Transient Ground Potential Rise Research Articles

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.

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.

Test Method for Transient Characteristics of Grounding Grid With Current Return Point Located in the Same Grid

Lightning strikes in substations may result in extremely uneven ground potential distribution, which will threaten the safety and stability of equipment in substation. However, the main parameters for evaluating the performance of grounding grids are grounding resistance and impulse impedance, and little attention is paid to the distribution of the transient ground potential differences. In addition, when measuring the impulse impedance of a grounding grid, the length of the current leads should be very large, which requires a high-capacity impulse generator to suppress the influence of lead inductance on current waveform. In this paper, a test method is proposed for the transient characteristics of grounding grid with the current-return point located in the same grid. The feasibility of the method is illustrated by analyzing the ground impedance between the current injection point and the return point, longitudinal current of the grounding conductor, transient ground potential rise and transient ground potential difference. The effects of parameters such as soil resistivity, lightning waveform, size of the grounding grid, spacing and materials of the grid conductor are discussed to demonstrate that the method can be applied to most substations. Finally, the practicality of the method is verified by experiments in a 220 kVsubstation.

Mitigation of transient ground potential rise in gas insulated substations during very fast transient overvoltage

• The paper proposes PEEC based a simulation technique the allow to take into account the complex 3D structure and the various electromagnetic coupling phenomena that take place between the metallic structure of a complex GIS and the associated earthing system during VFTO events. • The proposed GIS modeling and simulation technique is applied in case of 110 kV GIS in order to identify the grounding grid area that mostly effect the clearance of VFTO fault. • A mitigation procedure is show cased for the identified grounding grid area in order to accelerate the clearance of VFTO faults. This paper is focused on the assessment and mitigation of the transient response of a Gas Insulated Substation's (GIS) grounding grid to the fault due to voltage breakdown using the Partial Element Equivalent Circuit (PEEC) numerical approach. The adopted analysis methodology considers the magnetic induction by quantifying the electromagnetic couplings generated within the metallic components contained by the GIS configuration. The Transient Ground Potential Rise (TGPR) and transient current are computed and analyzed at several locations inside of GIS housing. With the aid of 3D graphical representation, the maximum amplitudes of the TGPR across the substation are illustrated. The mitigation efforts are considerably optimized by assuming the grounding grid sub-system is responsible for high frequency fault energy clearance based on identification method. By adopting several simplifications of the earthing system during the computational process, from a step-by-step analysis, it has been discovered that the grid located beneath the GIS enclosure will mostly attenuate the TGPR across the GIS building. Based on the aforementioned findings a successful mitigation technique is implemented.

Lightning Current Performance of Conventional and Enhanced Rod Ground Electrodes

The correct operation of surge arresters under lightning and switching transient conditions requires that grounding be effective at high frequencies as well as at power system frequency. Effective high frequency grounding also limits the electrocution risk to substation personnel due to transient ground potential rise. This article assesses the performance of high frequency electrodes at typical lightning impulse current magnitudes. The enhancement of such electrodes by addition of bonded horizontal arms in cross and star arrangement is also investigated. The effective impulse resistances for electrodes having lengths up to 4.8 m are calculated over a range of impulse current magnitudes at the same location. The results obtained indicate that, for low impulse current magnitudes, the preionization electrode's resistance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> ) falls with increasing rod length, a behavior reflected in the measured dc resistance. The presence of horizontal enhancement was found to reduce <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> in all cases. The occurrence of soil ionization in the immediate vicinity of the electrode resulted in a reduced postionization resistance ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">R</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ) at higher currents, tending toward a common asymptotic value independent of both the length of the rod and the presence of electrode enhancements. The observed behavior is supported by numerical simulation of electric field and current density distributions, indicating that the high current performance of a grounding rod is heavily influenced by soil ionization and breakdown in high-field regions at the electrode extremities.

Simplified Modelling of Transient Ground Potential Rise of GIS in Ultra-high-voltage Substations with Hybrid Reactive Power Compensation

The application of hybrid reactive power compensation (HRPC) in ultra-high-voltage substations has a nonnegligible impact on the characteristics of transient ground potential rise (TGPR) in the gas-insulated switchgear (GIS) enclosure. In this paper, according to the principle of series compensation and stepped controlled shunt reactors under a very fast transient overvoltage, a simplified model of an HRPC device is established. Based on the generation mechanism of TGPR and the theory of transmission lines, the equivalent simulation circuit of GIS in a substation is designed under the occurrence of TGPR. Simulation experiments comparing the characteristics of TGPR with and without HRPC are conducted to explore the factors that influence TGPR. This paper proposes specific methods of reducing TGPR, and provides a theoretical basis for the construction of GIS protection devices for ultra-high-voltage substations.

