Substation Grounding Grid Research Articles

Corrosion fault identification model of substation grounding grid based on PSO-LS-SVM

As one of the important equipment to ensure the normal operation of substation, the performance of grounding grid has been highly concerned. In recent years, researchers propose that the theory of electromagnetic induction can be used to diagnose and identify the corrosion fault of substation grounding grid. In this paper, a fault classification model based on LS-SVM optimized by PSO is proposed to identify the corrosion fault of grounding grid. Firstly, the wavelet packet transform principle is used to filter the original data, and the wavelet packet energy is used to construct the fault eigenvalue as the input of the fault classification model. Based on LS-SVM, a corrosion fault classification model is constructed, and particle swarm optimization method is used to optimize the parameters of the model, which solves the problem of traditional SVM parameter optimization. Through the practical application in substation, the model proposed in this paper can identify the corrosion of grounding grid conductor without excavation and power failure, which provides an effective scheme for engineering application.

Influence on Short-circuit of Substation Grounding Grids by the Use of OPGW Cables

Optical Ground Wire (OPGW) are widely used on power systems. However, the usage of such cables during a transient request may lead to an unusual distribution of current along the grounding electrodes. Thus, it is interesting observe if these cables would case decreased or increased of safety on the vicinity of substation. On the light of such possibility, this paper analyzes the influence of the use of such cables on the intensity of fault currents that flow through the interconnected substation ground grids. For the analysis a comparison between the conventional ground wires set and a system considering the presence of an OPGW are studied. For the modeling of these systems, an EMTP-type software is used as a computational tool for the generation of sensitivity analyzes. The results ilustrate that the use of OPGW significantly reduces the grid currents of the interconnected substations. The studies with this thematic founding in literature approach the subject using only conventional ground wires.

Research on High Voltage Insulation Performance of Grounding Grid in Large Substation

The gap between overhead ground wire insulators is changed by external force or subjected to overvoltage, intermittent breakdown will occur, and continuous arcing will occur in severe cases. Real-time monitoring of the current change on the ground wire is of significance to the reliable operation of the overhead ground wire major. The article proposes a method to detect the surface contamination of composite insulators by measuring the ground current of the insulator. The ground current characteristics of composite insulators are studied, and the test loops of composite insulator ground current, body leakage current and surface leakage current are established respectively. The above three currents of the insulator were measured and compared and analysed. At the same time, the article focuses on the design and development of the hardware system of the DC grounding system insulation resistance tester with digital display and multi-channel inspection function based on the microcontroller.

Comparison of Grounding Grid Parameters Between Copper and Galvanized Flat Steel

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.

The Impact of Substation Grounding Grid Design Parameters in Non-Homogenous Soil to the Grid Safety Threshold Parameters

It is important to ensure that a grounding system is designed with a low magnitude of earth resistance, so the protection system can divert the large fault current to earth effectively. The performances and protection level of a grounding system need to be acknowledged as the condition of soil structure changes with different soil characteristics. At present, there is a lack of systematic guide or standards for grounding grid designs that consider non-uniform soil and its impact on the grounding systems. By computing the grid safety threshold parameters consisting of the grid impedance, step, and touch voltages, a comparison has been made between uniform soil and two-layer soil models. Where the competence and level of safety of the grounding systems depend on the soil attributes, the significant impact of various soil conditions is seen. The evaluations on performance and safety assessment in two-layer soil conditions hold the novelty and originality as there is no such comparison and discussion have been made to date. These comparisons would help in forecasting the behavior and safety of the grounding system in various soil environments, which would provide engineers with additional expertise to design an effective and secure grounding system. This research would contribute to the existing body of knowledge by differentiating and predicting the performance of a grounding system when the characteristics of the soil differ significantly from uniform soil as most of the standards and guidelines only consider uniform soil while designing a grounding system, owing to its complexity at the site.

