Ground Conductivity Research Articles

Mathematical Modeling of Fluid Flow and Heat Transfer in Petroleum Industries and Geothermal Applications

This Special Issue of Energies is dedicated to all aspects of fluid flow and heat transfer in geothermal applications, including the ground heat exchanger, conduction, and convection in porous media [...]

On the ground thermal conductivity estimation with coaxial borehole heat exchangers according to different undisturbed ground temperature profiles

This paper concerns the modeling of vertical coaxial heat exchangers for Ground Source Heat Pump (GSHP) applications. Vertical coaxial borehole heat exchangers (CBHEs) can be buried at depths which are even higher than the conventional ones. In this case they are referred as Deep Borehole Heat Exchangers (DBHEs). As it is known, there is indeed a strong recent tendency, especially in the Scandinavian regions, to use high depth (500–1000 m) underground heat exchangers for the GSHP applications. This study is aimed at the analysis of the BHE behaviour in the early period, say for Fourier numbers typical of the Thermal Response Test (TRT) measurements. The novelty of the present numerical results is related to the applicability of standard TRT methods when referred to DBHEs and different geothermal gradients can be found. To this aim a Fortran code has been developed for describing a 2D transient conduction and convection problem able to provide the fluid and ground temperature evolution as a function of a series of boundary conditions, including the initial and far field ground temperature distribution along the depth. The application of the present model is related to coaxial BHEs for the assessment of the effects of the undisturbed ground temperature profile and the direction of the carrier fluid on the ground thermal conductivity estimation in TRT experiments. It is here demonstrated that different BHE depths (ranging from 150 to 800 m) and different undisturbed temperature profiles (including zero and positive geothermal gradients) can severely affect the TRT ground conductivity estimation (errors up to 25%) if the flow direction is based on the annular pipe or the central pipe inlets.

The Potential Use of Ground Conductivity Meters to Identify the Location of Seepages—Case Study of the Maniów Levee near Krakow, Poland

This paper presents an assessment of the potential usefulness of the Ground Conductivity Meter (GCM) method to locate seepage pathways in the Maniow levee zone near Kraków, Poland. We have realized this aim through geological recognition of the study area, which requires the implementation of GCM data inversion measured in the sounding version. The GCM measurements were performed along with the net of profiles using combined data from CMD Mini Explorer and CMD Explorer equipment. The methodology of the one-dimensional (1D) inversion of the GCM soundings located along profiles is presented in the article. The legitimacy of the inversion and the relationship of the results obtained in the form of conductivity sections along profiles with geology have been verified in detail. The inversion procedures were tested on the synthetic GCM soundings obtained from modeling processes, by using the electrical conductivity and thicknesses, known from the drilled formations and additionally based on DC-R sounding data. These soundings were performed at some selected reference points in the levee zone. We have used our software and IX1D Interpex software to calculate the forward modeling. Quantitative interpretation processed along the profiles has been proceeded by 1D inversion of GCM data at several referential points located close to boreholes and DC soundings. It was done to verify the correctness of the quantitative interpretation. The geoelectrical models, obtained in a section form, were correlated with the borehole lithology data, providing a reference geological structure in some places. As a result of the work mentioned above, the potential seepage zones were located on the conductivity sections. The thickness of the cohesive silty clay layer, lying near to the surface, in the seepage zones, was thin enough and less than a meter. When the water level in the Vistula river was high enough, water can flow in the noncohesive gravel layer occurring directly below the silty clays and lead to flooding on the landward side of the dams in the Maniow region.