Computation of ground potential rise and grounding impedance of simple arrangement of electrodes buried in frequency-dependent stratified soil

Grounding electrodes are used to provide a low-impedance dissipation path for the excess lightning or fault currents. Several studies have been dedicated to the computation of the grounding impedance of different electrode arrangements considering either the frequency dependence of soil parameters (resistivity ρ and relative permittivity εr) or the multi-layer nature of soil. This paper aims at the calculation of the grounding impedance and the ground potential rise (GPR) of simple electrode arrangements (vertical and cross electrodes) due to the injection of first and subsequent lightning currents in various configurations of soil, considering a frequency-dependent stratified soil.A frequency-domain full-wave electromagnetic solver based on the Method of Moment (MoM) that employs a stratified medium Green’s function is used to compute the grounding impedance in a frequency range of 100Hz to 10MHz. The transient GPRs are computed using the equivalent circuit of the grounding system, obtained through the application of the Vector Fitting (VF) technique and recursive convolution method.The simulation results show that considering the frequency dependence of the soil parameters has no effect on the low-frequency grounding impedance up to ≈10kHz. However, the frequency dependence of soil parameters leads to a considerable variation of the grounding impedance at higher frequencies especially for soils of higher resistivity. Furthermore, it is shown that considering the layers of soil has a more significant impact on the GPR of the vertical electrode than that of the cross electrode.

Performance of the recursive methods applied to compute the transient responses on grounding systems

Ground Potential Rise (GPR) is an important factor for a grounding system that must be properly designed to protect people against any dangerous induced voltages and to avoid damages in equipment. In this context, several approaches to assess GPR are available in the literature which can be developed either directly in time domain or frequency-to-time transforms. The purpose of this paper is to investigate the performance of two time-domain recursive methods to compute the transient GPR in grounding systems generated by different lightning currents. First, the grounding impedances are calculated by a full-wave electromagnetic software FEKO with numerical Method of Moments from 100 Hz to 5 MHz. The GPRs are assessed by a recursive convolution method (M1) and by a recursive trapezoidal integration method (M2). Both methods employ the Vector Fitting technique on each impedance curve adjusted into a poles-residues form. Then, simulation results from the recursive methods are compared with those obtained with frequency-to-time method using the Numerical Laplace Transform (NLT) and with the equivalent circuit incorporated in the ATP-software. Results show a good agreement between the responses from recursive methods in comparison with those from NLT and ATP-software. As advantages, the recursive methods are an alternative tool when no analytical expressions for lightning currents are known or only measured data is provided. Additionally, the circuit implementation in Electromagnetic Transient (EMT)-type software tools is not needed to compute the transient GPRs in time domain. This work is an extension of a 2019-SIPDA conference paper [1].

Investigating the Effect of Several Model Configurations on the Transient Response of Gas-Insulated Substation during Fault Events Using an Electromagnetic Field Theory Approach

Assessment of very fast transient overvoltage (VFTO) requires good knowledge of the behavior of gas-insulated substation when subjected to very high frequencies. The international standards and guidelines generically present only recommendations regarding the VFTO suppression without a technical and mathematical background. Therefore, to provide an accurate image regarding the critical locations across a gas-insulated substation (GIS) from a transient response point of view, a suitable modeling technique has to be identified and developed for the substation. The paper aimed to provide an accurate assessment of the GIS holistic transient response through an electromagnetic field theory (EMF) approach. This modeling technique has always been a difficult task when it came to gas-insulated substations. However, recent studies have shown that through suitable Computer-aided design models, representing the GIS metallic ensemble, accurate results can be obtained. The paper investigated several simplifications of the computational domain considering different gas-insulated substation configurations in order to identify a suitable modeling approach without any unnecessary computational effort. The analysis was performed by adopting the partial equivalent element circuit (PEEC) approach embedded into XGSLab software package. Obtained results could provide useful hints for grounding grid designers regarding the proper development and implementation of transient ground potential rise (TGPR) mitigation techniques across a gas-insulated substation.

