High Soil Resistivity Research Articles

Characterization of Soil Enhancement Mixtures at Low-Magnitude Currents

Regarding the installation of grounding systems, it is not common for the installation site to be re-located due to high soil resistivity. Enhancement materials have been widely used for their known advantages, including their ability to reduce the resistivity of soil. Although some studies have been conducted on the characterization of EMs under AC of various frequencies, limited studies can be found on their performance when mixed with various percentages of water content (WC) and soil. In this work, sand mixed with controlled percentages of enhancement materials (EM 1, EM 2 and EM 3) and controlled amounts of water content was placed on a parallel plate and tested under AC of various frequencies to obtain the resistivity and permittivity. It was found that dry sand–EM mixtures can be represented by an R-C parallel circuit, while wet sand–EM mixtures can be represented by a nonlinear R. These new test data providing the soil resistivity and permittivity of various sand–EM mixtures are important in selecting suitable EMs to be used in grounding systems.

Electromechanical analysis of underbuilt wire use in transmission lines

Electromechanical analysis of underbuilt wire use in transmission lines

Modeling and assessment of hydrogen-blended natural gas releases from buried pipeline

Modeling and assessment of hydrogen-blended natural gas releases from buried pipeline

Investigation of soil resistivity impacts on the electrodes of grounding system subjected to lightning strikes

AbstractIn this paper, the study of the homogeneous resistivity and two‐layer soil influences on the performance of the electrodes of grounding systems subjected to lightning strikes is carried out considering soil ionization. The study is done on the behaviour of the ground electrodes while the resistivity of the soil is altered from small to high value in the case of homogeneous soil, while the study is obtained on two‐layer soils in the case of diverse values of the reflection factor. In the suggested algorithm for two‐layer soils, each layer has its resistivity and dielectric constant, where the dielectric constant and soil resistivity depend on the lightning frequency. The field resulting from lightning strikes, which causes soil ionization, has been studied, and the results have been used to understand the behaviour of ground rods under the influence of lightning strikes. The credibility of the results has been strengthened by comparing it with what others have obtained recently. The article's novelty can be summarized in the investigation of the performance of the electrodes of grounding grids that are installed in high soil resistivity of uniform and two‐layer soils containing the impacts of soil ionization, lightning frequency, soil resistivity, and permittivity variations.

Effect of high resistivity soil under high impulse currents

In this paper, experimental test results of several ground electrodes surrounded with gravelly soil medium subjected to high impulse currents were studied, to investigate the effect of confined soil surround electrodes. Ground resistance measurements were performed at low magnitude of voltage and current, where the results are compared to the impulse characteristics of ground electrodes. This paper shows a significant difference in the RDC values and impulse characteristics of ground electrodes when gravelly soil medium surrounded the ground electrode in comparison to the electrodes installed in natural soil. This indicates that the confined soil around the electrode has a major effect on the performance of ground electrodes, whether at steady state or under high impulse conditions. Equivalent circuit for each tested electrode was developed with personal simulation program with integrated circuit emphasis (PSPICE), where the effect of inductance was seen in the electrodes surrounded with gravelly soil.

Lightning-induced voltages on low-voltage distribution lines

Lightning-induced voltages on low-voltage distribution lines

Field tests of square and double exponential pulses for transient resistivity measurements using Wenner arrays and hemispheres

Field tests of square and double exponential pulses for transient resistivity measurements using Wenner arrays and hemispheres

Influence of a shield wire flashover on the indirect lightning performance assessment of distribution lines

Influence of a shield wire flashover on the indirect lightning performance assessment of distribution lines

