Grounding System Impedance Research Articles

Traditional and alternative grounding system's impedance and resistance measurements of a 138 kV transmission line tower

One of the main causes of outages in transmission lines is lightning. To mitigate this occurrence, grounding electrodes are used at the base of the towers that make up the transmission lines. Since lightning is a phenomenon with components of low and relatively high-frequency energy (approximately up to 2 MHz), there is a certain complexity in accurately characterizing grounding systems. The primary parameter used to model a grounding system is the grounding impedance, which can be obtained through measurement. This paper presents measurements conducted on a 138 kV transmission line's traditional and alternative grounding system. The measured traditional grounding system consists of two horizontally buried copper grounding conductors and the alternative system comprises an electrode with four conductors encapsulated in concrete and buried vertically. The measurements were carried out using a 25 kHz earth resistance meter and impulse generators with waveform shapes of 1.2/50 μs, 1/70 μs, and 8/70 μs. Different measurement configurations are employed. The obtained measurements are compared with similar systems found in the literature, and the contributions of the concrete electrode to the grounding system are discussed.

Grounding system impedance influence on the surge arrester frequency-dependent model parameters using PSO-GWO algorithm

PurposeThis paper aims to focus on the inclusion of the frequency behavior of grounding system effect on surge arrester (SA) model parameters’ estimation.Design/methodology/approachThe grounding system impedance and its frequency behavior are the factors that have influence on the SA performance. Up to now, the grounding system impedance effect and the frequency behavior of the soil parameters have not been studied for the estimation of the parameters of the SA frequency-dependent model. In this paper, the grounding system’s influence on the SA dynamic model has been simulated for rod- and counterpoise-shaped electrodes. Particle swarm optimization with a grey wolf optimization algorithm has been implemented as an optimization algorithm to adjust the parameters of the SA dynamic model.FindingsThe results show that the frequency behavior of the grounding impedance and soil electrical parameters can impress the optimum parameters of the SA frequency-dependent model and should be considered for more reliable results. Also, the results evidence that the proposed optimization method provides more accurate results compared to other optimization methods.Originality/valueTo the best of the authors’ knowledge, this work is one of the first attempts to investigate the effect of frequency grounding system on SA frequency-dependent model parameters.

Transient impedance of grounding system with impulse superimposed sinewave

Investigating the transient performance of grounding systems subject to lightning (impulse or impulse superimposed sinewave) is valuable for protecting the power system and maintaining the system operation. In this work, the grounding system's impedance is computed when an impulse superimposed sinewave is applied to the grounding grid's proposed lumped circuit and grounding system can be simulated as an inductance in series with resistance, and all of them are in parallel with capacitance based on Thione's assumption. Several variables were investigated to study their effects on the grounding system's behavior. The variables were the soil resistivity, soil permittivity, main wire length, grid conductor radius, grid side length, grid configurationand its mesh number. The grounding system configuration varied between square and rectangular shapes, which connects to the protecting rod via the main wire conductor. A 3.69 kA peak of impulse current was applied to avoid soil ionization. The results indicated the performance of the grounding system when subjecting to impulse current.

Preliminary testing and assessment of safety conditions of HV substations located in urban areas

This paper presents a method enabling the elimination of the inductive influence of metal installations surrounding a test circuit on the estimated value of grounding system impedance in a tested HV substation. By disregarding this influence, the preliminarily estimated values of the ground potential rise and potential differences (touch and step voltages) within and in the vicinity of an HV substation can be significantly smaller in comparison to their actual values. Due to this, the definite assessment concerning the safety conditions in some HV substations can be considered as satisfied although it is not the case. The analytical part of the presented test method is developed on the basis of the analysis of a complex electrical circuit formed by many, known and unknown, inductively and conductively coupled elements during a simulated ground fault in the tested substation. The developed analytical expressions are based on the measured values of two currents obtained by simulated ground-fault in the tested substation. One of them is a simulated ground-fault current, while the other current is the one induced in one of the phase conductors included in the test circuit only for obtaining this induced current.