A Simple Design Method of Unequal Spacing Arrangement for Substation Grounding Grid

To balance the potential distribution on the surface of a substation, an equal spacing arrangement of the grounding grid conductors is not an economical solution. The implementable solution is an unequal placement of its constituent elements. The design methodologies of such a configuration are complex and require computer-assisted numerical analysis. This paper proposes and validates a very simple method, based on an arithmetic progression, of arranging the conductors of the grounding grid that guarantees the reduction of touch and step voltages, ensures the efficiency of the material used and has no limitations on its applicability for atypical substation surfaces (too large or too small), respectively for few or many parallel conductors. To certify the method, the proposed algorithm is analyzed, through the CYMGRD Substation Grounding Program, and compared to the technologies currently applied, for the substation grounding grid presented as an example in the IEEE Guide for Safety in AC Substation Grounding 80™- 2013 standard.

Effects of Soil Profile on the Transient Performance of Substation Grounding System

<table width="593" border="1" cellspacing="0" cellpadding="0"><tbody><tr><td valign="top" width="387"><p>Lightning transient characteristic of the grounding grid is fundamental for optimum performance of lightning protection of a substation. In order to design an appropriate grounding system for such substation, it is important to study its transient characteristics because the high impulse current is significantly different compared to power frequency current. In this paper, substation grounding grid model was developed using CDEGS software to analyze the grid transient performance in terms of ground potential rise (GPR), touch voltage and step voltage when the grounding system is struck by a lightning impulse current. Several parameters, such as lightning current amplitude, feed point and the number of sub-grids, were altered to study their relationship with the transient performance. The maximum transient GPR, touch voltage, and step voltage increase as the lightning current amplitude increase. The maximum transient GPR and step voltage are the highest at the corner of the grounding grid while the maximum touch voltage is the highest at the centre of the grounding grid. In addition, the maximum transient GPR and step voltage decrease when the number of sub-grid increases. In contrast, the touch voltage slightly increases as the number of sub-grid increases. The maximum transient GPR, and step voltage are the highest at the 2-layer and the lowest at the uniform soil or single-layer soil.</p></td></tr></tbody></table>

Analysis on corrosion of flat steel used in grounding grid for 220 kV substation

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 Grid Diagnosis Applying Optimization Techniques Based on Measurements and Field Tests

Considering urban substations ground grid diagnosis, some real-physical constraints result in measurement process challenges: 1) limited length between electrodes used to measure the equivalent impedance of the grounding system; 2) to determine the current that flows from ground grid conductors to the earth; and 3) to determine the grid resistance. In this scenario, an adequate diagnosis of the safety offered by the ground grid under test when a ground fault occurs is not a trivial task. This article describes a methodology that allows a reliable diagnosis regarding the safety provided by a substation ground grid. The methodology is applied to the parameters obtained in performed field tests. The method has two steps. First, the fall-of-potential method with reduced distances between electrodes is used to determine the equivalent impedance of the grounding system. Then, the ground current is obtained. In both stages, optimization techniques are applied to the specific equations that govern the phenomenon under investigation. Comparative case studies considering real-life data illustrate the effectiveness of the method.

Inverse features extraction for substation grounding grid: derivative and ICA combinatorial approach

Optimising the orientation of the unknown grounding grid is effective to measure its accurate configuration. On the other hand, burial depth and conductors’ current are essential for the status diagnosis of grounding grid. This study employs the derivative method to determine the above-grounding grid characteristics without excavation. Surface magnetic flux density after the current injection process is subjected to derivative on the circle. The orientation of the grounding grid is accurately measured from the location of gradient peaks. Moreover, the grounding grid depth and conductors current are calculated from peaks width and peak value. The problem of substation intense electromagnetic environment that readily distorts the results of the proposed method is also addressed. Blind source separation famous technique, the fast independent component analysis (FastICA), is utilised to separate the original signal from the mixed signal. Furthermore, the authors also probe the influence of circle radius for the alarming case of a diagonal conductor. Mathematical reasoning, simulation, and experimental results illustrate that the proposed method is feasible to find the inverse features of grounding grid. Furthermore, the signal recovered through FastICA delivers results with high accuracy.

