Grounding Grid Research Articles

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.

Electromagnetic disturbance characteristic of typical high voltage switchgear interruption process in offshore wind farm based on integrated conduction model

AbstractIn an offshore wind farm, a high‐voltage switchgear interruption in an offshore substation creates a high‐frequency, high‐amplitude overvoltage that can cause severe electromagnetic interference problems in the intelligent electronic device. To address this issue, mathematical models, vector fitting and finite element method were used to build an integrated electromagnetic disturbance conduction model, whose accuracy was verified by large current interruption tests. Through the simulation of a typical offshore wind farm's single‐phase grounding fault interruption process, the electromagnetic disturbance characteristics and the impact of the ground position are obtained. The results show that during the fault interruption process of phase B grounded, the dominant frequency of disturbance voltage can reach 4.34 MHz, and the amplitude can reach 1.12 kV. The ground grid has a large impact on the interference voltage, which can reach a maximum value of 2.28 kV under specific conditions. The disturbance voltage in the fault process mainly comes through the current transformer, while during the interruption process, it mainly comes through the ground grid. The authors provide a method to establish the integrated electromagnetic disturbance simulation model, which can improve the accuracy of the electromagnetic disturbance conduction process simulation of intelligent components.

Analysis of Transient in Secondary Cable Due to a Direct Lightning Strike on Grounding Grid

When a substation suffers from a lightning strike, beside the interference from the space, there are two main ways in which the transient disturbance affects the secondary cable through the grounding system: the uneven potential distribution and the mutual inductance between the secondary cable and the ground conductor. In this article, a circuit model of grounding grid is developed taking into consideration the mutual inductance between the secondary cable and the ground conductor. While a circuit model of the secondary cable is established with the consideration of uneven ground potential distribution and the mutual inductance between the secondary cable and the ground conductor. Then, the two models are unified to calculate the transient disturbance in the secondary cable due to a lightning strike on the grounding grid. The feasibility of the method is verified through experiments. Then, the effect of the ground potential difference of the grounding grid and its mutual induction with the cable is analyzed. The results show that both the mutual inductance between the cable and the grid and the uneven ground potential distribution greatly affect the transient disturbance in secondary cable.

The negative beam source with single driver for CRAFT NNBI: design and conditioning results

The Comprehensive Research Facility for Fusion Technology (CRAFT) is a large scientific facility that is preferentially deployed for the construction of major national science and technology infrastructures. A negative beam source based neutral beam injector (NNBI) with beam energy of 200–400 keV, beam power of 2 MW and beam duration of 100 s is one of the devices. A giant radio frequency (RF) based negative beam source was designed for the CRAFT NNBI system. In order to understand the physics and pre-study the engineering problems for RF negative beams source, several beam sources with different scales will be designed and tested. According to the R&D schedule, a negative beam source with a single driver was designed, developed and tested first. The single driver beam source is a quarter of the size of the full size negative beam source. It contains an RF driver, an expansion chamber and a negative ion accelerator with three electrodes, which are a plasma grid (PG), extraction grid (EG) and ground grid (GG). To enhance the negative ion production, Cesium is injected into the plasma chamber and a magnetic filter filed is produced by current flow through the PG to decrease the electron temperature. The negative beam source was tested on the test facility after assembly, including RF plasma generation, negative ion production, extraction and acceleration. The characteristic of plasma discharge, beam extraction and acceleration was studied without and with Cs injection. The long pulse of 105 seconds negative ion beam was achieved successfully. The extracted negative ion current is 4 A and the ratio of electron and negative ion is around 0.8. It lays a good foundation for the R&D of negative ion source with a multi-driver for the CRAFT NNBI system. The details of the design and experimental results of beam source was shown in this paper.

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.

Research on Magnetically Coupled Resonant Detection Method for Breakpoint of Four Mesh Grounding Grid

Research on Magnetically Coupled Resonant Detection Method for Breakpoint of Four Mesh Grounding Grid

Numerical Investigation of the Use of Electrically Conductive Concrete-Encased Electrodes as Potential Replacement for Substation Grounding Systems

This paper presents a numerical investigation regarding the possibility of using electrically conductive concrete (ECON) combined with concrete-encased electrode (CEE) technology to develop new substation grounding systems (SGSs) called ECON-EE as a replacement for conventional copper or galvanized steel grounding grids. In the first step, the validation of the commercial FEM software used to perform grounding system analysis was performed in terms of the grid resistance (RG), ground potential rise (GPR), and step and touch voltages, using a symmetrical 70 m × 70 m conventional copper SGS. Next, several numerical simulations of an ECON-EE grounding system with the same dimensions as the conventional copper grid used for FEM software validation were performed. Thus, several parameters of the ECON-EE grounding system were studied, such as the geometry, dimensions, and resistivity of ECON and the diameter of the rebar. The numerical results obtained permit us to demonstrate that ECON-EE grounding systems can perform better than conventional SGSs equipped with vertical rods, particularly in the case of high ground resistivity. Moreover, it was demonstrated that the two main ECON-EE parameters affecting the grounding resistance and the touch and step voltages are the section area and the resistivity of the ECON. As discussed in detail in this paper, the proposed ECON-EE grounding system can offer several advantages compared to conventional SGSs in terms of efficiency and durability, as well as in terms of simplicity of conception and implementation.

