Ground Conductivity Research Articles

A New Grounding Resistance Reduction Method for Wind Turbines by Grounding Grid Connection in Limited Areas

Restricted by cultivated land vegetation, road construction, and land acquisition compensation costs, the grounding electrode extension method is not applicable for grounding resistance reduction of some wind turbines in limited areas. A new grounding resistance reduction method is proposed and verified for wind turbines by connecting nearby wind turbine grounding grids. To study the efficiency of the proposed method, the grounding characteristics of connected grounding grids are calculated. Simulation results indicate that the grounding resistance of connected grounding grids is smaller than that of box extension grounding grids. The grounding characteristics of the grounding grid connection are affected by grounding current frequency and material parameters. The grounding grid connection increases the current dispersion area and reduces the ground potential rise of the grounding conductor.

A Self-Consistent Return Stroke Model That Includes the Effect of the Ground Conductivity at the Strike Point

A current generation type return stroke model which can take into account the possible modifications of the return stroke properties by the soil conductivity at the strike point of the lightning flash is introduced. The model is also capable of incorporating the reflection of the current at the ground end of the return stroke channel. In this paper, this return stroke model is used to investigate (a) the effect of the ground conductivity at the strike point on the source electromagnetic fields generated by return strokes and (b) the effect of current reflection at ground level on the electromagnetic field generated by return strokes. The source electromagnetic fields are the electromagnetic fields generated by lightning flashes calculated in such a way that they are not distorted by propagation effects. The results obtained show that the ground conductivity at the strike point does not significantly influence the return stroke current peak or the radiation field peak for ground conductivities higher than about 0.001 S/m. However, strike points with very poor conductivities (lower than 0.001 S/m) would result in a decrease of the peak electric field. In contrast to the peak values of the lightning current and the electric field, the peak values of the time derivatives of the lightning current and electric field are significantly reduced when the strike point of the lightning flash is located over a finitely conducting ground. The inclusion of the current reflection at ground level influences significantly the saturation of the close electric fields. The current reflection also gives rise to residual electric fields, a difference in the field levels generated by the dart leader and the return stroke. The residual field decreases as the fraction of the reflected current decreases.

Analysis of a Low-Cost, High-Gain, Horizontally Polarized Square Ring Antenna

In this research article, the design of an economical, high-gain, horizontally polarized antenna structure comprised of a simple metallic square ring and shorting strips for higher-band (5.23–5.77 GHz) wireless local area network (WLAN) frequency applications is discussed. The proposed structure acts like an array of two horizontal dipole antennas over a circular ground plane. The analytical formula for resonance frequency and directivity of the designed antenna is also derived over a perfect electric conductor (PEC) ground plane. The structure is measured after successful fabrication; the measurement yields a 10 dB impedance bandwidth (IBW) of 9.8% (5.23–5.77 GHz) and a gain of 10.5–10.8 dBi over the entire BW. The analytical results are in fairly good agreement with the results obtained from the simulation and measurements. Moreover, a sensitive analysis of the proposed structure for various geometrical parameters of the same, such as suspended height (h), ring height (H), strip width (w), and ground plane radius (R), is presented. As well, with slight modifications to the geometrical parameters, a suitable performance can be achieved for the targeted band of frequencies with a simple feeding type at low-installation areas.

Simulation of Geomagnetically Induced Currents in a Low‐Latitude 500 kV Power Network During a Solar Superstorm

AbstractGeomagnetically induced currents (GICs) are one of the main manifestations through which space weather affects human technical facilities, and GICs constitute the final link in the solar wind‐magnetosphere‐ionosphere‐ground interaction chain. Therefore, understanding the responses of power grids to solar superstorms is crucial for space weather research and emergency preparedness purposes. In this work, we combine the Space Weather Modeling Framework with a ground conductivity model and a model of the Chinese Guangdong 500 kV power grid to investigate the response of the whole power grid if the 23 July 2012 solar superstorm had struck the Earth. The maximum |GICs| produced in the power grid by this event reach approximately 400 A, which is more than thrice those measured during a strong magnetic storm with Kp = 8. Based on statistical analyses of the strength and duration of large GICs at 54 substations and a comparison with the GICs responsible for the Hydro‐Québec power outage on 13 March 1989, we stipulate that the risk of GICs in the Guangdong 500 kV power grid is very high. The simulation results also reveal that field‐aligned currents can play an important role in producing GICs in middle‐ and low‐latitude power grids during solar superstorms. This finding provides crucial insight for understanding the factors that generate strong GICs at middle and low latitudes.

