Ground Potential Rise Research Articles

Time domain modeling of lightning transients in grounding systems considering frequency dependence and soil ionization

This paper presents a new model for analyzing transient grounding system behavior during a direct lightning strike. The modeling that we propose allows us to consider a simple grounding conductor buried horizontally or vertically, a grounding grid, wind turbine grounding system and grounding circuits for wind farms while including the aerial parts (towers and blades). This modeling is developed directly in the time domain taking into account the frequency dependence of the impedance and admittance of the wired conductors and of the electrical parameters of the soil (ρ, ε) and also considering the ionization of the soil. This formalism is based on transmission line equations, rational approximation by vector fitting and the Finite Difference Time Domain numerical method. The proposed formalism is verified considering both simulations and experimental results from available published researches. The Ground Potential Rise GPR in the grounding circuits of wind farms are discussed during the first stroke and also during the subsequent stroke whose frequency range generates more propagation of electrical waves along conductors. This formalism makes it possible to contribute to all knowledge/research of grounding systems.

An experimental study on fire ignition in collector cable in wind power generation system caused by direct lightning strike

AbstractA separable connector is used for the power cables and apparatuses in renewable energy systems. The shield of the collector cable is sometimes an open circuit at one end to reduce power loss due to the shield current. However, this has a disadvantage from the viewpoint of lightning protection. The semiconductive part of the separable connector is grounded for safety. The ground potential rise due to a direct lightning strike to a wind tower sometimes damages the collector cables and power apparatuses in the wind tower. Combustion in a cable is one of the most serious types of lightning‐caused damage. This paper describes an experimental study on fire ignition in a collector cable caused by a ground potential rise due to a direct lightning strike to a receptor. The mechanism leading to fire ignition is discussed based on the experimental results. This paper also proposes a countermeasure against such fire ignition.

Exploration of sustainability of micro grid grounding design in proximity to the pole grounding through experimental measurement of safety parameters

Customarily, while designing the micro grid (MG) grounding the impact of close by grounding is not surmised. Due to which their grounding design becomes more flawed as it results in the fallacious computation of safety parameters, evincing the surplus cost to meet the safety standards. Dynamic seasonal condition, if ignored, makes the grounding design even shoddier. Usually, both these stipulations are not well thought out concurrently, which is the need of the hour. To surmount this, here, a practical case of MG grounding having nearby pole grounding is proposed which is examined in diverse seasons in uniform and three layer soil structures by utilizing finite element method (FEM). Substantiation of the results is done with IEEE standard 80–2013. This article also proposes an experimental setup for the measurement of safety parameters of two groundings in proximity to each other. Moreover, results are corroborated through experimental measurements by building the scaled model. With the contemplation of nearby pole grounding in different seasons, apart from reduction in ground potential rise (GPR) and increase in touch voltage (TV), large deviations in GPR and TV, which otherwise gourd observed, is discovered. Also, with consideration of pole grounding in proximity, a large discrepancy in TV with alteration in resistivity of soil and thickness of soil (concerning grid burial depth) are determined in rainy and freezing seasons.

Analysis of the calculation methods for shell circulating current and grounding current in 500 kV HGIS and the optimization of grounding scheme

The strong electromagnetic coupling between the wire and the shell of Hybrid Gas Insulated Switchgear (HGIS) will lead to a large induced current on the shell, which will further cause local heating of the outside shell. Moreover, the utilization of grounding wire to release this current may also lead to the problem of its heating and ground potential rise. This study is intended to further promote the calculation accuracy of the shell circulating current and grounding current of the 500 kV HGIS and also propose the proper grounding schemes. The simulation results show that the ground grid must be considered in the calculation model and the phase difference of the conductor current could be ignored when the three-phase spacing exceeded 7.5 m. Furthermore, the influences of shorting bars and ground grid on the simulation results were compared and analyzed, and the optimization of grounding scheme and corresponding suggestions were put forward. Generally, it was not recommended to erect shorting bars and auxiliary ground grids. But if the temperature rise exceeds the limit, the shorting bars can be added at the two ends of a HGIS branch and the auxiliary ground grid should be laid using materials with higher flow capacity.

