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Studying the frequency and impulse characteristics of grounding grids is of great reference value for the optimal design of the substation. As the frequency increasing, the variation trend of the grounding resistance under different conditions is not same, which is affected by many factors. Therefore, this study focuses on the influence of grounding grid sizes, sparsity, soil resistivity, and grounding material on frequency and impulse characteristics. Based on these factors, the corresponding value of the grounding resistances at different frequencies and the impulse resistances are obtained by simulation. The trends of grounding resistances under different factors are analysed by using the dispersion mechanism. The simulation results show that the impulse grounding resistance will decrease with the increase of the grounding grid sizes and the conductor radius, or will decrease with the decrease of the spacing and the soil resistivity. With the increasing in frequency, the inductance effect of grounding resistance is strengthened, and the effect of soil resistivity and grounding grid parameters on grounding resistance become remarkable.

Developing cracks in the soil by means of explosions in the holes, as is called the explosion grounding electrode in this study, is a very effective way to reduce the grounding resistance in the area with high resistivity soil. In this study, the influence of the grounding grid scale and the arrangement of the grounding electrode on reducing the grounding resistance of three-dimensional grounding grid with explosion grounding electrode are studied. There is a strong shielding effect between the explosion grounding electrodes. When the distance between the explosion grounding poles is short, the effectiveness of reducing the grounding resistance by using the long explosion grounding electrode is obviously restrained. The distance between the explosion grounding electrodes should be more than half the length of the electrodes.

The wire loop method of the transient electromagnetic (TEM) method is used to nondestructively detect conductor breaks of grounding grid. For this purpose, grounding grids serve as an underground wire loop, and the measuring points are arranged on the ground. At each measuring point, a receiving loop is employed to detect the electromagnetic response generated by transmitting the current of the transmitting loop. Conductor breaks can be diagnosed by analyzing the slices of the electromagnetic response. We study the effect of loop size and height difference through the simulation of an intact 2×2 grounding grid, confirming that it is easier to obtain the topological structure using a small transmitting loop and a small height difference. Furthermore, simulations of an intact 4×4 grounding grid and grids with different locations of conductor breaks are also conducted with a small transmitting loop. It is easy to distinguish the topological structure of the grounding grid and the locations of conductor breaks. Finally, the detection method is applied experimentally. The experimental results confirm that the proposed method is an effective technique for conductor break diagnosis.

The mathematical models proposed in the literature are used to determine the grounding resistance value for electrical installations. These models are mathematical expressions that change according to grounding type and the mechanical properties of the grounding system elements. Besides, the inclusion of nonlinear terms is another important issue in the modeling studies. For the modeling of nonlinear systems and the analysis of the faults that may occur, the finite element analysis (FEA) approach provides realistic results. In the present study, the simulation of a grid fault that may occur in the grounding system of a sample wind turbine (WT) is modeled by 2D electrostatic solver in FEA software. The simulation results prove that the findings are similar to the realistic faults in the grounding system. © 2019 Published by peer-reviewed open access scientific journal.

In the intelligent substation, the shell of the secondary equipment is connected to the ground grid locally. When the short circuit fault current is injected into the grounding grid to cause the ground potential rise, the potential difference between the two points of the grounding grid will affect the normal operation of the secondary equipment. In this paper, aiming at the grounding grid of a 220kV substation, the grounding impedance, ground potential rise and ground potential difference between galvanized flat steel and copper grounding grid are calculated by using CDEGS software. The results show that the copper ground grid has a significant effect on reducing the potential difference of the ground grid.