Characterizing Pulse Attenuation of Intra-Cloud and Cloud-to-Ground Lightning with E-Field Signal Measured at Multiple Stations

In this paper, we analyze the waveform data of nearly 200,000 intra-cloud (IC) and cloud-to-ground (CG) lightning discharges detected by the Jianghuai Area Sferic Array on 26–29 August 2019 to investigate the propagation features of lightning electromagnetic fields. Through the analysis of variation in the electric field (E-field) signal of lightning during the actual propagation, it was found that (1) the attenuation of lightning E-field signal with distance can be fairly well described by the power-law relationship E = ar−b, and the attenuation index is b = 1.02 (for IC) and b = 1.13 (for CG); (2) under the situation of the same propagation path, the IC pulses experience less attenuation than CG pulses; and (3) through the comparison with simulations, it can be seen that the attenuation of lightning E-field pulse is affected by the conductivity of the ground surface, and according to the attenuation factor of lightning E-field strength, it can be inferred that the conductivity in the Jianghuai area ranges between 0.005 S/m and 0.01 S/m, which is in good agreement with the measured conductivity in this area. Our results suggest that lightning radiation could provide a feasible means for remotely sensing the ground conductivity.

Design of low profile high gain antenna using loop-based wideband artificial magnetic conductor for UWB applications

AbstractIn this work, a low profile ultra-wideband (UWB) antenna is designed and investigated using a novel loop-based wideband artificial magnetic conductor (WB-AMC) for gain enhancement. Initially, a compact loop antenna is designed using stub loading and further optimized for the UWB range by applying curve ground methodology. The average gain of the proposed antenna without WB-AMC is 2.7 dBi. To enhance the gain of the entire UWB range, loop-based WB-AMC in [2 × 2] forms is integrated. WB-AMC is used as a ground plane beneath the antenna. To validate the performance, the UWB antenna and WB-AMC are fabricated and tested. The measured results confirm the entire UWB range. Proposed antenna provides a peak gain of 9.4 dBi and an average gain of 5.8 dBi. Vertical profile reduction of 50% is achieved compared to perfect electric conductor ground. The proposed UWB antenna is a potential candidate for UWB wireless applications due to its attractive features such as low profile, wide bandwidth coverage, omnidirectional pattern, constant high gain, and group delay.

Galloping Vibration Monitoring of Overhead Transmission Lines by Chirped FBG Array

A distributed online fiber sensing system based on the phase-sensitive optical time domain reflectometer (Φ-OTDR) enhanced by the drawing tower fiber Bragg grating (FBG) array is presented and investigated experimentally for monitoring the galloping of overhead transmission lines. The chirped FBG array enhanced Φ-OTDR sensing system can be used to measure the galloping behavior of the overhead transmission lines (optical phase conductor or optical power ground wire), which are helpful for monitoring the frequency response characteristics of the ice-induced galloping, evaluating the motion tendencies of these cables, and avoiding the risk of flashover during galloping. The feasibility of the proposed online monitoring system is demonstrated through a series of experiments at the Special Optical Fiber Cable Laboratory of State Grid Corporation of China (Beijing, China). Results show that the proposed system is effective and reliable for the monitoring of galloping shape and characteristic frequency, which can predict the trend of destructive vibration behavior and avoid the occurrence of cable breaking and tower toppling accidents, and these features are essential for the safety operation in smart grids.

