Soil Ionization Effect Research Articles

Galerkin boundary element method for simulating lightning response of grounding grid in horizontal multilayered soil model considering soil ionization effect

AbstractThis work proposes a novel mathematical model based on the Galerkin time‐domain boundary element method for accurately calculating the lightning current distribution and lightning impulse response of the buried substation grounding grid, in a multi‐layer horizontal layered soil model, by taking into account the soil ionization effect. To improve computational efficiency, the quasi‐static complex image method and its closed form time‐domain Green's function have been introduced into the model that has the ability to analytically calculate the mutual inductance coefficient between the branch currents of any two conductor segments and the mutual resistance coefficient between the leakage currents. The Galerkin time‐domain boundary element method proposed in this work can simulate the transient lightning impulse response of a substation grounding grid buried in the multi‐layer horizontal layered soil.

Lightning Transient Impulse Problem of Substation Grounding Grid in Multilayer Horizontal Layered Soil Considering Soil Ionization Effect and Frequency Characteristics

Lightning Transient Impulse Problem of Substation Grounding Grid in Multilayer Horizontal Layered Soil Considering Soil Ionization Effect and Frequency Characteristics

Lightning Response Transient Characteristics of Substation Grounding Grid in Multilayer Horizontal Stratified Earth Model Considering Soil Ionization Effect

This article proposes a new time-domain partial element equivalent circuit method mathematical model. The mutual impedance matrix between the potential on the discrete node and the leakage current on the conductor connected around the discrete node is adopted. To reduce the amount of calculation, the matrix equation that minimizes the unknown quantity is derived and adopted. The model can accurately calculate the lightning current distribution and lightning impulse response in a horizontal multilayered soil model considering the soil ionization effect. To improve computational efficiency, the quasi-static complex image method and its closed form of Green's function in the time domain are introduced into the model.

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 Practical Method for Transient Analysis of Grounding Grids

A practical method is proposed in this paper for analysis of the lightning transient in the grounding grids. The circuit parameters of the grounding electrodes are evaluated by a set of analytic formulas, in which the soil ionization effect is taken into account. By means of the circuit parameters, the grounding electrode segments are represented by the π‐type circuits and a circuit model is built for the grounding grids. The lightning transient responses in the grounding grids can be calculated from the circuit model. The calculated results are compared with the measured ones to check the validity of the circuit model. In view of the actual distribution randomness, the lightning current amplitude is taken as a random variable and a statistical algorithm is further presented for statistical analysis of the lightning transient in the grounding grids. In the algorithm, the accumulative probability function is introduced to describe the random distribution of the lightning current amplitude. The lightning transient responses calculated in a large interval of the lightning current amplitude are weighted by the corresponding probability density. Then, the statistical values of the lightning transient responses can be obtained from the weighted sum. A numerical example is also given to discuss the difference between the statistical values and the nonstatistical ones calculated by the conventional method. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Modeling soil ionization effect based on experimental data

• Measurements of Soil Ionization. • Modeling Soil Ionization effect based on experimental data. • Means for estimating soil ionization on the response of grounding electrodes. • Ionization of soils subjected to uniform electric field. • Ionization of soils subjected to non-uniform radial electric field. Results of a huge number of experimental tests involving soil ionization developed by the authors were used in this paper for analyzing the phenomenon and developing means for predicting the effect on the response of grounding electrodes subjected to lightning currents. These results refer to samples of fifteen different soils (from about 100 to 10,000 Ωm at natural moist content) subjected to impulsive current waves exhibiting front times similar to those of first and subsequent return stroke currents. The tests considered conditions of uniform and radial non-uniform electric fields with intensities comparable to those resulting from the impression of real lightning currents on grounding electrodes. A curve was suggested for taking the effect of ionization on the lightning response of electrodes into account for soils in general, by means of an equivalent increase of the electrode radius as a function of the linear density of current dispersed to the soil.

An EMTP Extension for Computing Earthing System Transient Step and Touch Voltages

This paper presents a novel technique for computing dangerous voltages due to lightning transients imposed on earthing system, which is based on the use of the well-known ATP-EMTP software package. Earth surface transient potential distributions, as well as step and touch voltages computations, are performed through extending the widely used EMTP software package with a new post-processor (computer program), developed especially for that purpose. The earthing grid is approximated by the circular cross-section conductors. In numerical model, conductors are subdivided into segments (1D finite elements) and Clark's model with distributed constant parameters is then applied. Leakage conductance of conductor segments is modeled in EMTP as an additional lumped parameter. Analytical expressions for distributed and lumped segment parameters are derived using the average potential method. Due to the limitations of the EMTP, EM coupling between segments is neglected. The earth model is limited to the homogenous earth. Soil ionization effect is not accounted for, but could be incorporated, through some modifications of algorithms. Lightning surge model used is based on the Heidler's model of current source.

