Ground Conductivity Research Articles

Grounding System Design for Wind Power Generation System Considering the Effective Length of Grounding Conductor

Human safety is the most important factor to determine any grounding system, therefore low‐frequency grounding resistance (LFGR) of wind power generation systems should be very low. Lightning protection is another factor for the grounding system design. Grounding conductors (GCs) are used to reduce the LFGR. A long GC however, does not reduce peak voltages for lightning currents with steep‐front waveshapes. Thus, the GC length is an important factor for an effective grounding system. This paper proposes a method for determining the effective length of GC based on traveling wave theory in time domain. Based on this calculation, it describes a grounding system design for wind power generation systems that considers both, the LFGR and the lightning protection. © 2024 Institute of Electrical Engineers of Japan and Wiley Periodicals LLC.

A tri-band low-profile shared-aperture mesh patch/Fabry-Perot cavity antenna

ABSTRACT A tri-band low-profile shared-aperture antenna is proposed. Based on structural multiplexing, a mesh patch is proposed to function as part of the partial reflective surface (PRS) of the Fabry-Perot cavity antenna (FPCA) in the middle- and high-frequency bands, as well as to function as the radiator of the patch antenna in the low-frequency band. Thus, the FPCA and the mesh patch antenna share the same aperture. A dual-band PRS is proposed, which can adjust its reflection amplitude independently in two frequency bands. By introducing artificial magnetic conductor (AMC) grounding to compensate for the transmission phase of the middle-frequency band, the proposed antenna can realize dual-band FPC resonance in a single cavity while maintaining a low profile. To validate the design concept, an antenna prototype is fabricated and measured. Measured results show that the impedance bandwidths of the proposed antenna are 4.74% (1.03–1.08 GHz), 0.42% (4.79–4.81 GHz), and 3.83% (11.52–11.97 GHz). The peak gain is 7.85 dBi at 1.06 GHz, 12.47 dBi at 4.81 GHz, and 20.6 dBi at 11.7 GHz. The isolation between the three bands is better than 30 dB. The three operating bands of the proposed antenna have a high degree of independence and can be flexibly adjusted.

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

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

Compact Wideband Tapered Slot Antenna Using Fan-Shaped and Stepped Structures for Chipless Radio-Frequency-Identification Sensor Tag Applications.

In this paper, two kinds of miniaturization methods for designing a compact wideband tapered slot antenna (TSA) using either fan-shaped structures only or fan-shaped and stepped structures were proposed. First, a miniaturization method appending the fan-shaped structures, such as quarter circular slots (QCSs), half circular slots (HCSs), and half circular patches (HCPs), to the sides of the ground conductor for the TSA was investigated. The effects of appending the QCSs, HCSs, and HCPs sequentially on the input reflection coefficient and gain characteristics of the TSA were compared. The compact wideband TSA using the first miniaturization method showed the simulated frequency band for a voltage standing wave ratio (VSWR) less than 2 of 2.530-13.379 GHz (136.4%) with gain in the band ranging 3.1-6.9 dBi. Impedance bandwidth was increased by 29.7% and antenna size was reduced by 39.1%, compared to the conventional TSA. Second, the fan-shaped structures combined with the stepped structures (SSs) were added to the sides of the ground conductor to further miniaturize the TSA. The fan-shaped structures based on the HCSs and HCPs were appended to the ground conductor with the QCSs and SSs. The compact wideband TSA using the second miniaturization method had the simulated frequency band for a VSWR less than 2 of 2.313-13.805 GHz (142.6%) with gain in the band ranging 3.0-8.1 dBi. Impedance bandwidth was increased by 37.8% and antenna size was reduced by 45.9%, compared to the conventional TSA. Therefore, the increase in impedance bandwidth and the size reduction effect of the compact wideband TSA using the second miniaturization method were better compared to those using the first method. In addition, sidelobe levels at high frequencies decreased while gain at high frequencies increased. A prototype of the compact wideband TSA using the second miniaturization method was fabricated on an RF-35 substrate to validate the simulation results. The measured frequency band for a VSWR less than 2 was 2.320-13.745 GHz (142.2%) with measured gain ranging 3.1-7.9 dBi.

