Substation Grounding Grid Research Articles

Derivative Method Based Orientation Detection of Substation Grounding Grid

The grounding grid is a key part of substation protection, which provides safety to personnel and equipment under normal as well as fault conditions. Currently, the topology of a grounding grid is determined by assuming that its orientation is parallel to the plane of earth. However, in practical scenarios, the assumed orientation may not coincide with the actual orientation of the grounding grid. Hence, currently employed methods for topology detection fails to produce the desired results. Therefore, accurate detection of grounding grid orientation is mandatory for measuring its topology accurately. In this paper, we propose a derivative method for orientation detection of grounding grid in high voltage substations. The proposed method is applicable to both equally and unequally spaced grounding grids. Furthermore, our method can also determine the orientation of grounding grid in the challenging case when a diagonal branch is present in the mesh. The proposed method is based on the fact that the distribution of magnetic flux density is perpendicular to the surface of the earth when a current is injected into the grid through a vertical conductor. Taking the third order derivative of the magnetic flux density, the main peak coinciding with the position of underground conductor is accurately obtained. Thus, the main peak describes the orientation of buried conductor of grounding grid. Simulations are performed using Comsol Multiphysics 5.0 to demonstrate the accuracy of the proposed method. Our results demonstrate that the proposed method calculate the orientation of grounding grid with high accuracy. We also investigate the effect of varying critical parameters of our method.

Realization of Harmonic Impedance Simulation Calculation Method for Grounding Grid in Substation

There is a difference between the actual impedance of substations’ ground grid under harmonic interference and that measured under power frequency. Especially under strong harmonic interference, the difference becomes more obvious between the actual one and that measured under power frequency. A method is proposed in this paper to calculate parameters of ground grid models by measuring the ground grid impedances under power frequency and then calculate those under harmonic interference. This method is capable of solving the problem that it is impossible to measure the actual grounding impedance of substations operating under harmonic waves. The feasibility of the method is verified by means of simulating calculations. After correcting by this method, the grounding impedance modulus error becomes less than 2% and the impedance angle error less than 10%. This method may be applied to the measurement and analysis of grounding impedances of substations under harmonic interference.

Corrosion Detection and Analysis of the Underground Grounding Grid in a 220kv Transformer Substation

The first corrosion detection for the large grounding grid of a 220kV substation was performed based on electrical impedance tomography (EIT) technology. The impedance value of grounding grid branch which represented the corrosion state of metal was calculated using the current and voltage data acquired on-site through injecting a direct current from one down conductor and collecting voltage data from other down conductors. The results indicated that the impedance increase ratio of the No.143 grounding grid branch in test area D was higher than the warning value (>15 times), indicating a breakage has occurred on this grounding grid branch. The two-dimension corrosion image of the whole underground grounding grid was calculated and drawn accurately and visually using the corrosion diagnosis software. The corrosion rate of carbon steel was monitored in the serious corrosion area later, to realize the online corrosion monitoring of grounding grid metal. EIT technology realized the underground grounding grid statues visible exhibition, and could be used to detect the corrosion state, corrosion area and failure location of the underground grounding grid rapidly and effectively. This could reduce the blindness of corrosion detection for grounding grid and provide guidelines on the corrosion maintenance of underground grounding grid in large substation.

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.

Substation Grounding Studies With More Accurate Fault Analysis and Simulation Strategies

This paper describes hands-on modeling and simulation experience for designing substation ground grids. The grounding studies enable an optimized ground grid design to protect utility personnel and the public. These optimized ground grids meet the IEEE-80 standard [1] for safety and have been simulated and designed using more accurate transient and steady-state fault current calculations. The SI and MI methods are used to simulate the actual fault locations and fault currents at a small station and a large extremely high-voltage station, respectively. The simulations primarily focus on substation specific data for the application rather than utilizing predetermined split-factor curves and the decrement-factor table in IEEE-80. In addition, the new clearing time analysis and grounding study safety assessment strategy will be implemented instead of using the widely applied longest clearing time and its corresponding threshold calculation, which could further optimize the ground grid. With AEP's research and applications, the authors hope it can benefit similar industrial substation design projects.

