Substation Grounding Grid Research Articles

Design of substation grounding grid in CFETR

This paper aims to propose a method for the design of the substation grounding grid in China Fusion Engineering Test Reactor (CFETR). In order to evaluate the safety of the grounding grid, Electrical Transient Analysis Program (ETAP) was used to simulate the fault current, contact voltage, and step voltage, and the results are compared with theoretical calculations to verify the correctness of the design. This will help reduce faults caused by the defects of grounding grid This method is special in that the designed grounding grid not only meets the requirements of relevant standards, but also reduces the number of conductors. During the design process, factors such as voltage level, fault location, and soil resistivity were fully considered to adapt to different occasions. This method can also guide the design and renovation of grounding grids for other buildings in CFETR.

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.

Grounding grid effective area and impulsive impedance considering statistical–probabilistic characteristics of lightning currents

The grounding grid transient behavior is an important substation design criterion. This behavior is determined through interaction with impulsive currents typical of lightning. Based on the technical literature, the behavior in question is determined considering fixed current waves, with median parameters (peak values and front and tail times etc.). Therefore, important statistical–probabilistic characteristics of lightning currents, such as correlations and statistical regressions, are not included. From this perspective, this paper includes research into the sensitivity of impulsive impedance and effective area values of substation grounding grids in relation to the waveform of currents typical of the first return strokes. The results (original) illustrate significant sensitivity of the grids transient behavior in relation to those mentioned statistical–probabilistic characteristics, considering a wide range of resistivities in both current injection points considered in this study.

Defect test of substation grounding grid based on impulse response

Abstract The substation grounding grid has been in the open air for a long time, and it is prone to problems such as fracture and desoldering, which leads to a decrease in grounding capacity and becomes a threatening factor affecting the normal operation of the substation. Based on the principle of state response, this paper demonstrates the feasibility of using impulse current to evaluate the defects of the grounding grid, constructs an impulse impedance test system, and conducts defect detection tests on 8 m×8 m (2 m equal intervals) and 28 m×25 m (unequal interval) grounding grids in the laboratory. It analyzes the measured impulse impedance and amplitude-frequency response curves. After testing the grounding grid of a substation of a power grid company, the test results show that the test system based on the principle of state response is effective. The response voltage waveform and amplitude-frequency response curve when detecting the conductor fracture of the grounding grid are different from the waveform curve when there is no defect. It can be applied to the defect evaluation of the grounding grid and has a certain reference value for practical engineering applications.

Development and Application of Substation Grounding Grid Topology Detection and Recognition System

Abstract To solve the problem of substation grounding grid faults difficult to diagnose in the case of non-power non-excavation, based on the inductive apparent magnetic resistance method developed a set of grounding grid topology detection and identification systems, to achieve non-destructive detection and real-time imaging of the grounding grid location, structure, breakpoints, and other information to identify and rebuild the topology of the grounding grid. The paper introduces the system design and practical experiments and applications in a substation in Guangzhou City, the system has achieved good application results, reaching the level of engineering prototype, the development of the system device has a good practical significance, and has a broad application prospect.

Lightning current Risetime influence on inductive coupling effect of secondary shield cable in substation

Secondary cables are susceptible to lightning surge currents when substation is struck by lightning. Little work has been made to the effects of surge currents in substation secondary cables, particularly the effects of surge current rise time. Six types of simulated lightning surge currents with different rise times, ranging from 5.7 μs to 25.4 μs, were injected into the substation grounding grid, and the inductive voltage from core wire to ground and the shield current in the closed loop of the buried secondary cable were measured simultaneously. The inductive coupling characteristics and the effect of rise time on shielding factor (SF) of buried secondary cables were investigated using time-frequency domain method. The results indicate that the surge current with shorter rise time will induce higher core-wire voltage and higher the shield current on the secondary cable. Double-end grounding of the shielding layer can significantly reduce the cable coupling response, especially reduce the high-frequency component of the inductive voltage at 10 to 100 kHz with steeper surge currents. The SF of secondary cable increases exponentially from 1.91 dB to 8.15 dB as the rise time of the lightning surge current decreases.

