Performance Of Grounding Grids Research Articles

Test Method for Transient Characteristics of Grounding Grid With Current Return Point Located in the Same Grid

Lightning strikes in substations may result in extremely uneven ground potential distribution, which will threaten the safety and stability of equipment in substation. However, the main parameters for evaluating the performance of grounding grids are grounding resistance and impulse impedance, and little attention is paid to the distribution of the transient ground potential differences. In addition, when measuring the impulse impedance of a grounding grid, the length of the current leads should be very large, which requires a high-capacity impulse generator to suppress the influence of lead inductance on current waveform. In this paper, a test method is proposed for the transient characteristics of grounding grid with the current-return point located in the same grid. The feasibility of the method is illustrated by analyzing the ground impedance between the current injection point and the return point, longitudinal current of the grounding conductor, transient ground potential rise and transient ground potential difference. The effects of parameters such as soil resistivity, lightning waveform, size of the grounding grid, spacing and materials of the grid conductor are discussed to demonstrate that the method can be applied to most substations. Finally, the practicality of the method is verified by experiments in a 220 kVsubstation.

Corrosion fault identification model of substation grounding grid based on PSO-LS-SVM

As one of the important equipment to ensure the normal operation of substation, the performance of grounding grid has been highly concerned. In recent years, researchers propose that the theory of electromagnetic induction can be used to diagnose and identify the corrosion fault of substation grounding grid. In this paper, a fault classification model based on LS-SVM optimized by PSO is proposed to identify the corrosion fault of grounding grid. Firstly, the wavelet packet transform principle is used to filter the original data, and the wavelet packet energy is used to construct the fault eigenvalue as the input of the fault classification model. Based on LS-SVM, a corrosion fault classification model is constructed, and particle swarm optimization method is used to optimize the parameters of the model, which solves the problem of traditional SVM parameter optimization. Through the practical application in substation, the model proposed in this paper can identify the corrosion of grounding grid conductor without excavation and power failure, which provides an effective scheme for engineering application.

Numerical Analysis of Transient Performance of Grounding Grid with Lightning Rod Installed on Multi-Grounded Frame

In large substations, many lightning rods are installed on multi-grounded frames. The lightning rods, the frame, the grounding grid and the soil form a whole body, and the lightning current will be discharged from many grounding points. In this paper, based on the partial element equivalent circuit method, a numerical model, in the time domain, is developed to simulate the lightning-caused electromagnetic transients on the frame and the grounding grid. The model is verified by field testing and by comparison with commercial software. The model has several features: (1) it has a simple time domain form; (2) it is stable due to a staggered arrangement of space and time variables and an implicit difference scheme used, and (3) the dimension of the equations is relatively small because the unknown variables are divided into several groups, which are calculated one by one. With this method, the transient characteristics of the grounding grid with lightning rods on the frame are calculated, and the factors affecting the results are analyzed. It can be seen that although the frame causes the ground potential rise in an evenly distributed manner, compared with the situation in which the lightning strikes an independent lightning rod, the ground potential decrease rate near the main grounding point is almost the same because most of the current still enters the soil from the grounding electrode closest to the lightning strike. Therefore, even if there is a frame, the nearby facilities should take the same protective measures as in the case of an independent lightning rod. The ground conductors near the grounding points of the frame should be dense enough to reduce the potential gradient. The equipment should be kept at least 10 m away from the grounding point for lightning.

Analysis of the performance of grounding grids buried in heterogeneous soil under impulse current

The present paper is devoted to analyzing the transient behaviour of simple grounding grids subjected to impulse lightning current. The transmission line method (TLM) involving mutual coupling between conductors will be used. The transient behaviour of grounding grids buried in homogeneous and in heterogeneous soil is going to be evaluated into a complete time domain solution. Different simulations carried out altering, the influence of the grid dimensions, the kind of the ground and the current injection point on the grid voltage and impedance will be presented. Simulation results will be shown for two extreme cases: in the first case the current is in the center of the grid and in the second one it is injected in one corner of the two configurations of grids. The obtained results show that the grid 1x1 gives the lowest transient potential when the injection point is in lower resistivity side, and the grid 2x2 presents better behavior when the current is injected at center point. It is obvious that the suggested simulations are in a good agreement, with corresponding results of other researchers.