Performance of Grounding Electrodes Under Lightning Strokes in Uniform and Two-Layer Soils Considering Soil Ionization

This article presented the characteristics of the grounding electrodes in uniform and two layer soils when subjected to lightning including the impacts of soil ionization with frequency, soil resistivity, and permittivity variations. The critical breakdown field strength of two layer soils with different values of the reflection factors was presented. The transient probabilistic grounding potential rise and the transient impedances of the horizontal and vertical electrodes were investigated in uniform and two layer soils including the effect of soil ionization with frequency. Finally, the influences of resistivity and permittivity variations which have substantial impacts on the electric field at the occurrence of the soil ionization were considered. Moreover, transmission line approach (TL) with the aid of ATP has been used to compute the transient grounding voltages. The results indicated that the reflection factor has a significant impact on the equivalent radius of the grounding electrode. It is also observed that the peak values of the lightning induced voltages decreases sharply when the soil ionization phenomenon considering the variations in soil resistivity and permittivity with the stroke frequency changes. Furthermore, the impedances of the burial electrodes that have negative reflection factors were lower than that in case of positive reflection factors.

Transient lightning response to grounding grids buried in horizontal multilayered earth model considering time domain quasi-static complex image method and soil ionization effect

PurposeThe purpose of this paper is to propose a fast, accurate and efficient algorithm for assessment of transient behavior of grounding grids buried in horizontal multilayered earth model considering soil ionization effect.Design/methodology/approachThe purpose of this paper is to develop a numerical simulation method to calculate the lightning impulse response of the grounding grid buried in a horizontal multilayered earth model. The mathematical model about the hybrid method based on PI basic function belonging to time domain is proposed in the paper; the mode can precisely calculate the lightning current distribution and lightning impulse response to grounding grids buried in horizontal multilayered soil model considering soil ionization effect. To increase computing efficiency, quasi-static complex image method (QSCIM) and its time-domain Green’s function closed form are introduced in the model.FindingsThe hybrid model is rather stable, with the respect to the number of elements used and with excellent convergence rate. In addition, because this mathematical model belongs to the time domain algorithm, it is very powerful for the simulation of soil ionization caused by high amplitude lightning current.Research limitations/implicationsTo increase computing efficiency, QSCIM and its time domain Green's function closed form are introduced in the model.Practical implicationsThe mathematical model about the hybrid method based on PI basic function can precisely calculate the lightning current distribution and lightning impulse response to grounding grids buried in horizontal multilayered soil model considering the soil ionization effect.Social implicationsConsidering the soil ionization effect, the simulation calculation of lightning impulse response of substation grounding grid buried in the actual horizontal multilayered earth can effectively support the scientific and efficient design of lightning protection performance of substation grounding grid.Originality/valueThe hybrid model in time domain is originally developed by the authors and used to precisely calculate the lightning current distribution and lightning impulse response to grounding grids buried in horizontal multilayered soil model considering soil ionization effect. It is simple and very efficient and can easily be extended to arbitrary grounding configurations.

General Formulas for Lightning Impulse Impedance of Horizontal and Vertical Grounding Electrodes

Voltage drop developed between the grounding electrode under lightning current and distant neutral ground determines the protection efficiency. The peak value of such voltage can be computed from known impulse impedance and current peak value. For the first time, in this letter, general formulas are derived for impulse impedance of horizontal and vertical electrodes valid for any length up to 100 m, soil's resistivity of 30 to 1000 Ωm, and current impulse front time of 0.2 to 10 μs. Waveforms of typical lightning impulses given in IEC standards are used, but it is shown that results are also relevant for other impulse waveforms. Soil ionization effects are taken into account, and the accuracy of the formulas is investigated. New formulas enable an estimate of lightning protection grounding's surge efficiency in a wide range of practical situations.