Investigation of impedance compensation in radio frequency circuits with bonding wire

Bonding wires are extensively used to provide electrical interconnections in communication systems. From the perspective of circuit analysis, the effects of such elements are often treated as an inductance. Bonding wires may cause inductive impedance discontinuity, which negatively impacts signal integrity. In this work, an impedance compensation technique using a chip capacitor was introduced. The electrical performance was improved significantly in the frequency band below 4 GHz. In order to expand the operating frequency of the circuit, another compensation approach based on adding a ground conductor was also studied. This compensation strategy is shown to be effective for frequencies up to 18 GHz. The results obtained from the model simulation for both strategies were also validated experimentally. The model simulation results for both approaches show good agreement with those obtained from the experimental measurements.

Soil impulse ionisation model based on dynamic changes of electric field

Soil ionisation has an important influence on impulse characteristics of grounding conductor. This paper introduced improvements to an existing soil ionisation model considering the influence of electric field on the change of soil resistivity, while soil resistivity is not directly dependent on soil electric field. The validity of improved soil ionisation model was verified by surge response of vertical conductor in uniform soil and horizontally stratified soil. Furthermore, the impulse experiment was carried out on horizontal conductor in soil with finite volumes. Based on experimental configuration, the corresponding calculation model was built, and calculated results were in good agreement with experimental results.

Design of a frequency selective surface‐backed microstrip reflectarray antenna using Minkowski ring elements

A novel frequency selective surface (FSS)-backed subwavelength reflectarray element is proposed in this article. The element consists of an inner square ring and an outer Minkowski ring. The proposed fractal element could achieve smaller interelement spacing and better reflection phase performance due to its space-filling property and self-similar geometry. An 11 × 11-element reflectarray with reduced element spacing of 0.38 λ 0 ( λ 0 -the free space wavelength at 5.8 GHz) is designed. A FSS is used to replace the perfect electric conductor (PEC) ground. In the working frequency, the electromagnetic waves are reflected and result in a smoother and more linear reflection phase curve. Moreover, the radar cross section (RCS) of the reflectarray antenna is also reduced by using the FSS ground. A prototype antenna is then fabricated and measured. The measured results show that the antenna has a peak gain of 18.6 dBi, and an aperture efficiency of about 31.9%. A measured 1-dB gain bandwidth of 14.3% is obtained. Meanwhile, the measured cross-polarization and side-lobe levels are −20 dB and −13 dB, respectively. The simulated results demonstrate that the monostatic RCS can be significantly reduced with a fractional bandwidth of 32.76% and 44.83% for the lower and upper bands with reduced levels of 5 dB, respectively.

Lightning Observation System by Measuring Current Flowing through the Grounding Conductor on Mt. Fuji

Lightning Observation System by Measuring Current Flowing through the Grounding Conductor on Mt. Fuji

Design grounding grid resistance of substation for two soil layer model

All Grounding planning of a substation is important and various design applications are available using calculation uniform soil resistivity, even though actual resistivity data measured is more than one layer. This is caused by limited availability of the application in processing data only for resistivity one layer. Substation grounding grid application (ASPG) 1.0 can be used for designing grid grounding. The ASPG was developed from Lab View software and has ability to data process for resistivity two-layer that to refer IEEE Std. 80-2013. Grid grounding resistance is considering a combination of grid conductor and ground conductor. This paper discusses the calculation of the magnitude of substation grid grounding using formulas developed by Schwarz, Sulivan and Sunde. The design result obtained is more accurate in substitute resistivity for resistivity two-layer model and calculation grounding resistance substation.