Designing of cost minimum substation grounding grid system using DE, SCA, and HDESCA techniques

This study presents three optimisation techniques to obtain optimum design of grounding grid with equal and unequal spacing between grid conductors. Different algorithms such as differential evolution (DE), sine–cosine algorithm (SCA) and hybrid DE SCA (HDESCA) are used in the design, and its efficacy are analysed. Aim of the present work is not only to limit the value of safety parameters, also to achieve the optimum grounding system by reducing total cost involved in designing of the grid. Here, necessary safety and security conditions as mentioned in ANSI/IEEE Standard 80–2000 is adopted to design the grounding grid. The cost function used here includes grid depth, dimension of grounding rod, conductor, number of rods and conductors, revetment and excavation area. The economic grounding grid system has been obtained to reduce the total cost related with grid materials, installation, and excavation. The effectiveness of proposed method and its results are theoretically examined with recently reported techniques that ascertain the validity and efficiency. Parameters obtained by DE, SCA, and HDESCA are compared to design the equal and unequal spaced grounding grid. The design based on HDESCA technique gives less cost and minimum safety parameters than those obtained by DE and SCA.

Non‐destructive depth detection approach for substation grounding grids based on magnetostatics

Grounding grid depth is one of the important factors to diagnose the grounding grid faults. However, due to the drawing loss and back fill during the reconstruction, the real buried depth of the grounding grid is changed and unknown. A magnetostatic method to calculate grounding grid depth is proposed in this Letter. Initially, the proposed method is applied on a single buried conductor where the depth is calculated from the extremum points in the surface magnetic flux density function. Furthermore, the branch current is calculated from the main peak value in the derivative of magnetic flux density function. Finally, a comparative analysis is performed regarding grounding grid depth and branch current. It is shown that the horizontal component of surface magnetic flux density yields results with low error as compared to the vertical component.

TEM apparent resistivity imaging for grounding grid detection using artificial neural network

Transient electromagnetic (TEM) method is a reliable means of non-destructive testing for fault diagnosis of grounding grid in substation. In view of the small transmitter loop of the TEM system and many measuring points and survey lines of grounding grid detection in substation. This study presents a fast solution to TEM apparent resistivity imaging for grounding grid detection using artificial neural networks. The input -output mapping relation of neural network is established based on TEM response characteristics of the grounding grid. The built network could map the recorded TEM data of grounding grid detection and quickly obtain the resistivity image. The proposed method offers accuracy and fast computation for the resistivity imaging of grounding grid. Feasibility and technical attractiveness of the proposed method in fast imaging of apparent resistivity is investigated with the measurement of grounding grids in the actual substations. It can be used in real time so that the recorded TEM data in substation can be calculated without re-training, which avoids time-consuming inversion computation. The rapid processing of massive data and submitting the detection results of the grounding grid to customers rapidly and in real time, which is expectation for a modern power industry.

A Non-Destructive Testing Method for Fault Detection of Substation Grounding Grids.

The grounding grid is critical to the safety and stability of a power system. Corrosive cracking of the grounding conductor is the main cause of deterioration of grounding grid performance. Existing fault diagnosis methods for grounding grids are limited by the number and distribution of grounding leads, and some of them cannot be used for online detection. This paper proposes a grounding grid detection method based on magnetic source excitation. The measuring device consists of four coils, two horizontal excitation coils, and two vertical receiving coils. The secondary magnetic field signal is extracted from the primary field and the background field by properly positioning the coils, such that the measured signal can reflect the underground media more accurately. The measuring device of the method is portable, the measurement process is contactless with the grounding grid, and it is not limited by the grounding leads. Furthermore, it has a strong anti-interference ability and can realize online detection. It was proven by simulations and experiments that the proposed method has a higher measurement accuracy and stronger anti-interference ability when compared with existing methods. This paper also discusses the influence of various factors such as the number and the location of the breakpoints, the frequency of the excitation source, the soil resistivity, and stratification from the measurement data. It was proven that the method has high precision and a wide application range, and is important for guiding significance and reference value in engineering applications.

Grounding grid design in electrical power substation using optimization methods

A good substation grounding grid is essential to ensure safety of personnel working in the substation, and also to protect the equipment to ensure continuous operation of the substation. The design of the substation grounding grid is often carried out to meet the IEEE Std 80-2000 requirements of grounding resistance, touch voltage and step voltage at an economical cost. However, the conventional grounding grid design is normally over calculated to meets these IEEE requirements without considering the total cost. The grounding grid is often costly to implement due to high number of grounding conductors and rods, and large area size of the interconnected bare conductors. In this study, Gravitational Search Algorithm (GSA) and Particle Swarm Algorithm (PSO) are proposed to achieve an effective grounding grid calculation. The reliability of these algorithms has been validated using a typical medium voltage substation grounding grid parameters. It was found both that GSA and PSO were capable to achieve a lower cost with of grounding grid with 29% cost saving as compared to the conventional calculation technique, without compromising the safety requirements of grounding grid.

