Ground Mesh Research Articles

Development of a new methodology for measurements of earth resistance, touch and step voltages within urban substations

This paper discusses the development of a new methodology for measurements of earth resistance and touch and step voltages in ground mesh of urban power substations. The main challenge of the work is to find a feasible solution for performing earth resistance measurements from short distances, given that this is the condition actually found in the majority of urban substations. A test field with four ground mesh units of different geometric configurations was implemented and used for performing numerous measurement tests. Based on all the data collected and analysis of the measurement results, a mathematical model was developed to estimate and predict the correct distance in order to obtain earth resistance measurements from short distances, the PRED Method – Polynomial Regression from Database Method. A discussion of the proposed method, as well as analysis of its accuracy and susceptibility to external interference is performed, in addition to its validation in real substations, so as to prove the efficiency and applicability of the proposed method.

Calculation of Lightning-Induced Voltages and Currents on the Transformers Courtyard of Tucuruí Hydroelectric Generation Plant Using the Finite-Difference Time-Domain Method

In this work, voltages and currents induced due to lightning occurrence on the transformers' courtyard of Tucurui hydroelectric generation plant are calculated by employing the Finite-Difference Time-Domain method. The transient functions are obtained for 500 kV-transmission lines at the output of the power plant. In order to the simulations become viable from the computational point of view, it was necessary to use parallel processing for dividing the analysis region into 24 subdomains (24 computer cores were used). The simulated problem in this work consists on an 1 kA-lightning stroke on phase A of the output transmission system of the Tucurui's plant. In this work, induced voltages between the phase A of the line and the following reference points were obtained: a) the courtyard grounding mesh for voltage transformers, b) ground grid in the first floor concrete, c) rock (basalt) surface at the base of the plant, d) the soil's layer and water surfaces. Transient voltages induced between the phases A, B and V of the transmission line are also analyzed. These data are important because the electrical system is based on voltage differences between phases. It is also noticed that, in this case, the maximum induced voltage between phases A and B is approximately 157.9 kV/kA. It is also performed a study regarding voltage supportability for line insulators on the structure.

Mutual Influence of a Deeply Buried Grounding Electrode and the Surrounding Grounding Mesh

In recent years, the ripple effects of damage to home electrical appliances of private residences near a cellular phone base stations due to lightning strikes on the station have become a problem. The damage is primarily caused by the ground potential rise of cellular phone base stations during lightning strike. To prevent such damage, instead of conducting lightning current from the grounding system of cellular phone base stations to the ground, a deeply buried grounding electrode that releases the lightning current deep into the ground through a separate grounding line has been employed in some cellular phone base stations. However, this technique is not versatile and may lead to a large overvoltage in the insulated conducting wire of the deeply buried grounding wire and may cause a dielectric breakdown, thus causing concern that this technique can no longer fulfill its role. Therefore, in this paper, we study the effectiveness and problems of employing deeply buried grounding electrodes using the finite-difference time-domain method.

Improved electrospray design for aerosol generation and flame propagation analysis

Although the hazards of aerosol fires and explosions have been studied for decades the data for aerosol flame propagation is still scarce. Additionally there is a lack of standard techniques and measurement apparatus, which impedes the development of optimal aerosol hazard mitigation measures. The focus of this study is development of an improved aerosol electrospray device for the generation of high quality aerosol data. The goal is achieved through higher nozzle packing, precise nozzle and mesh hole alignment and adding two ground meshes. In addition to a flat ground mesh, the utilization of a cylindrical ground mesh demonstrated improved confinement and guidance of droplets. Duratherm 600, heat transfer fluid, was examined to demonstrate the modified electrospray device capabilities as compared to previous design. Results show the modified electrospray can produce more uniform droplets, more even test chamber dispersion, smaller droplet size and higher concentration aerosol, which is essential to study aerosol flame propagation. Accordingly, the results of aerosol flame speed tests for the improved design were more reproducible. Moreover, it was found that a traditional propane pilot flame was unable to ignite the smaller aerosol droplet size due to the strong turbulence generated by the open flame. However, by careful modification of the pilot flame length, the turbulence decreased dramatically and the small droplet size aerosol can be tested.