Analysis of the disturbance voltage and gpr in substation and mobile base station co-construction

It is essential to consider the electrical safety protection distance when the mobile base station and the substation are building together. This paper makes an analysis from three aspects: the influence on the disturbance voltage of the secondary cable in substation when the station is struck by lightning; the influence on the base station grounding grid caused by the station switching operation and short circuit faults. According to the relevant national and international standards, the electrical parameters are calculated when the substation and mobile base station grounding grid connected in different ways and different distance. The conclusion of the paper provides a theoretical basis for engineering construction with much higher practical value. Meanwhile, it is of great significance to develop the win-win co-operation between the power and telecommunications operators and to explore the diversified businesses of electric power.

A study on high-voltage substation ground grid integrity measurement

The condition of the substation grounding grid is vital for the safety of the people. Inadequate grounding may cause failures in major substation's equipment, as well as in control, metering and telecommunication equipment. Therefore, it is necessary to clearly identify damaged elements on grounding grid. This paper presents an approach to test the integrity of the grounding grid in a general framework of IEEE Std. 81-2012. More precisely, in order to locate damaged grounding riser(s) and/or grounding grid conductor(s), this paper is focused on novel unambiguous criteria for post-processing of raw-data collected from the measurements. In order to avoid the effect of power frequency interference on the measurement, we use DC test current of 100A. The field test is described and discussed in details. The outcome of field test clearly shows the validity and feasibility of the proposed approach.

A Method of Defect Diagnosis for Integrated Grounding System in High-Speed Railway

An integrated grounding system (IGS) plays a significant role in reliable operations of a high-speed railway (HSR). The defect problems of grounding conductors have been frequently occurring due to the long-time service of an IGS and the large current from a traction system. Therefore, defect diagnosis should be conducted. Considering the topology of an IGS and the distribution feature of the surface potential, a method is proposed here to diagnose and locate the defect of the IGS. The grounding conductors can be classified into two main categories, i.e., the grounding grid in a traction substation and the integrated grounding line along a track. The surface potentials, which resulted from the IGS, can be investigated through the electromagnetic calculation of the grounding conductors. Thus, the relationship between the surface potentials and the levels of conductor corrosion can be quantified. As a result, the breakpoint location and the levels of the conductor corrosion of the grounding conductors can be determined by the surface potentials calculated. Finally, the IGS model is simulated in the current distribution, electromagnetic fields, grounding, and soil structure (CDEGS) analysis software, and the results verify the accuracy of the proposed model.

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.

Safe Utilization of Existing Grounding Systems for Expansions and Upgrades of Substations

Utilization of existing grounding systems for the expansions and upgrades of substations offers unique challenges. The identification of current conditions of grounding systems is crucial for safety and for the proper design of their expansions and/or upgrades, which may include the interconnection of an existing grid to a new one. It is also important to note that the evaluation of the conditions of existing substation ground grids may require personal protective equipment to be worn, as well as appropriate safety precautions. In this paper, the authors provide procedures to evaluate the prospective performance of existing grounding systems based upon measurements, as-built and/or contract drawings, site inspections, and examination of key grid points utilizing nonintrusive methods. Safety solutions that can be utilized during the construction phase of the project are also illustrated. A case study that addresses the upgrade of an existing grid is discussed. This paper seeks to clarify for practitioner engineers the problems and variables introduced by the work to be performed on older substation grounding systems. Readers will be provided with tools in compliance with applicable technical standards, which can assist in ensuring continued operation of the substation grounding system during construction.

Numerical simulation of a grounding grid buried in horizontal multilayered earth based on ‘T’ typical basic elements in the frequency domain

In this study, the authors propose a new mathematical model that allows the accurate computation of currents flowing through a substation's grounding grid buried in horizontal multilayered earth, which is a hybrid of Galerkin's method of moment and the conventional nodal analysis method based on ‘T’ typical basic elements. The dynamic state complex image method and the closed form of Green's function of a horizontal dipole or monopole in the earth model are introduced into this mathematical model to enhance its efficiency. In addition, an analytical formula for mutual induction and impedance coefficient calculations are used to accelerate the application of this method. Finally, some numerical results related to a practical grounding problem are discussed and some conclusions are given.

