Ground Impedance Measurements Research Articles

Sound propagation modeling in forests using the transmission line matrix method: Comparison with experimental in situ measurements

We present efforts to adapt the time-domain Transmission Line Matrix (TLM) method for modeling sound propagation in forests. It is relevant to professionals and researchers in environmental acoustics and to those interested in studying sound propagation in outdoor environments using numerical modeling techniques. The study aims to demonstrate the applicability of the method in complex media where sound waves undergo multiple reflections combined with ground effects during their propagation from a sound source to a receiver point. The TLM method is used to numerically model sound propagation in a 3D forest geometry generated based on a real tree distribution case. Data from an experimental campaign conducted in the rainforest of French Guyana are used as a reference. The results show an encouraging comparison between them and the in situ measurements, even if the hypotheses made to adapt the input data in the model were strong. We find that more measurement points and more specifications (ground impedance measurements, canopy density, etc.) about the experimental site are needed for further simulations, even if obtaining them presents technical difficulties.

Development of Wide-band Ground Impedance Measurement System based on LabVIEW for Grounding System Evaluation

Development of Wide-band Ground Impedance Measurement System based on LabVIEW for Grounding System Evaluation

A systematic review on grounding impedance measurement in electrical installations

The grounding impedance measurement is an important issue related to the safety and reliability of electrical power systems. It is a widely studied topic on which standards are available presenting practical instrumentation methods to measure grounding impedance associated with an electrical installation. However, an updated review covering standardized and state-of-the-art methods is not currently found in the scientific literature. Thus, this paper presents a systematic review of the subject, intending to summarize the evidence of the benefits and limitations of ground resistance measurement methods, identify gaps in current research to suggest areas for future investigations, and provide a basis for adequately positioning new research activities. • A review of standardized and state-of-the-art ground impedance measurement methods. • A comparative study of grounding impedance measurement methods. • Most ground impedance measurement techniques derive from fall-of-potential method. • Limitations and advantages of the grounding impedance measurement methods. • The clamp-on ground meter method offers a vast field of research to be explored.

Measurement and analysis of impulse grounding impedance of tower grounding device subjected to artificial lightning M‐component

The impulse grounding impedance of tower grounding device is one of the important factors in the lightning protection evaluation of transmission line. The impulse characteristic test of the actual tower grounding device under lightning was rarely carried out due to the limitation of the test conditions. With the help of Guangzhou Field Experiment Site for Lightning Research and Testing, the artificial lightning characteristic test of the true tower grounding device was carried out. This paper presented partial observation experimental results and related analysis of the impulse grounding impedance of tower grounding device subjected to artificial lightning M-component. A calculation model of the tower grounding device subjected to lightning M-component was established. The changes of the surface soil resistivity under the action of rainwater were taken into account in the calculation. The test data and calculation results of the tower grounding device under the impact of the artificial lightning M-component had achieved good agreement. The non-linear ionization of the soil around the tower grounding device can be ignored, and the real impulse grounding impedance was very close to the DC grounding resistance or power frequency grounding impedance, when the tower grounding device in the experiment was subjected to lightning current M-component.

Investigation of ground impedance measurement techniques up to 1 MHz frequency in urban dense power substations

Investigation of ground impedance measurement techniques up to 1 MHz frequency in urban dense power substations

Investigation of Ground Impedance Measurement Techniques Up to 1 Mhz Frequency in Urban Dense Power Substations

Investigation of Ground Impedance Measurement Techniques Up to 1 Mhz Frequency in Urban Dense Power Substations

Uticaj podzemnih kablova na merenje impedanse sistema uzemljenja primenom FSM koncepta

Ground impedance measurement in medium voltage substations, designed to operate in a predominantly cable network, is a complex research task. Namely, the inability to consider all the factors that can affect the measured value, in a situation where one deenergized cable line is used to form the Fall-of-Potential (FOP) measurement scheme, is directly reflected to an adequate assessment of safety risks. This paper proposes an alternative measurement method so called Frequency Shift Method (FSM), which inherently guarantees "better" measurement than any of the conventional methods. By providing insight into the behavior of the active and reactive ground impedance components, and at the same time taking into account the topological structure of the existing cable network, the application of the FSM concept in the FOP measurement scheme points out to alternative paths of test current distribution, and in that way pointing to the illogicality of the obtained measurement results. Experimental verification was conducted under real operating conditions, and can serve as a guide for solving similar problems in practice.