Impulse Characteristics of Ground Electrodes in Low Resistivity Soil

Soil properties have been known to be the factors that influence the ionization process in soil, which cause the impulse impedance, Zimpulse to be lower than that at steady state resistance, RDC. Many studies have established the relationship between the percentage reduction of Zimpulse from RDC in such that the percentage reduction is more pronounced in high resistivity soil, or in high RDC, than that at low resistivity soils. Nevertheless, Zimpulse is not the only parameter in representing the characteristics of soil under high impulse conditions, where from the voltage and current waveforms, the current rise and discharged times can also be established, where more accurate and extensive analysis of the electrical characteristics of ground electrodes subjected to high impulse currents can be achieved. This paper presents the experimental results of four ground electrodes, installed in agricultural land, with soil resistivity, of below 3 Ωm, subjected to high impulse currents, where the parameters of current rise times, Zimpulse and current discharged times were investigated. Two of these ground electrodes are having close RDC values, despite having different electrode's configurations, were also investigated. © 2023 Institute of Electrical Engineer of Japan and Wiley Periodicals LLC.

Lightning Efficient Counterpoise Configurations for Transmission Line Grounding

Different configurations of counterpoises are often used to reduce the resistance and impulse impedance of the transmission line grounding. However, there are no general rules for an actual design. This paper analyses the performance of several configurations of counterpoises under typical lightning current impulses. The basis is a parametric analysis derived from time responses of 11,386 test cases for each configuration with parameters in broad ranges computed using a rigorous electromagnetic model based on the method of moments. The contributions of the paper are: Simple formulas for the resistance, impulse impedance, and effective length of counterpoise configurations are derived from and verified by the simulation results; a configuration with an 8-leg counterpoise bent parallel to the line is proposed, which extends the effective length and is efficient in high resistivity soil; and the method does not depend on the different lightning current impulse waveform representations based on Heidler, CIGRE, and double-exponential formulas, since the results can be easily converted. A simple procedure is provided to compare the capabilities and limitations of counterpoise configurations. New formulas and procedures make up a general and straightforward method for analyzing the optimal design, considering the cost-effective and best protection against lightning.

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.

Influence of a lossy ground on the lightning performance of overhead transmission lines

• Accurate lossy ground representation impacts lightning overvoltages simulation. • Carson's classic formulation may lead to inaccuracies for high-resistivity soils. • Accurate lossy ground representation in simulations leads to higher TLs outage rate. • An increase up to 15% in TL outages was found when ground is accurately represented. This paper investigates the impact of incorporating both displacement currents and frequency-dependent soil parameters in the calculation of the ground-return impedance for the determination of the backflashover rate of 138 kV and 230 kV overhead transmission lines due to direct lightning strikes. This is done by considering the Sunde's formulation for calculating the ground-return impedance, which is incorporated in a time-domain simulator using an alternative implementation of Marti's transmission line model. The obtained results show that the peak of the lightning overvoltages computed considering Sunde's formula, along with frequency-dependent soil parameters, leads to higher amplitudes in comparison with those simulated using the classical Carson's formula, which neglects the frequency dependence of soil parameters and assumes conductive currents in the soil much larger than displacement currents. This effect is more pronounced in high-resistivity soils and leads to an increase in the line backflashover rate within 4-6%, 7-12% and 9-15% for 1000 Ωm, 5000 Ωm and 10000 Ωm soils, respectively, considering 138 kV and 230 kV lines, and assuming a typical median first stroke lightning current. Analyses performed with slow and fast first stroke currents confirm the trend of increase of the backflashover rate with the consideration of Sunde's formula.

Stopping criterion for Monte Carlo method-based simulations of the lightning performance of transmission lines

• Lightning performance of 230- and 500 kV TL is assessed by computational simulations. • Technical-economic analysis of techniques to improve lightning performance is shown. • Installation of extended counterpoise wires and underbuilt wires is considered. • Decrease of 88%–94% in BFOR is obtained with the use of underbuilt wires. • Underbuilt wires are economically viable mainly for high resistivity soils. A stopping criterion to be applied on Monte Carlo-based computational simulations of the lightning performance of transmission lines in terms of backflashover is proposed. Considering typical 138 kV and 230 kV transmission lines as case studies and the application of an elaborated probabilistic calculation approach, the influence of the number of iterations of the Monte Carlo simulation on the calculated critical current, backflashover probability, error of the distribution and the dispersion coefficient is assessed. The obtained results leaded to the proposed stopping criterion that establishes limits for the error (5%) and the dispersion coefficient (0.35). Its application yields consistent results with the decrease on the number of required iterations up to 95% and higher than 90% for simulations related to the 230 kV and 138 kV TLs, respectively, when compared to simulations of reference with 20000 iterations.