Grounding resistance model considering propagation time between grounding electrodes

The velocity of electric field in the soil is sufficiently lower than that in the air. Conventional grounding resistance models based on an electric circuit theory ignore the propagation time between grounding electrodes (GEs). If the GEs are connected using an aerial lead conductor, the propagation time along the lead conductor is apparently different from that along a grounding conductor (GC) in the soil. The propagation time of mutual grounding resistance between GEs should be considered in accurate lightning surge analysis. This paper proposes a simulation model of the mutual grounding resistance considering the propagation time between GEs.

Modeling Geomagnetically Induced Currents in the Alberta Power Network: Comparison and Validation Using Hall Probe Measurements During a Magnetic Storm

AbstractDuring space weather events, geomagnetic disturbances (GMDs) induce geoelectric fields which drive geomagnetically induced currents (GICs) through electrically‐grounded power transmission lines. Alberta, Canada—located near the auroral zone and thus prone to large GMDs—has a dense network of magnetometer stations and surface impedance measurements to better characterize the GMD and ground conductivity, respectively. GIC monitoring devices were recently installed at five substation transformer neutrals, providing a unique opportunity to compare data to modeled GICs. GICs are modeled across the >240 kV provincial power transmission network during a moderate GMD event on 24 April 2023. GIC monitoring devices measured larger neutral‐to‐ground currents than expected up to 117 Amps during peak storm time, providing unequivocal evidence linking network GICs with GMDs. The model performs reasonably well (correlation coefficients >0.5; performance parameter >0.15) at four of five substations, but generally underestimates peak GIC values (sometimes by a factor >2), suggesting that the present model underrepresents overall network risk. The model performs poorly at one of the five substations (correlation = 0.46; performance parameter = 0.10), the reasons for which may be due to simplifications and/or unknowns in network parameters. Despite these underestimates, during this GMD, the model predicts the largest GIC at substations located in the northeastern part of the province (240 kV) or around Edmonton (500 kV)—regions which have significant electrical and industrial infrastructure. Further refinement of the network model with transformer resistances, more line and earthing resistances, and/or including lower voltage levels is necessary to improve data fit.

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.

Advanced machine learning techniques: Forecasting thermal resistance in borehole heat exchanger system through RSM and hybrid DFNN-GA approaches

The thermal efficiency of ground heat exchanger (GHEs) relies on optimizing borehole thermal resistance and total internal thermal resistance for cost-effective and efficient design. This study aims to establish a robust correlation among various parameters, including thermal conductivity of pipe, grout, and ground, borehole depth, borehole and pipe diameter, pipe-pipe distance, fluid velocity, and heat transfer rate of the ground, with the 3D borehole thermal resistance (Rb,3D) and total internal thermal resistance (Ra,3D). This exploration of eight influential factors results in an l-130 design matrix with 130 data points. A 3D computational model, utilizing a four-resistance method, accurately calculates Rb,3D and Ra,3D, while analyzing heat transfer in both solids and fluids. Two prediction models, Response Surface Methodology (RSM) and a hybrid Deep Feedforward Neural Network-Genetic Algorithm (DFNN-GA), establish the correlation between Rb,3D and Ra,3D and the eight variables. The results highlight the efficacy of the prediction models, achieving R2 values of 79.87% and 87.90% for RSM and 94.00% and 99.15% for DFNN-GA, corresponding to the predictive accuracy of Rb,3D and Ra,3D, respectively. Furthermore, lower RSME, MAE, and AARE values are observed. A rigorous comparative analysis assesses the relative effectiveness of these methodologies in achieving the research goals.

Data transmission path planning method for wireless sensor network in grounding grid area based on MM‐DPS hybrid algorithm

AbstractAt present, in order to conduct non‐destructive testing on the grounding grid of substations under the condition of continuous power supply and no excavation, researchers have applied wireless technology based on electrochemical methods to remotely monitor the corrosion state of grounding conductors online. Nevertheless, wireless signals are affected by the environment when they are transmitted underground. In the field of grounding gird wireless monitoring, how to plan the information transmission path of wireless sensor network (WSN) with high accuracy of data transfer and low energy consumption earns growing research attention. To address the problem of WSN path planning in grounding grid area, a path planning method for WSN based on the hybrid algorithm of map‐matching algorithm and double‐pole search algorithm (MM‐DPS) is proposed in this paper. The map‐matching algorithm is employed to calculate the optimal sampling node number of the data transmission path. On the basis of the optimal sampling node number, the double‐pole search algorithm is employed in seeking out each sensor node of the path, and two groups of path plans are obtained. In the simulation experiment, compared with the A‐star algorithm, the MM‐DPS algorithm shortens the data transmission path length by about 39% and reduces the energy consumption by about 57%. The research work brings a method to alleviate the problem of data transmission underground of WSN in grounding grid area. The method not only ensures the accuracy of data transmission, but also shorts the transmission distance and reduces energy consumption.