Design and Fabrication of Metamaterial Absorbers Used for RF-ID

Radio frequency identification (RF-ID) uses electromagnetic fields to automatically identify and track tags attached to objects. In response to the need to suppress the electromagnetic interference between adjacent RF-ID equipment or systems, this study aims to achieve a thin and multi-resonance absorber using metamaterials composed of patterned grids on a grounded dielectric substrate in the frequency region of UHF and microwaves. A computational tool (ANSYS HFSS) was used to model and estimate the reflection coefficient and surface current distribution. The samples used to measure reflection loss were fabricated by the printed circuit board (PCB) method in which a copper film was deposited on both sides of a photosensitized board. The reflection loss was measured using a free space measurement system, composed of a pair of horn antennas and network analyzer. The grid-patterned metamaterial absorbers exhibited dual-band absorption peaks at 0.88 GHz and 2.45 GHz with a small substrate thickness (about 3.7 mm) that can be usefully applied to electromagnetic compatibility in RF-ID system. Magnetic coupling is achieved via antiparallel currents in the grid conductor on the top layer and the ground conductor on the bottom layer. Since the magnetic response is influenced by the dimension of the resonators, it is possible to achieve two resonances by scaling the resonating structures. The metamaterial absorbers also exhibited good oblique incidence performance. A high level of absorption (above 10 dB) was maintained at up to 30 degrees of incidence angle for both TE and TM polarization.

Electromagnetic Effect of an Alternating Current Traction Power Supply System with a High-Voltage Power Cord on Electrical Installations and Networks of Nontraction Consumers

In this paper, we ground a method for calculating switching overvoltages including the discharge of lightning currents into the contact network and into a high-voltage power wire (HVPW) to isolate the contact network in the power supply system with the HVPW. It was established that the protection of outdoor signaling, centralization, and blocking (SCB) devices from switching overvoltages in a power supply system with a high-voltage power wire (PSS HVPW) can be solved by connecting the reinforcement of the support foundations of the contact network to an extended artificial grounding conductor (GC) located under the ground and not connected to the rail track. The use of a GC, along with limitation of pulse overvoltages on the insulation of the contact network supports, solves the problem of ensuring reliable protection of the traction networks from short-circuit currents in the traction network. An algorithm for calculating the voltage of the zero sequence of phase voltages of overhead power lines (OPLs) with an isolated neutral relative to the ground when they are located in the zones of electromagnetic influence of the PSS with the HVPW was developed. Due to the electrical effect of the HVPW voltage, the induced voltage in an OPL is shown to reach values ​​that significantly exceed the levels allowed by regulatory documents. An analysis of the obtained results indicates the feasibility of placing OPL wires on free-standing supports outside the reserved strip. The need for such a solution is also determined by keeping the HVPW voltage from entering the OPL wires, with their possible breakage.

Metodología para Determinar la Distribución de Corrientes de Desbalance en Líneas Aéreas de Transmisión de Energía Eléctrica

Las líneas aéreas de transmisión de energía eléctrica presentan un régimen de operación constante y deben soportar esfuerzos mecánicos debido a posibles descargas atmosféricas, en este sentido es importante realizar una adecuada selección de sus conductores de fase y de guarda. Para soportar los esfuerzos mecánicos los conductores de guarda tienen un componente de acero que presenta características eléctricas variables en función de la corriente circulante por el mismo, por otra parte, esta corriente puede determinarse si se conocen los parámetros eléctricos del cable de guarda.En este contexto, el presente documento detalla dos métodos para determinar la distribución de la corriente entre la tierra y el cable de guarda en condiciones de desbalance, con el cual es posible seleccionar los parámetros eléctricos para la modelación adecuada de una línea de transmisión.Los resultados de estos métodos, aplicados en cuatro casos de estudio, se verifican en su respectiva simulación en el software Alternative Transients Program (ATP).