A Practical Algorithm for Calculating the Impulse Earthing Resistances of Vertical Earthing Electrodes

An algorithm is proposed in this paper for calculating the impulse earthing resistances of vertical earthing electrodes. The proposed algorithm employs the average potential method to derive the formula of the low current earthing resistance. Unlike the previous algorithm, the soil ionization effect under high impulse current is taken into account by introducing a nonlinear characteristic to represent the relationship between the electric field and current density in the ionization zone around the earthing electrode. On the basis of the nonlinear characteristic, the effective radius is evaluated for the equivalent earthing electrode. Then, the impulse earthing resistance can be calculated by substituting the effective radius into the formula of the low current earthing resistance. A comparison is also made between calculated and measured results to confirm the validity of the proposed algorithm. Keywords: Earthing Resistance; Vertical Earthing Electrode; Average Potential Integral; Soil Ionization; Current Density;

Lightning Impulse Impedance and Surface Potential Distribution of 10 kV Distribution Line Tower: Field Test and Simulation

The impulse grounding performance of distribution lines tower is the key factor to lightning protection. Few field high-current impulse test researches are conducted on distribution line tower. In this paper, we used a mobile high-current impulse generator to conduct test on a 10 kV distribution line tower. The peak value of the current injection is 6 kA to 16 kA. The impulse impedance and the surface potential distribution are measured and analyzed. Based on the CDEGS software, an equivalent modeling of the experiment was carried out. The influence of soil ionization was taken into account by the method of changing the conductor radius through two rounds of calculation. The simulation and measured results were basically consistent. Experiments have shown that the soil ionization effect has an important impact on lightning performance of distribution line tower. The graphite earthing modules (GEMs) and pulling wires can significantly reduce the impulse impedance of the tower. The potential rise of the earth surface at a distance of 30 m from the tower can reach 1 kV at peak, under an injection of 7.15 kA.

Grounding System Modeling and Evaluation Using Integrated Circuit Based Fast Relaxed Vector Fitting Approach, Considering Soil Ionization

Since high voltage transmission line towers or wind turbines structures are installed in high-altitude areas, it is essential to achieve a high overvoltage protection system against direct and indirect lightning strikes collisions. The lightning current must be discharged quickly into the protective earth, to prevent the dangerous over-voltages formation and define a reference voltage node. This paper presents a novel model to assess the behavior of the grounding system, based on Pocklington integral equations under lightning magnetic fields and variations in soil ionization, in which an explicit circuit-based vector fitting RLC admittance branches are proposed. The frequency-dependent behavior of grounding system frequency response and soil ionization effect is modeled in time domain, straightly to implement into the electro-magnetic transient program (EMTP). The model verification contains horizontal, vertical, and their combinations of grounding grids to represent the complete investigations under lightning strikes. The harmonic impedance mathematical formulations and principles are derived based on a rational function, that could be applicable on ground potential rise (GPR) investigation.

Comprehensive formulae for effective length of multiple grounding electrodes considering different aspects of soils: Simplified multiconductor transmission line‐intelligent water drop approach

AbstractIn 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.

Soil ionization effects on surge characteristics of grounding electrodes

For finite‐difference time‐domain (FDTD) simulations, Ala et al. (2008) proposed a simplified engineering soil ionization model on the basis of the dynamic soil‐resistivity model of Liew and Darveniza (1974), and tested its validity against experiments on a 0.61‐m single vertical grounding conductor. In the model, the resistivity of each soil‐representing cell is controlled by the instantaneous value of the electric field there and time. In this article, to test the validity of this model, it was applied to FDTD simulations of the surge responses of different grounding electrodes: an 8.1‐m single horizontal grounding cylindrical electrode buried at a depth of 1 m in a homogeneous soil, and a 1.5‐m single vertical grounding cylindrical electrode in a homogeneous soil. The FDTD‐computed responses agree reasonably well with the corresponding ones measured by Sekioka et al. (1998) and Asaoka et al. (2005). Also, influences of ground‐surface soil ionization, direction‐dependent or direction‐independent resistivity, and three parameters (ionization constant, deionization constant, and critical electric field) of the model were investigated. Surface ionization has a non‐negligible influence only on a short grounding electrode buried in a relatively high‐resistivity soil. Direction‐dependent resistivity yields a little higher voltage and an acute ionization zone near the tip of electrode. Both ionization constant and critical electric field have significant effects: the voltage generated decreases with decreasing ionization constant and/or critical electric field. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Grounding systems under lightning surges with soil ionization for high voltage substations by using two layer capacitors (TLC) model

