Soil Ionization Effect Research Articles

An EMTP Comprehensive Model of Tower Grounding and its Simulation Analysis

For the purpose of designing the grounding device of the poles and towers an improved EMTP model is put forward in this paper. The impulse characteristics of the tower grounding under impulse currents are simulated and analysed based on circuit theory. Only the non-linear effects caused by soil ionization are considered in the current studies. And the interactions deriving from the coexistence of segmented grounding electrodes have been neglected. Consequently, the calculated results of the impulse grounding resistance of the complex grounding device such as the tower grounding are not enough accurate using the traditional models. The soil ionization effects are simulated through the non-linear resistance. The current-controlled voltage sources are introduced in the model to take into account the interactions of the segmented grounding electrodes. Then the comprehensive model of the tower grounding is established. Comparison of simulation results with experimental data implies that the tower grounding model proposed in this paper is more accurate and effective than the traditional model.

A new soil ionization model for grounding electrodes

This paper proposes a new model of soil ionization, in the form of an equivalent circuit containing capacitive and resistive elements representing a network of soil particles and air voids. In previously published models, the effect of soil ionization is only indirectly considered by changing the soil resistivity and the electrode radius. This has resulted in inferior performance of those models in terms of voltage response accuracy. In this work, the energy balance concept was applied to compute the arc resistance. The soil structure is modeled by using two-layer capacitor elements. The soil ionization process is incorporated inside the two-layer capacitor elements using specially derived differential equations. Unlike previous models, a discrete form of soil ionization is used. The accuracy of the proposed equivalent circuit model was confirmed by the small differences between the computed and experimental results.

The effect of soil ionization on transient grounding electrode resistance in non-homogeneous soil conditions

The soil ionization phenomenon effectively reduces the grounding electrode resistance. The existing methods to determine the soil ionization effect on the transient resistance of a grounding electrode are valid only for homogeneous soils. However, most soil structures are non-homogeneous. Realizing the importance of the issue, this study proposes a hybrid method to incorporate the soil ionization effect on the transient resistance of a grounding electrode located in non-homogeneous soil condition. The electromagnetic field approach is utilized to compute the ionized soil volume around the electrode to determine the equivalent radius of the electrode. A circuit-based method of computing the grounding resistance of the electrode in non-homogeneous soil conditions is proposed based on the per-unit-length distributed parameter method. The proposed method is validated by using an electromagnetic field-based numerical solution for the non-homogeneity effect of the soil on grounding electrode resistance.

Protection from Direct Lightning Strike in the Main Building of the Polytechnic University of Tirana

This paper presents a model of analyzing the transient process of dissemination of electromagnetic wave of the lightning protection system, which is placed on the terraces of the Polytechnic University of Tirana. According to this study simulations were conducted by using the well-known ATP-EMTP software. We have calculated the values of voltages and currents and have also analyzed them. The modeling of conducting segments of protective grid is made by line losses with distributed parameters according to Clark’s model. Direct lightning strike to the protection network, is modeled with the Heidler’s type of current source. Analytical expressions for distributed and lumped segment parameters derive from use of the average potential method. The number of the segments required for an accurate simulation depends on the highest frequency of the injected impulse. This paper presents a transmission line model (TLM). Direct lightning strike onto the top of the building of the Polytechnic University of Tirana is considered. By comparing the results obtained by TLM model and those developed by a more exact electromagnetic model, a specific similarity has been observed, both in the computed amplitude of the overvoltage, as well as in the temporal and spatial overvoltage distribution. Due to the limitations of the transmission line model approach and the application of the ATP-EMTP software package, the electromagnetic coupling between segments is not be taken into account. The earth model is limited to the heterogeneous earth. The soil ionization effect can be included. DOI: 10.5901/ajis.2015.v4n2s2p250

An Improved Circuit-Based Model of a Grounding Electrode by Considering the Current Rate of Rise and Soil Ionization Factors