Evaluation of the optimum safety performance of the nuclear reactor compact grounding system under lightning strikes and ground fault

Abstract The electrical system of a nuclear reactor facility (NRF) must incorporate a grounding grid in order to ensure it functions safely and reliably. Any disturbance in the electrical system affects the nuclear process, so it is, therefore, crucial to estimate the safety performance of the research nuclear reactor facility grounding system. The paper discusses CYMGrd 6.3, which is based on IEEE Standard 80-2013, and the optimization approaches for finding the best grounding grid design for a nuclear reactor facility connected substation of 500/11 kV in the case of a ground fault and lightning strikes. The result shows that the surface, step and touch potentials along the diagonal coordinates of the proposed grounding grid are below the safety limits in case of a ground fault but also results indicate that 100 kA lightning stroke poses a considerable threat to reactor equipment and personnel safety because the measured grid surface potential exceeds the safe ground potential rise of 3.2 kV standard at the striking point in conjunction with the proposed ground grid, so it must be modified. In this paper, three different optimization algorithms are investigated in order to determine the optimal design of the grounding grid with respect to mesh size: gradient method (GM), the genetic algorithm (GA), and simulated annealing (SA). These methods are used to achieve the purpose of obtaining an effective ground grid design. Comparing these techniques of GM and SA is good for quickly locating local minima, but they may fail to identify global solutions. In contrast, a genetic algorithm is often excellent at achieving a global minimum. Also, the utilization of GA, SA, and GM achieve the reduction of the surface potential of a proposed grounding grid by 16 %, 10 %, and 6 % respectively.

The Decreasing Ground Potential Rise by Lessening Soil Resistance in Arrester Grounding System

The Decreasing Ground Potential Rise by Lessening Soil Resistance in Arrester Grounding System

Evaluation of the transmission tower and frequency-dependent soil parameters influence on the grounding potential rise waveforms

In this paper, the influence of the transmission tower and the frequency-dependent soil parameters on the grounding potential rise (GPR) waveform is evaluated. This evaluation is performed using a physically consistent electromagnetic model that determines the transient behavior of the grounding system submitted by lightning, together with the Alternative Transients Program for the representation of aerial elements (tower, phase cables and shield wires). This model was developed in the frequency domain and, in this way, allows the inclusion of frequency-dependence of soil electrical parameters. In this sense, three formulations of the dependence in question are considered, widely disseminated in the literature, and determined through systematic measurement processes. The results illustrate that the concomitant inclusion of the tower and the frequency-dependence substantially modifies the GPR waveforms, when compared with those in which isolated grounding is considered, especially for soils with high resistivity values and for first return strokes. This is of most importance when evaluating personal safety criteria in the transmission tower vicinity. In these situations, the GPR waveforms should be determined by considering the presence of the tower and not only with the isolated grounding, since the transient step and touch voltages are directly associated with GPR.