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.

An Improved Magnetic Field Method to Locate the Grounding Conductor.

The location of the grounding grid conductors is critical for performing corrosion diagnosis and maintenance work. An improved magnetic field differential method to locate the unknown grounding grid based on truncation errors and the round-off errors analysis is presented in this paper. It was proven that a different order of the magnetic field derivative can be used to determine the position of the grounding conductor according to the peak value of the derivative. Due to the accumulative error of higher differentiation, the truncation error and rounding error were used to analyze to accumulative error and to determine the optimal step size to measure and calculate the higher differentiation. The possible range and probability distribution of the two kinds of errors at each order are described, and the index of peak position error was derived, which can be used to locate the grounding conductor in the power substation.

Three-Dimensional FDTD-Based Simulation of Lightning-Induced Surges in Secondary Circuits With Shielded Control Cables Over Grounding Grids in Substations

Nowadays, plenty of sensitive electronic devices are installed in secondary circuits in substations. When lightning strikes a substation and transmission line, lightning currents flow into the grounding structure of the substation through shield wires and lightning surge arresters in the primary circuit, and lightning overvoltages are induced on control cables in the secondary circuit owing to the effect of transient ground potential rises of the grounding structure and electromagnetic coupling. Shielded control cables are one of the countermeasures against lightning overvoltage induced on control cables; thus, it is useful to evaluate the effectiveness of shielded control cables for designing protection measures properly. Recently, the finite-difference time-domain (FDTD) method, which is one of the full-wave numerical approaches, has been commonly used for simulating electromagnetic transient phenomena in grounding structures, such as the grounding grids of substations. In this work, first, we studied the modeling of tape-type shielded control cables used in substations for FDTD-based electromagnetic transient analyses. Then, using the control cable model, we simulated a test platform of primary and secondary circuits in a substation and calculated the transient response of a grounding grid and voltages induced on the control cable when a lightning impulse current was injected into the grounding grid. We then compared the calculated results with the measured waveforms for validation.

Measurement of Multipath Transients in Secondary Cables Near a 500 kV Gas-Insulated Switchgear During Operations

Operation of SF <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> gas-insulated switchgear (GIS) produces very fast transient overvoltage, which may interfere with the secondary system through many paths. As more and more smart devices are placed near GIS, their anti-EMI capability becomes more and more important. In response to the above problems, this paper carried out on-site measurement on the EMI in the secondary system during the operation of a 500 kV GIS. The EMI in the cable connecting the cabinet near the GIS and the control center 60 m away was paid attention to. By simultaneously measuring the electric field in space, the current through the grounding lead of the GIS, the EMI in the cables with different grounding methods, and the transient ground potential difference between the cabinet and the control center, the effects of different interference paths such as the spatial electromagnetic coupling and grounding system were analyzed. Results show that, the GIS operation will not only generate a spatial electric field, but also induce a circulating current on its grounding leads, resulting in an apparent ground potential difference on the grounding grid. When the shielding of the cable is grounded at both ends, the EMI is mainly determined by the spatial electric field and current in the shielding. As for the cable with single end grounded, the core-shielding voltage contains stronger high frequency components than that when the cable is grounded with both ends. The ground potential difference is the main source of core-ground voltage below 3 MHz when the cable is grounded at single end. Above 3 MHz the space electric field is the main source.

Inversion of one‐dimensional parameters of horizontal multi‐layer soil model based on dynamic state electromagnetic field theory and ant colony optimization algorithm

AbstractBuilding a reliable soil model is a prerequisite for accurately calculating the ground potential distribution of the grounding grid. Research shows that the soil electrical parameters are frequency‐dependent, so frequency domain inversion of soil parameters should consider the soil inhomogeneity and the frequency characteristic of parameters. A method for retrieving parameters of horizontal multilayer soil model is proposed. The theoretical formula of apparent complex resistivity with considering dynamic state electromagnetic field theory is derived from Green's function. Discrete dynamic state complex image method is introduced to solve the infinite integral in Green's function. Ant colony optimization algorithm is applied to optimize the inversion process of soil parameters. In the first stage, applicability of this method is confirmed by interpreting field data under DC field. DC parameters including DC resistivity, thickness and number of layer are determined. The performance of different optimization algorithms in terms of computational efficiency is compared at this stage. In the second stage, soil resistivity and relative dielectric constant are retrieved by inverting frequency domain experimental data. Different representations based on quasi‐static electromagnetic field and dynamic state electromagnetic field theories are taken into account. The frequency characteristic of soil parameters is concluded by discussing the inversion results. In the study of parameter inversion of horizontal multi‐layer soil model, our method has shown strong performance in computational efficiency and accuracy of inversion results.