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

&lt;table width="593" border="1" cellspacing="0" cellpadding="0"&gt;&lt;tbody&gt;&lt;tr&gt;&lt;td valign="top" width="387"&gt;&lt;p&gt;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.&lt;/p&gt;&lt;/td&gt;&lt;/tr&gt;&lt;/tbody&gt;&lt;/table&gt;

Impulse Impedance and Effective Area of Grounding Grids

High values and uneven distribution of the transient ground potential rise (TGPR) at grounding grid conductors in cases of lightning can disrupt the system safety and reliability. To assess the transient performance of grounding grids under lightning currents, a parametric analysis was performed with a computer simulation of 13,978 cases of time-domain responses with a broad range of parameters. From this study, graphs of impulse impedance and a new formula for the effective area have been developed. The graphs are general, describe grids of any shape and size and depend on three parameters: grid conductor spacing, the resistivity of earth, and the zero-to-peak time of the lightning current pulse. Although the parametric analysis was based on a uniform soil model, the graphs can also be used for the two-layer soil model. In this paper, graphs and formula are used in a simple procedure to estimate the effectiveness of a mitigation measure to reduce the TGPR by increasing the grounding grid mesh density in a limited area around the current injection points. The results from the procedure are compared with experimental results, and the application and limitations of the procedure are illustrated by considering large grounding grids as examples.

Effects of Various Earth Grid Configurations on Ground Potential Rise Caused by Lightning Strike

Ground Potential Rise (GPR) caused by lightning strike is a potential hazard for electrical equipment inside an oil and gas refinery plant. In order to mitigate the risk, horizontal grounding grid is applied. The best mitigation is to install a grounding grid with mesh size as small as possible. This condition requires a high cost. In order to obtain the optimal mesh size, a series of simulation of a grounding grid with mesh size variations on GPR caused by lightning strike has been carried out. CDEGS software was used to observe the GPR with various mesh size from 6.5 x 6.5 m to 20 x 20 m. Simulation results show that the maximum transient GPR rises as the grounding grid mesh size is increased, while the GPR distribution throughout the grounding grid area does not change much for different mesh sizes. In the other hand, decreasing the grid size would mean that more conductors are required, hence the cost would increase accordingly. The result shows that grid sizes from 6.5 x 6.5 m up to 20 x 20 m have no significant difference in term of GPR. In term of cost, 10 x 10 m does not show significant difference with 20 x 20 m, on the other hand, there is a significant difference for grid sizes 1 x 1 m to 10 x 10 m. From the results, grid sizes between 10 x 10 m up to 20 x 20 m are still applicable as stated in Petronas Technical. To comply with proper GPR value, additional protection devices are needed to protect the electrical equipment from potential damage.Keywords –GPR, grounding grid, mesh size

Diagnostic analysis and protective measures of transient ground potential rise in a 1000 kv UHV substation

With the continuous expansion of power grid capacity and growth of voltage levels, the transient ground potential rise (GPR) caused by the switchgear operation has become great threaten to the safety of the grid. In the startup operation of 500 kV part of Taizhou 1000 kV ultra-high voltage (UHV) substation, the electromagnetic lock installed in the switchgear filed was broken by the GPR in case of switchgear operation. There are two possible transmission paths of the GPR, one is the ground copper bar connecting the ground and the other is the control cable connecting the control cabinet and electromagnetic lock. In order to find out the transmission path of the electromagnetic disturbance, the experiment is carried out to distinguish the two possible paths. The waveform of the GPR in case of switchgear operation from different measuring points are recorded and compared, the results are analysed by comparing the signal characteristics and the transmission path is eventually diagnosed. Finally, the protective measures are proposed by wrapping the control wires with the conductive metal cube to reduce the influences of GPR. The outcomes in the study provide beneficial methods to analyse the GPR disturbance and positive guidance for the protection of locally installed equipment.