Measurements for Qualifying the Lightning Response of Tower-Footing Electrodes of Transmission Lines

The lightning response of tower-footing electrodes of transmission lines can be estimated from concise parameters, namely the low-frequency and 25-kHz grounding resistances (R T and R 25kHz ) and the impulse grounding impedance Z P . Methodologies for measurement of these parameters are addressed and their constraints are discussed. Experimental and simulated results were developed for assessing the consistency of these methodologies and the errors of the results they provide. Measurements obtained in real transmission lines confirm the theoretical expectation that R T > R 25kHz > Z P . Procedures for reliable measurement of the three parameters are explained. The use of 25-kHz instruments is strongly disseminated, as it does not require disconnecting shield wires. As instruments dedicated to the measurement of the impulse grounding impedance are becoming available, the direct measurement of ZP is expected to become the most common practice in the near future, due to the superior results it provides for qualifying the lightning response of tower-footing electrodes.

Tower and Path-Dependent Voltage Effects on the Measurement of Grounding Impedance for Lightning Studies

We present an analysis aimed at evaluating the effect of the presence of the tower on the measurement of the grounding impedance. The Numerical Electromagnetics Code NEC-4 is used for the full-wave modeling of the structure including the tower and its footing grounding system, as well as the experimental setup used for the measurement of the grounding impedance. First, the effect of possible path-dependence in the evaluation of the integral of the electric field is investigated. It is shown that, up to a frequency of about 100 kHz or so, the voltage, and consequently the evaluated impedance are independent of the path of integration. At higher frequencies, differences appear, which might be significant especially for poor conducting ground. The effect of the distance to the reference remote earth on the evaluated voltage is also analyzed and it is shown that a distance of 100 m to the remote earth is appropriate to evaluate the grounding impedance potential rise. The simulation results show that at low frequencies (up to about 200 kHz or so for the considered 140-m tall tower), the effect of the presence of the tower can be disregarded. At higher frequencies, the evaluated impedance is affected by the presence of the tower. The poorer the ground conductivity, the more significant the effect of the presence of the tower on the evaluated impedance. Two injected current waveforms, representative of typical first and subsequent return strokes, are considered for the time-domain analysis. The effect of the presence of the tower can be significant for subsequent return stroke excitation, which has a wider frequency spectrum compared to first return strokes. It is shown that in the early-time region, part of the injected current flows into the tower. For a ground conductivity of 0.001 S/m, the tower peak current increases to about 10% of the exciting current, for the case of a subsequent strokes. It is also shown that the presence of the tower would cause a decrease in the peak potential rise leading therefore to an underestimation of the so-called impulsive grounding impedance.

Doprinos racionalizaciji merenja impedanse sistema uzemljenja srednjenaponskih transformatorskih stanica

Doprinos racionalizaciji merenja impedanse sistema uzemljenja srednjenaponskih transformatorskih stanica

Using Fall-of-Potential Measurements to Improve Deep Soil Resistivity Estimates

When measuring the ground impedance of an electrically isolated grounding system, it sometimes happens that the test electrodes are placed at considerably greater distances from the installation under test than the maximum electrode spacing used during the soil resistivity measurements carried out during the predesign phase of the grounding system. As a result, ground impedance measurements carried out with the fall-of-potential method may contain valuable supplemental information about deep soil strata that can improve grounding system performance predictions made during the design phase with computer modeling software and explain discrepancies encountered between predicted and measured ground impedance values. These data can be also used during subsequent grounding design work associated with facility expansion. It is shown in this paper how, in the absence of interfering metallic infrastructure, such ground impedance measurements can be converted into apparent soil resistivity values corresponding to deeper soil layers, with an example showing how dramatic improvements in grounding system performance predictions can be obtained.

