Buried Cables Research Articles

Comprehensive analysis of soil electrical conductivity: an experimental and machine learning approach

Experimental test is conducted to find a relation between soil electrical conductivity with some soil properties. Five input parameters namely water content (w), dry density of soil (γd), degree of saturation (Sr), porosity (η) and voltage (V) are considered to compute electrical conductivity of soil (SEC). The effect of w, γd, Sr and η on SEC are analyzed. These datasets are used in soft computing technique to predict SEC. Five hybrid models namely ANN-GA, ANN-PSO, ANN-FA, ANN-GWO and ANN-MFO are used to predict SEC. To check the performance of these hybrid model, numerous statistical performance parameters (R2, a-10 index, VAF, LMI, RMSE, MAE, MAD and U95) are used. On the basis of these performance parameters, ANN-GA performs better (Due to higher value of R2, VAF, a-10 index and LMI and lower value of RMSE, MAE, MAD and U95) as compare to the other proposed model. The model's performance is also examined using rank analysis, regression curve, Williams plot, error matrix, objective function (OBJ) criterion, and Akaike information criterion (AIC). By applying all the above criteria, it has been observed that ANN-GA model outperforms than the other model to predict SEC. This was recognized to its maximum R2 = 0.9998 and the lowest RMSE = 0.0041 during the training phase, as well as R2 = 0.9975 and RMSE = 0.0112 during the testing phase. The model's reliability index (β) is calculated using the first-order second moment (FOSM) approach, and the result is compared to its actual condition. Additionally, a sensitivity analysis is carried out to ascertain the impact of each input parameter on the output (SEC).Based on the results, the hybrid model of ANN i.e., ANN-GA is potential to assist engineers to predict SEC in the design phase of high voltage buried power cables, ground modification techniques or in the field of agriculture.

Wykorzystanie metody radaru penetrującego grunt w badaniu gleby zanieczyszczonej węglowodorami w obszarze Navodari - Rumunia

Ground penetrating radar (GPR) is a very useful geophysical method for use in hydrogeologic and near-surface mapping studies. It can be used to study contaminants in groundwater, subsurface faulting, and underground cavities (natural or man-made), all of which pose potentially dangerous geological hazards. The GPR technique is similar in principle to seismic reflection and sonar techniques. The propagation of the radar signal depends on the frequency-dependent electrical properties of the ground.Electrical conductivity of the soil or rock materials along the propagation paths introduces significant absorptive losses which limit the depth of penetration into the earth formations and is primarily dependent upon the moisture content and mineralization present.Reflected signals are amplified, and transformed to the audio-frequency range, recorded, processed, and displayed. From the recorded display, subsurface features such as soil/ soil, soil/rock, and unsaturated/saturated interfaces can be identified. In addition, the presence of floating hydrocarbons on the water table, the geometry of contaminant plumes, and the location of buried cables, pipes, drums, and tanks can be detected. The GPR data are presented as a two-dimensional depth profile along a scanned traverse line in which the vertical axis is two-way travel time measured in nanoseconds. The location of hydrocarbon contamination in the ground using the GPR method is based mainly on information taken from reflected signals. In the cases investigated in Romania contaminated sites (Navodari area), such signals were very rarely recorded. A long time after spillage, contamination takes the form of plumes with different size and distribution, which depends on the geological and hydraulic properties of the ground. The survey discussed in this paper was carried out using the GPR system-Noggin with two antennas (250 and 500mHz) Data collected were processed using software(EKKO_Project™ GPR Data Analysis) to produce 2D radargram in time scale. The presence of contaminant plumes as well as the water table are observed in the GPR sections at depths approximately of 0.5 to 1.5 m. In the GPR section, the oil contaminated layer exhibits discontinuous, subparallel, and chaotic high amplitude reflection patterns. Promising results were also obtained in the GPR survey where three obvious reflection patterns representing the top sand-silt layer, oil-contaminated zone and, the underlying thick soft clay were detected in all 2D radargrams of the GPR traverse lines.

Electromagnetic Impact of Overhead High-Voltage Lines during Power Transmission on Buried Signaling Cables of the Traffic Control Systems in Modernized Railway Lines

The railway transport system is a key factor supporting industrialization in all aspects of human activity. However, in order not to lose its importance, it must meet the challenge of modern civilization. The safety, reliability, and efficiency of railway transport, to a large degree, depend on using highly integrated electronics, which are very sensitive to various disturbances generated in the electric traction system and train or coming from the environment. One of the sources of electromagnetic disturbances are high-voltage (HV) power lines running close to the railway infrastructure. The purpose was to assess the electromagnetic impact of overhead HV transmission lines on buried signaling cables of the railway traffic control system crossbreeding with them. The levels of voltage induced in the cable under steady state and the earth fault in the HV line at various soil resistivity were estimated. A software tool based on a hybrid numerical method that combines circuit theory and electromagnetic field theory was used for computations. It was found that very high voltages may be induced in the signaling cables during earth faults in the HV lines, which may lead to serious interference or damage to the equipment. The results provide useful knowledge for implementing modern railway traffic control systems and protection measures.