Transferred Potential—A Hidden Killer of Many Linemen

The causes of electrical accidents which occur during maintenance of power lines are sometimes not traceable. Unfortunately, a grounding practice which has been widely adopted in the utility industry in India, U.K., and some other countries unintentionally causes so many fatal accidents every year. The conclusion was arrived after analyzing some fatal accidents. This practice of protective grounding is still continued by many distribution companies without realizing the hazards involved. For de-energized line maintenance, grounding the line at source end is commonly practiced for the purpose of personal protection. This paper explains how this safety practice turns into hazard by transferring the substation ground grid potential to the worksite and why this transferred potential cannot be controlled by any means in three-wire overhead distribution systems which run with no separated ground wire. This paper suggests the solution to avoid the transferred potential and to describe it in IEEE Std. 1048-Guide for Protective Grounding of Power Lines, IEEE Std. 80-2000-Guide for Safety in AC Substation Grounding, British Std. 7430-Code of Practice for Earthing, and Indian Std. 3043-Code of Practice for Earthing to bring an end to the accidents caused by this safety practice.

The protection of 500kV substation grounding grids with combined conductive coating and cathodic protection

Purpose – The purpose of the paper was to design an anti-corrosion system that combined conductive coatings with cathodic protection for a 500-kV substation ground grid, and provide a basis for the anti-corrosion construction of the installation. Design/methodology/approach – The study took the Shaoguan 500-kV substation grounding grid as the research object. The anti-corrosion performance of KV conductive coatings on grounding metal was researched. In parallel, the alkalinity of substation soil was evaluated according to the German DIN50929 Standard, and the combined protection system comprising conductive coatings and impressed current cathodic protection was designed. Findings – KV conductive coatings, that have resistance to acids, alkalis and salts, can effectively slow down the corrosion rate of the grounding grid. The investigation also provided the outline design, installation, construction requirements and monitoring methods for the 500-kV substation grounding grid. Originality/value – This report contains some guiding significance for anti-corrosion engineering of 500-kV substation grounding grids.

IMPACT OF COMPRESSION RATIO ON SUBSTATION GROUNDING GRID RESISTANCE IN LAYERED SOIL

This paper presents impact of grid compression ratio on substation grounding resistance. The minimization of substation grounding resistance is one of the very important criterions in design of substation grounding grid. The decrease in grid resistance reduces the ground potential rise and hence the transfer potential and to a certain extent the safety criterion touch voltage. The term compression ratio is related to unequally spaced grid. We have analyzed the grounding grid for various values of compression ratios for uniform soil model with and without vertical rods. Further the impact of compression ratio on grid resistance is analyzed for various values of soil resistivity reflection factors and top layer height in case of two layer soil model. The simulation has also been carried out for multilayer soil models using Autogrid-pro grounding software. The study results reveals that every ground grid has optimal compression ratio which makes the grid resistance minimum as compared to equally spaced grid for the same area, soil model and number of conductors. Use of ground rods, increases the compression ratio, makes the grid more uniform and decreases the grid resistance.

A Model of Predicting Corrosion Rate for Substation Grounding Grid Based on the Similarity and Support Vector Regression

In this paper, we proposed a training model to predict the corrosion rate for substation grounding grid based on the Similarity and Support Vector Regression (SSVR). In the proposed model, the effect of grounding grid corrosion rate was acted as a feature vector and processed by a dimensionless treatment. Then, the similarity between the feature vector of training terminal and index vector of actual site would be calculated. In the prediction of corrosion rate, the traditional Linear Average Method (LAM) to describe the nonlinear contribution has some fault defects. Therefore, we proposed the training model named SSVR. From the experimental results, the proposed SSVR can obtain better predicting performance than the traditional LAM.