Direct Characterization of Grounding System Wide-Band Input Impedance

In this article, direct characterization of the wide-band input impedance of grounding system buried in multilayer soil is presented. The problem is formulated by mixed-potential integral equations solved by the method of moments (MoM). The method accommodates both delta-gap voltage and impressed-current excitations. The input impedance is then directly obtained from the MoM matrix. The proposed method does not rely on the integration of the electric field on the ground surface. Hence, the calculated input impedance is unique and path-independent. The accuracy of the proposed method is evaluated for the case of vertical ground electrodes buried in homogeneous soil. The cases of vertical grounding electrode buried in multilayer soil as well as square and circle-plates buried in homogeneous soil are studied. It is shown that for plate-shape grounding systems, the total surface area determines the grounding system input impedance and the effect of plate geometry is negligible.

Impedansa sistema uzemljenja - opseg frekvencijske linearnosti

The measurement of grounding system impedance of in-service power facilities is a very complex issue since the power system frequency interference and harmonic frequencies may adversely affect the measurement. Recently, to overcome this problem the Frequency Shift Method (FSM) has been proposed. FSM requires that two of three test frequencies must be above power system frequency (in our case 50 Hz). However, due to the nonlinear dependence of the grounding system impedance versus frequency, the choice of test frequencies is not arbitrary. In this paper, this issue is experimentally examined based on the analysis of grounding system impedance linearity range. For this purpose, the grounding system impedance, for a sample of 16 substations (HV and MV), is examined. We find that the highest test frequency should be ≤80 Hz.

Pregled metoda za eliminisanje uticaja sistemske smetnje u aktivnom visokonaponskom postrojenju

In this paper, practical and conceptual problems related to the way of suppressing or eliminating the influence of interference (at a frequency of 50 Hz) in an active high-voltage power facility are discussed. The problem is relevant in the context of measuring the safety characteristics of the grounding system: grounding system impedance, touch voltage and step voltage. The paper gives an evolutionary overview of title methods. The review focuses on the characteristic problems and shortcomings of individual methods. Also, the basic characteristics of the author's FSM (Frequency Shift Method) method, which guarantees precise control of interference, are elaborated. In this sense, the FSM method is the basis for accurate and economical measurement of the safety characteristics of the grounding system.

Hybrid continuous circuit‐trapezoidal integration method analysis of multi‐cross structure of grounding system

An essential requirement to improve the lightning performance of transmission line is the achievement of low impulse impedance of grounding system, which diminishes the occurrence of the external overvoltages. In this study, for the first time, a multi-cross structure used as transmission line tower-footing grounding system is investigated by means of hybrid continuous circuit-trapezoidal integration method (HCCTIM). It is discovered that the angle of minimum impulse impedance or the optimal structure of multi-cross grounding system is mainly dependent on the branch length compared to the effective length of a single horizontal conductor. Furthermore, in the current work, the trapezoidal integration method is used to solve the continuous circuit equations which elements are extracted from electromagnetic integral method, called HCCTIM. Coupling elements and soil ionisation are considered in this model. This method is an accurate, simple, and less time-consuming computational method. The comparison of the results with measurements, other recent simulations and CDEGS software, satisfactorily validate the proposed method.

Harmonic Impedance of Grounding Electrodes Buried in a Horizontally Stratified Multilayer Ground: A Full-Wave Approach

The effect of multilayer stratified ground on the harmonic impedance of grounding systems is evaluated. To this aim, the mixed-potential integral equation is used. The method is general as it allows taking into account 1) stratified soil structure with any number of layers and 2) grounding electrodes with arbitrary shapes. Moreover, the method has no limitation in terms of the maximum working frequency. The impressed-current model is used as the excitation and the harmonic impedance is directly obtained from the method of moments matrix. This is in contrast with the conventional methods where the harmonic impedance is calculated from the integration of the electric field at ground surface. The cases of horizontal and vertical electrodes buried in soils with different layers are analyzed. The accuracy of the proposed approach is validated by comparing the results with those obtained by independent numerical methods.

Notice of Retraction: Direct Characterization of Grounding System Wide-Band Input Impedance

In this article, direct characterization of the wide-band input impedance of grounding system buried in multilayer soil is presented. The problem is formulated by mixed-potential integral equations solved by the method of moments (MoM). The method accommodates both delta-gap voltage and impressed-current excitations. The input impedance is then directly obtained from the MoM matrix. The proposed method does not rely on the integration of the electric field on the ground surface. Hence, the calculated input impedance is unique and path-independent. The accuracy of the proposed method is evaluated for the case of vertical ground electrodes buried in homogeneous soil. The cases of vertical grounding electrode buried in multilayer soil as well as square and circle-plates buried in homogeneous soil are studied. It is shown that for plate-shape grounding systems, the total surface area determines the grounding system input impedance and the effect of plate geometry is negligible.