Geomagnetically Induced Current Model in New Zealand Across Multiple Disturbances: Validation and Extension to Non‐Monitored Transformers

AbstractGeomagnetically induced currents (GICs) produced during geomagnetic disturbances pose a risk to the safe operation of electrical power networks. One route to determine the hazard of large and extreme geomagnetic disturbances to national electrical networks is a validated model to predict GIC across the entire network. In this study, we improve upon an earlier model for New Zealand, expanding the approach to cover transformers nationwide by making use of multiple storms to develop national scaling factors. We exploit GIC observations which have been made and archived by Transpower New Zealand Ltd, the national grid operator. For some transformers the GIC observations span nearly 2 decades, while for others only a few years. GICs can vary wildly between transformers, particularly due to differences in the electrical network characteristics, transformer properties, and ground conductivity. Modeling these individual transformers is required if an accurate representation of the GIC distribution throughout the network is to be produced. Here we model the GIC during 25 disturbed periods, ranging from large geomagnetic storms to weakly active periods. We adopt the approach of scaling model output using observed GIC power spectra, finding that it improves the correlations between the maximum model and observed GIC by between 10% and 40% depending on the transformer. The modeled GIC at the 73 transformers which have measured GIC are analyzed to create local and national scaling curves. These are used to allow modeling for transformers without in‐situ GIC. We present approaches to utilize this technique for future storms, including non‐monitored transformers.

Fault Diagnosis of Tower Grounding Conductor Based on the Electromagnetic Measurement and Neural Network

The performance of the tower grounding conductor is very important for the safe and reliable operation of the power transmission system. Under the current excitation, the grounding conductor in different states will produce different magnetic fields on the earth’s surface. By measuring the surface magnetic fields, the fault types and location of the grounding conductor can be evaluated. However, the process of traditional manual analysis is extremely complex. This paper proposes a fault diagnosis method for tower grounding conductors based on deep learning to replace the manual diagnosis. The earth’s surface magnetic field data-set generated by the grounding conductor consists of simulation data and experimental data. For practical application, the fine-tuning method is proposed to improve the diagnosis performance of the One Dimensional-Convolutional Neural Network (1D-CNN). Compared with the original 1D-CNN model, the results demonstrate that the proposed fine-tuning 1D-CNN has improved the diagnostic ability of the tower grounding conductor. For the six kinds of faults of rectangular tower grounding conductor, the average classification accuracy of the fine-tuning 1D-CNN model reaches 80.50% when only the classifier and dense connection layers are trained. The proposed method can be used in the fault diagnosis of tower grounding conductors, which has significant potential applications in detecting and maintaining tower grounding conductors.

A New Arraying Technique for Band-Switchable and Polarization-Reconfigurable Antenna Arrays With Wide Bandwidth

Modern antenna arrays desire antenna apertures which can support a wide frequency range and reconfigurable polarization states. It is challenging to realize such antenna apertures with high isolation among different antenna elements when they are closely packed, particularly for wide-band (>2:1 frequency ratio) operations. In this paper, we demonstrated switchable-band antenna arrays which can be reconfigured from S to C band with an instantaneous bandwidth close to 2:1. The major novelty in this antenna array is that a new arraying technique is adopted to reduce the number of feeding ports by 50%. As a result, the isolation among antenna elements can be significantly improved, thereby increasing the overall radiation efficiency. It should be noted that vertical, horizontal and circular polarizations are supported by this antenna array when all ports are provided with appropriate phases. Herein two arrays are demonstrated. Array I is based on a fractal-shaped slot-ring structure. Each antenna element is fed by a microstrip along the diagonal direction. The common antenna aperture can be reconfigured to operate at 2.5-4.0 GHz or 4.2-7.2 GH, using PIN diode switches. Array II is extended from Array I but with an Artificial Magnetic Conductor (AMC) ground to enhance the instantaneous bandwidth to 2:1. The length of the microstrip feeding lines are reduced to enable modular design. In addition, PIN diode switches are embedded in the feeding lines to further improve the isolation and radiation efficiency. The return losses, port isolations, radiation patterns, gains, radiation efficiencies and IIP3 are simulated and measured.

A 2.45- and 5.8-GHz Dual-Band Stacked Differential Rectenna With High Conversion Efficiency in Low Power Density Environment

This paper proposes a novel stacked dual-band differential rectenna. The proposed rectenna consists of two rectifying diodes and a dual-band array antenna with four 5.8-GHz patch antennas arrayed on a three-element 2.45-GHz array. The dual-band array antenna provides high gains of 12.2 and 13.8 dBi at 2.45 and 5.8 GHz, respectively. The matching circuits between the antenna elements and diodes are designed to provide the highest conversion efficiency at both 2.45- and 5.8-GHz band. The measured conversion efficiencies are 36.4% and 6.2% at 2.48 and 5.96 GHz under the low power density condition of 0.016 W/m², respectively. The proposed dual-band differential rectenna can easily realize large-scale rectenna arrays by simply connecting the ground conductors on the back.