A Comparison of Ground Grid Mesh Design and Optimization for 500kv substation using IEEE 80-2000 and Finite Element Methods

An Air Insulated substation is chosen for the analysis located in Pakistan. The protective scheme installed in any substation should be fully active to ensure its proper and accurate operation in case of any fault. Ground Grid mesh used under substation ground consist of horizontal conductors connected with vertical rods. The function of mesh is to dissipate extremely high current generated in any scenario related to fault. In this regard, firstly 500KV substation is chosen for analysis of protection scheme with focus especially on Ground Grid mesh. The analysis of mesh is carried out using both IEEE 80-2000 and Finite Element Methods for the evaluation of important ground grid mesh parameters. A Software is used for analysis i.e. ETAP -12 having more enhanced features than previous versions. The problems regarding existing functioning ground grid mesh are brought to light in one case study. In second Case study, the remedies for the rectification of mesh are provided. In third, case study a new ground mesh is designed for the existing substation considering new methodologies and latest analysis techniques. In fourth case study, a new ground mesh for Ultra High Voltage Substation is designed for 750KV substation. Finally, a inter comparison is done between mesh designed using IEEE 80-2000 and FEM methods to effectively establish the efficiency and effectiveness of each method by each Case study. A recommendation is given regarding the best method to be used for the future designing of ground grid mesh of all AIS substations.

Real-time terrain storage generation from multiple sensors towards mobile robot operation interface.

A mobile robot mounted with multiple sensors is used to rapidly collect 3D point clouds and video images so as to allow accurate terrain modeling. In this study, we develop a real-time terrain storage generation and representation system including a nonground point database (PDB), ground mesh database (MDB), and texture database (TDB). A voxel-based flag map is proposed for incrementally registering large-scale point clouds in a terrain model in real time. We quantize the 3D point clouds into 3D grids of the flag map as a comparative table in order to remove the redundant points. We integrate the large-scale 3D point clouds into a nonground PDB and a node-based terrain mesh using the CPU. Subsequently, we program a graphics processing unit (GPU) to generate the TDB by mapping the triangles in the terrain mesh onto the captured video images. Finally, we produce a nonground voxel map and a ground textured mesh as a terrain reconstruction result. Our proposed methods were tested in an outdoor environment. Our results show that the proposed system was able to rapidly generate terrain storage and provide high resolution terrain representation for mobile mapping services and a graphical user interface between remote operators and mobile robots.

Experimental Studies of the Transient Characteristics of a Deeply Buried Grounding Electrode and a Grounding Mesh

SUMMARYWhen lightning strikes the tower of a cellular phone base station or other such facility, power and communications equipment in the vicinity of the tower may suffer extensive damage due to the lightning current flowing backward from the grounding system of the tower. The use of a deeply buried grounding electrode has been proposed recently to suppress such backflow currents and potential rises in the vicinity of towers. The deeply buried grounding electrode is a bare conductor buried deeply in the ground, which is connected to a lightning rod on the ground by an insulated wire. When lightning strikes the lightning rod, the lightning current is directed to the electrode, from which it diffuses to the ground. Deeply buried grounding electrodes have been installed at cellular phone base stations and other such facilities to solve problems caused by backflow currents and potential rises. A grounding mesh is usually laid around such base stations as a grounding system for the facilities on the ground. Therefore, it is important to understand the interactions between the deeply buried grounding electrode and the grounding mesh. In this paper, experiments on the interactions between a grounding mesh and a deeply buried grounding electrode are described. Additionally, the transient characteristics of the mesh grounding have been investigated. © 2013 Wiley Periodicals, Inc. Electron Comm Jpn, 96(12): 52–60, 2013; Published online in Wiley Online Library (wileyonlinelibrary.com). DOI 10.1002/ecj.11488

제한된 부지 다층 대지구조에서 위험전압을 고려한 접지설계

In Korea, where most of the sites are narrow in space and their earth resistivity is relatively high, the spaces between grounding conductors are likely to be designed narrow in order to lower ground resistance and dangerous voltage below to the permitted safety values. In addition, ground nets are in the shape of square or rectangle depending on the location and size of the facilities and ground contact area, and inner conductors are laid out in grids like the pattern of nets. Nevertheless, with the existing designs, the marginal voltage for safety gets higher as the area is extended further outside, in comparison with that of inner mesh grounding, thus causing much difficulty maintaining them equipotential, and there exist limits in the burial, grounding grid design considering the dangerous voltage of muti-layered model in the constrained sites, was studied.

22.9kV 수전설비 Mesh 접지설계의 안전성 평가 사례

There is increasing demand for practical groundings for small-area substations because of the recent revision of Korea"s Electrotechnical Regulations, which necessitates the method of evaluating their safety. This paper proposes a practical mesh grounding system for 22.9kV substations and studies how to evaluate its safety. The proposed grounding system is proved to obey the safety criteria of ANSI/IEEE Std. 80 via ANSI/IEEE Std. 80 method and computer simulation.