An alternative approach for touch and step voltages measurement in high-voltage substations

This paper presents the study of a measurement technique for touch and step voltages. In essence, we elaborate an approach which is very similar to the measurement of the grounding system impedance. In addition, the main focus is on the measurements at energized substation where different types of coupling between the test leads, grounding grids, sheats of underground cables and overhead ground wires affect the precise measurement. In order to avoid the measurement difficulties, we use low magnitude variable frequency AC test current (so called Frequency Shift Method – FSM). We compare FSM measurement results with the corresponding results obtained by well-known Test Current Reversal Method. The field tests were conducted in two quite different substations. Experimental results demonstrate the validity and usability of this approach.

Current Impulses in the Lightning Protection System of a Test House in Poland

The full scale test house was equipped with the lightning protection system and connected to the 15 kV/400 V transformer station. The simulated stroke current was injected into the installation with a current surge generator. Distribution of current in the lightning protection system and connected power supply installation is presented. Measurements were done for several configurations of the LPS, and for current amplitudes ranging from 1 to 10 kA. The results indicated variation with both the amplitude and the shape of the waveforms. The resistance was measured for several groundings individually and for entire grounding system with respect to the surge generator location. Measured waveforms showed frequency-dependent behavior of the circuit. Therefore, in order to improve current simulation accuracy the grounding system impedance should be considered rather than pure resistance. The vertical ground rods of the test house have capacitive impedances, while the long underground cable connected to the grounding system of the transformer has inductive impedance.

Analysis of earth resistivity frequency dependence: Test method and its practical application

The first step in planning and designing of the proper grounding system, is the earth resistivity measurement. Measurements are carried out before the construction of the power facility. However, it is not an uncommon situation that during construction, subsequent leveling and raising of the ground level is performed. For this purpose, it is customary to use the land from the locations far away. Delivered soil has largely different electromagnetic characteristics (electric conductivity, permittivity and dielectric constant) in relation to the soil on which the previous measurement of the earth resistivity was conducted. Since the value of the earth resistivity directly affects the grounding system electrical parameters - grounding system impedance, touch and step voltages - additional measurements are required and according to this appropriate corrections of the grounding system In this paper, we propose a practical method for earth resistivity measurement. The method is applicable in the design phase, and also for the revision of the installed grounding system. A practical example of a power facility (RP 400 kV Mladost, Elektromreža Srbije), based on laboratory measurements of the soil samples earth resistivity and grounding system impedance measurement, clearly shows what consequences might occur by leveling and raising of the ground level using ash coal dump.

On the Concept of Grounding Impedance of Multipoint Grounding Systems

An N -port equivalent circuit approach is adopted to model a multipoint grounding system, N being the number of injection points. A methodology is proposed to determine the parameters of the N -port equivalent circuit from either numerical simulations or experimental measurements. For the case of a symmetrical grounding system, analytical closed-form expressions are derived for the equivalent parameters of the N -port circuit. We show that the concept of the equivalent input impedance (harmonic impedance) could be used in the case of a symmetrical multipoint grounding system. We show also that the experimental evaluation of the impedance of a grounding system using a single injection point is a conservative engineering practice, since the obtained impedance might be overestimated at high frequencies.

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 impedance characterization using FEM

The exact knowledge of the grounding system impedance, including its expected variability, is a matter of paramount importance in the design of medium and high voltage infrastructures. The principles underlining the physical processes involved in grounding are well established and so are the engineering concepts regarding safe operation of the grounded systems. Quite a few theoretical expressions are widely used in the project stage of any installation. Unfortunately, these expressions are only valid for simple geometries and simplified material characteristics. Uncertainty arise from the intrinsic complexity of the grounding environment: buried grids and rods, reinforced concrete foundations surrounding them, weather dependent and non-uniform soil characteristics, etc To overcome these limitations, in this paper the finite element method is applied to obtain the grounding impedance and the potential distribution around a real grounding system excited with sinusoidal currents at several frequencies. Additionally, for validating purposes, a single vertical ground rod has been simulated and compared with the results obtained by other authors. FEM commercial software, in addition to some specific purpose user functions, has been used. The method presented in this paper can be applied to any real geometry, electrode configuration and type of soil.