The behavior of a grounding system can be predicted by using either the electrical equivalent circuit models or electromagnetic computation. Despite its advantages over the latter, the equivalent circuit model fails to accurately predict the behavior under transient conditions due to the absence of two key factors, namely: 1) the current rate-of-rise and 2) soil ionization. This paper proposes a method to enhance the performance of the equivalent circuit model by taking into consideration of both mentioned factors. It is discovered that by using the proposed method, the estimated values of R and L of the equivalent circuit model are improved. The computed inductance dynamically changes with the change in the lightning current parameters, thus improving its accuracy for all current rate-of-rise conditions. The soil ionization effect is implemented as recommended by CIGRE, and this further improves the accuracy of the model. As a result, the voltage response of the model becomes more accurate and comparable to the electromagnetic computation results. Another important feature of the proposed model is that it can be directly applied or connected to power system equipment. Thus, an accurate grounding system effect on the transient performance of key power equipment, such as surge arresters, can be obtained.

The Effect of Grounding Electrode Parameters on Soil Ionization and Transient Grounding Resistance Using Electromagnetic Field Approach

The soil ionization phenomenon occurs during the dispersion of lightning current into the earth. This phenomenon causes the grounding electrode resistance to be effectively reduced. The extension of the soil ionization depends on the current amplitude along the electrode and the resultant electric field intensity surrounding the electrode. The electrical and physical parameters of the grounding electrode system are found as factors that affect the electric field intensity. In this study the electromagnetic field approach and the soil breakdown theory are taken into account to investigate the effect of the mentioned factors on soil ionization and grounding resistance. Changing the parameters of the grounding electrode system affect the electric field distribution around the electrode. Based on the conditions the grounding electrode resistance was reduced between 12% to 75% by considering the soil ionization effect.

High-frequency modeling of Zafarana wind farm and reduction of backflow current-overvoltages

SUMMARY The wind turbine is subjected to lightning due to its geographical location and size. The struck wind turbine suffers from backflow current-overvoltages affected by the grounding system. This issue is highlighted in this paper, and, therefore, the grounding system of the wind turbine is modified. In order to accurately examine the proposed grounding system, we present a model that takes into account both soil ionization and frequency-dependence effect. Also, wind farm components, such as wind turbine down conductor, transformers, surge arresters, overhead, and distributed line, are modeled using high-frequency models. More factors affecting backflow current-overvoltages are analysed such as the lightning inception angle, in-service and out-of-service wind farm, and the number of wind turbines. The simulation is carried out using ATP/EMTP software. Copyright © 2012 John Wiley & Sons, Ltd.

An optimized transmission line model of grounding electrodes under lightning currents

In this paper, an optimized transmission line model (OTL) for modeling transient behavior of grounding electrodes under lightning currents is presented. The soil ionization effect is considered in OTL, and all electromagnetic couplings between different parts of grounding electrode are also considered by selecting the size of segment conductor properly and calculating the mutual coupling parameters between segment conductors accurately. Comparing with the traditional transmission line model, the optimized model can be used to accurately predict the effective length and transient potential rise (TPR) of grounding electrodes. Transient behaviors of grounding electrodes are simulated by OTL and the results are in good agreement with those of the electromagnetic model proposed by Grcev, and experiment results performed by Electricite de France and Geri. Furthermore, non-uniform discharging phenomenon of grounding electrode under lightning current is discussed, and the effective lengths of horizontal grounding electrode under lightning currents are presented.