Research on High Voltage Insulation Performance of Grounding Grid in Large Substation

The gap between overhead ground wire insulators is changed by external force or subjected to overvoltage, intermittent breakdown will occur, and continuous arcing will occur in severe cases. Real-time monitoring of the current change on the ground wire is of significance to the reliable operation of the overhead ground wire major. The article proposes a method to detect the surface contamination of composite insulators by measuring the ground current of the insulator. The ground current characteristics of composite insulators are studied, and the test loops of composite insulator ground current, body leakage current and surface leakage current are established respectively. The above three currents of the insulator were measured and compared and analysed. At the same time, the article focuses on the design and development of the hardware system of the DC grounding system insulation resistance tester with digital display and multi-channel inspection function based on the microcontroller.

Influence of Driven Rods on Performance of Grounding Grids in Stratified Soils.(Dept.E)

The variation in soil structure has a great infleunce on the grounding grid performance. This influnce can be measured in terms of ground resistance, touch and step potentials. The addition of driven rods 10 the grid significantly affects the grounding grid performance. This paper presents a comprehensive experimental study for the influence of adding driven rods on the performance of grounding grids. The study is applied on three constructed scale models. The models have been performed to simulate a single-, double- and triple-layer soils. A comparison between results obtained experimentally and that computed by mathematical equations is introduced.

Impulse Impedance and Effective Area of Grounding Grids

High values and uneven distribution of the transient ground potential rise (TGPR) at grounding grid conductors in cases of lightning can disrupt the system safety and reliability. To assess the transient performance of grounding grids under lightning currents, a parametric analysis was performed with a computer simulation of 13,978 cases of time-domain responses with a broad range of parameters. From this study, graphs of impulse impedance and a new formula for the effective area have been developed. The graphs are general, describe grids of any shape and size and depend on three parameters: grid conductor spacing, the resistivity of earth, and the zero-to-peak time of the lightning current pulse. Although the parametric analysis was based on a uniform soil model, the graphs can also be used for the two-layer soil model. In this paper, graphs and formula are used in a simple procedure to estimate the effectiveness of a mitigation measure to reduce the TGPR by increasing the grounding grid mesh density in a limited area around the current injection points. The results from the procedure are compared with experimental results, and the application and limitations of the procedure are illustrated by considering large grounding grids as examples.

Evaluations of the apparent soil resistivity and the reflection factor effects on the grounding grid performance in three‐layer soils

In this study, the apparent soil resistivity evaluation is estimated for three-layer soils by four strategies and the obtained values are compared with experimental measurements done by using the four-electrode method. Different methods are suggested with the aid of IEEE 80 to estimate the apparent soil resistivity of three-layer soils, in which a grounding system consisting of a grid with rods is constructed. The effect of the reflection factor on the mesh and the step voltages, the grounding system resistance and the mesh voltage is investigated. It is concluded that the first three methods are close together, and also with the experimental findings done by the authors and others the fourth method gives some tolerance with the first three, but it is in agreement with the experimental measurements. It is concluded also that the reflection factors of non-uniform soil have significant effects on the apparent soil resistivity, the step and the mesh voltages and the ground resistance. For the verification of the calculated results, experimental model is used. It is noted that the measured values are slightly high compared with the calculated values; the reason may be due to the boundary effects of the used model.

A Non-Destructive Testing Method for Fault Detection of Substation Grounding Grids.

The grounding grid is critical to the safety and stability of a power system. Corrosive cracking of the grounding conductor is the main cause of deterioration of grounding grid performance. Existing fault diagnosis methods for grounding grids are limited by the number and distribution of grounding leads, and some of them cannot be used for online detection. This paper proposes a grounding grid detection method based on magnetic source excitation. The measuring device consists of four coils, two horizontal excitation coils, and two vertical receiving coils. The secondary magnetic field signal is extracted from the primary field and the background field by properly positioning the coils, such that the measured signal can reflect the underground media more accurately. The measuring device of the method is portable, the measurement process is contactless with the grounding grid, and it is not limited by the grounding leads. Furthermore, it has a strong anti-interference ability and can realize online detection. It was proven by simulations and experiments that the proposed method has a higher measurement accuracy and stronger anti-interference ability when compared with existing methods. This paper also discusses the influence of various factors such as the number and the location of the breakpoints, the frequency of the excitation source, the soil resistivity, and stratification from the measurement data. It was proven that the method has high precision and a wide application range, and is important for guiding significance and reference value in engineering applications.