Technical-economic analysis of conventional and non-conventional techniques to improve the lightning performance of transmission lines: Extended counterpoise grounding wires and underbuilt wires

• Lightning performance of 230- and 500 kV TL is assessed by computational simulations. • Technical-economic analysis of techniques to improve lightning performance is shown. • Installation of extended counterpoise wires and underbuilt wires is considered. • Decrease of 88%-to-94% in BFOR is obtained with the use of underbuilt wires. • Underbuilt wires is economically viable mainly for high resistivity soils. This work presents a technical-economic analysis of using extended counterpoise wires and underbuilt wires to improve the lightning performance of typical 230 kV and 500 kV transmission lines. The installation of underbuilt wires leaded to decreases up to 88% and 94% on the backflashover rate of the lines with high tower-footing grounding impulse impedance. Also, it is shown that the cost of installing one underbuilt wire combined with the extension of counterpoise wires converges to the cost related to the intervention only on grounding for increasing values of soil resistivity. A difference of only 3% between the costs of both techniques was indicated for the 230 kV TL installed over a soil with resistivity of 20,000 Ω.m. These aspects indicate the use of underbuilt wires as an economically viable solution for improving the lightning performance of transmission lines, mainly for high resistivity soils.

Assessment of Ground-Return Impedance and Admittance Equations for the Transient Analysis of Underground Cables Using a Full-Wave FDTD Method

In this paper, the validity of two extended transmission line approaches proposed for calculating the ground-return impedance and admittance of an underground insulated cable is evaluated taking as reference a full-wave approach based on the 3-D finite-difference time-domain (FDTD) method. The transient responses of an underground cable with realistic radius are calculated for a wide range of soil resistivities and cable lengths. It is shown that the extended transmission line approaches lead to transient waveforms in good agreement with the FDTD method even for relatively short cables and high soil resistivity. The limitations of a traditional formulation that neglects the influence of the ground-return admittance on the calculation of the cable parameters are also demonstrated. Overall, the results confirm the accuracy of the newly-proposed expressions for the calculation of underground cable parameters.

Improving Grounding System for Oil Tanks Using Finite Element Method, Taking into Account the Frequency Dependence of Soil Parameters

This work was devoted to the development of a simulation model of the grounding and lightning protection system for oil tanks, taking into account the frequency dependence of soil parameters, where we, based on the equations mentioned in previous studies, designed a grounding model for an oil tank taking into account the frequency dependence of soil parameters by using the finite elements method. and for different configurations, where it was observed that the grounding potential rise GPR was significantly reduced at high frequencies, especially in the case of high soil resistivity, the percentage of decrease in the grounding potential rise in the case of dry soil for the studied site 1266.65 Ω.m and for wet soil 596.27 Ω.m, respectively, 22.8% and 23.8%, respectively. and it was pointed out the necessity of conducting soil resistivity measurements before the tank construction process, and the need to use the network configuration of the oil tank grounding model in some cases where the soil resistivity is high and it is difficult to eliminate the effect of lightning current with the typical design mentioned in NFPA 780 for tank grounding.