ВИЗНАЧЕННЯ ОПОРУ ЗАЗЕМЛЮВАЛЬНИХ ПРИСТРОЇВ ПІДСТАНЦІЙ 330(220) кВ

In the electric power industry of Ukraine, the main system-forming objects are power transmission lines and substations with 330(220) kV switchgear. The most powerful sources of danger at substations are short circuits on the busbars, a direct lightning strike or the operation of overvoltage limiters and arresters.The purpose of the article is to develop a method for determining the resistance of the grounding system of substations with open switchgear 330(220) kV, aimed at increasing accuracy, taking into account the most influential independent factors. The provisions of the theory of experiment planning, the theory of electric circuits, mathematical modeling in the package Grounding 1.0, LiGro and Microsoft Excel were used to conduct the research. In the paper, a comparative analysis of the known formulas for determining the resistance of the grounding system is carried out: the formula of the GOST 12.1.30-81 standard, Ohlendorf-Laurant, Laurent and Neumann, Schwartz, Sverak formulas, as well as the formula of the international standard IEEE Std 80-2013. The results of multifactorial experiments to determine the dependence of the resistance of the grounding system on its area, the size of the grid cell, the perimeter of the cross-section of the grounding, the equivalent specific resistance of the soil, the short-circuit current and the depth of the grid location are given. A graphical comparison of the results of determining the resistance according to the considered formulas was carried out. In the paper, the method of determining the parameters of grounding system of 330(220) kV substations was further developed, aimed at ensuring standardized values of the resistance of the grounding system and the ground potential rise using formulas obtained from the results of multifactorial experiments. The results obtained in the work will make it possible to reduce the probability of damage to the insulation of 6-10 kV cables, as well as cables of secondary circuits from low-frequency and high-frequency (pulse) voltages when large currents flow into the grounding system in the mode of a single-phase short-circuit to the ground in electrical grid with a grounded neutral. References 9, tables 2, figures 6.

Full-wave electromagnetic analysis of lightning strikes to wind farm connected to medium-voltage distribution lines

This paper studies the voltages developed on a wind turbine (WT) and a medium-voltage distribution line (MVDL) connected to a wind farm subjected to lightning strikes and located on frequency-dependent (FD) soils. The ground potential rise (GPR), voltages at the blade tip and on phase conductors of the MVDL are calculated using the full-wave electromagnetic software XGSLab® employing the rigorous Partial Element Equivalent Circuit (PEEC) method. The wind farm comprises four wind turbines with interconnected grounding systems using cables buried in resistivity soils of 1,000 and 5,000 Ω m. The voltages are computed for the first positive impulse (FPI) of 100-kA 10/350μs and for the subsequent negative impulse (SNI) of 50-kA, 1/200μs. Results have shown that voltage peaks increase notably as the soil resistivity increases. When the WTs are assumed, oscillations in the GPR waveforms for the SNI occur due to the multiple reflections between the blade and the turbine’s base. However, the voltages for the FPI present smooth time-domain responses. Furthermore, the overvoltages developed at the MVDL are significantly dependent on the soil resistivity and lightning current waveform.

Tower-foot grounding model for EMT programs based on transmission line theory and Marti's model

This paper proposes a tower-foot grounding system model compatible with EMT programs which might be useful for the simulation of lightning transients in overhead lines. The proposed model is based on the solution of the telegrapher's equations and the application of the classical Marti's transmission line model. The model is implemented in the Alternative Transients Program (ATP) and validated considering a benchmark electromagnetic model. Its accuracy is evaluated and shown both in terms of the simulated ground potential rise (GPR) and line overvoltages developed through the insulator strings due to lightning currents. Finally, the model accuracy is also demonstrated in terms of the line backflashover outage rate.

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

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

Transient analysis of power transmission towers above lossy ground with frequency dependent electrical parameters considering the water content of soil

Adequate soil modeling is fundamental to assessing the grounding impedance of the grounding system and the transient responses in power systems. This paper aims to investigate three soil models with electrical parameters varying with frequency and water content, namely Smith-Longmire, Scott, and Messier models, and their impact on the ground potential rise (GPR) waveforms of vertical grounding rods. Besides that, the transient induced voltages across the string of insulators induced are also investigated for lightning currents representative first, and subsequent return strokes are employed. The harmonic grounding impedance (HGI) is calculated for rods of 3, 15, and 30 m buried in frequency-dependent (FD) soil model using commercial electromagnetic software (FEKO) with the Method of Moments (MoM) for a range of 100 Hz to 10 MHz. Simulation results show a significant modification of the calculated HGI beyond a particular frequency. The induced transient GPR waveforms show a notable reduction in their voltage peaks when the FD soil model is compared with those computed using the frequency-independent (FI) soil model. Finally, a backflashover analysis is carried out that demonstrates its dependence on the rod length, water content, and the specific soil model employed.

