Vertical Grounding Electrodes 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.

STATISTICAL DATA ON GROUNDING DEVICES AND WAYS TO IMPROVE THEIR DURABILITY

Grounding devices of switchgears of substations differ in design, dimensions, operating conditions. Obviously, the damageability of grounding device elements should depend on the length of horizontal and the number of vertical ground electrodes, soil structure, the content of water-soluble salts in the soil, the type of element, etc. Estimates of the frequency of damage to an element of grounding devices reflect the effectiveness of existing methods for monitoring the technical condition of grounding devices. The article examines the presence of a connection between electrical equipment and metal structures of substations with grounding devices and non-exceeding of the ground resistance of standard values when measured by low-current devices, cannot serve as a sufficient sign of a satisfactory state of the elements of grounding devices. Keywords: corrosion failures, soil electrical resistivity, electrical protection of oil and gas pipelines, environment settings.

Rod Insertion TDR for Detecting Corrosion Damage in Vertical Grounding Electrodes

Faults in a grounding network pose a serious threat to power system equipment protection and worker safety. A large number of vertical electrodes are used in a grounding network and break-points in these due to soil induced corrosion is one of the prime reasons for faults. We present a rod insertion time domain reflectometry (TDR) technique for vertical grounding electrode break-point detection. A secondary bare rod is inserted adjacent to the grounding electrode while a fast risetime pulse is continuously applied to excite a transverse electromagnetic (TEM) wave that propagates along the rods and reflects back from the break-point. The reflected signals for different depths of the secondary rod are analyzed to identify the location and severity of the break-point. We show that fault detection is possible without prior knowledge of soil electrical parameters. To show the feasibility of the proposed technique, a full wave simulation approach is used to evaluate the wideband input impedance of the grounding and inserted rod system and then FFT is applied to obtain TDR responses. The results show the method is capable of detecting faults for a wide range of soil conductivity for a system bandwidth of 300MHz.

Method of Line for Modeling of Grounding Electrodes Buried in Stratified Multilayer Soil

An efficient full-wave semi-analytical method based on the method of line is developed for rigorous modeling of grounding electrodes buried in stratified multilayer soil. As compared to the existing full-wave modeling techniques, the proposed method is extremely computationally efficient while enables modeling of any number of vertical and/or horizontal soil layers. Furthermore, the proposed method is not prone to any stability or convergence numerical issue. The efficiency and accuracy of the proposed method is evaluated using the cases of horizontal and vertical grounding electrodes buried in vertically or horizontally stratified multilayer soil.

Study on the characteristics of the potential rise of shell under VFTO in the GIS pumped storage power station

Compared with the traditional GIS station, complex wiring and operation mode of pumped-storage plant diversity, working condition of frequent transformation, makes the plant to produce very fast transient overvoltage (VFTO) probability increase greatly. VFTO will form a transient coupled to the GIS shell casing transient earth voltage (TEV), and then to station personnel safety and the reliability of the secondary equipment poses a great threat. But at the moment because of the limitation of testing technology such as understanding of the academic study of TEV is lack of system. Based on a typical 500 kV gis pumped-storage power station, this paper established a system equivalent model of GIS, network frame and calculates the amplitude, frequency spectrum characteristic of the TEV and influence on VFTO characteristics, and analyzes the fault location, power supply mode, branch bus, the influence of vertical grounding electrodes on the TEV characteristics, For the characteristics of the TEV rules and parameters. Research on TEV characteristics of GIS of pumped storage power station has important reference value for further perfecting relevant theories.

Lightning Performance of Multiple Horizontal, Vertical and Inclined Grounding Electrodes

Single horizontal and vertical grounding electrodes are often used for an earth connection of the lightning protection system. However, there are many practical situations when such electrodes have to be enhanced for better efficiency and replaced by multiple horizontal, vertical and/or inclined electrodes. This paper presents a systematic approach to evaluating and comparing the lightning performance of such grounding arrangements based on simple formulas. The contributions of this paper are: It is shown that impulse impedance <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> may be derived from known formulas for low-frequency grounding resistance <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> ; a new definition of effective length is introduced that allows for such a derivation; a collection of accurate formulas for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> of all considered grounding electrode arrangements is presented; and a new concept of “effective volume” is described that enables a simple procedure to increase electrodes’ effective length. The new formulas for <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> , <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Z</i> , and effective length of the different electrode arrangements allow an analysis that might help search for a choice of cost-effective configuration and dimensions of the grounding systems in the early design stage.