Research on evaluation method of soil corrosive property to grounding grid in transformer substation

In the paper, a nine-index evaluation method of soil corrosive property to grounding grid is established based on analysis of soil physical and chemical properties in 120 transformer substation test stations, inspection of index corrosion condition about soil corrosion to buried metals as well as the test results of influence of soil temperature, water content, pH value, chlorine ion content, sulfate ion content and other factors on metal corrosion. The method is simple and practical, comprehensive influence factors are considered, the accuracy is high, thereby providing scientific basis for surveying and designing newly-established transformer substations, and monitoring corrosion of transformer substation grounding grid in operation. Two factors of air capacity and regional annual average temperature are included into the evaluation method for the first time in China, and the evaluation method of galvanized steel and copper grounding grid is proposed for the first time according to the nine-index evaluation method determined in the paper.

High current field test of impulse transient characteristics of substation grounding grid

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.

An EEMD-Based Electromagnetic Induction Method for Nondestructive Testing of Buried Metal Conductors

Nondestructive testing of substation grounding grids is an issue that has increasing importance. The traditional EMI method transforms the condition of the undergrounding conductors to the surficial induced electric signal in the sensing coil. However, The EMI signals excited by multiple coexisted faults combining with other unknown noises surrounding the substation often cause the failure of detection. Therefore, the observed EMI signals rather complex and cannot be used directly. To address this problem, the separation of individual signatures from the mixture is posed as an SCBSS problem. To extract the induced signal, an EEMD-based EMI method is proposed. The desired signal is then reconstructed to visualize the structure of the grounding grids by a virtual instrument that consists of DAQ and digital signal processing modules. The numerical simulation and practical experiments are employed. The results show the proposed method can be used to effectively detect the topological structure of grounding grid in real substations' electromagnetic environment.

Investigation on Impulse Characteristic of Full-Scale Grounding Grid in Substation

Impulse performance of grounding grid is needed for lightning protection design of power system. This paper describes an impulse test facility established for the full-scale grounding grid (50 m long and 52.5 m wide) in a 110 kV substation. Test method is presented, including configuration of current injection and return point, measurement of potential rise and longitudinal current. Impulse test is carried out with 2.6/50 and 8/20 μ s current waveform, and the maximum current amplitude is 4 kA. A Current Distribution, Electromagnetic fields, Grounding and Soil structure simulation for the tested grounding grid is also adopted. Impulse performance of full-scale grounding grid is affected by soil ionization and conductor inductance. There is steeper peak on the potential rise waveform near the injection point with shorter wave front current, which leads to more uneven potential rise distribution. Partial soil ionization could increase the current dispersing into the soil at partial area of the grounding grid, and the longitudinal current flowing to the next area decreases. These two factors pose a high potential difference hazard to the secondary equipment via the secondary cable.

Study on the Calculation Method of Interference Voltage of Shielded Cable under the Condition of Lightning Strike in Smart Substation Grounding Grid

When lightning strikes the substation grounding grid, there will be a great transient ground potential difference between the two grounding points of the shielded cable with two terminal grounding. It will be coupled to the cable core line and affects the normal operation of second order system devices and even jeopardize the safe operation of the whole system. Therefore, it is of great significance to study the lightning characteristics of the relevant components when lightning strikes the grounding grid of smart substations. This paper mainly studies the calculation method of interference voltage generated by shielding cables when lightning strikes the grounding grid of smart substations. Firstly the equivalent circuit and the multi-conductor transmission model of the cable are established. Then, using the frequency domain method in the multi-conductor transmission line and combining the fast Fourier transform technique, the steps of calculating the interference voltage and current produced in the two cable are given. Finally, in order to test the validity of the proposed calculation method, the lightning impulse grounding test is carried out on the test grounding network. The test results show that the method is effective.