Analysis of voltages induced on power outlets due to atmospheric discharges on Radio Base Stations

For the first time, full-wave simulations regarding voltages induced on power outlets installed inside buildings, due to lightning strokes on a Radio Base Station located nearby, are performed. The scenario consists of nine buildings with outlets connected to low-voltage distribution lines, conductive ground, a Radio Base Station and grounding systems. Loads connected to the power outlets are also considered. This scenario was modeled with a computer software developed in this work that can numerically represent/model real-world complex structures with realistic parameters. In order to obtain realistic results, Maxwell’s equations are solved numerically by using the FDTD method, which generates full-wave solutions of the problems. Here, electrical conductors are represented with the aid of a thin-wire technique. The analyzed domain is truncated by using the UPML formulation. In order to deal with large tridimensional numerical models, a Beowulf cluster with 16 CPUs is used to accelerate the calculation process. The induced voltages at the energy sockets inside the buildings have been calculated initially without an electric grounding mesh connected to them. In a second moment, the calculation of these induced voltages has been performed for the same structure with a grounding mesh connected to it. In a third simulation, electric loads with resistive–inductive characteristics have been added to the scenario (connected to the energy sockets), simulating residential equipment.

Experimental Studies about Transient Characteristics of a Deeply Buried Grounding Electrode and a Grounding Mesh

When lightning strikes the tower of a cellular phone base station or other such facilities, power and communication equipments in the vicinity of the tower may suffer extensive damages due to the lightning current flowing backward from the grounding system of the tower. The use of a deeply buried grounding electrode has been proposed recently to suppress such back flow current and a potential rise in the vicinity of the tower. The deeply buried grounding electrode is a bare conductor buried deep in the ground that is connected to a lightning rod on the ground by an insulated wire. When lightning strikes the lightning rod, the lightning current is directed to the electrode from which it diffuses to the ground. The deeply buried grounding electrodes have been installed in cellular phone base stations and other such facilities to solve such problems caused by the back flow current and the potential rise. A grounding mesh is usually laid around such base stations as a grounding system for the facilities on the ground. Therefore, it is important to understand the interactions between the deeply buried grounding electrode and the grounding mesh. In this study, experiments on the interactions between a grounding mesh and a deeply buried grounding electrode have been carried out. Additionally, the transient characteristics of the mesh grounding have researched.

Classification of sorted patterned ground areas based on their environmental characteristics (Skagafjörður, Northern Iceland)

A multivariate statistical method (factor analysis of mixed data and hierarchical classification) was used to classify the environmental settings where sorted patterned ground develops in a wet oceanic periglacial area (Skagafjörður, Northern Iceland). A total of 750 periglacial features, distributed over 75 sites, were studied. Nine explanatory variables were assessed by fieldwork and using a digital elevation model, the variables were subdivided into three groups (latitude, topography and soil characteristics) and then integrated into a geographical information system. Furthermore, a correlation between the environmental variables and an intrinsic variable (patterned ground mesh diameter) was determined by a bivariate test. The results show that sorted patterned ground are spread over three homogenous areas, mostly differentiated by altitude, insolation, grain size characteristics and type of drift. In addition, feature diameters differ significantly from one group to another. Finally, it appears that patterned ground diameters are positively correlated with (i) the proportion of clay to medium silt content ( r = 0.35), (ii) altitude ( r = 0.51), and especially with (iii) clast length ( r = 0.97). This strong relationship with clast length is observed in each homogenous patterned ground area at both site and feature scales.

봉상접지극과 Mesh접지극의 매설깊이 변화에 따른 위험전압 분석에 관한 연구

Grounding electrodes with higher burial depths are evaluated to have better performance, due to the domestic practice that puts the grounding resistance as the standard of performance evaluation, while grounding resistance decreases as the burial depth increases. However, The dangerous voltage is necessary for the analysis. Because the performance evaluation of grounding electrodes should include not only grounding resistance but also the dangerous voltage(mesh voltage and step voltage). So in this paper, The dangerous voltages of mesh grounding and rod grounding were analyzed for using computer simulation and miniature grounding model.

메쉬접지극의 내부도체 배치에 따른 개선된 메쉬접지극 모델

국내?외 메쉬접지극은 격자형태의 등간격 접지Grid로 설계하고 있다. 격자형 접지Grid의 경우 구석의 접촉전압이 중심 부분에 비해 높아지는 문제점이 있다. 이러한 문제점을 극복하기 위해 사선형태의 접지 Grid를 사용하면 메쉬전압이 발생하는 구석부분의 면적이 감소함으로써 메쉬전압이 감소한다. 따라서 본 논문에서는 기존의 격자형태의 접지Grid의 형태와 다르게 사선형태의 접지Grid를 제안하며, 격자형태의 접지Grid와 사선형태의 접지Grid로 설계된 메쉬접지극에 동일한 접지설계제원을 적용하고 메쉬전압, GPR, 접지저항, 접지도체의 총길이를 비교 검토하여 사선형태 접지Grid의 우수성을 검증하였다.