대지의 접지 시스템 설치는 안전성과 전기 기기의 올바른 작동을 위해 필수적이며, 대지 파라미터, 특히 토양의 저항률은 대지 접지 시스템 설계에서 결정되어야 한다. 토양의 저항률을 측정하기 위한 가장 흔한 방법은 Wenner의 4전극 방법이 있으며, 이 방법은 1차원의 저항률을 얻기 위하여 가변 전극 간격을 갖는 큰 측정 세트가 요구되어 번거롭고, 시간소모가 많으며 비용이 많이 든다. 전기 저항 단층촬영법은 저비용이며 빠른 측정이 가능하다는 장점 때문에 토양의 저항률 분포를 추정하기 위해 적용될 수 있다. 전기 저항 단층은 관심지역에 놓인 전극에서 얻은 측정데이터를 사용하여 토양 저항률 분포를 특성화한다. 이때 전기 단층 촬영법의 역문제는 비선형성이 강하여 저항률 분포를 추정하기 위하여 Tikhonov 조정 방법을 갖는 반복적 Gauss-Newton 방법을 사용한다. 다양한 시뮬레이션을 수행하여 3차원 토양의 저항률 분포를 추정하는데 전기 저항 단층 촬영법은 유용한 성능을 제공하고 있음을 확인하였다.

The role of the grounding system in the safety of the power system and protection of personnel is obvious during an unexpected short circuit or lightning discharge at the substation. The aim of this work is to analyze the effects of several parameters: lightning impulse front time, soil resistivity and types of grid materials on the grounding system of the Substation. The ground potential rise (GPR), touch voltage and step voltage of a 50 m x 60 m grounding grid buried at a depth of 0.5 m were computed using CDEGS when injected by impulse with different front times. Results show that the shorter the front time of lightning impulse waveform, the higher the value of GPR, touch voltage and step voltage. Meanwhile, when the value of soil resistivity is increased, the value of GPR, touch voltage and step voltage is also increased. Lastly, different types of grid conductor materials give different values of GPR, touch voltage and step voltage. However, it can be said that the differences are too small to be of any significance.

By analyzing the lightning protection and grounding requirements of the respective systems of the communication base station and the power tower, the impact of the towers on their respective systems is analyzed. By establishing a simulation calculation model of the shared tower’s grounding grid, a mature algorithm is used to analyze the current distribution of the typical shared tower. And ground potential distribution, so as to obtain the degree of influence of the equipment when the respective system is struck by lightning. According to the impact, the lightning protection grounding technical requirements and common scheme of the shared iron tower are proposed.

Grounding grid plays an important role in protection of main device for power system. With the increase of power capacity and voltage level, the safety of grounding grid is particularly important. In this paper, the seriously corroded flat steel of grounding grid in 220kV substation was investigated by means of different test methods. The result showed that electrode potentials difference existed between different locations on the surface of the buried grounding electrode was the major reason to cause electrochemical corrosion. Meanwhile, higher sulphur and chlorine content of the soil around the substation caused by long-term industrial pollution, led to rapid depletion of zinc coating and acceleration of corrosion process of grounding material. Additionally, effective suggestions were presented in order to reduce the grounding resistance and improve the anti-corrosion performance.

Substation grounding has proved to be a vital action in high voltage substations for safety of persons and equipment. This paper first describes the potential impacts of increasing the earth fault current of high voltage transformers substations more than the designed value on the performance of the grounding system of these substations. New designing methods for system grounding are suggested in this paper to avoid such problems. These proposed new methods aim at designing and constructing the grounding grid system in a way such that it can accommodate the system expansion more easily and safely. A real case 66/11 kV substation is considered as a case study and ETAP 12.6 is used as a simulation tool. The IEEE 80-2000std is adopted as a reference standard for design.

The metro stray current will flow through the neutral point of the transformer from the grounding grid in the soil, causing the transformer DC bias phenomenon. In order to effectively evaluate the influence of metro stray currents on the transformers, the traction current in metro, the “rail-current drainage net-earth” grounding network structure, and the DC bias current loop were equivalent, so a resistance model for the transformer DC bias caused by stray current was built. Then the dynamic equation of transformer neutral point current with time and metro train position was established, and the neutral point current can be solved by LU decomposition. The software CDEGS was used to build train and transformer simulation model. By comparative analyzing the transformer neutral point current between the simulation results and the calculation results of the proposed modeling method, the model error was small, which can be effectively applied to the evaluation of transformers affected by metro stray current.