Estimation of water table depth using DUALEM-2 system

Most of the agricultural fields are generally irrigated or drained uniformly without considering the spatial and temporal variation in water table depth (WTD). Investigating WTD is important for scheduling irrigation, drainage system designs and water balance models. The objective of this study was to develop a software interface to estimate the variations in WTD via electromagnetic induction (EMI) methods using frequencies of a DUALEM-2 system. Two fields (Field 1: 45.38°N, 63.23°W and Field 2: 45.37°N, 63.25°W) were selected and thirty perforated observation wells were installed to calibrate the DUALEM-2 for predicting WTD. Boundaries of the selected sites and location of the wells were marked using a real time kinematics global positioning system (RTK-GPS). The user interface program was developed in Delphi 5.0 software and imported in a laptop computer to retrieve data from the DUALEM-2 system. The horizontal co-planar (HCP) geometry, perpendicular co-planar (PRP) geometry and WTD were recorded simultaneously from each well before and after every significant rainfall for three consecutive days. Comprehensive surveys were conducted to measure apparent ground conductivity (ECa) with DUALEM-2 and corresponding locations of the sampling points using Trimble Ag GPS 332. The regression model showed significant correlation between the HCP and WTD with co-efficient of determination (R2 = 0.71) for field 1 and (R2 = 0.53) for field 2. Maps were generated in ArcGIS 10 software to examine the accuracy of predicted WTD in comparison with actual values. Results indicated that the DUALEM-2 system was efficient in mapping variation rapidly and reliably in WTD in a non-destructive fashion rather than following conventional way of repeated well drilling for WTD determination. This information could be used for measuring the depletion of WTD during dry periods (droughts), site-specific irrigation and drainage design with the aided advantage of labor and time savings in case of observing precision water management practices at large fields.

Определение сопротивления защитного заземлителя по условию обеспечения безопасного проведения работ на отключенной линии электропередачи

It is proposed to ensure safety in carrying out work on a disconnected overhead power line by using a grounding conductor at the workplace having the impedance at which the induced voltage will be decreased down to permissible values. For reliably determining the necessary grounding conductor impedance, the results from multiple measurements of the induced voltage and current at the overhead power line point in which the work is carried out are used. Based on the results of measurements and solution of the inverse problems, empirical formulas for the functions of induced voltage and current in the considered place at which work on the overhead power line is carried out are determined. The necessary impedance of the grounding conductor at the workplace is determined using the obtained empirical formulas. As a result, a procedure has been developed using which it is possible to determine the grounding conductor impedance that ensures safety of work carried out at the considered place of the disconnected overhead power line whatever the combination of operating currents through the influencing overhead power lines.

Analysis on Intensity Matching Coefficient of Power Distribution Circuit Based on System Reliability Theory

The design intensities of four parts, i.e. ground conductor, hardware fittings, pole tower and foundation are greatly different, so it is difficult to evaluate the reliability of the whole power distribution circuit exactly. In this thesis, the intensity distribution functions of ground conductor, hardware fittings, pole tower and foundation have been calculated respectively, and then based on the system reliability theory, the reasonable failure sequence of power distribution circuit conforming to economic optimization principle is recommended. Under the assumed failure sequence, the calculation about intensity matching coefficient at the target confidence level is implemented, and finally, the intensity matching coefficients of ground conductor, hardwire fittings, pole tower and foundation of power distribution circuit are given.

Multi-Band and High Gain Antenna Using AMC Ground Characterized With Four Zero-Phases of Reflection Coefficient

In this paper, a multi-band AMC-backed antenna system characterized with high gain and low-profile is proposed. It is constructed by placing a quad-band coplanar-waveguide (CPW) antenna over an AMC with four zero-phases in the reflection coefficient. The CPW antenna consists of an ornamental-pillar-shaped patch with the specially designed parasitic elements, and a defected ground structure (DGS), for the application in the frequency bands of 2.45, 3.5, 4.6 and 5.8 GHz. To improve the CPW antenna’s radiation performance, an artificial magnetic conductor (AMC) ground with four zero-phases of the reflection coefficient is designed and employed as the reflector. The AMC unit cell is composed of four metallic nested rings (FMNR), whose innermost ring is connected in series to four lumped capacitors. It is observed that the proposed quad-band AMC ground can not only increase the gains of the multi-band antenna greatly but also combine the two intermediate frequency bands of the antenna into a broadband one. The prototypes of the antenna and the AMC array with $5\times {5}$ unit cells were fabricated and measured. It is found that in comparison to the antenna without AMC, the AMC-backed antenna obtains a gain enhancement by amounts of 4.93, 5.92, 5.54 and 4.95 dB at the frequencies of 2.45, 3.5, 4.6 and 5.8 GHz. The 10-dB impedance bandwidths of the AMC-backed antenna include three bands of 2.13–2.87, 3.22–4.75, and 5.54–5.86 GHz, with the corresponding relative bandwidths of 14.8%, 38.4%, and 5.3%. The proposed antenna can be potentially applied to the applications in WLAN, WiMAX, and 5G mobile communication systems.