Comparison of Grounding Resistance Using Grounding Rod Electrodes with Different Fault Current Types in Podzolic Soil at Prabumulih Substation

For protection against electric shock in electrical equipment, particularly in control or instrument installations in substation equipment, a quality earthing system is required. The earthing system is also affected by soil resistivity with different soil types. In the equipment grounding system, knowledge of the types of electrodes and the type of soil is required. At the Prabumulih substation, Podzolic soil is required to evaluate the stress distribution that happens in the soil in order to reduce Ground Potential Rise (GPR). In addition to obtaining the economic value of the rod electrode type employed. In this study the resistivity value of the podzolic soil type is very decisive so that the resistivity value of the podzolic soil type at the pre-selection substation land is 150 Ωm.

Alternative study to reduce backflashovers using tower-footing grounding systems with multiple inclined rods

This paper investigates the influence of the inclination angle on the harmonic grounding impedance (HGI) of three arrangements with multiple rods. Then, Ground Potential Rise (GPR) and the lightning performance (backflashover prediction) on transmission towers using these grounding systems are studied. A full-wave electromagnetic software FEKO using Method of Moments (MoM) is utilized to compute the HGI in a frequency range of 100 Hz to 10 MHz, assuming the soil with low-frequency resistivity of 1,000 Ω m and modeled considering the frequency effect on the ground parameters. The analysis is carried out for grounding systems of multiple rods composed of 2, 3, and 4 inclined electrodes considering inclination angles of 0°, 15°, 30°, 45° and 60°. The transient GPR developed for the first and subsequent return strokes are evaluated. The calculated HGI showed expressive differences for each topology and also for various inclination angles. Consequently, transient GPR waveforms present expressive mitigation for each grounding system whose difference can be obtained only by varying the inclination angle of the rods. Finally, the backflashover probability is reduced when these arrangements with multiple rods combined with highly inclined electrodes are used as tower-footing grounding systems, improving the lightning performance of power systems. • Harmonic impedance of inclined rods is computed for frequency-dependent soil. • GPR is significantly influenced for arrangements with multiple electrodes and angle. • Backflashover is reduced when multiple rods are used as a grounding system. • These arrangements are an alternative for lines located in limited urban areas.

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

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

Harmonic grounding impedance of rods in horizontally stratified soils using ABCD-matrix approach

Grounding electrodes play a fundamental role in the operation of power systems. In this context, precise computation of grounding impedance must consider the frequency-dependence of the soil parameters and the ground organized in stratified layers of soil. This paper proposes an ABCD matrix approach to compute the harmonic grounding impedance of rods buried in frequency-dependent stratified soils directly in the frequency domain. This technique is based on the traditional ABCD matrix used for overhead multi-phase transmission lines extended to grounding systems. In this approach, each rod segment is modeled as a short transmission line where the equivalent harmonic grounding impedance is calculated. Then, the Ground Potential Rise (GPR) waveforms are computed by lightning currents injected into the rods buried in different scenarios. Results indicated that the ABCD matrix approach has shown a good agreement with those obtained using a full-wave electromagnetic software FEKO. The frequency-dependence of the soil electrical parameters causes a significant modification in the harmonic impedance of grounding rods which reduces the GPR peaks considerably, being this reduction more pronounced in homogeneous and 2-layer soils. The proposed technique is an attractive tool since that considers the frequency dependence on each layer of soil, with a low computational cost and good accuracy from 100 Hz up to 1 MHz.

Experimental analysis of horizontal grounding wires buried in high-resistivity soils subjected to impulse currents

• Experimental response of grounding wires in high-resistivity soils is presented. • Grounding impulse impedance is lower than resistance for higher resistivities. • Experiments show relevant influence of frequency dependence of soil parameters. • Influence of increasing the front-time on impedance depends on electrode length. This paper presents experimental results of the ground potential rise (GPR) developed by grounding wires buried in high-resistivity soils and subjected to impulse currents. A large experimental dataset is presented, comprising grounding wire lengths ranging from 10 m to 50 m, buried in soils of resistivities between around 1100 Ωm to 1600 Ωm, and subjected to impulse currents with front-time ranging from around 1.2 μs to 7 μs. The experimental results further confirmed some important aspects regarding the lightning response of grounding electrodes buried in high-resistivity soils, namely the influence of the frequency dependence of soil parameters and the value of impulse impedance lower than the grounding resistance for electrodes shorter than effective length. Comparison between experimental and simulated results reinforces the need to consider the frequency-dependence of soil parameters for obtaining accurate results of the lightning response of grounding systems buried in poor conducting soils.