The following paper presents an overview of the current state of art on the subject of Gas Insulated Substation (GIS) technology in order to understand the necessity of the grounding grid design models. Furthermore, different studies regarding existing applied technologies are considered in order to create an accurate review on GIS grounding models. For a better understanding of current GIS modeling methods an evaluation of the procedures regarding GIS grounding system design is conducted. The focus was to identify a suitable model technique for the GIS assemble and to obtain a proper grounding grid design procedure.

In the first part of this paper, the calculation method of grounding parameters of nano carbon fiber grounding grid have been analyzed under the condition of split current distribution. In this paper, the calculation methods of ground potential increase, grounding grid potential difference, contact potential difference and step potential difference of nano-carbon fiber grounding grid after considering the distribution of short-circuit current are studied, and the control strategies of various performance indexes are studied. The research results show that: due to the high resistivity of carbon nanofibers material, the inner selfimpedance of the grounding grid is large, the reflux current and the shunt current have a great influence on the calculation of the grounding parameters of the carbon nanofibers grounding grids, and have the greatest influence on the potential difference within grounding grids.

It is significant to research the impulse characteristics of substation grounding grid for its optimal design and safe and stable operation. In order to obtain the impulse transient characteristics of substation grounding grid under lightning impulse current more accurately, the impulse current field test was done on a real substation grid. By monitoring the impulse grounding impedance, impulse coefficient, longitudinal current, and node potential under different test conditions, impulse characteristics curves and the effect of some influence factors are gotten, then the main zones of current dispersion and voltage drop are proposed, as well as the effective areas under different conditions are proposed combined with simulation analysis. The results show that: the impulse grounding impedance and impulse coefficient are smaller when the current is injected from the central of the grid. The main current dispersion region of the large-scale grounding grid is about 40 m around the injection point. The potential drops about 30% within 20 m around the injection point, and the change of the potential is small in the far distance. The effective area of substation grounding grid is affected by soil resistivity, and its side length is usually only tens of meters.

In this paper, the present situation of secondary system grounding in substation is comprehensively analyzed, some improvement measures are put forward, such as perfecting setting of secondary grounding grid, improving anti-interference ability of secondary equipment, canceling insulated copper bar in cabinet, making clear grounding mode of cable shielding layer, increasing protection of the weak electrical signal cable, have solved the problem of grounding frequently occurring in engineering.

Individual and equipment accidents of substations are mainly caused by the ground potential rise and the uneven voltage. The consequences of an accident are affected by lots of random elements, such as the type of the grounding faults, the magnitude of the fault current, the duration of the fault clearance time and the withstand voltage of equipment. While the traditional threshold means by judging the resistance of the grounding system, makes it difficult to accurately evaluate the risk of grounding system. Therefore, this paper presents a comprehensive method to calculate and assess the risk of grounding grid, especially for the equipment safety which has not been discussed before. Firstly three kinds of characteristic parameters was proposed which relate closely to individual and equipment safety, namely, the step voltage (Us), the contact voltage (Ut), and the ground potential difference (GPD), to calculate the risk of individual and equipment safety. Afterwards, the security level of the ground system was obtained according to the as low as reasonably practicable (ALARP criteria).

This paper presents the design of 220kV substation grounding grid with difference resistivity soil according to horizontal and vertical two layer soil model is structure using the MALT program of CDEGS Software. The target of this paper is to minimize the touch and step voltages when the resistivity soil is high, in 220kV urban substation pending a direct lightning stroke. Also, it is shown that for a sensor located on the ground, close to 220kV substation, the magnetic field component vertical to the structure can also experience a considerable attenuation, perhaps due to the effect of the induced currents in the substation. The results are confirming by numerical simulations, obtained using NEC-4 and IEEE Guide for Safety in AC Substation Grounding. The step by step procedure for designing 220kV substation grounding grid has been presented for which design parameters were obtained by CDEGS Software.