Location and Corrosion Detection of Tower Grounding Conductor Based on Electromagnetic Measurement

Location and Corrosion Detection of Tower Grounding Conductor Based on Electromagnetic Measurement

Development of a drone‐borne electromagnetic survey system for searching for buried vehicles and soil resistivity mapping

ABSTRACTWe developed a drone‐borne electromagnetic survey system using a commercial multi‐frequency electromagnetic sensor equipped with a GPS receiver, a WiFi serial transceiver, and an ultrasonic distance sensor to measure the height of the electromagnetic sensor above the ground surface. The electromagnetic sensor was suspended from a drone with ropes. The distance between the drone and the electromagnetic sensor was adjusted to minimize the influence of electromagnetic noise generated by the drone, and to stabilize the electromagnetic sensor during flight. The system was tested at two experimental sites. The first site consisted of two buried vehicles to simulate a landslide. We assumed a scenario in which the search for the buried vehicles was urgent and accessibility to the area was limited. The second site consisted of wet and dry agricultural fields to test resistivity mapping. In the first test, we used the in‐phase component of the measured data to locate the vehicles. The shallower vehicle was identified clearly, while the deeper vehicle was located successfully, albeit less easily. In the second test, the quadrature component was used for one‐dimensional inversion after data processing, which included data smoothing, resampling and bias noise correction. The bias noise was measured while hovering the drone at a high altitude to negate the influence of ground conductivity. The results showed that the resistivity distributions could be mapped at some depths by using a five‐frequency‐processed quadrature component, and clearly showed the difference between the wet and dry fields. The crucial parameter in the evaluations of these targets was the height of the electromagnetic sensor above the ground surface, which was measured continuously during flight. The results demonstrated the potential of the survey system to search for buried metal objects and for shallow subsurface resistivity mapping over relatively large areas.

Analysis of Induced Voltage on Pipeline Located Close to Parallel Distribution System

Gas and oil pipelines are widely used to supply customers. They are often laid in parallel with high voltage power lines, sharing right of way. When the pipeline is located near overhead high-voltage power, corrosion caused by induced voltages from AC power lines can occur in utility pipelines. Therefore, the calculation of induced voltage is always required for both interference and maintenance workers as well as pipeline facility safety. For parallel distribution lines, the calculation method for the induced voltage is not suitable due to the excessive error caused by using the screening factors of the neutral current. For a more practical analysis of the induced voltage, a new analysis is needed using the actual neutral current and which also considers the overhead ground conductor and the neutral conductor. This paper analyzed the induced voltage from a parallel distribution system using Carson’s formula and vector analysis. Simulation analysis results are verified by separate Electromagnetic Transient Program (EMTP) simulation.

Simple Formula for Surge Impedance of Horizontal Grounding Conductor

Horizontal grounding conductor is often used to obtain low grounding resistance. Simulation results of voltages and currents in a circuit including a grounding system are sometimes different from measured results because the grounding resistance depends on temperature and water content. Lightning surge characteristics of a grounding conductor are important for lightning protection design. Simple formulas for the surge characteristics of the grounding conductor are useful for engineers to estimate the influence of parameters of grounding system on lightning overvoltages. This article describes measurement results of the surge characteristics of grounding conductors for various conductor lengths and terminal conditions. This article proposes simple formulas for surge impedance and propagation velocity of horizontal grounding conductor based on the measured results. A simple equivalent circuit of grounding conductor is described. The constants of the equivalent circuit are obtained using the proposed formulas. Simulation results of voltage on a grounding grid using the proposed formulas and the equivalent circuit of grounding conductor are compared with experimental results.