Impacts of Terrain Conductivity Survey for Groundwater Investigation in a Typical Sedimentary Formation; A Case Study of Itori, South-West Nigeria

A geophysical investigation for groundwater development involving conductivity measurement using Electromagnetic profiling was conducted to locate fractured and fissured zones and associated groundwater containing media at Itori communities, Southwestern Nigeria. The area is underlain by the typical sedimentary rocks of South-West, Nigeria with the local geology predominantly clay, shale, clay sand, limestone and Sandstone. Measurements of the ground conductivity were carried out with Geonics EM 34-3 along 5 traverses whose profile lengths varied between 160 and 200 m. Intensive geophysical fieldworks were performed utilizing Frequency Domain Electromagnetic Method (FDEM) using Geonics-EM-34 to determine the vertical and lateral variations of subsurface conductivity probing depths of 20 m, 40 m and 60 m. The EM data were acquired at 500 m intervals along 10 profiles. The Vertical Dipole Moment in the first layer exhibited the highest true conductivity and lowest true conductivity of 42.65 mS/m and 29.1 mS/m for EMITO1 and EMITO2 respectively and the corresponding Horizontal Dipole Moment exhibited the highest true conductivity of 36.0 mS/m and 25.41 mS/m for EMITO1 alongside EMITO2 and EMITO8 respectively while the Vertical Dipole Moment in the second layer exhibited the highest true conductivity of 45.62 mS/m and lowest true conductivity of 34.76 mS/m for EMITO1 and EMITO8 respectively and the corresponding Horizontal Dipole Moment exhibited the highest true conductivity of 44.0 mS/m and lowest true conductivity of 36.3 mS/m for EMITO3 and EMITO8 respectively. The qualitative interpretation of EM results identified areas of hydrogeologic importance and forms a predictive and suggestive basis for Vertical Electrical Sounding (VES) investigation; points of positive EM anomalies were considered as priority area for electrical resistivity sounding and prospective groundwater development, since they suggest lithological variations within the unconsolidated overburden and/or water–filled fissures in the bedrock. The identified major geological interfaces were suspected to be of weathered zones

Investigating the influence of additional ground conductors influence on the characteristics of stripline devices with modal decomposition based on a meander line turn

Investigating the influence of additional ground conductors influence on the characteristics of stripline devices with modal decomposition based on a meander line turn

Common mode far field radiation mechanisms and prediction of a buck converter with cables based on common mode voltage mutation method

AbstractIn the field of electromagnetic compatibility (EMC) research, the knowledge of the formation mechanism of the far field electromagnetic radiation and its prediction is essential for the electromagnetic noise suppression design of a switched mode power supply. This paper investigates the equivalent driving sources of the common mode (CM) current of a Buck converter with cables. Based on the concept of CM voltage mutation, this paper proposes two mechanism models of the same‐direction CM voltage driving mode and the opposite‐direction CM voltage driving mode and derives the approximate analytical formulas for the far field intensity estimation of the horizontal cables. To evaluate the predictive effectiveness of the CM far field radiation model, a 30 MHz very high frequency (VHF) Buck prototype with shielded cables is built and tested, and a shielding shell and low impedance ground conductor suppression designs are then verified. The CM electromagnetic radiation mechanisms of a non‐isolated power converter are demonstrated here. The proposed electromagnetic radiation models, approximate analytical formulas, and improvement design can help to advance the CM radiation analysis and optimization design.

Monitoring of simulated clandestine graves of victims using UAVs, GPR, electrical tomography and conductivity over 4-8 years post-burial to aid forensic search investigators in Colombia, South America

In Colombia there are estimated to be over 121,000 missing people and victims of forced disappearances. Forensic investigators therefore need assistance in determining optimal detection techniques for buried victims, to give victims’ families closure and for the wider community to see that justice is being served. Previous research has created 12 controlled simulated clandestine graves of typical Colombian murder victim scenarios at 0.5 m – 1.2 m depths in savannah and rainforest sites in Colombia. The 0–3 years of geophysical monitoring results of were published, with this paper reporting on 4–8 years monitoring of both UAV drone results and geophysical data. The UAV results from the year 8 survey, published for first time from Colombia, showed that the simulated graves could still be located using NDVI and NIR multi-spectral data, but not using optical or other multi-spectral data. The 0–3 years of geophysical data found the simulated clandestine graves could be detected with electrical resistivity and GPR methods, with the 4–8 year surveys evidencing that they could still be detected using bulk ground conductivity surveys, GPR horizontal time slice datasets and 2D ERT profiles. Research implications suggest initial use of UAV remote sensing technology to pinpoint likely search areas, before subsequent ground reconnaissance, geophysical surveys and their interpretation, before intrusive investigation methods are employed for detecting missing and disappeared persons in Colombia.