Numerical modelling of different applications in Energy Foundation Technology

Energy foundation technology is expected to make a significant contribution to the use of renewable energy. In this context, this paper presents the use of Finite Element simulation using PLAXIS software for modelling different benchmark applications in Geothermal Foundations. An implicit fully-coupled numerical scheme with global adaptive time stepping are implemented to ensure computational efficiency and stability. Firstly, a transient simulation of thermal response tests [1], often used to estimate the thermal conductivity of ground and thermal resistance of pile, is presented. In the second part, a Thermo-Hydro-Mechanical analysis is performed to simulate the behavior of a single heat pile subject to a thermal load cycle [2]. Several ingredients (constitutive behavior, interface finite elements etc.) are employed to simulate soil-structure interactions. The obtained solutions are validated against available simulation and experimental data to demonstrate the applicability of the simulator to energy foundation analysis and design.

Электромагнитная совместимость электроустановок нетяговых потребителей и системы электроснабжения с высоковольтным питающим проводом

A procedure for calculating switching overvoltages, including those that occur when lightning currents discharge in a power supply system’s contact system with a high-voltage power lead, is substantiated. It has been found that the floor-mounted signaling arrangements can be protected from switching overvoltages in the power supply system with a high-voltage power lead (HVPL PSS) by connecting the contact system supports with a long grounding conductor laid in the ground and not connected with the railway. An algorithm for simulating the spectral composition of zero sequence phase voltage components in overhead power lines with the insulated neutral with respect to ground in the case of their location in the HVPL PSS electromagnetic influence zone and the presence of a zero sequence voltage filter (ZSVF). If the studied system does not contain a ZSVF, this results in a multifold increase of the power line zero sequence voltages, imbalance of the phase voltages, and the occurrence of interference both at the line beginning and end points. The use of filters made it possible to smooth and flatten the spectral composition of voltage and to minimize the effect of resonance phenomena at high frequencies.

Safety analysis of live working operators under zero potential

With the application of the live working method of the zero phase potential of the working phase more and more widely, the safety of the live working operators is urgently needed for research. Considering the influence of electric shock time and frequency on the allowable current of the human body, the safe current is analyzed during live operation, and it is concluded that in the frequency range of 50~60Hz, the current below 50mA can basically guarantee that it will not die after electric shock. In the three scenarios where the insulator maintenance personnel accidentally touch the ground, the grounding wire shocks the electric shock and the charged electric shock of the tower, the human body electric shock is further analyzed. Finally, based on the CDEGS, the model of the human body contacting the grounding conductor is established. The simulation verifies the influence of the allowable current on the time and frequency of the human body withstand current under the zero potential state through the contact voltage diagram and the danger degree diagram.

Оценка выноса потенциалов с заземлителей подстанций при определении наведенного напряжения на отключенной воздушной линии электропередачи

It is shown that during normal operation of a power system, a conductive component of induced voltage may arise apart from its inductive and capacitive components, which is caused by the spread of potentials from the substation grounding conductors to which the disconnected line is grounded. It has been established that under normal operation conditions the conductive voltage component may be several times higher than the maximum permissible induced voltage value. For determining the maximum possible induced voltage value at a certain point of the disconnected line, including its conductive component, an empirical method based on full-scale induced voltage measurements is proposed. The idea of the method consists in constructing an empirical formula for the induced voltage function in solving the inverse problem with subsequently determining the maximum possible induced voltage value by solving the direct problem. As a result, a procedure for determining the maximum possible value of the voltage induced at the considered point of the disconnected line with taking into account its conductive component has been developed.