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.

Investigation on Impulse Characteristic of Full-Scale Grounding Grid in Substation

Impulse performance of grounding grid is needed for lightning protection design of power system. This paper describes an impulse test facility established for the full-scale grounding grid (50 m long and 52.5 m wide) in a 110 kV substation. Test method is presented, including configuration of current injection and return point, measurement of potential rise and longitudinal current. Impulse test is carried out with 2.6/50 and 8/20 μ s current waveform, and the maximum current amplitude is 4 kA. A Current Distribution, Electromagnetic fields, Grounding and Soil structure simulation for the tested grounding grid is also adopted. Impulse performance of full-scale grounding grid is affected by soil ionization and conductor inductance. There is steeper peak on the potential rise waveform near the injection point with shorter wave front current, which leads to more uneven potential rise distribution. Partial soil ionization could increase the current dispersing into the soil at partial area of the grounding grid, and the longitudinal current flowing to the next area decreases. These two factors pose a high potential difference hazard to the secondary equipment via the secondary cable.

The Effect of a Large Backfill Area on Grounding Grid Performance

The construction of a substation will undoubtedly change the properties of any surrounding native soil. In order to study the influence of backfill material on grounding grid performance and in turn optimize that performance, current distribution, electromagnetic fields, ground, and soil structure analysis (CDEGS) was undertaken to simulate the secondary peak of the step voltage generated by a large backfill soil area. As for the various parameters of the finite soil volume, the influence of the soil length L, the edge gradient tan θ, and the resistivity ρ on the secondary peak of step voltage was researched. Then, a grounding test system was established, the selection process of the protection resistors was clarified, and the usage method of agar gel was improved. The feasibility of simulating backfill material with agar gel was verified, and the influence of resistivity and soil scale on the secondary peak of the step voltage was tested. The results show that the larger the backfill material length is, the larger the resistivity is, and the lower the peak voltage is. The effect of soil resistivity on the secondary peak will be greater when the range of backfill material is larger, which means that reducing soil resistivity can effectively reduce the secondary peak. Therefore, a smaller slope can be formed at the edge of the earthwork in the actual substation to reduce the project amount and save investment, which has a certain degree of engineering significance.

Influence of Design Parameters on Grounding Grid Performance:

Many design parameters are known to affect the characteristics of a substation grounding system, in terms of its quality and efficiency. The most relevant of theseparameters are soil resistivity, number of meshes within a grounding grid, and the use of grounding rods in the grid. Grounding rods may contribute to quality and efficiency of substations in terms of their dimensions, distribution within the grid, and material. In this study, the effects of the number meshes and grounding rods on the quality and efficiency of Al khoms substation have been investigated.

Configuration Detection of Substation Grounding Grid Using Transient Electromagnetic Method

Optimizing the grounding grid configuration is an effective approach to improve the performance of grounding grid. On the other hand, configuration of grounding grid is necessary for some defect diagnosis method to detect the faults existing in grounding conductors. This paper employs the transient electromagnetic (TEM) method to draw the configuration of a substation grounding grid. The surface magnetic field is recorded by receiver coils above the grounding grid. Based on the regular distribution characteristics of a recorded magnetic field, the grounding conductor is accurately located from the curve of magnetic intensity. The complete process of configuration detection of the grounding grid is described in detail. After fast inversion calculation of the recorded magnetic field, the equivalent resistivity is obtained. The configuration of the grounding grid will be clearly and accurately shown in the contour map and three-dimensional (3-D) surface map of equivalent resistivity. Model study is performed, and a field test is also conducted. The results are in good agreement to demonstrate the effectiveness of TEM method for configuration detection of the substation grounding grid.