Evaluation of lightning‐induced overvoltage on a 10 kV distribution line based on electromagnetic return‐stroke model using finite‐difference time‐domain

AbstractAccurate simulation of lightning‐induced overvoltage for overhead distribution lines is helpful to prevent lightning trip accidents. An electromagnetic return‐stroke model was used to represent lightning and then a 3D finite‐difference time‐domain (FDTD) method was adopted to simulate the lightning‐induced overvoltage on a distribution line without a field‐line coupling model. How lightning‐induced overvoltage behave for different ground conductivity and varying distance between the distribution line and the lightning channel was analysed. The results showed that the overvoltage waveforms at the centre point of the line corresponding to lightning strikes on the lossy ground and an ideal ground (σ = ∞) were similar; however, the peak amplitudes of the waveform were affected by soil conductivity at a close distance. The relationship between magnitude of the overvoltage and distance can be described by a second‐order exponential decay equation. Finally, the overvoltage calculated using the proposed model was compared with those obtained based on Agrawal's model and measurements made using the newly developed intelligent insulator on site. From these comparisons, it could be concluded that the FDTD method with the electromagnetic return‐stroke model produces reasonably accurate results of the attenuated oscillation waveform, which can better reproduce the overvoltage on operational distribution lines.

Omnidirectional Circularly Polarized Monopole Antennas on Artificial Magnetic Conductor Ground Plane

Omnidirectional Circularly Polarized Monopole Antennas on Artificial Magnetic Conductor Ground Plane

Evaluation of ground conductor corrosion based on EMI technique with asymmetric sensor layout

ABSTRACT The ground conductor is prone to corrosion, which affects its ability to diverge current and the normal operation of the power system. The traditional detection method can’t detect its corrosion degree intuitively. This paper proposes a novel method based on Electromechanical impedance (EMI) technique to evaluate the corrosion degree of the grounding conductor. Firstly, based on the analysis of corrosion of metals. The change of ground conductor radius Δr is used as the corrosion parameter. A linear model of peak frequency Δf m and corrosion parameter Δr in asymmetric layout is established by analysing EMI and conductor mechanical admittance. Secondly, the EMI coupling models with different sensor layouts were built on the finite element software. It is verified that the asymmetric sensor layout effectively improves the sensitivity to corrosion. The linear model greatly improves the assessment accuracy compared with the Mean Absolute Percentage Deviation (MAPD) and Root Mean Square Deviation (RMSD) damage index. Thirdly, the proposed method is verified in a real grounding conductor corrosion experiment. The method based on the EMI technique with asymmetric sensor layout can evaluate the corrosion of the grounding conductor well.

ОБЕСПЕЧЕНИЕ КАЧЕСТВА ПРОЕКТИРОВАНИЯ РЕЗИСТИВНОГО НАГРЕВАТЕЛЬНОГО КАБЕЛЯ НА ОСНОВЕ РАЗРАБОТКИ МЕТОДИКИ МАТЕМАТИЧЕСКОГО РАСЧЕТА

The article is devoted to developing a mathematical model for calculating the electrical and design parameters of a resistive heating cable. The aim of the work is to consider the main stages of designing a heating cable and to develop a methodology for calculating its main parameters and design, which will ensure the quality and performance characteristics of the future product that meets all modern technical, technological and economic requirements. The main stages of the heating cable design process are described and recommendations are given on selecting materials, calculating the electrical and design parameters, namely: rated power, electrical resistance, diameters and mass of conductors, insulation, shield and shell. Based on the electrically conductive shield design the paper examines in detail methods for calculating the weight and size parameters of shields in the form of a copper grounding conductor with foil, as well as in the form of a screening braid made of copper wires. The proposed methodology for calculating a resistive heating cable allows considering the design process in more detail. It is at this stage that the future product quality is determined, while ensuring the required characteristics and parameters, as well as reliability and consistency of the performance throughout the product entire life cycle.