Simulation and Structure Optimization of Grounding Circuit Model for Power Transmission Line Tower

The lightning current dispersion process through the steel bar inside the concrete pile foundation of the transmission line tower is impeded by the high concrete resistivity. In order to improve the current dispersion performance of the pile foundation, this paper proposes a method to place flexible graphite grounding electrode along the shaft wall of the tower foundation and verified its feasibility. Both single-pile and four-pile foundations are applied to build vertical grounding models of transmission line tower with three different grounding structures, respectively, including flexible graphite grounding line, flexible graphite grounding fabric and combined graphite electrode. The effect of three grounding structures on the current dispersion and resistance reduction is studied by finite-element method. Simulation results indicate that by applying the above three grounding structures on the vertical pile foundation can significantly improve the current density distribution of the excavated pile foundation and reduce the grounding resistance. When the grounding resistance is [Formula: see text], the resistance reduction efficiencies of the above three methods can reach 48.56%, 53.86% and 54.53%, respectively. Considering the limited construction area, this paper compares the foundation that is placed combined graphite grounding electrode with square-ray grounding grid, and it can be seen that by placing vertical grounding electrode can save the land area of 295.99[Formula: see text]m2. This paper can provide reference for the design of excavation pile foundation grounding structure under limited construction area.

Analytical Solution for the Transient Current Induced along the Vertical Grounding Electrode

The paper deals with the analysis of the Pocklington integro-differential equation in the time domain and its analytical solution for the transient current induced along the vertical grounding electrode and, as such, represents a continuation of the research pertaining to the horizontal grounding electrode previously reported by one of the authors. The electrode is excited by a current source impressed at one end of the electrode, representing the model of the lightning strike current. A novel analytical solution is derived using the Laplace transform. Results obtained with this time domain solution are compared with the results obtained via analytical solution of the corresponding Pocklington equation in the frequency domain in conjunction with inverse fast Fourier transform (IFFT). The results obtained via different methods are shown to be in a very good agreement. The results of the time domain analytical solution for the vertical electrode are also compared with the results of the time domain analytical solution for the horizontal electrode, where greater influence of earth-air interface on an induced current is observed. These procedures can be implemented as benchmarking techniques as well as tools for rapid estimation of the observed phenomena.

A Method for Grounding Resistance Calculation of the Vertical Grounding Electrode

A Method for Grounding Resistance Calculation of the Vertical Grounding Electrode

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.

Direct Characterization of Grounding System Wide-Band Input Impedance

In this article, direct characterization of the wide-band input impedance of grounding system buried in multilayer soil is presented. The problem is formulated by mixed-potential integral equations solved by the method of moments (MoM). The method accommodates both delta-gap voltage and impressed-current excitations. The input impedance is then directly obtained from the MoM matrix. The proposed method does not rely on the integration of the electric field on the ground surface. Hence, the calculated input impedance is unique and path-independent. The accuracy of the proposed method is evaluated for the case of vertical ground electrodes buried in homogeneous soil. The cases of vertical grounding electrode buried in multilayer soil as well as square and circle-plates buried in homogeneous soil are studied. It is shown that for plate-shape grounding systems, the total surface area determines the grounding system input impedance and the effect of plate geometry is negligible.

Simple Formulas for Impulse Characteristics of Vertical and Horizontal Ground Electrodes

Although the underlying phenomena when grounding electrodes discharge lightning currents are very complex, it is possible to derive simple formulas of impulse characteristics that allow for important engineering estimates. The interest in simple formulas was recently renewed, resulting in many contributions in the literature. In this paper, a parametric analysis is performed by a simulation of time-domain responses, with parameters in broad ranges. From this study, new formulas of impulse characteristics have been derived, including the expressions for ranges of parameters when grounding electrodes exhibit dominant inductive, resistive, or ionization effects. New formulas are compared with the existing ones, with experimental results, and their accuracy has been investigated.

Electromagnetic transient modeling of grounding electrodes buried in frequency dependent soil with variable water content

The increasing demand for electricity over the past few decades has been continuously urging for more reliable power systems. Power transmission line networks, due to their vast physical dimensions, are the most critical components of a complex power system concerning the direct lightning strike. Grounding systems are widely used to mitigate the transient overvoltages for the protection of electrical component and human safety. The goal of this paper is to investigate the effect of frequency dependence of soil electrical parameters on the performance of vertical and horizontal grounding electrodes subjected to direct lightning strike, considering a variable water content of soil. Four soil models that take into account the variation of soil water content are reviewed and compared. The numerical simulations are performed using a full-wave electromagnetic model based on the Finite Element Method (FEM) in the frequency range from 1 kHz to 5 MHz and applying different soil models with varying water content. Then, electromagnetic transient (EMT) compatible equivalent circuits of grounding electrodes are developed using Fast Relaxed Vector Fitting (FRVF). Typical first and subsequent return stroke current waveforms measured at two different locations are adopted. The results of this paper demonstrate the importance of considering the variation of soil water content in the transient response of grounding electrodes. Simulation results demonstrate that the frequency dependence of the soil parameters lead to a decrease of the potential rise of the grounding electrodes compared to the case where the soil parameters are assumed constant. The effect of soil water content on the grounding performance is also shown to be dependent on the soil type, value of soil water content, and length of electrode.