An adaptive procedure based on combining finite elements with meshless methods

This paper presents a new method for combining finite elements with meshless methods, which increases the accuracy of computational solutions in a coarse mesh by adding nodes in the domain of interest. The present method shares the features of the finite element and meshless methods such as (a) the meshless interpolation of the MLS type is employed; (b) integration domains are consistent with support domains; and (c) essential boundary conditions can be applied directly. In the present method, a ground mesh with triangular or quadrilateral elements is constructed to define polygonal support domains, and then additional nodes are placed arbitrarily in a domain without the reconstruction of a mesh. The method is very useful in an adaptive calculation, because nodes can be easily added or removed without any remeshing process.

Experimental and analytical studies on lightning surge characteristics of ground mesh

AbstractLightning surge characteristics of a ground mesh have an influence on electromagnetic transient behaviors in low‐voltage and control circuits. This paper describes experimental and analytical studies on lightning surge characteristics of a ground mesh. The experimental studies are carried out under various conditions. The experimental parameters considered in this measurement include earth resistances, current injection points, and injection current waveforms. These measured results are compared with calculated results based on the theoretical studies by Sunde. A comparison of the measured results with the calculated results shows good agreement. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(4): 16– 23, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20559

Measurement of Inductive Coupling in Wireless Superconnect

An inductive inter-chip wireless communication scheme in three-dimensional (3D) stacked chip has been reported to achieve high-speed, low-power, and low-cost inter-chip communication. In this scheme, inductive coupling becomes a fundamental of communication and it should be modeled to realize communication. In inter-chip communication, it is considered that eddy current effect and the reflection of electromagnetic field degrade transmission power. However, there is as yet no report on inter-chip inductive coupling showing these effects. In this study, the scattering parameter of inductive coupling in 3D stacked chip has been measured under three conditions. The first measurement is carried out by changing the inductance alignment vertically and horizontally to verify the estimation scheme of coupling coefficient. The second measurement is carried out to evaluate ground mesh effect on inductive coupling. The third measurement is carried out by changing bulk thickness with constant communication distance to evaluate eddy current effect in bulk. The results show that eddy current does not become a problem and power grid degrades communication efficiency.

수조모델을 이용한 메쉬접지극의 접지저항에 관한 연구

Recently, a number of equipments related with electricity, electronics, and communication in the same building are needed to the grounding system for safety from unexpected accidents. When the faulted electric current flows into a certain grounding system, the potential rise in that system takes place and it might induce the potential rise to other grounding system. This potential interference was strongly affected by the surface potential, which was deeply related with the electrode shape. In this paper, the fundamental formula was deduced on the basis of surface potential of two grounding electrodes. Which corresponds to source of the potential interference and other grounding electrode, respectively. Therefore, the degree of potential interference in this mesh grounding electrode system was verified by the simple model simulation. In addition, in order to identify the difference between the grounding resistance in the realistic construction site and the expected value from the corresponding simulation, the experiment was performed with model on a reduced scale about the realistic grounding system. It consists of stainless steel hemisphere electrodes in a water tank. From this work, the grounding resistance in the mesh grounding electrode showed the good coincidence results between those. Consequently, it is confirmed that the grounding resistance in the mesh electrode is possible to be estimated by performing the experiment using the water tank model.

Experimental and Analytical Studies on Lightning Surge Characteristics of Ground Mesh

Lightning surge characteristics of a ground mesh have influence on electromagnetic transient behaviors in low voltage and control circuits. This paper describes experimental and analytical studies on lightning surge characteristics of a ground mesh. The experimental studies are carried out under various conditions. The experimental parameters considering in this measurement include earth resistances, current injection points and injection current waveforms. These measured results are compared with calculated results based on the theoretical studies by Sunde. A comparison of the measured results with the calculated results shows good agreement.

Sonda de TDR para estimativa da umidade e condutividade elétrica do solo, com uso de multiplexadores

Com esse trabalho, objetivou-se a caracterização e avaliação de sondas de TDR para determinação da umidade e da condutividade elétrica do solo. As sondas foram construídas para uso direto com a TDR, ou para serem conectadas a multiplexadores, avaliadas para dois tipos de cabo coaxial e para diferentes comprimentos desses cabos (4 a 19 m). A constante K da equação de Giese-Tieman e as impedâncias das sondas foram determinadas e realizadas leituras de diferentes níveis de condutividade elétrica no solo, para diferentes umidades e temperaturas. Verificou-se, comprovada a necessidade do uso de um resistor de 15 ômega em série com a haste central das sondas de TDR para uso com multiplexadores com leitura automática por computador. O cabo de maior espessura da malha de aterramento e maior diâmetro do condutor interno foi o mais adequado ao uso para as sondas, enquanto o de cabos coaxiais com até 13 m de comprimento total não afetou significativamente as leituras de umidade; por outro lado, sondas de 0,10 e 0,15 m de comprimento de hastes funcionam com eficiência na medição da condutividade elétrica do solo. A faixa de condutividade elétrica do solo, possível de ser medida com essas sondas, situa-se a até 1,0 dS m-1.