In this paper, development of a data processing software for grounding grid fault diagnosis of power substation based on the state response analysis (SRA) with impulse current is introduced. The SRA method with impulse current for grounding grid of power substation is described in detail firstly. Then the main function of the developed software used to analyze and display the measured current and voltage waveshapes is presented, including data loading, data display, parameter calculation, database management and correlation analysis to achieve fault diagnosis for grounding grid of power substation. At last, two examples of tests to the grounding grids with filed measured data are shown. All of that provides an effective technical support for grounding grid fault diagnosis based on the SRA.

The corrosion diagnosis of grounding grid can locate the corroded branches and provide guidance for the maintenance and repair of the grounding grid. This paper proposed the electrical impedance tomography (EIT) method on the corrosion diagnosis of grounding grid and described how it works. Firstly, the inverse problem model of the electrical impedance tomography on grounding grid is developed. Secondly, in order to weaken the ill-posedness of the inverse problem, a Newton iterative algorithm with Tikhonov regularization is proposed to solve the problem. Then, due to the high resistivity contrast between the soli and steel and the large size of imaging region, this paper presents the method of soil-separation and block-diagnosis to accomplish these problems. Finally, field experiments were carried out to verify the effectiveness of the proposed method and the results show that the location and degree of the corrosion in the grounding grid can be easily judged from the imaging results.

Grounding grid is an indispensable important component in the substation, which has important meaning for protecting the personal safety, equipment safety and system safety. Due to the grounding grid is always in the complex soil, it faced the varying degrees of corrosion threat. When the soil resistivity is high, engineers usually use an impressed current cathodic protection (ICCP) system to suppress corrosion. But the existing design and installation process of ICCP systems has some drawbacks. Engineers can only get the effect of the system after ICCP systems installed and run. If the effect is not up to standard, they need to re-design and re-install, which will waste a lot of manpower and resources. This paper mainly analyses the ICCP systems and proposes a new method to design the substation grounding grid ICCP systems by COMSOL Multiphyscis simulation software, which can effectively solve the above problems.

Secondary devices are important components of a substation. The overvoltage due to the short circuit fault may interfere and do harm to the secondary devices. Based on the short circuit test of a ±500 kV converter station, the overvoltage of secondary cables in the substation was measured. The ground potential distribution of the grounding grid was calculated. Results show that the ground potential difference between two ends of secondary cables may cause overvoltage between core and shield and they are in the same order of magnitude.

In unequally spaced grounding grid the buried horizontal interconnected conductors are placed at unequal space in such a manner that denser and closely spaced grid conductors placed near periphery of the grid than center of the earth grid. So grounding grid design in unequally spaced manner may be more safe than equally spaced in which there are greater space between horizontal conductors at the center of grid and distance between adjacent horizontal conductors are gradually decreased from center to the periphery of grid. This paper describes the method to design safe and economic unequally spaced grounding grid from equally spaced grounding grid for 220/132 kV substation without using ground rods in uniform soil to overcome the drawback of equally spaced grounding grid. By designing grounding grid in unequally spaced manner may save grounding grid materials also.

The behavior of grounding systems excited by high-current show great differs from that at low-frequency and low-current. Simulation of high-current draining to earth require accurate modeling of tower grounding system. The current model cannot meet this requirement. This paper proposed an accurate time-varying nonlinearly model of grounding systems established by ATP-EMTP, aiming at simulating the impulse characteristic of grounding systems. The results indicated that the strong agreement between the model and experimental values. At the end of this paper come to the calculation that the active length of the grounding bodies ray is 40 m in the grounding grid. And increasing the ray length infinitely is not conducive to reducing the impulse grounding resistance. The results above can be used for optimizing the grounding grid and selecting the length of grounding bodies ray.