Optimization of impulse resistance reduction for tower grounding device of transmission line

When the lightning strikes the tower, the lightning current is discharged into the ground through the tower grounding device. The magnitude of the impulse earthed resistance of the tower grounding device determines the lightning discharge capacity of the tower. Therefore, the tower grounding device directly affects the lightning protection level of the tower. This paper first introduces three commonly used shock resistance reduction methods: long vertical ground electrode, acupuncture ground electrode, and externally induced rays. Then, the CDEGS software is used to simulate and analyze the long vertical grounding electrode, and a method of insulation short shield is proposed to determine the optimal length of the vertical grounding conductor of the grounding device. Finally, the different resistance reduction effects under the change of length and number of roots are explored, and the optimal resistance reduction arrangement under the same economic conditions is realized.

Mathematical Modelling of Electric Field Generated by Vertical Grounding Electrode in Horizontally Stratified Soil Using the FDTD Method

Mathematical Modelling of Electric Field Generated by Vertical Grounding Electrode in Horizontally Stratified Soil Using the FDTD Method

Определение эффективного радиуса действия вертикального заземлителя в условиях экранирования катодного тока подземных нефтегазопроводов площадных объектов

Определение эффективного радиуса действия вертикального заземлителя в условиях экранирования катодного тока подземных нефтегазопроводов площадных объектов

Novel Grounding Electrode Model with Axial Construction Space Consideration

Grounding electrodes are used to ensure safe operation of electrical apparatus. The limited axial construction space for grounding electrodes is a significant constraining factor. Grounding performance will attenuate rapidly under the influence of the reduced length of horizontal or vertical grounding electrodes. However, if additional resistance-reducing measures are adopted, the operation and maintenance cost of grounding electrodes will considerably increase. To solve above problem, this study proposed a novel grounding model that uses a helical grounding electrode to improve grounding performance within limited axial construction space. Firstly, a calculation model of finite element methods (FEM) is built based on the concept of increasing the contact area between the grounding electrodes and the soil. Grounding performance parameters of helical grounding electrodes, grounding resistance, electrical potential rise (EPR) distribution and maximum touch voltage, are analyzed. At the same time, structural parameters and buried depth for the helical grounding electrodes are studied and the optimal design criteria for the parameters are given. Results show that the helical grounding electrode exhibits better grounding performance in a limited axial construction area.

Topological study on electrode wells of vertical grounding electrodes of UHVDC

Topological study on electrode wells of vertical grounding electrodes of UHVDC

Research on Discharging Current Distribution of Grounding Electrodes

Grounding electrodes with good current discharging performance can ensure the reliability of power system security. Discharging current is not only the reason for accelerating the corrosion, but also the key indicator of the grounding electrodes' grounding performance, which directly affects the grounding resistance, step voltage, ground potential distribution, and other macro grounding parameters. This paper focuses on the discharging current distribution of horizontal and vertical grounding electrodes. Based on the FEM of space tetrahedron and space coordinate transformation method, the calculation model of the horizontal grounding with ground lead and the vertical grounding is proposed, and distribution of discharging current on grounding electrodes with different length is analyzed. Results reveal that discharging current distribution on different location of the aforementioned grounding electrodes. Components of discharging current density on grounding electrodes surface and ground lead exhibit sinusoidal distribution along the circumference of the section on grounding electrodes, and discharging current inside the section are more concentrated on the surface of the section and less on the center. Most discharging current near the junction between horizontal grounding electrodes and ground lead is perpendicular to plane defined by grounding electrodes and ground lead.

Experimental Study on Gas Evolution Characteristics of DC Deep Well Grounding Electrodes

Deep well grounding electrodes (DWGE) have small occupied areas. The number of sub-ground electrodes is less than that of traditional vertical grounding electrodes. Thus, the former has a favorable development prospect. However, given that the active part of a DWGE is buried in the deep earth, DWGE faces more complex gas exhaust problem than shallow-buried grounding electrodes. To research the gas evolution characteristics of DWGE, a U-shaped gas evolution experimental platform that can collect anode and cathode gases separately is designed. Carbon steel material is used as the electrode, and experiments have been conducted on water and saturated coke on the basis of the designed platform and a 30-m DWGE test. The results show that the operating environment and mode (anodic/cathodic) affect gas evolution. When inside water, only the reaction of Fe dissolution occurs at the anode, and Fe is transformed into Fe 2+ while hydrogen evolution and oxygen consumption reactions occur simultaneously at the cathode. When in saturated coke, the gas production at the cathode increases with ampere-hours, thereby changing the contact resistance between the electrode and the coke and forming a “bubble resistance”, then leading to a gas block. The test result of a 30 m well at 100 A further verifies the experimental results of the designed platform and confirms that a vent pipe plays a role in practical use.