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.

Optimal design analysis of substation ground grid mesh

Substations are grounded by means of earth-embedded electrodes in order to provide safety during normal or fault conditions. Electric substations are effectively grounded to guarantee the proper operation of electrical devices, minimize the likelihood of flash-over during transient conditions as well as dispel lightning strokes. A structure is termed grounded if it is electrically bonded to earth-embedded metallic frames. The earth-embedded metallic frames provide a conducting pathway of electricity to the earth and it is called a ground grid system. Substation ground grid mesh is comprised of vertical and horizontal conductors as well as vertical rods buried beneath the substation ground. Electric current flow through the human body is hazardous. Therefore, ground grid systems should be designed such that the likely electric body current in an operator or passer-by should not exceed the standard defined limits under any foreseeable harmful circumstances and as well provide protection of equipment. The objective of this study is to determine substation, safe ground grid system parameters as well as the cost-effectiveness of designing substation ground grids by comparing the IEEE Std. 80-2000/2013 and the Finite Element Method (FEM). ETAP 16.0 Power Tool is employed in carrying out this analysis. The substation expected maximum short circuit current is stated. The design analysis using both methods is presented separately and suggestions are made with reference to the most cost effective and safest method for the effective designing of the substation ground grid system.

Protection of Substation Grounding Grid by Gadolinium Magnesium Sacrificial Anode

Abstract Since lower galvanic efficiency and potential reversal might occur in magnesium (Mg) sacrificial anode applied in anti-corrosion project for grounding grid in substation, rare earth gadolinium (Gd) was incorporated into Mg sacrificial anode material for activating and improving the performance of the anode, and the influence of Gd concentration on properties of Mg sacrificial anode was evaluated by electrochemical method. The results revealed that the incorporation of Gd could effectively improve the electrochemical properties of magnesium sacrificial anode. The present of 0.1%(wt) Gd in the anode caused the best electrochemical properties as follows: the OCP decreased to as low as -1.78V (SEC) while the galvanic efficiency increased to as high as 62%, and the minimal anodic corrosion current, 0.0186mA, was realized, also the reverse potential and current density in DC leakage process increased from 500mV to 900mV and 1mA/dm2 to 2.27mA/dm2, respectively.

Coupling Analysis and Protection Design of Substation Grounding Grid and Surrounding Metal Pipe Grid

When the substation grounding grid and part of the underground metal pipe grid are close to each other, the two produce resistive coupling, and the current of the transmission line will flow through the grounding body and through the soil to the buried pipe grid, which may break through the anti-corrosion layer of the pipe grid, and may burn the body of the pipe grid in serious cases; the underground metal pipe grid will also have an impact on the parameters of the grounding grid. To this end, this paper is based on the numerical calculation method of field-path coupling, combined with the actual situation of substation, using CDEGS and ETAP software to simulate and analyze the current dissipation process when a short-circuit fault occurs in the substation after the ground grid is put into operation under multi-layer soil environment, and to study the influence of resistive coupling between the grounding grid and the surrounding metal pipe grid during an industrial frequency grounding short circuit. Optimize the structure of the grounding system so that the contact voltage across and step voltage is lower than the safety limit to protect the personal safety in the station; at the same time, take certain protective measures to slow down the corrosion of the pipe grid.

접지망에서의 과도 전위 변동으로 인한 2차 케이블의 전압변동 예측을 위한 등가 회로모델 개발에 대한 연구

In this paper, an equivalent circuit model of the surge transmission path was proposed to analyze the effect of potential fluctuations in the substation grounding grid on secondary cables. For the surge hitting the grounding grid, the surge waveform defined in the international standard surge immunity test standard IEC 61000-4-5 was referred to. Based on the FFT result of the surge waveform, the effective frequency band was set up to 20 ㎒. In addition, an equivalent circuit model for each model was produced by dividing the structure of the substation into four parts, and the individual models were verified through comparison of the 3D EM simulation. Finally, the equivalent model of the complete system were verified by comparing the results from 3D simulation in the time domain, and the voltage induced at both ends of the secondary cable when the grounding network was struck was compared.