Lightning Surge Efficiency of Grounding Grids

Two phenomena are important in the dynamic behaviors of grounding systems: soil ionization and inductive behavior. This paper solely focuses on the inductive effects that might impair dynamic performance. This is in agreement with conclusions of recent investigations that the effect of soil ionization can be ignored for grounding grids in high-voltage substations. The inductive effects are enhanced by fast front current pulses that have high-frequency content. We improve the analysis by applying a rigorous electromagnetic model and a realistic waveform of lightning current pulses. The new computer simulation results suggest that values of the grounding grid impulse coefficient are nearly linearly dependent on the side length of square grids. We derive new empirical formulas that approximate the impulse impedance, impulse coefficient, and effective area of grounding grids. These new formulas enable identification of parameters for which the surge performance of grounding grids might be significantly impaired in comparison to low-frequency performance. We verify the simulation method used for deriving the new formulas by comparing our data with published experimental results.

Time- and Frequency-Dependent Lightning Surge Characteristics of Grounding Electrodes

Two phenomena dominantly influence the dynamic performance of grounding electrodes during lightning discharge: 1) the time-dependent nonlinear behavior related to soil ionization during high-current pulses and 2) the frequency-dependent electromagnetic (EM) effects related to fast rise-time current pulses. The first phenomenon improves the grounding performance, while the second might have the opposite effect of impairing the grounding characteristics. It is important to simultaneously analyze these opposing effects; however, modern approaches that take into account both phenomena are mostly based on circuit theory, which does not allow for accurate analysis of fast rise-time pulses. This paper proposes a procedure that combines a rigorous EM approach based on the method of moments with an approximation method for assessing soil ionization effects as recently recommended by the CIGRE and IEEE Working Groups. Based on this procedure, we derive a simple new formula for approximating the surge characteristics that include time-dependent ionization and frequency-dependent inductive effects. We verify the model and formula by comparing our data with published experimental results. We also describe a parametric analysis of the opposing ionization and inductive effects.

Modeling of Grounding Electrodes Under Lightning Currents

More precise modeling of the dynamic performance of grounding electrodes under lightning currents must include both the time-dependent nonlinear soil ionization and the frequency-dependent phenomena. These phenomena might have mutually opposing effects since the soil ionization effectively improves, while frequency-dependent inductive behavior impairs, the grounding performance. Modern approaches that take into account both phenomena are based on circuit theory that does not allow for accurate analysis of high-frequency behavior. This paper aims to further improve the understanding of the dynamic behavior of grounding electrodes under lightning currents by focusing on the following aspects: analyzing the validity domains of popular modeling approaches, based on circuit, transmission line, and electromagnetic theory; providing parametric analysis that takes into account both the propagation and soil ionization effects; analyzing simple formulas for surge characteristics; and comparing the modeling with experimental data. A model and a simple formula that combine the electromagnetic approach, suitable for high-frequency analysis, with the method that accounts for the soil ionization effects, recommended by the International Council on Large Electric Systems (CIGRE) and the IEEE Working Groups, are used for the parametric analysis. Both the model and the simple formula are verified by comparison with experimental results available in the literature.

Grounding Systems Modeling Including Soil Ionization

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> This paper presents a hybrid frequency-time domain methodology for the modeling of grounding systems considering the nonlinear effect of soil ionization. The method is validated by analyzing two typical grounding systems under high soil ionization effects. It is clear from the gotten results the reduction effect of the so-called grounding system “equivalent impedance” when soil ionization takes place. </para>

Lighting electro magnetic field generated by grounding electrode considering soil ionization

Abstract A circuit model with lumped time-variable parameter is proposed to calculate the transient characteristic of grounding electrode under lighting current, which takes into consideration the dynamic and nonlinear effect of soil ionization around the grounding electrode. The ionization phenomena in the soil are simulated by means f time-variable parameters under appropriate conditions. The generated electromagnetic field in the air is analysed by using electrical dipole theory and image theory when the lighting current flows into the grounding electrode. The influence of soil ionization on the electromagnetic field is investigated. *Supported by National Natural Science Foundation of China (Grant Nos. 50407002), and the major state basic research development program of china(Grant No. 2004CB217906)

The simulation of the soil ionization phenomenon around the grounding system by the finite element method