Lightning current Risetime influence on inductive coupling effect of secondary shield cable in substation

Secondary cables are susceptible to lightning surge currents when substation is struck by lightning. Little work has been made to the effects of surge currents in substation secondary cables, particularly the effects of surge current rise time. Six types of simulated lightning surge currents with different rise times, ranging from 5.7 μs to 25.4 μs, were injected into the substation grounding grid, and the inductive voltage from core wire to ground and the shield current in the closed loop of the buried secondary cable were measured simultaneously. The inductive coupling characteristics and the effect of rise time on shielding factor (SF) of buried secondary cables were investigated using time-frequency domain method. The results indicate that the surge current with shorter rise time will induce higher core-wire voltage and higher the shield current on the secondary cable. Double-end grounding of the shielding layer can significantly reduce the cable coupling response, especially reduce the high-frequency component of the inductive voltage at 10 to 100 kHz with steeper surge currents. The SF of secondary cable increases exponentially from 1.91 dB to 8.15 dB as the rise time of the lightning surge current decreases.

Development of Underground Perimeter Intrusion Detection System

An underground passive security system based on minimal electric charge detection was developed and implemented in the real application field. The fixed length of the sensor cable is buried underground named a security zone. It is generated an alarm when an intruder goes into the security zone. A shielded telecommunication cable can be used for sensing the generated minimal charges by the external intrusion. If two different types of materials are rubbed with each other, minimal electric charges are generated, called the triboelectric effect. Minimal electric charges are generated between the cable shield and conductors when forces and impacts are applied to the underground buried cable. The control device detects and amplifies generated minimal charges due to the intruders on the sensor cable. The proposed system can be shown a reliable intrusion detection rate of up to 96%-97% when we have kept and considered all installation and environmental conditions.

Climate change–induced stress disrupts ectomycorrhizal interaction networks at the boreal–temperate ecotone

The interaction networks formed by ectomycorrhizal fungi (EMF) and their tree hosts, which are important to both forest recruitment and ecosystem carbon and nutrient retention, may be particularly susceptible to climate change at the boreal-temperate forest ecotone where environmental conditions are changing rapidly. Here, we quantified the compositional and functional trait responses of EMF communities and their interaction networks with two boreal (Pinus banksiana and Betula papyrifera) and two temperate (Pinus strobus and Quercus macrocarpa) hosts to a factorial combination of experimentally elevated temperatures and reduced rainfall in a long-term open-air field experiment. The study was conducted at the B4WarmED (Boreal Forest Warming at an Ecotone in Danger) experiment in Minnesota, USA, where infrared lamps and buried heating cables elevate temperatures (ambient, +3.1 °C) and rain-out shelters reduce growing season precipitation (ambient, ~30% reduction). EMF communities were characterized and interaction networks inferred from metabarcoding of fungal-colonized root tips. Warming and rainfall reduction significantly altered EMF community composition, leading to an increase in the relative abundance of EMF with contact-short distance exploration types. These compositional changes, which likely limited the capacity for mycelial connections between trees, corresponded with shifts from highly redundant EMF interaction networks under ambient conditions to less redundant (more specialized) networks. Further, the observed changes in EMF communities and interaction networks were correlated with changes in soil moisture and host photosynthesis. Collectively, these results indicate that the projected changes in climate will likely lead to significant shifts in the traits, structure, and integrity of EMF communities as well as their interaction networks in forest ecosystems at the boreal-temperate ecotone.

Modelling buried cables illuminated by incident fields for electromagnetic transient analysis in the Laplace domain

Modelling buried cables illuminated by incident fields for electromagnetic transient analysis in the Laplace domain

Rapid calculation model for transient temperature rise of complex direct buried cable cores

Actual direct buried cable is a complex model that contains backfill sand and external soil. To improve dynamic load level and utilization of buried power cables, it is crucial to quickly calculate power cable core temperature under sudden changes in load. The complex buried cable structure is decomposed into three parts so as to improve the accuracy of calculation. These three parts are the cable body, the backfill sand and the external soil, which temporary temperature rise can be solved by respect transient thermal circuit models separately and then add them up to obtain the cable core temperature. In actual project, the values of the transient thermal circuit model elements can be solved in advance and made into a table, and the relevant parameters can be obtained by checking the table in use. The backfill sand is only related to its heat conductivity, the external soil is related to its heat conductivity and burial depth. There transient thermal circuit model elements values can be fitted by an expression with the environment parameters, which can improve application scope of the transient thermal circuit model. The experimental results of the simulation show that, after knowing cable type and environment parameters, the transient thermal circuit model elements can be obtained by looking up the table and calculating by expressions, thus enabling fast calculation of the value for the cable core temperature variation while ensuring the accuracy of the results, and can meet the requirements in engineering.