Countermeasures for reduction of screen currents due to cross country faults in MV cable distribution networks

• Cross-country faults can involve large currents liable to damage MV cable sheaths. • Methodologies to reduce cross-country fault currents in cable screens are presented. • Methods are compared by means of ATP-EMTP simulations on a 20 kV test network. • Additional ground wires are effective but viable only for newly built cable lines. This paper investigates the reduction of Cross-Country-Faults currents in medium voltage (MV) cable networks in order to decrease thermal stress of cable screens, especially inside joints. Four methods are analyzed: 1) disconnection of cable screens from the earth electrode of primary substation (PS); 2) buried ground wire laid near the cable lines and connected to each earth electrode of secondary substations (SSs) and PS; 3) buried ground wire and disconnection of the bonded cable screens from the earth electrode only at sending/receiving end of each cable line between two consecutive SSs; 4) cross bonding of cable screens between two consecutive SSs. Methods are analysed by ATP-EMTP simulations of a 150/20 kV radial test system formed by eight 5 km long cable lines equipped with 50 mm 2 copper conductors per phase and 16 mm 2 copper screen per cable. Compared to the limiting reactors countermeasure presented in a previous paper by the authors, which seems the solution less burdensome both technically and economically for existing lines, method 3 is more effective but its implementation is limited only to newly built lines, whereas the main drawback of method 1 is the increase of ground potential rise at fault locations.

An optimal design for grounding grid configuration with unequal conductor spacing

The earthing system is considered as a very important aspect of electrical power system in terms of reliability, dependency and safety. Carrying the fault current and ensuring the safety of the operator and the equipment are the two fundamental requirements of an electrical earthing system. Moreover, by modifying the grid configuration or by reducing the earth fault current, the performance can be improved. Normally the reduction of fault current may cause changes in grid shape and size by changing the conductor spacing, grid dimensions, conductor length, grid depth and adding vertical grounding rods. A square and rectangular grid, buried in two-layer soil model is considered with unequal spaced grounding grid. This paper aims to ascertain the ideal grounding grid configuration about safety factors such as Ground Potential Rise (GPR), earthing grid resistance, touch as well as step voltages. Moreover, a square and rectangular grid, buried in a two-layer soil model are considered with Unequal Conductor Spacing. For developing an effective and economic square and rectangular earthing system for the unequally spaced design, a mathematical cost function (CF) is presented along with the modern computational intelligent technique. Hence, a Modified Harris Hawks Optimizer (MHHO) technique was proposed which is the conceptual improvement of the standard Harris Hawks Optimizer (HHO). Accordingly, the cost obtained by the proposed MHHO technique is 8.19%, 9.6%, 3.44%, 11.1% and 2.43% which is lower than other existing methods like PSO, GA, FF, HHO, MOPSO at 60th iteration, for population size 10.

Expendable and Distributed Measurement Scheme for Acquisition of Naturally Sparse Events

A common reason for electronic measurement anomaly is the inadvertent rise in ground potential with respect to measurement ground. The ground potential rise happens during current leakage to ground from lightning or from power grid and leads to catastrophic failure unless appropriate preventive action is taken to isolate the sensitive measurement systems. A networked system for acquisition and transmission of ground potential measurements to data monitoring station is presented here. The system is aimed to implement using low-cost IoT devices with limited resources since these units are planned to be expendable. The limited processing power of such devices is not sufficient to run high efficient computation intensive routing algorithms. A lightweight routing algorithm for this purpose is proposed here. The discussion on reliability of such systems is also presented. The multipath route discovery strategy presented here reconfigures the network to an optimal configuration with respect to energy dissipation and node distribution.