Topological measurement and characterization of substation grounding grids based on derivative method

Derivative method, which avoids pathological solution of the magnetic field inverse problem, was proposed to solve the problem of drawing loss or unknown of grounding grids. First, a shape function was introduced to describe the distribution of magnetic field which is perpendicular to the surface of grounding grids. Since its odd-order derivatives contain main peaks, the 1st-, 3rd- and 5th-order derivatives were chosen to solve the topology of substation grounding grids and measure the branch current of the grid by determining the position and value of main peak, respectively. Numerical example and experimental result show that the 1st- and 3rd-order derivative method works well with low error and less computation.

Evaluation of Soil Corrosivity for Ground Grid of Substations in an Area by Factor Analysis

Soils in a depth corresponding to half length of the buried grouding grids are sampled from sites of 123 substations of a 110 kV transmission network in an area. Their physical and chemical properties(11 indexes) are measured, which then are analyzed and processed by using the method of factor analysis. The results show that soil corrosivity for substation ground grid in this area is mainly influenced by calcium and magnesium ions, pH value, chloride ion and water content. A comprehensive evaluation is made based on these five key corrosive factors. It follows that the soil corrosivity for substation ground grids in this area may be divided into four levels as: exceptionally strong(11 substations), strong(86 substations), relatively strong(14 substations) and middle(12 substations). Meanwhile, the corrosivity of all the soil samples are evaluated according to German Beckman standard method. The results of the two methods are in accord with each other, which indicates that factor analysis can be applied to evaluate the soil corrosivity for substation ground grid with a good reliablility.

Analysis of electromagnetic transients in secondary circuits due to disconnector switching in 400 kV air-insulated substation

This paper describes the electromagnetic transients caused by disconnector switching in 400kV air-insulated substation. Transient overvoltages in the secondary circuits of capacitor voltage transformer (CVT) have been calculated using the EMTP-ATP software. The transfer of electromagnetic transients through substation's grounding grid has been analyzed in order to determine the overvoltages at the terminals of protective relays located in the control (relay) room. The overvoltages in secondary circuits have been recorded during on-site test.

The Study of Grounding Grid State Parameter Measuring System Based on IPC Platform

It is well known that state detecting and evaluating of grounding grid in substation especially defect diagnosis is highly necessary for power system. To detect and evaluate the state efficiently, relevant parameters should be obtained exactly as existing standards all put great emphasis on different parameters should be well-considered. This paper proposed a grounding grid parameter measuring system composed of three devices, through which grounding grid resistance, step voltage, contact voltage under alternating current, connection resistance under direct current and surface potential under square current are available, square current is present in this paper for defect diagnosis . IPC is utilized as the superior computer in this system together with digital touch screen that directly lead to larger storage capacity, simple operation and more friendly convenience for communication between human and computer compared with traditional SCM system. Through experiments it is proved to be accurate ,reliable and repeatable, especially effective for square current devices in defect diagnosis. This template explains and demonstrates how to prepare your camera-ready paper for Trans Tech Publications. The best is to read these instructions and follow the outline of this text.

An Optimal Design of Substation Grounding Grid Considering Economic Aspects Using Particle Swarm Optimization

Design of a safety grounding system is an important part of substation design in power systems. An appropriate designed grounding system ensures the adequate safety for people and protects the installation. Also, due to increasing the electrical equipment price and cost of land, the implementation of grounding system is faced with restrictions. Therefore, the design of optimal substation grounding grid considering the practical limits such as economic aspects is one of the important problem in system designing. This study presents to design an optimal grounding grid considering the economic aspects of designing. In this study, the number and diameters of conductors and rods which can carry the fault current, space between conductors for having the safety factors, the depth of burring the grounding system and investment cost are considered as parameters which affected on total cost of grounding system. Also to conducting the simulation to finding the best parameters of grounding grid to be optimum in all aspects, the Particle Swarm Optimization (PSO) algorithm is employed. Finally, the PSO is applied to a typical grounding system in two different scenarios and the results are compared to each other.