The grounding system behavior in the time domain for the high voltage substations is the key-parameter to ensure the system reliability during transient conditions. Many approaches are used to investigate the behavior of the grounding systems subjected to the lightning surges. These approaches aim to simplify the grounding systems by equivalent lumped circuit-parameters (RLC) or by using the electromagnetic field theory. The soil ionization phenomenon can effectively reduce the grounding electrode resistance because of changing the electrode equivalent radius located in the soils. Yet, most of these approaches have their relative assumptions with merits and demerits. The current work introduces a proposed model based on a developed grounding unit cell using the Two Layer Capacitors (TLC). The proposed cell is implemented as a unit cell to simulate the performance of the grounding system under lightning strikes with considering the soil ionization effects. Different developed models of the grounding-cells are used to simulate the behavior of the grounding system including the soil ionization process. Finite Difference Time Domain FDTD scheme is used to calculate the electromagnetic fields inside the different proposed unit cells during lightning surges. The application of the grounding unit cell is extended to be implemented for a typical high voltage substation of 500/220 kV. The grounding unit cells are presented as T neighboring sections to evaluate the overlapping between the different elementary electrodes and conductors of the complex grounding systems over the whole area of the substation. The circuit-model of the grounding unit cell is developed using EMTP-RV/MATLAB. Finally, the obtained results are compared with the similar results found in the literature with good consistency.

Lightning Grounding Grid Model Considering Both the Frequency-Dependent Behavior and Ionization Phenomenon

A grounding grid is essential to the lightning protection of power systems. This paper presents a modified partial element equivalent circuit method for predicting the transient behavior of the grounding grid. The frequency-dependent parameters of the grounding grid are obtained first by using the image method. Both modified nodal formulation and vector fitting techniques are applied to derive an extended equivalent network for time-domain simulation. In this method, the soil ionization effect is considered using a nonlinear resistance. The proposed method is verified with experimental results available in the literature. Finally, lightning transients in the grounding grid of a radio base station is presented. The ionization and propagation effects on grounding grid performance are discussed.

Time-Domain Modeling of Grounding Systems’ Impulse Response Incorporating Nonlinear and Frequency-Dependent Aspects

At lightning discharge, the grounding systems’ transient behavior is influenced by time-dependent nonlinear behavior and frequency-dependent effects. These effects are related to complex phenomena arising from the soil ionization surrounding the conductors at high current and to the fast risetime of the impulse current, respectively. Most of the performed investigations were either focused on soil ionization effects or frequency-dependent effects. This paper proposes a model that incorporates both aspects including the mutual coupling and air–soil interface effects, giving a more realistic representation of the grounding systems behavior. Based on the transmission line approach, the model can compute the grounding systems transient response buried in uniform and nonuniform soil. The model is applied to horizontal, vertical electrodes, and grounding grid subjected to impulse currents of variable magnitudes and shapes. The model results are validated against published measurement results obtained with low-current and high-current impulses. The time-domain transient potential and transient impedances show good agreement with experimental results. Other impulse impedance parameters used for the grounding systems analysis are reproduced quite accurately. As an application, the impulse impedance of a horizontal electrode and a grounding grid buried in two-layer soil is discussed when the upper layer depth and the resistivity of soil layers are varied.

Transient lightning response of grounding grids in a horizontal, multilayered soil model that considers soil ionization effects with time‐domain quasi‐static complex images

AbstractA novel mathematical model is proposed that can accurately calculate the lightning current distribution and lightning impulse response of a grounding horizontal grid with a vertical rod embedded in a horizontal, multilayered earth model, under the consideration of soil‐ionization effects. To improve the computational efficiency, a quasi‐static complex image method and the closed form of the time‐domain Green's function were introduced into the model.

An Improved Soil Ionization Representation to Numerical Simulation of Impulsive Grounding Systems

This paper presents a hybrid method based on the transmission line modeling method (TLM) aiming to represent the soil ionization effect for grounding systems simulation. This natural phenomenon can be better represented by taking into account the variation of the conductive components present in the TLM circuit and considering the residual resistivity remaining in the soil. The proposed analytical formulation is developed with a focus on the computational implementation of the method. The model is validated by comparing synthetized test results with measured data and other numerical models (residual resistivity, TLM, and analytical model). High precision together with an easy to implement formulation indicates that the methodology presents potential for real-life applications.