Shell circulating current and transient ground potential rise in 220 kV GIS

Shell circulating current and transient ground potential rise in 220 kV GIS

Evaluation of Ground Potential Rises in a Commercial Building During a Direct Lightning Stroke Using CDEGS

This paper utilizes CDEGS software to calculate the transient ground potential rise (GPR) in a commercial building, with a base of $39 \hbox{m} \times 13 \hbox{m}$ and a height of 21 m, during direct lightning strokes. The influences of soil resistivity, location of the lightning strike point, and wave shape of the lightning current on the transient GPRs of three scenarios for the building are analyzed. Such scenarios within the building include the following: 1) devices are grounded independently; 2) devices are grounded via vertical ground electrodes that are connected to each down conductor fixed on the outside of the building; and 3) devices are grounded via a ring ground electrode that is sited around the periphery of the building. The results show that the ring ground electrode provides effective lightning protection for the building under lightning and, therefore, is recommended.

Analysis of effective factors on transient ground potential rise in gas insulated substations

This study presents the manner in which transient modeling concepts, which are fully analyzed in the referred standards, are implemented, for the purpose of evaluating the Transient Ground Potential Rise (TGPR). This is a phenomenon of 10–100kV voltages with up to 10µs duration on the grounded enclosure of Gas Insulated Substations (GIS), which may cause concern for personnel safety and problems for protection and control circuits in substations. This article summarizes the results of the investigation for influential factors on TGPR, such as, different contingency conditions and grounding system models. This article focuses on the TGPR study of Siah-bishe 400kV gas insulated substation. The study was carried out by modeling all pieces of equipment in the ElectroMagnetic Transients Program (EMTP)-RV, with careful consideration of different modeling guidelines and instructions described in the available standards. Article history:

ANALYSIS OF TRANSIENT ENCLOSURE VOLTAGES IN GIS (EMTP SIMULATION STUDIES)

Abstract Transient Enclosure voltage is special case of very fast transient overvoltages which occurs due to disconnect switch operation or earth ground. Transient Enclosure Voltage appears on external of earthed enclosure of Gas Insulated Systems. Despite of proper grounding, this phenomenon indicates presence of high potentials on Gas Insulted System enclosures so the grounding system impedance is thoroughly examined and designed. In this study EMTP Software is used for analysis. Simulation was done by varying the different parameters. Variations of waveforms of the Transient Enclosure Voltage with various parameters have been studied. Index Terms: Transient Enclosure Voltage (TEV), Gas Insulated System (GIS), Very Fast Transient Overvoltages (VFTO) Transient Ground Potential Rise (TGPR), Disconnector Switch ----------------------------------------------------------------------***------------------------------------------------------------------------ 1. INTRODUCTION

Grounding system analysis in transients programs applying electromagnetic field approach

Lightning protection studies of substations and power systems require knowledge of the dynamic behavior of large grounding grids during electromagnetic transients. This paper presents strategies which allow incorporation of complex grounding structures computed using a rigorous electromagnetic model in a transients programs. A novel technique for rational function representation of frequency-dependent grounding system impedances in the EMTP is described. An arbitrary number of feeding points can be modeled as mutual coupling is taken into account. Overvoltages throughout electrical power systems and the transient ground potential rise in the surroundings of grounding structures can be computed.

Grounding System Analysis in Transients Programs Applying Electromagnetic Field Approach

Lightning protection studies of substations and power systems require knowledge of the dynamic behavior of large grounding grids during electromagnetic transients. This paper presents strategies which allow incorporation of complex grounding structures computed using a rigorous electromagnetic model in a transients programs. A novel technique for rational function representation of frequency-dependent grounding system impedances in the EMTP is described. An arbitrary number of feeding points can be modeled as mutual coupling is taken into account. Overvoltages throughout electrical power systems and the transient ground potential rise in the surroundings of grounding structures can be computed.

Frequency dependent and transient characteristics of substation grounding systems

In spite of the existence of a number of analytical models aimed for transient analysis of large grounding systems, more detailed analysis of the influence of different parameters on the transient performance of large ground grids subjected to lightning current impulse is not available. This paper presents analysis of the influence of soil conductivity, location of feed point, grid size, depth, conductor separation, ground rods, and shape of the lightning current impulse, on the transient performance of ground grids with sizes ranging from 10/spl times/10 m/sup 2/ to 120/spl times/120 m/sup 2/ and with 4 to 124 meshes. Maximal transient ground potential rise and frequency dependent impedance are analyzed in time and frequency domain, respectively. Computations are made with computer model based on the electromagnetic field theory approach, taking accurately into account frequency dependent characteristics of large ground grids. Instead of usual simple approximations of the lightning current impulse, recorded channel base currents from triggered lightning are used for the time domain analysis.