접지 그리드에서의 보조전극 배치에 따른 접지임피던스 측정 및 분석

This paper describes the measurement and analysis of ground impedance according to arrangement of auxiliary probe around ground grid using the fall-of-potential method and the testing techniques to minimize the measuring errors are proposed. The fall-of-potential method involves passing a current between a ground electrode and a current probe, and then measuring the voltage between a ground electrode and a potential probe. To minimize interelectrode influences due to mutual resistances, the current probe is a generally placed at a substantial distance from the ground electrode under test. In order to analyze the effects of ground impedance due to the arrangement of auxiliary probe and frequency, ground impedances were measured in case that the arrangements of auxiliary probe were straight line, perpendicular line, and horizontal line. The distance of current probe was located from 10[m] to 200[m] and the measuring frequency was ranged from 55[Hz] to 513[Hz]. As a consequence, the ground impedance increases with increasing the distance from the ground electrode to the point to be tested, but the ground impedance decreases with increasing the frequency.

Grounding impedance measurement method of integrated grounding system in high‐speed railway roadbed section

Integrated grounding system (IGS) in china high-speed railway is formed through two long horizontal copper lines named run-through ground wire buried on both sides along the railway, which is also the longest horizontal grounding system in the world through the interconnection of railways. The grounding impedance measurement of IGS of high-speed railway is a novel, important problem to ensure the human and equipment safety. The placement approach of test electrodes for the grounding impedance measurement of the IGS in the roadbed section of high-speed railway was discussed by the simulation calculation and field test results in this study. Numerical analysis and measurement arrangement of IGS grounding impedance based on short-current lead wire was evaluated by analysing the soil structure, the distance of test electrodes and the ratio of measured grounding impedance and true grounding impedance. The test route was suggested that the potential electrode be placed on the opposite side with respect to the current electrode for measuring the grounding impedance. The suitable and convenient test electrode arrangement and the corresponding correction coefficients were obtained. Compared with the computer-aided calculation, the field test maintained acceptable measurement error. Thus, a useful measurement method was proposed for grounding impedance measurement of IGS.

Grounding Impedance Measurement of High Speed Railway Integrated Grounding System

The high-speed railway integrated grounding system is the basic guarantee for the safe and stable operation of the railway. It is the world’s largest long-distance horizontally elongated joint grounding system, which stretches the length of hundreds to thousands of kilometers, and its structure is not only different from power station and substation grounding system, but also different from the transmission line tower, lightning rod and other small grounding devices. There is little research information on the grounding impedance of high-speed railway integrated grounding system. This paper adopted 0.618 compensation method and reverse away method respectively, measured a section of high-speed railway integrated grounding system grounding impedance by JD16 and CA6425. Measurement results are in good agreement using those two type instrument. By using 0.618 compensation method, the measurement result will be gradually converged at 0.3 Ω with the increasing of current electrode distance, which is the real grounding impedance of integrated grounding system. By using reverse away method, the maximum measurement result difference is less than 0.024 Ω with the lead of current electrode distance increasing. The measurement results will be rapidly converged 0.25 Ω. The results showed that the reverse away method is helpful to shorten the length of current electrode wiring. The measurement error will be small when the current electrode wiring is longer.

Point source equalised by inverse filtering for measuring ground impedance

A point source for measuring ground impedance which complies with the omnidirectionality requirements of the ANSI S1.18 standard is presented. The source consists of a small aperture connected to a conventional loudspeaker through a cone. Whilst this source radiates with deviations lesser than ±1dB within ±45°, its frequency response exhibits strong peaks arising from resonances of air inside the cone. To equalise these resonances, inverse filtering is applied. Inverse filters pre-emphasise the electrical signal driving the sound source so that zero-phase (or minimum-phase) cosine-magnitude signals are radiated. Equalisation by inverse filtering has two main advantages in the ground impedance measurement. On the one hand, flattening the frequency response avoids large fluctuations of the excess attenuation curve, which can make difficult its inversion to ground impedance data. On the other hand, inverse filtering shorten the time response of the sound source, this in turn making easier the positioning of a time window to separate ground reflection from reflections/diffractions coming from nearby objects usually present in the acoustic scenario.