An Equilateral Arm Inverted U-Slot and Notch Loaded UWB-CPMA with Rendered Ground Plane

In this paper, a microstrip fed modified circular patch monopole antenna (CPMA) with the rendered ground surface is presented for bandwidth enhancement. In order to extend the bandwidth of a demonstrated antenna, symmetrical slots and equilateral arms inverted U-slot are loaded on the partial ground and patch individually. For additional enhancement in the secured bandwidth, symmetrical notches are truncated from the bottom of the patch. The antenna has a dimension of 30x40x1.6 mm3, which is erected on low cost, FR-4 substrate with relative permittivity , permeability and loss tangent of . The proposed design is analyzed and simulated using high frequency structure simulator (HFSS). The analyzed results are validated through experimented results. The proposed antenna offers a bandwidth of 140.2 % with a maximum radiation efficiency of 94 % over the frequency scope of 2.54 GHz to 14.47 GHz. The crosspolarization levels are also found to be 20-30 dB and 12-23 dB smaller than the co-polarized level for E-plane and H-plane respectively. For better execution and assessment of proposed antenna, a parametric study has been done to analyze the performance of antenna with variations in the length of a partial ground conductor beside the other parameters. The exhibited antenna is suitable for various applications incorporating WiMAX, WLAN, UWB, C-band, X-band and UWB.

FDEMtools: a MATLAB package for FDEM data inversion

Electromagnetic induction surveys are among the most popular techniques for non-destructive investigation of soil properties in order to detect the presence of either ground inhomogeneities or of particular substances. This work introduces a MATLAB package for the inversion of electromagnetic data collected by a ground conductivity meter. Based on a nonlinear forward model used to describe the interaction between an electromagnetic field and the soil, the software reconstructs either the electrical conductivity or the magnetic permeability of the soil with respect to depth, by a regularized damped Gauss-Newton method. The regularization part of the algorithm is based on a low-rank approximation of the Jacobian of the nonlinear model. Both the relaxation parameter and the regularization parameter are chosen by automatic procedures. The package allows the user to experiment with synthetic data sets and different regularization strategies, in order to compare them and draw conclusions.

The Propagation Effects of Lightning Electromagnetic Fields Over Mountainous Terrain in the Earth-Ionosphere Waveguide.

In this paper, a full‐wave two‐dimensional Finite‐Difference‐Time‐Domain model is developed to evaluate the propagation effects of lightning electromagnetic fields over mountainous terrain in the Earth‐ionosphere waveguide. In the model, we investigate the effect of the Earth‐ionosphere waveguide structure and medium parameters, including the effect of the ionospheric cold plasma characteristics, the effect of the Earth curvature, and the propagation effects over mountainous terrain. For the first time, the obtained results are validated against simultaneous experimental data consisting of lightning currents measured at the Säntis Tower and electric fields measured in Neudorf, Austria, located at 380‐km distance from the tower. It is shown that both the time delays and amplitudes of the lightning electromagnetic fields at 380‐km distance can be strongly affected by the ionospheric electron density profile, the mountainous terrain, and the Earth curvature. After taking into account the effect of the irregular terrain between the Säntis Tower and the field measurement station, the vertical electric fields calculated by using our model are found to be in good agreement with the corresponding measured cases occurred in both daytime and nighttime. The ideal approximation used in either the classical solutions or the simplified models might lead to inaccuracies in the estimated reflection height. Furthermore, we discuss the sensitivity of our results by considering different return stroke models, as well as different typical values of the return stroke speed and of the ground conductivity.