First Experience in Monitoring of Line Surge Arresters Installed on 110 kV Transmission Line Ston – Komolac in Croatia

In paper are presented some first results and experience in real time monitoring of line surge arresters installed on 110 kV transmission line Ston – Komolac in southern part of Croatia. Mentioned line is the first line in Croatian transmission network equipped with line surge arresters (LSA). The line with its length of 43,95 km is situated in region with high soil resistance, exposed to one of the highest level of lightning activity in Croatia. At the same time it is the most important line in connecting HPP Dubrovnik (240 MVA) to the main part of 110 kV transmission network. Due to all mentioned reasons and great number of annual outages, it was decided to equip the line with LSA for improving the lightning performance and the availability of line. As result of performed numerical simulations on simulation line model it was decided to install 110 kV gapless, IEC Class II line arresters. Also, to improve analysis of expected results the 61 line arresters were equipped with Excount-II type of monitoring sensors. The main goal was to determine the behaviour of line arresters arrangement across the line during overvoltage events on towers. This installed “realtime” monitoring system enables remote control and wireless exchange the collected data from local data logger installed on LSA. Line arresters activity is monitoring through numbers, date and time and level of surges and the condition state of LSA, through the measuring of leakage current. First results in application of LSA are showing significant reduction of line outages with registered relatively strong activity of monitored line arresters. Also, as it was expected some particular part of line is espied to be exposed to higher frequency and higher level of registered arresters surge current. During collecting the data of LSA activity, some practical problems were encountered with time synchronization between monitoring devices and it is mentioned and discussed in paper, too. Although the analysed time period of eight months with LSA application is too short to allow strong final conclusions, obtained first experience will be very helpful in assessment of further LSA application in Croatian transmission network.

DECREASING BACKFLASHOVER NUMBERS ON MEDIUM VOLTAGE OVERHEAD LINES LOCATED IN REGIONS WITH HIGH SOIL RESISTIVITY

The possibility of decreasing backflashover numbers on medium voltage overhead lines located in regions with high soil resistivity has been analyzed in this paper. Until now, activities in this field of protecting overhead lines have been limited by existing surge protection equipment and possibilities of grounding systems. The possibility of using chemical rods for getting better ground resistance and introducing metal oxide surge arresters like line arresters alongside the medium voltage overhead lines is analyzed here. The idea of this paper is based on facts that metal oxide surge arresters have become very high quality products with low prices, and so many important experiences in using them like line arresters exist in the world; and we, in Croatia, have a 10-year-old experience in using chemical rods like part of grounding system. The paper treats the problems of backflashover on medium voltage overhead lines, chemical rods working principles and ways of designing grounding systems like this. Finally the techno – economic analysis of using chemical rods and metal oxide surge arresters possibilities has been made, with determining justifiability criteria of using them. In the conclusion, comparison with knowledge until now has been made, as well as a suggestion for future use.

Lightning protection of overhead distribution lines installed on high resistivity soil

The paper presents a comprehensive study on the lightning performance of overhead distribution lines located on high resistivity soil considering both indirect and direct strokes. An evaluation of the effect of high grounding resistance values of the neutral conductor, shielding wires and surge arresters is presented. A lightning induced voltage calculation methodology is presented and validated. The estimated performance results for distribution lines placed at high resistivity soils, with and without neutral conductor and surge arresters, are presented together with a discussion on the induced voltage problem. Additionally, the protection of distribution lines against direct strokes is analyzed and an innovative solution to reduce the number of arrester failures is proposed. The new solution is compared with the classical one, which uses a shielding wire to protect the arresters, followed by a discussion on the line lightning performance against direct strokes. The results point to different alternatives to improve the distribution lines lightning performance considering direct and indirect strokes together.

Research on Protection Effects of Drainage Line on Secondary Cable in Substation

Ensuring the operation safety of secondary cable is an important part of substation grounding system design. In some cases with high soil resistivity and large grounding grid, the safety of secondary cable can not be guaranteed by optimizing the design of grounding grid. This paper compares the core-to-skin potential difference and the shielding layer current of secondary cable with or without drainage line. It is shown that the drainage lines, which are laid in parallel with the secondary cable, can significantly reduce the core-to-skin potential difference and shielding layer current of secondary cable during power frequency short-circuit and lightning stroke. When the radius of the drainage line reaches 5mm, core-to-skin potential difference and shielding layer current of secondary cable will be reduced to 1/3 of those when it is not laid.