Faults in the grounding grid are a hidden danger to the safety of power systems and cause significant economic loss every year. This paper presents a new means to locate faults in grounding grids using the transient electromagnetic imaging method. The method compares the distribution characteristics of the equivalent resistivity of the underground covered by grids for the no-fault case and those with break points. We describe why and how the proposed method can be used for the break-point diagnosis of grounding grids. Simulation was performed using the Ansoft finite-element method package, and a field experiment was conducted to verify the effectiveness of the proposed method. This study provides a practical means for break-point diagnosis with no requirement of power shut down or soil excavation. Moreover, the proposed method does not require the design drawings of grounding grids.

In this paper, we present a numerical model based on the boundary element method that allows to analyze the grounding systems (GSs) of aboveground and underground substations under different locations and considerations. The proposed formulation allows to consider most of the specific properties and conditions of this kind of substations, i.e., complex geometry, different material properties, and different grounding grid configurations, and to study phenomena like transferred potentials by earthing electrodes. Finally, GSs of real substations have been analyzed as application examples.

Since more elements are involved in the construction projects, the decision making process of Resource-constrained Project Scheduling Problems (RCPSP) cannot be determined by a manager, but multiple level decision makers. This study focuses on the RCPSP in a practical grounding grid system project in Jin’ An Qiao hydropower station, which consider the hierarchical organization structure and hybrid uncertainty environment simultaneously. In this practical RCPSP, the construction contractor is the Upper Level Decision Maker (ULDM), while the outsourcing partner is the Lower Level Decision Maker (LLDM). Considering the operations difficulties and practical decision making process in the RCPSP, a bi-level multi-objective RCPSP model with bi-random coefficients is developed. To deal with the bi-random variables in the model, the Dependent-Chance Programming (DCP) method is introduced and the equivalent crisp model is derived. Subsequently, motivated by the particular nature of model, Bi-level Global-local-neighbor Particle Swarm Optimization Algorithm (BGLN-PSO) is designed to obtain the optimal schedule for grounding grid system project. A practical application is presented to verify the efficiency of proposed bi-level multi-objective RCPSP model and algorithm.

The grounding system in a solar farm has unique characteristics due to its extended footprint and varying type of grounding components. The changing physical properties of the soil within the perimeter of a solar farm result in the nonuniform resistivity of the top soil layers. Measurements of the as-built grounding grid could indicate higher grounding resistance than that predicted by design. Once this difference is detected, it is the duty of the designer to modify the existing grounding grid such that the touch potential is below the limits specified by the applicable codes. This paper presents the analysis of the touch potentials in solar farms and also provides some recommendations to reduce these potentials when the grounding resistance is higher than that predicted by the design. An actual grounding grid design and field measurements are used in an example to illustrate the concepts introduced in this paper.

The configuration of grounding grids which are used to earth electrical substations could be equally or unequally spaced. Unequally spaced grids were introduced to improve the requirements of the grids such as grounding grid resistance (Rg), ground potential rise (GPR), maximum touch voltage (Et) and maximum step voltage (Es) values. Also, unequal spacing can reduce the cost of the grids and enhance the level of safety for people and equipments. In this paper two different approaches were used to determine the best possible configuration of grounding grid. These approaches based on sequential multiplicative and sequential power techniques.

The corrosion of grounding grids can result in a grounding accident of a power system, and much attentions has been concentrated on the method used to detect a corrosion fault in a grounding grid, in which the methods of voltage measurement and magnetic field measurement are usually used. In this paper, a cycle voltage measurement method and L-curve regularization method are proposed to locate the faults in grounding grids. The L-curve method was used to select the appropriate regularization parameter, which can effectively balance the error and stability of the solution to the inverse problem. The uncertainty of the solution due to the ill-posed problem in the inverse problem has been well-solved. Experiments were conducted in a laboratory with two network types. In addition, a field experiment was carried out in a 110-kV substation. Both of the results showed that the method can effectively locate a branch fault with a single branch and multiple branches in the grounding grids.