Forecasting potato tuber yield using a soil electromagnetic induction method

AbstractTimely forecasting of crop yield is vital for precision agriculture management practices. This study used on‐the‐go proximal soil sensing using electromagnetic induction (EMI) readings of apparent ground electrical conductivity (ECa) to map ECa and forecast potato tuber yield in four fields across Atlantic Canada. The ECa data, measured in the horizontal co‐planar (HCP) configuration mode of the DualEM‐2 instrument, were segmented to the top 0.30‐m thickness of the soil layer using a standard method to compare mapping/prediction accuracy. Results showed that ECa correlated well (R2 = 0.81–0.90) with a 1:5 soil‐to‐water ratio solution's electrical conductivity (EC1:5). The actual tuber yield, which moderately varied (CV = 18.9–27.5%) across the fields and significantly correlated with ECa, explained more than 55% of the yield variability (R2 = 0.57–0.66). The forecasted tuber yield calculated from cubic regression models of the actual tuber yield versus ECa was non‐significantly different from the actual tuber yield (RMSE = 12.2–18.3%; R2 = 0.57–0.66). Interpolated maps of the predicted and the actual yields, and their correlation analyses, showed similar trends of variations within the study fields (r = 0.69–0.80). The higher values of cation exchange capacity, calcium, phosphate, potash, organic matter and soil moisture content in the New Brunswick soils compared to the Prince Edward Island soils resulted in an overestimation of the predicted tuber yield than the actual yield at the lower ECa values, and an underestimation of the predicted tuber yield at higher ECa values for New Brunswick. The results revealed that the province‐based calibrations produced more accurate predictions when compared with the single calibration by combining all of the data from New Brunswick and Prince Edward Island. The non‐destructive prediction of potato tuber yield can enable the development of precision agricultural techniques and management practices for yield forecasting, in addition to making informed decisions for enhanced potato productivity.Highlights Potato cropping is highly important to the economy of Atlantic Canada. The DualEM‐2 sensor was used to forecast and map tuber yield to advance crop management. The tuber yields significantly correlated with ground conductivity that explained >55% of variability in yield. The DualEM‐2 sensor can accurately predict potato yield under agricultural conditions similar to Atlantic Canada.

Closed-Form Expression for Ground Return Admittance in Underground Cables

This letter presents a closed-form expression for ground return admittance for a system of underground cables. It is based on the approximation of the infinite integral found using a quasi-TEM (transverse electromagnetic) formulation of the electromagnetic field. The results indicate that the frequency behavior of the closed-form expression provides useful responses up to a few megahertz, thus being a suitable alternative to the numerically challenging infinite integrals. The agreement of the closed-form results and those obtained using the infinite integrals is very good regardless of the ground conductivity considered.

Microstrip Transmission Line RF Coil for a PET/MRI Insert

Purpose:We proposed and developed a new microstrip transmission line radiofrequency (RF) coil for a positron emission tomography (PET) insert for MRI, which has low electrical interactions with PET shield boxes. We performed imaging experiments using a single-channel and a four-channel proposed RF coils for proof-of-concept.Methods:A conventional microstrip coil consists of a microstrip conductor, a ground conductor, and a dielectric between the two conductors. We proposed a microstrip coil for the PET insert that replaced the conventional single-layer ground conductor with the RF shield of the PET insert. A dielectric material, which could otherwise attenuate gamma photons radiated from the PET imaging tracer, was not used. As proof-of-concept, we compared conventional and the proposed single-channel coils. To study multichannel performance, we further developed a four-channel proposed RF coil. Since the MRI system had a single-channel transmission port, an interfacing four-way RF power division circuit was designed. The coils were implemented as both RF transmitters and receivers in a cylindrical frame of diameter 150 mm. Coil bench performances were tested with a network analyzer (Rohde & Schwarz, Germany), and a homogeneous phantom study was conducted for gradient echo imaging and RF field (B1) mapping in a 3T clinical MRI system (Verio, Siemens, Erlangen, Germany).Results:For all coils, the power reflection coefficient was below −30 dB, and the transmission coefficients in the four-channel configuration were near or below −20 dB. The comparative single-channel coil study showed good similarity between the conventional and proposed coils. The gradient echo image of the four-channel coil showed expected flashing image intensity near the coils and no phase distortion was visible. Transmit B1 field map resembled the image performance.Conclusion:The proposed PET-microstrip coil performed similarly to the conventional microstrip transmission line coil and is promising for the development of a compact coil-PET system capable of simultaneous PET/MRI analysis with an existing MRI system.