접지임피던스 측정시 보조전극의 배치 기준 연구

Among ground impedance measurement methods, the fall-of-potential method is the most thorough and reliable method. In the fall-of-potential method, ground electrode and auxiliary probes are placed in a straight line, and then, auxiliary potential probe is moved away from the ground electrode. The point at which plotted resistance curve flattens out is taken as right position of auxiliary potential probe. However, in some cases, it is hard to place ground electrode and auxiliary probes in a straight line. Therefore, we provided alternative placement method in this research. The method can be easily applicable to placing auxiliary probes. Also, this paper analyzed and compared ground impedance measurement standards of large grounding systems. Based on the analysis, practical measurement method using an earth tester was proposed. The proposed methods presented in this paper will be useful when determining locations of auxiliary probes in alternative positions, and the methods can be applied practically and easily.

A revised standard method for ground impedance measurement.

ANSI S1.18 (1998) for ground impedance measurement has been revised to combine the previously existing template method with direct deduction of impedance from data for the complex level difference between vertically separated microphones. It has been found that, despite the improved sensitivity at low frequencies that should be achievable through use of a longer range, the combined approach ceases to give reliable information for horizontal source‐receiver separations of more than 1 m. The revised standard contains four worked examples: three grass‐covered ground surfaces and a gravel road. The first example has been used to show that although use of consecutive measurements with a single microphone produces data that is usable with the template method, the phase information is not sufficiently robust to allow direct impedance deduction. In the three grassland examples, the widely used single parameter model is found to overpredict the real and imaginary parts of ground impedance at lower frequencies. The fourth example shows that the geometries prescribed in the standard are not appropriate for determining impedance spectra of relatively hard surfaces but are sufficient to establish that the surface is acoustically hard.

Improved Methodology for High-Frequency Low-Current Measurement of Grounding Rod Impedance

The high-frequency behavior of grounding rods is a major concern in several applications where high-frequency currents are involved, such as lightning currents or transient phenomena. Some measuring systems of high-frequency impedance of grounding rods are now available. However, the widely used method is the fall of potential using a three-rod method configuration such as in low-frequency measurements. A special spherical real-scale setup presented in this paper shows the influence of the ground current distribution on the impedance measurement. This effect is not relevant for the usual low-frequency measurements. Thus, careful attention should be paid to current distribution before concluding on the behavior (capacitive, inductive) of a grounding system.

Sources and potential influences of uncertainty in ground impedance measurements and estimations

Knowledge of acoustic impedance of ground surface is essential for determining noise levels outdoors. At distances up to a few hundred metres from the source ground effect may be the dominant factor. The short-range measurement of sound level spectra from an omni-directional source has been used as a standard method to deduce the acoustic impedance spectrum of ground surfaces (e.g. ANSI S1.18, 1999). However, there remain a number of uncertainties in such measurement methods. For example, at low frequencies the difficulties in fitting theoretical or phenomenological models to short range data may result is a large uncertainty in predictions of sound levels at larger distances. Another source of uncertainty is the variability of the acoustic impedance of apparently uniform ground. Another potential influence on predictions of long term equivalent noise levels is seasonal variation. This paper discusses the extent and potential influences of such uncertainties in measured and deduced ground impedance spectra.

Effect and minimization of errors in in situ ground impedance measurements

The transfer function method is a procedure to measure the surface impedance of grounds in situ. In this article, the influence of measurement errors on the predicted surface impedance is investigated numerically. Even small errors in the range of accuracy of common measurement equipment can lead to significant errors in the impedance. This is especially true for errors in the transfer function at frequencies below about 500 Hz and for highly reflecting grounds. To a lesser degree, errors in the measurement geometry contribute to the uncertainty of the estimated impedance. To minimize these effects, an improved geometry is suggested for the frequency range 100–400 Hz significantly reducing the average error. However, even with this optimized geometry the average error for high impedance grounds, like compacted silt, in this frequency range will be around 50%. Therefore, the use of the transfer function method cannot be recommended in this case unless the requirements in accuracy are very low for a specific application or particular favourable measurement conditions are given.