Soil Dryout in the Vicinity of Cables With Cyclic Load Installed in a Backfill

The IEC Standard 60287-1-1 provides the procedure for modelling of soil dryout in the vicinity of current currying power cables. Two important assumptions limit the application of the formula to the cases with uniform burial conditions and a uniform current with 100% load factor. Another standard in this series, 60287-2-1, contains the formula for the calculations of the external thermal resistance of cables laid in thermal backfills. It is based on the pioneering work of Neher and McGrath published in 1957. The Neher/McGrath paper provides also a modification of the external thermal resistance of buried power cables with a non-unity load factor with an assumption of the uniform burial conditions. This paper develops new formulae for the calculation of cable current ratings taking into account all three factors; that is, consideration of the soil dryout for cables laid in a thermal backfill and loaded with a variable current with known load factor. The results obtained with the proposed approach are compared with detailed finite element studies.

Insights into the Thermal Performance of Underground High Voltage Electricity Transmission Lines through Thermo-Hydraulic Modelling

In this paper, a flexible numerical framework to provide thermal performance assessment for the underground buried cables, considering different geological and meteorological conditions, has been presented. Underground cables tend to retain the heat produced in the conductor, so complex coupled thermo-hydraulic response of the porous medium surrounding the cables needs to be assessed to prevent cable overheating and the associated reduction in cable capacity for carrying current. Applying a coupled thermo-hydraulic model within the developed numerical framework to conduct a health assessment on a subset of National Grid Electricity Transmission’s underground cables, this study provides novel insights into the thermal behaviour of buried circuits. The results indicate that backfill and surrounding native soil have the dominant effect on the thermal behaviour of cables, while the amount of precipitation and ambient temperature were found to have less impact on cable’s thermal behaviour. The findings strongly infer that the nature of the overloading which is undertaken in practice would have no ongoing negative impact, suggesting that more frequent or longer duration overloading regimes could be tolerated. Overall, this study demonstrates how the developed numerical framework could be harnessed to allow safe rating adjustments of buried transmission circuits.

A novel transient thermal circuit model of buried power cables for emergency and dynamic load

In order to improve the utilization rate of cable while ensuring safety and reliability, accurate and rapid evaluation of transient temperature rise of directly buried power cables is useful to improve the management level of dynamic capacity increase and emergency load conditions. Since the existing thermal circuit model is relatively complex or not very accurate, an equivalent three-branch transient thermal circuit model is presented for the complex cable structure and heat dissipation environment based on the uniqueness of the temperature field. Considering the electric circuit similarity, the transient analysis method of the centralized parameter network in the circuit is used to establish the transient adjoint model of the thermal capacity branch, provide the node conduction matrix of the transient thermal circuit model, and write the node temperature rise equation as a function of the node heat flow. By comparing the solution of the thermal circuit model with the finite element results, and the genetic algorithm is used to optimize and obtain the equivalent thermal resistance and thermal capacity parameters of the transient thermal circuit model. The comparison of finite element calculation results proves that the proposed three-branch transient thermal circuit model is more accurate than the two-branch thermal circuit model. Compared to the traditional all-part thermal circuit model, the three-branch model can be rapidly solved and easily applied in engineering.

Effects of warming on physicochemical property of Cunninghamia lanceolata branch and leaf litter in subtropical plantation

At the regional scale, substrate properties are the key factors driving litter decomposition rate. In this study, soil temperature was increased by buried heating cables to explore the impacts of climate warming on the physical and chemical properties in branch and leaf of Cunninghamia lanceolata litter. The results showed that after 5 years of soil warming (4 ℃), the contents of nitrogen (N), phosphorus (P) and water-soluble substance in branch litter increased by 35.2%, 40.8% and 7.6%, while that in leaf litter increased by 41.2%, 45.9% and 5.9%, respectively. The contents of carbon (C), cellulose and C/N in branch litter decreased by 5.1%, 11.6% and 28.8%, and in leaf litter decreased by 5.3%, 11.3% and 33.3%, respectively. Soil warming led to 29.8% increase in specific leaf area (SLA) and 40.7% decrease in tensile strength (LTS) of leaf litter. However, warming did not affect lignin content and pH value in both branch and leaf litter. 13C NMR and infrared spectrum analysis showed that the contents of amino acids, polysaccharides, polyphenols and aliphatic compounds in litter changed significantly after warming. Warming effect differed between litter organs, in that polysaccharides increased significantly only in leaf litter and the increase of amino acids in branch litter was greater than that in leaf litter. Overall, soil warming significantly changed the physical and chemical properties in C. lanceolata branch and leaf litter, which might accelerate the decomposition rate at the initial stage due to the increase of N, P contents and the decrease of LTS, but might decelerate the decomposition rate at the later stage due to an increase of complex polymers content in the litter.