Probabilistic Evaluation Method of Transformer Neutral Direct Current Distribution in Urban Power Grid Caused by DC Metro Stray Current

With the coupling of the DC metro network and urban power grid, the DC metro stray currents flowing into transformers have caused serious DC bias. There is, therefore, a need to evaluate transformer neutral direct currents caused by the DC metro stray current. To achieve this, an evaluation model considering the coupling of DC metro network and urban power grid is proposed. In the modeling principle, metro lines are coupled with grounding grids of transfer stations. The DC metro system and the urban power grid are coupled with the soil and grounding systems. The train operations on DC metro lines are simulated using the Monte Carlo method. And, considering the conditions of one-way conduction devices (OWCDs) and over-voltage protection devices (OVPDs), transformer neutral direct currents are calculated. Moreover, two probability indexes are proposed to evaluate distributions of transformer neutral direct currents. The applicability of the proposed model is verified by comparing the calculation results with test data of the transformer neutral direct current. Using the evaluation model, transformer neutral direct currents are evaluated. The result indicates that substation supplying power to the DC metro network has a large probability of a high-level neutral direct current.

Modeling Of Generator Neutral Ground System Using Labview 2017 Application IEEE std C62.92.2TM

The generator is a device for an important source of electrical energy, so the continuity of the generator operation must be maintained and well controlled, in controlling the grounding on the generator can use in control with software such as MATLAB and Modeling the design of the grid grounding system using LabView 2017, Determination of the grounding system for the neutral value of the generator through the distribution transformer, can be done through manual calculation. The use of many parameters considered in the calculation to obtain appropriate and measurable results there is a possibility of repeated calculations. This is very difficult and causes a large difference in calculation results. Therefore, a computer-based computing system is needed to overcome problems like this. Several papers have developed calculations of the amount of generator neutral grounding required that consider the voltage level, short circuit fault current and ground fault protection system. This paper discusses modeling and simulation in designing generator neutral grounding using LabView 2017 application. The goal is to be easier, faster and more accurate. As an implementation of modeling, data from std C62.92.2TM-2017 is used.

Comparative Analysis of Equal and Unequal Grounding Grid Configurations by Compression Ratio and Least Square Curve Fitting Techniques

The primary aim of the power system grounding is to safeguard the person and satisfying the performance of the power system to maintain reliable operation. With equal conductor spacing grounding grid design, the distribution of the current in the grid is not uniform. Hence, unequal grid conductor span in which grid conductors are concentrated more at the periphery is safer to practice than equal spacing. This paper presents the comparative analysis of two novel techniques that create unequal spacing among the grid conductors: the least-square curve fitting technique and the compression ratio technique with equal grid configuration for both square and rectangular grids. Particle Swarm Optimization (PSO) is adopted for finding out one optimal feasible solution among many feasible solutions of equal grid configuration for both square and rectangular grids. Comparative analysis is also carried out between square and rectangular grids using the least square curve fitting technique as it results in only one unequal grid configuration. Simulation results are obtained by the MATLAB software developed. Percentage of improvement in ground potential rise, step voltage, touch voltage, and grid resistance with variation in compression ratios are plotted.

Analysis of the Impact of Newly Built Grounding Grid on the Original Grounding Grid Based on the Method of Moments

On the basis of the method of moments, the resistive coupling effect between the newly built grounding network. When the horizontal distance between two grounding networks of a substation changes, this original grounding network of a certain substation is analyzed. And establish corresponding soil models based on actual engineering soil resistivity data. Use the grounding grid analysis function of CDEGS software and Powerstation software simulation software to simulate and calculate some parameters of the new and old grounding grids. The analysis parameters mainly include the grounding resistance, step voltage, and contact voltage of the grounding grid system. And the obtained parameter indicators are compared and analyzed with safety limits to determine the safety performance of the newly built grounding grid system in the substation. And the impact on the grounding performance of the original grounding network of the substation. Provide certain theoretical data support for the actual promotion of substation grounding network engineering.

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.

A Detection Method for Fast Electrical Impedance Imaging of Grounding Grid Based on Optimized Differential-Multigrid-Homotopy Algorithm

A Detection Method for Fast Electrical Impedance Imaging of Grounding Grid Based on Optimized Differential-Multigrid-Homotopy Algorithm

Assessing Grounding Grid Robustness Through Analysis of Static Fields

Assessing Grounding Grid Robustness Through Analysis of Static Fields

The impact of fusion welding in corrosion diagnosis of joint systems using ultrasonic technique

Nowadays the ultrasonic guide wave technique is the most accurate method in defect detection. Defect detection in the joined and continues systems make some measurement problems due to the structure and propagation of ultrasonic waves in these systems that must be considered for obtained accurate results. In this paper we analysis the manner and the effect of welded points in joint systems. For this aim we specially considered the grounding grids as a joint system and study the problem of the ultrasonic waves in corrosion diagnosis of this system. The grounding grids are the most important systems that increasing safety of power equipment in substations. The conductors of grounding grids usually connected together by fusion welding or bolts and nuts. But fusion welding make some problems for corrosion diagnosis of grounding grids and also pipelines while using ultrasonic technique. The main problem is incorrect results that obtained due to the interference of ultrasonic waves. This paper presented a new method to eliminating the effect of fusion welding points by placing the ultrasonic transducers in right locations. The influence of the soil is considered. Computer simulation results have shown the effect of this interference in accuracy of the result and effectiveness of the new method.