A simulation model based on finite-element method is presented to simulate the soil ionization phenomenon around the grounding system. The advantage of the methodology proposed in this study against analytical methods is that both simple and complex grounding systems buried in homogeneous or nonhomogeneous soil taking into account soil breakdown process can be modeled. The suggested modeling is validated by comparison of the calculated results, which are laid out for grounding rod and grounding grid, with experimental tests results and simulations results found in literature. The performance of grounding system, considering the soil ionization effect at high-magnitude current, is also compared with the one not considering the soil ionization effect

Numerical analysis of transient performance of grounding systems considering soil ionization by coupling moment method with circuit theory

Soil ionization has a great effect on the performance of grounding electrodes fed by currents of high magnitude. In this paper, a numerical method is proposed to analyze the transient performance of grounding system, which takes account of the dynamic and nonlinear effects of soil ionization. The method couples moment method with circuit theory and Fourier transform. The transient performance of grounding system considering the soil ionization effect is compared with that not considering soil ionization effect.

Effective Length of Counterpoise Wire Under Lightning Current

In a high soil resistivity area, counterpoise wires are applied to decrease the grounding resistance of tower grounding devices. If the conductor of counterpoise wire is very long, although the power frequency grounding resistance of the tower grounding device is decreased, the lightning protection performance of the transmission line is still not good. The influences of the length of grounding electrodes on the lightning transient characteristic were analyzed. The dynamic and nonlinear effect of soil ionization around the grounding electrode was considered in the analysis model of transient characteristics for the grounding electrodes under lightning impulse. The counterpoise wire has an effective length when lightning passes through it. When the length of a grounding electrode exceeds the effective length, the grounding conductor will not be utilized effectively. The simulating experiments were performed to analyze influences of the length of the counterpoise wire on the impulse characteristics. The formulae to calculate the impulse effective lengths of counterpoise wires were proposed. The model proposed in the paper has been validated by comparing the numerical results with experimental tests.

Time domain analysis of grounding electrodes impulse response

Lightning protection studies require estimation of grounding systems dynamic behavior. This paper presents the results of a new methodology for calculating the lightning response of the basic component of any grounding system, the grounding electrode. Lightning strike is modeled using a double exponential time function. Closed-form mathematical formulae are used to describe current and voltage distribution along the electrode. The effect of soil ionization can be also taken into account. The proposed methodology is validated by comparison of the obtained results with experimental and simulated waveforms found in literature.

Time Domain Analysis of Grounding Electrodes' Impulse Response

Lightning protection studies require estimation of grounding systems' dynamic behavior. This paper presents the results of a new methodology for calculating the lightning response of the basic component of any grounding system, the grounding electrode. Lightning strike is modeled using a double exponential time function. Closed-form mathematical formulae are used to describe current and voltage distribution along the electrode. The effect of soil ionization can be also taken into account. The proposed methodology is validated by comparison of the obtained results with experimental and simulated waveforms found in literature.

Nodal frequency analysis of grounding systems considering the soil ionization effect

Soil ionization takes place when the current leaking into the earth is high enough to produce an electric field intensity greater than a critical value. This phenomenon lowers the ground impedance and it is similar to an apparent increase in the electrode dimensions. Soil ionization has a great influence on the performance of small grounding electrodes fed by currents of high magnitude (i.e., lightning waves). In this paper, a new way of including the nonlinear soil ionization in the grounding system analysis is proposed. The study of the grounding system is performed in the frequency domain by means of an equivalent electric circuit.

Impulse Impedance of Grounding Grids

A method and an empirical formula to calculate the inductance of square grounding grids fed at either centre or one of the corners is presented. Empirical formulae for the effective area and impulse coefficient for centre fed and corner fel square grids are determinel. The valility of the analytical methol has been verified experimentally with model tests. It is shown that the effect of soil ionization on the impulse impedance of grounding grils can be ignored for grounding grids in high voltage sub-stations.