In order to study the influence of vertical grounding electrode on impulse grounding resistance of substation ground network, the grounding model was built in COMSOL, and the impulse grounding resistances of substation grounding grid in different distribution, length and quantity of vertical grounding electrode were simulated and calculated. The results show that the closer the vertical ground to the lightning current injection point is, the smaller the impact grounding resistance is. The impulse grounding resistance, that has a minimum value, decreases first and then increases with the increase of the vertical grounding electrode length. When the additional vertical grounding electrodes are placed in accordance with the evacuation outside and internal density manner within a certain region ranging from the lightning current injection point, the impact grounding resistance has the best reduction effect.

When lightning current is injected into the grounding device, large ground potential rise may occur near the grounding device. When grounding devices of power system are built near civic facilities in the earth, it is necessary to restrain the ground potential rise around the grounding device. The influence of the insulating wall on the impulse characteristics of a 110kV substation grounding grid was studied. Impulse current was injected into the grounding grid and the ground potential rise nearby was measured. Results showed that the ground potential is apparently restrained behind the insulating wall, which means that the insulating wall can provide fine protection to the facilities near the grounding device.

This paper presents the design of 110kV substation grounding grid with high resistivity soil. A horizontal two layer soil model is built by means of the MALT program of the Software (CDEGS). The purpose of this paper is to minimize the touch and step voltages when the resistivity soil is high, in urban substation during a direct lightning stroke. The touch and step voltages in surface of the ground was calculated based on its soil resistivity in top and bottom layers. The calculated results are compared with the standard values that formulated in IEEE Guide for Safety in AC Substation Grounding.

When substations suffer from lightning, the potential difference occurs within the grounding grid, which will generate induced voltage between the core, shield and the armor of the two-end grounded cables and significantly affect the secondary system in substation. This paper analyses the potential difference within large grounding grid and its influence on the secondary cables through the field test. The induced voltage in cable was measured and analyzed. The usage of drain wires was studied.

Grounding system plays very important role in AC substation station for person and equipment safety. Proper design of grounding system is achievable by following IEEE Std-80 on safety in AC substation grounding but novice professionals find it not easy to use. The advantage of this paper presents evaluation of grounding system for AC substation by case studies presentation thus easing the understanding of IEEE Std-80 and its usage. This was carried out by using homegrown Sub-ground software with capability to identify the safety status of a grounding system design procedures. The grounding system is evaluated with six different cases. Different parameter is changed in each case to observe the result of the grounding system. The result shows that there are several important parameters in designing a grounding system. The parameters are grounding grid size, number of parallel rod, level of fault current, crush rock layer, cross sectional area of ground rod and level of soil resistivity. The tolerable and calculated step and touch voltage as well as the mesh voltage of the grounding system are presented in manner to tutor novice professionals on AC grounding system design. Last but not least the software developed in the laboratory useful for novice professionals training for AC substation grounding system.

As the large grounding grid occupies large area, the potential difference on the grounding grid is obvious, and the proportion of inductive components in the grounding impedance is larger. Then the design and the operation of the grounding grid are different from the small grounding grid. The paper studies the characteristics of resistive component and inductive component in the grounding impedance of the large grounding grid. The factors affecting the grounding impedance and the features of the large grounding grid are discussed. The results can provide a technical reference for design, operation and maintenance of the large grounding grid.

The grounding system requires for maintaining safety of operators and apparatus and ensuring reliable working of power network. A grounding of substation connects electrical apparatus and the metallic structures to the common ground. Grounding system of substation should be such that it should limit the potential gradients with in and around substation during normal and fault condition. Ground Fault creates potential rise within and around the substation which increases the step and touch potential. These potentials should be less than the permissible human body limit. For examination grounding grid of substation needs to calculate parameters related to earth and grounding for safe operation. In this paper parameters of existing design of grounding grid of substation are calculated with IEEE standard 80-2013 and some techniques are discussed for increasing grounding system safety. ETAP (Electrical power system analysis) software is used for analysis.