Safety Performance of Large Grounding Grid With Fault Current Injected from Multiple Grounding Points

Due to the overhead ground wires of transmission lines or the transformer's neutral point connected to a substation grounding grid, it looks like that there are many currents injected into or drawn out of the grounding grid from different grounding points when fault occurs. As the grounding grid is becoming larger and larger in area, the potential difference within the grounding grid may become obvious, and the assumption that the grounding points can be regarded as one point may not be suitable. This paper proposes a method to analyze the non-equipotential grounding grids with the fault current injected from multiple grounding points due to the overhead ground wires of transmission lines or the transformer's grounded neutral point. With the method, the influences of the grid area, soil resistivity, material of the grid conductor, and relative position of the grounding points on the performance of the grounding grid are thoroughly analyzed.

A new monitoring technique for the grounding grids

AbstractThe performance and reliability of grounding grids depend on its structural integrity. If grounding conductors are damaged, it may cause misoperation of protective relay which leads to trip feeders unnecessarily. It can also cause not only failures on the surroundings such as the grounding grid, secondary circuits’ cables, and structural elements but also voltage hazard for human. The circuits may attain unacceptable voltages when short-circuit fault currents occur in these grids. This paper presents the development of a new technique to monitor the operating conditions of the grounding grids of high voltage apparatus and systems without any diggings and forced outages. New concept, principals, a technique and a device shown in the paper have never been described before by the other authors. The technique is based on the evaluation of the electromagnetic field distribution pattern over the damaged horizontal elements of the grid.

A Probabilistic Approach for Human Safety Evaluation of Grounding Grids in the Transient Regime

A statistical description of safety aspects of grounding grids based on a new definition for risks of shock for human safety in the transient regime is presented in this paper. The procedure is based on a mathematical approach to evaluate the statistical distribution of lightning current followed by the Monte Carlo simulation of the grounding grid response to the probabilistic distribution of the injected current. The frequency-domain method of moments solution of the governing electric-field integral equation is used to simulate the grounding grid performance. The mapping of frequency-domain data to the corresponding transient data and vice-versa are achieved through appropriate use of the fast Fourier transform (FFT) and inverse FFT techniques, respectively. The proposed simulation methodology is used to obtain the probability by which the safety limits of a given grounding grid are violated. The safety limits are defined by comparing a severity parameter that is calculated by integration of an appropriate function of the current passing through human body over the time span of lighting current. Simulation results demonstrate the compatibility of the low-frequency safety index with that recommended in this paper for transient (high frequency) excitation of a grounding grid.

GROUNDING GRID PERFORMANCE OF SUBSTATION IN TWO LAYER SOIL - A PARAMETRIC ANALYSIS

During ground faults, fault current flows in the ground which results in potential gradient and ground potential rise (GPR). The potential gradient affects the safety of operating person due to step and touch voltage and GPR affects the insulation of protective devices and control cables. The potential gradient and GPR are the functions of ground electrode geometry. In this paper, performance assessment and analysis of grounding grid is carried out for different types of grid electrodes with two layer soil model for both positive and negative reflection factor K. The simulation is carried out to evaluate grounding grid performance indices such as Ground resistance, Mesh voltage, Step voltage, Ground Potential Rise. The various parameters used for the simulation are, depth of ground grid, Number of meshes and length of ground rods. The results are tabulated, and discussed. The SES Autogrid Pro grounding software, Canada is used for the analysis.

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.

The Influence of an Additional Substance in the Trenches Surrounding the Grounding Grid's Conductors on the Grounding Grid's Performance

In this paper, we present how the finite-element method can be utilized to analyze the influence of an additional substance in the trenches surrounding the grounding grid's conductors on the grounding grid's performance. For this purpose, we modified the preliminarily existent FIELD_GS program code in such a way that the additional substance in the immediate vicinity along the grounding grid's conductors can be simulated. Different soil structures and various volumes of the additional substance in the soil have been analyzed to prove the suitability of surrounding the grounding grid's conductors in trenches with the additional substance