Unique laboratory “Currents in the ground”

A brief description of the scientific laboratory is given, which has become a flagship in the field of electrical energy, which made it possible to obtain unique results on grounding and electrical safety, which were included in state regulatory documents. It is shown that a well-known scientific school has been created in the laboratory for the study of processes in grounding devices of electrical installations. The laboratory was founded in 1971 and has not been described previously. The article shows the main building in the form of a two-story building and a nearby stack-type pulse voltage generator for a voltage of 1,250,000 V. The circuit allows for reconnecting capacitors on floors to obtain different capacitances in the discharge. To connect to the grounding device under study, a portable overhead line with split wires is used. A map of grounding fields on the laboratory territory is provided. This allows you to design almost any design of a grounding device. Fields of vertical and horizontal grounding conductors of various lengths are used; fields of complex mesh grounding conductors; groups of single vertical electrodes of different lengths. The laboratory has several sets of self-powered electronic high-speed oscilloscopes, shielded and isolated from ground to avoid interference. The range of research questions can be significantly expanded by using already installed objects: an experimental overhead line with a voltage of 220 kV on nine reinforced concrete supports; cable line 600m long; a dynamic and thermal test stand, equipped with a circuit for obtaining industrial frequency currents of up to 4 kA at a voltage of 0.4 kV; 120 linear meters of reinforced concrete trays were laid on the field of a complex mesh grounding device for laying communication and control cables in them; two additional pulse voltage generators 1,600,000 V and 1,000,000 V (the latter allows transportation to full-scale test sites outside the laboratory); test transformers IOM-100/100.

Analysis of the Geoelectric Field in Sweden Over Solar Cycles 23 and 24: Spatial and Temporal Variability During Strong GIC Events

AbstractGeomagnetic storms can produce large perturbations on the Earth magnetic field. Through complex magnetosphere‐ionosphere coupling, the geoelectric field (E) and geomagnetic field (B) are highly perturbed. The E is the physical driver of geomagnetically induced currents. However, a statistical study of the E in Sweden has never been done before. We combined geomagnetic data from the International Monitor for Auroral Geomagnetic Effects network in Northern Europe with a 3‐D structure of Earth's electrical conductivity in Sweden as the input of a 1‐D model to compute the E between 2000 and 2018. Northwestern Sweden presents statistically larger E magnitudes due to larger |dB/dt| variations in the north than in the south of Sweden and relative lower conductivity in the west compared to central and eastern Sweden. In contrast, the 15 strongest daily maximum |E| events present more frequently a maximum magnitude in central Sweden (62.25°N) and their relative strengths are not the same for all latitudes. These results highlight the different regional response to geomagnetic storms, which can be related to ground conductivity variability and the complex magnetosphere‐ionosphere coupling mechanisms.

Low-Cost Distributed Thermal Response Test for the Estimation of Thermal Ground and Grout Conductivities in Geothermal Heat Pump Applications

The design process of a borehole heat exchanger (BHE) requires knowledge of building thermal loads, the expected heat pump’s COP and the ground’s thermophysical properties. The thermal response test (TRT) is a common experimental technique for estimating the ground’s thermal conductivity and borehole thermal resistance. In classic TRT, a constant heat transfer rate is provided above ground to the carrier fluid that circulates continuously inside a pilot BHE. The average fluid temperature is measured, and from its time-dependent evolution, it is possible to infer both the thermal resistance of the BHE and the thermal conductivity of the ground. The present paper investigates the possibility of a new approach for TRT with the continuous injection of heat directly into the BHE’s grouting by means of electrical resistance imparted along the entire BHE’s length, while local (along the depth) temperature measurements are acquired. This DTRT (distributed TRT) approach has seldom been applied and, in most applications, circulating hot fluid and optical fibers are used to infer depth-related temperatures. The distributed measurements allow the detection of thermal ground anomalies along the heat exchanger and even the presence of aquifer layers. The present paper investigates the new EDDTRT (electric depth-distributed TRT, under patenting) approach based on traditional instruments (e.g., RTD) or one-wire digital sensors. The accuracy of the proposed method is numerically assessed by Comsol Multiphysics simulations. The analysis of the data obtained from the “virtual” EDDTRT confirms the possibility of estimating within 10% accuracy both thermal ground and grout conductivities.