This paper presents the design of grounding grid system for substations. In last past years the design engineers follows steps of grounding grid design as per IEEE standard 80–2013, which is complicated process. This digital application is mainly concerned with development of Standalone software with using Visual Studio, named by “Grounding Grid Designer”, which calculated accurate grounding system as per guidelines given by IEEE standard 80–2013. After applying this computer aid application the complexity as well as time will reduces. This paper mainly conduct three mostly applicable grounding grid design:-Square Shape, Rectangular Shape, and L-shape. After developed software, the results obtained by standalone software is compared by sample calculation of square grid with ground rods design which is given into the IEEE 80–2000 standard in Annex B.

The grounding grid plays an important role in the safe and reliable running of substation, The study on detection and fault diagnosis of grounding grid will provide an effective means for its state evaluation. This paper proposes a multiple parameter imaging method for grounding grid by pulsed electromagnetic inverse, that aims at accurate positioning and quantitative evaluation of corrosion and breakpoint for power system grounding grid, and the new method intends to realize the image reconstruction of electrical conductivity, permittivity and structure for grounding grid. Using the characteristics of electromagnetic wave propagating in different medium surface, the new method establishes the mathematical-physical model and analyzes the electromagnetic field propagation characteristics between grounding grid and the surrounding medium.

This paper proposes a solution of inverse problems for grounding grids. The grounding grid determines the safe and reliable running of substation, The study on inverse problem of grounding grid will provide an effective means for its state evaluation. The grounding grids model is half homogeneous space model, these problems are usually underdetermined due to the lack of enough data to contain a unique solution. In this paper, we present a method for the solution of underdetermined inverse problems. We present a general adjoint state formulation which can improve the calculation speed of sensitivity matrices.

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.

The corrosion characteristics of grounding grid in different kinds of resistance-reducing agent were analyzed. The corrosion characteristic of carbon steel in different resistance-reducing agent was presented. Comprehensive evaluation on construction technology was made. Moreover, reference for the protection of the grounding grid and the safe operation were provided.

A nonparametric cluster classification prediction model was established aiming at small sample and parametric modeling of grounding grid corrosion rate. First of all, a grounding grid corrosion rate level classification strategy was used to reduced the complexity of the prediction model; secondly, a selfhelp method (Bootstrap) was utilized to produce Bootstrap subsets, avoiding small sample problem; finally, multiple weak classifiers were generated for all bootstrap subsets with nonparametric – KNN classification and the Adaboost method and were clustered into a strong classifier. The experimental result shows that, compared with the KNN classification method, corrosion rate levels resulting from the nonparametric cluster algorithm can be matched with the actual results better, and this model is suitable for the grounding grid corrosion rate prediction.

The configuration is essential to diagnose the status of the grounding grid, but the orientation of the unknown grounding grid is ultimately required to diagnose its configuration explicitly. This paper presents a transient electromagnetic method (TEM) to determine grounding grid orientation without excavation. Unlike the existing pathological solutions, TEM does not enhance the surrounding electromagnetic environment. A secondary magnetic field as a consequence of induced eddy currents is subjected to inversion calculation. The orientation of the grounding grid is diagnosed from the equivalent resistivity distribution against the circle perimeter. High equivalent resistivity at a point on the circle implies the grounding grid conductor and vice versa. Furthermore, various mesh configurations including the presence of a diagonal branch and unequal mesh spacing are taken into account. Simulations are performed using COMSOL Multiphysics and MATLAB to verify the usefulness of the proposed method.

With the development of modern power grids to ultra-high voltage, large capacity and long-distance, the grounding short-circuit current of power systems is getting larger and larger, and higher requirements are put forward for the safe and stable operation of grounding systems.The importance of studying the corrosion status of grounding grids is even more prominent. In this paper, from both static and dynamic aspects, the corrosion state prediction methods of the grounding grid are discussed. And the prediction technology is prospected, it is pointed out that the development of a device combining detection and prediction techniques will fill the gap in the international arena. It can not only provide effective guidance for corrosion protection of grounding grids, but also can be applied to other fields.