An Online Method for Monitoring Substation Grounding Grid Impedances—Part II: Verifications and Applications

This paper presents extensive verification, sensitivity, and application studies for an online substation grounding grid condition monitoring method proposed in a companion paper. The studies are conducted using a realistic substation grounding grid and associated feeder configurations commonly encountered in North America. The verification studies confirm that the proposed method is able to estimate the substation grounding impedances with acceptable accuracy. Main factors impacting measurement accuracy are identified and quantified through sensitivity studies. The findings lead to a guide for the implementation and operation of the proposed method. An application case is presented to demonstrate how the gradual deterioration of substation grounding grid can be monitored using the proposed method.

An Online Method for Monitoring Substation Grounding Grid Impedances—Part I: Methodology

This paper presents an online method to monitor the conditions of the substation grounding grid. The proposed method utilizes phase-to-ground faults occurring in downstream feeders as test current sources and the neutral of a specially selected feeder as the electrode for GPR (ground potential rise) measurement. The measured fault currents and GPRs are then used to estimate substation grounding grid impedance. The method, once established, can monitor the grounding grid impedance continuously and automatically, and the trend of the impedance change can be observed. As a result, the proposed method can yield much more reliable information on the substation grounding conditions. The method also overcomes many disadvantages of the offline methods. The proposed idea, algorithm, and hardware setup are described in the paper. Factors contributing to measurement errors are investigated in detail.

Assessment of the Grid Safety Values for Substation Grounding Grid Design Parameters in Vertical Two-Layer Soil Structure

Typically, the impact of the structure of vertically layered soil on the grounding behavior is not considered while designing a substation grounding system. Therefore, it will result in poor grounding designs due to computed inaccurate grid safety values. Besides, no comparative analysis of the grounding design parameters’ impact on the grounding grid systems’ behavior and protection level between vertical and horizontal two-layer soil structures is presently available. Computing and analyzing the grounding behavior of apparent soil resistivity installed in a vertical two-layer soil structure is more challenging than in a horizontal two-layer soil. There are many other parameters to consider, such as the distance ‘a’ between the test electrodes and the angle ‘β’ between the perpendicular line to the soil boundary and the location of the test electrodes. One of the important findings of the assessment shows that the influence of vertically layered soil on grid impedance, step, and touch voltages of a grounding system is insignificant compared to a homogeneous and horizontally layered soil structure. The current flow is affected by an entire grounding grid placed in a specified layer of soil with a specific resistivity for horizontally layered soil. In contrast, soil boundaries separate a grounding grid with various resistivities for vertically layered soil. The outcome of this work is crucial in helping the engineers to understand the behavior of grounding systems in diverse soil conditions and tropical climates.

Research on Electromagnetic Interference of Lightning Current on Secondary Cable in Substation

Secondary cable is an important equipment for ubiquitous power Internet of things to transmit information. When the substation grounding grid is struck by lightning, part of the lightning current flows through the shielding layer of secondary cable and produces core-to-sheath potential difference, which seriously threatens the safety of the secondary system. Fourier transform was used to decompose the lightning current in frequency domain, and the core-to-sheath potential difference at the end of the secondary cable was obtained by calculating the shielding layer current and transfer impedance at each frequency component. The effects of soil resistivity, lightning current waveform, distance between lightning stroke point and cable and grounding grid on the core-to-skin potential difference of secondary cable were studied. It is shown that the core-to-sheath potential difference of secondary cable increases with the increase of soil resistivity, the peak value, and the tail time of lightning current. The core-to-sheath potential difference decreases with the increase of the distance, while the core-to-sheath potential difference increases with the increase of conductor spacing of the grounding grid. The core-to-sheath potential difference with copper grounding grid is smaller than that with steel grounding grid.