Testing and evaluating grounding systems for substations located in urban areas

This study presents a method that enables elimination of the influence of metal installations surrounding a test circuit on the results of measurements. For substations located in urban areas, this influence is unavoidable and so intensive that it cannot be disregarded. Consequently, the test values of the potential differences (touch and step voltages) appearing on the grounding system and grounding system impedance can be significantly different in comparison with the actual values. Owing to this, estimated safety conditions of certain urban high-voltage/medium-voltage substations may be completely incorrect. The presented analytical method is developed on the basis of analysis of a complex electrical circuit formed during the ground fault by feeding line conductors and the many different metal installations involved with a fluctuating magnetic field around and along the feeding line.

접지그리드의 접지임피던스 측정의 정확도 평가

최근 대형 건축물들은 접지그리드를 기반으로 한 공통접지방식을 채택하고 있다. 이러한 접지시스템의 성능평가는 접지저항만으로 불충분하므로 접지임피던스의 측정이 요구된다. 대형 접지시스템의 접지임피던스에 대한 측정방법은 IEEE standard 81.2에 기술되었으나 세부적인 평가방법들은 제시되지 못한 상태이다. 본 논문은 15[m]×15[m] 접지그리드에 대하여 수정된 전위강하법에 기반한 접지임피던스의 정확한 측정방법과 보조전극의 위치에 따른 도전유도 및 전자유도에 의한 측정오차를 기술한다. 그 결과 도전유도에 의한 오차는 보조전극의 거리가 늘어날수록 감소하였다. 전자유도에 의한 오차를 배제하기 위해서 전위측정선은 전류측정선과 90도를 이루어야 한다. 전위측정선과 전류측정선이 예각 또는 둔각을 이루었을 때 전자유도전압은 각각 + 또는 -를 나타내었다. 일반적으로 전자유도에 의한 오차는 예각에 비해서 둔각의 경로가 작게 나타났다.

Influence of foundation on pillar grounding system's characteristics

PurposeThe purpose of this paper is to estimate influence of the pillar concrete foundation approximated by a semiconducting semi‐sphere on the pillar grounding system.Design/methodology/approachUnknown current distributions and impedance of pillar grounding system, which consists of a ferro armature modelled as a single electrode inside concrete foundation, ring electrode and two earthing conductors, are determined in this paper. Concrete foundation is approximated by a semi‐spherical semiconducting inhomogeneity. The expressions for electric scalar potential are formed using the quasi‐stationary image theory, including a recently proposed Green's function for the point source in the presence of a semiconducting sphere. Based on the quasi‐stationary antenna model, unknown currents are determined solving the system of integral equations using the moment method and polynomial approximation for current distributions.FindingsThe influence of inhomogeneity is not negligible for real values of specific conductivity of the inhomogeneity domain. The same goes for earthing conductor influence, especially the one on electric scalar potential distribution on the ground surface.Practical implicationsBesides the analyzed system, the model is applicable for solving for example a grounding system in the vicinity of large holes in the ground (pond and small lake) filled with water, treated as semi‐sphere or near vertical container (silage and reservoir) having semi‐spherical basis with a lower one buried in the ground.Originality/valueObtained results give possibility to analyze influence of semiconducting ground inhomogenities, which can be treated as semi‐spherically shaped ones, on grounding system. It results in better accordance of projected and real grounding system's characteristics.

임펄스전류의 인가위치에 따른 심매실 봉상 접지전극의 과도접지임피던스 특선

본 논문은 임펄스전류의 인가위치에 따른 심매설 봉상 접지전극의 과도접지임피던스와 규약접지임피던스 특성에 관하여 기술하였다. 과도접지임피던스는 심매설 접지전극의 길이 및 임펄스전류의 상승시간과 인가위치에 강하게 의존하며, 접지전극의 자체 인덕턴스는 짧은 시간 영역에서 접지시스템의 과도접지임피던스에 크게 영향을 미치는 것으로 나타났다. 심매설 봉상 접지전극의 자체 인덕턴스의 저감은 과도접지임피던스 특성의 개선에 결정적인 역할을 한다. 접지도선의 길이는 최대한 짧게 하여 접지전극의 상단에 접속하는 것이 효과적이다.