974) 123) and our own laboratory experiments (Time domain modelling of the response of grounding systems subjected to lightning currents, Licenciate Thesis, Uppsala University, 2003). Compared with modelling the soil ionization as an increase in the size of the ground conductor, the model presented here will not overestimate the beneficial influence of the soil ionization in reducing the ground potential rise, especially in high resistivity soil. The model is also applied to study the transient behaviour of grounding conductors in stratified soil under lightning strike including soil ionization. It shows that making the grounding conductor to penetrate the lower resistivity soil layer could help to decrease the ground potential rise at the injection point several times.

GIS地下変電所における接地系の過渡応答特性

GIS地下変電所における接地系の過渡応答特性