Design grounding grid resistance of substation for two soil layer model

All Grounding planning of a substation is important and various design applications are available using calculation uniform soil resistivity, even though actual resistivity data measured is more than one layer. This is caused by limited availability of the application in processing data only for resistivity one layer. Substation grounding grid application (ASPG) 1.0 can be used for designing grid grounding. The ASPG was developed from Lab View software and has ability to data process for resistivity two-layer that to refer IEEE Std. 80-2013. Grid grounding resistance is considering a combination of grid conductor and ground conductor. This paper discusses the calculation of the magnitude of substation grid grounding using formulas developed by Schwarz, Sulivan and Sunde. The design result obtained is more accurate in substitute resistivity for resistivity two-layer model and calculation grounding resistance substation.

Optimization of substation grounding grid design for horizontal and vertical multilayer and uniform soil condition using Simulated Annealing method.

Grounding systems are critical in safeguarding people and equipment from power system failures. A grounding system’s principal goal is to offer the lowest impedance path for undesired fault current. Optimization of the grounding grid designs is important in satisfying the minimum cost of the grounding system and safeguarding those people who work in the surrounding area of the grounded installations. Currently, there is no systematic guidance or standard for grounding grid designs that include two-layer soil and its effects on grounding grid systems, particularly vertically layered soil. Furthermore, while numerous studies have been conducted on optimization, relatively limited study has been done on the problem of optimizing the grounding grid in two-layer soil, particularly in vertical soil structures. This paper presents the results of optimization for substation grounding systems using the Simulated Annealing (SA) algorithm in different soil conditions which conforms to the safety requirements of the grounding system. Practical features of grounding grids in various soil conditions discussed in this paper (uniform soil, two-layer horizontal soil, and two-layer vertical soil) are considered during problem formulation and solution algorithm. The proposed algorithm’s results show that the number of grid conductors in the X and Y directions (Nx and Ny), as well as vertical rods (Nr), can be optimized from initial numbers of 35% for uniform soil, 57% for horizontal two-layer soil for ρ1> ρ2, and 33% for horizontal two-layer soil for ρ1< ρ2, and 29% for vertical two-layer soil structure. In other words, the proposed technique would be able to utilize square and rectangle-shaped grounding grids with a number of grid conductors and vertical rods to be implemented in uniform, two-layer horizontal and vertical soil structure, depending on the resistivity of the soil layer.

Design and Optimization of Substation Grounding Grid for Ensuring the Safety of Personnel and Equipment

Design and Optimization of Substation Grounding Grid for Ensuring the Safety of Personnel and Equipment

Effect of Non-Homogeneous Soil Characteristics on Substation Grounding-Grid Performances: A Review

Designing an effective grounding system for AC substations needs predetermination of ground resistance and ground potential distribution caused by fault current’s presence in the ground. Therefore, it is necessary to have a suitable grounding grid structure in the soil properties in which the grid is buried. Though the soil composition where the grounding grid is located is typically non-homogeneous, the soil is often presumed to be homogeneous due to the complexities of grounding system analysis in non-homogeneous soil. This assumption will lead to inaccuracies in the computation of ground resistance and ground potentials. Although extensive research has been done on non-homogeneous soil structure, comprehensive literature on grounding system performance in non-homogeneous soil is yet to be reviewed. Thus, this paper reviews the effect of non-homogeneous soil on the grounding system, with different soil characteristics in horizontal and vertical two-layer soil structure and the horizontal three-layer soil structure. In addition, the effect of design parameters on the grounding performance in non-homogeneous soil conditions for non-transient fault conditions is also studied. The significance of this study is that it provides a comprehensive review of grounding performance as grounding design changes and their effects as soil layers and their corresponding features change. This knowledge will be useful in developing safe grounding designs in non-homogeneous soil.