A Case Study of Completely Buried Wind-Power Cable Detection Using 3D Acoustic Imaging

As offshore wind power is renewable energy produced through the installation and operation of large-scale offshore infrastructure, risk management is crucial in power platforms. Safety accidents caused by external factors during the operation of submarine power cables can lead to enormous costs, thus necessitating the monitoring of burial depth and route information of cables. In this study, we developed a 3D acoustic imaging method that obtains information on the route and depth of completely buried power cables. An acoustic source-based engineering ocean seismic 3D (EOS3D) system has been used to detect buried objects in the subsurface because conventional sonars, such as multi-beam echo sounder (MBES) and side-scan sonar (SSS), which are used to analyze seafloor characteristics, have limitations in detecting completely buried cables in the subsurface. Field data were obtained as 8-channel data using a chirp source (2–8 kHz) designed to obtain a 25 × 25 cm horizontal spatial resolution from real-time kinematic (RTK) positioning. The image stack method was proposed to effectively detect buried cables, with the vertical gradient analyzed using signals decomposed into representative bin sizes and low-mid-high-frequency components. The acoustic anomalies of buried objects, identified as export cables and protectors, were processed into images using the proposed image stack method and gradient analysis. This case study of buried wind power cables using 3D acoustic imaging could be utilized in burial assessment survey (BAS)-data acquisition, processing/analysis processes, and operation and management of buried cables.

Application of Image Sensors to Detect and Locate Electrical Discharges: A Review.

Today, there are many attempts to introduce the Internet of Things (IoT) in high-voltage systems, where partial discharges are a focus of concern since they degrade the insulation. The idea is to detect such discharges at a very early stage so that corrective actions can be taken before major damage is produced. Electronic image sensors are traditionally based on charge-coupled devices (CCDs) and, next, on complementary metal oxide semiconductor (CMOS) devices. This paper performs a review and analysis of state-of-the-art image sensors for detecting, locating, and quantifying partial discharges in insulation systems and, in particular, corona discharges since it is an area with an important potential for expansion due to the important consequences of discharges and the complexity of their detection. The paper also discusses the recent progress, as well as the research needs and the challenges to be faced, in applying image sensors in this area. Although many of the cited research works focused on high-voltage applications, partial discharges can also occur in medium- and low-voltage applications. Thus, the potential applications that could potentially benefit from the introduction of image sensors to detect electrical discharges include power substations, buried power cables, overhead power lines, and automotive applications, among others.

3D FEM analysis of induced current in the shield of the buried cable by non-vertical channel

The induced current in the buried cable shield is evaluated by solving the full-wave Maxwell equations with the Finite Element Method (FEM). Three different cases are considered for the lightning channel, including the “straight inclined” channel, “bent channel”, and “Tortuous channel”. Straight inclined lightning is one part channel that could have different angles with Z-axis at XZ and YZ plane. The bent lightning is included the upper part and lower part that are joined to each other at the “bent” point at height Ha. Different sizes are considered for the Ha, and angle of each part. The tortuous channel is a linear piecewise approximation of realistic lightning. The impact of the channel shape, channel angle, bent height, and lightning current waveform on the induced current in the buried cable shield is investigated. The results reveal that waveforms and peak value of the induced current are significantly affected by channel shape. Comparing the results of different lightning shapes reveals that the induced current peak and waveforms highly depends on the lightning channel shape between ground to 250 m height from the ground. Comparing the tortuous channel results with inclined and bent lightning reveals that bent lightning is a better approximation than inclined lightning. Statistical analysis of the results shows the effect of the channel shape for the case that lightning current waveform have faster rising time is more significant.

A Flexible Model to Calculate Buried Cable Ampacity in Complex Environments

The ampacity of buried cables is significantly influenced by the thermal properties of the burial environment. When these thermal properties are not homogeneous it is usually necessary to utilize simulations with a relatively high computational cost that may also use commercial software. In this paper an alternative approach is proposed using conformal maps. Temperature is calculated in an annular domain which is a conformal mapping of the half plane space. Circumferential dependence is captured by expanding temperature as a Fourier series, a finite difference solver then determines temperature components radially. The model is as flexible as any two-dimensional slice model of heat transfer through thermal conduction only. Two case studies are considered: three land-based cables in planar configuration and a submarine export cable. The thermal properties of both burial environments are based on conditions which may be encountered in the field and exhibit a high level of stratification. Using a finite element analysis simulation as a benchmark, typical percentage differences in cable ampacities were 0.5%−1%. In addition to accuracy and flexibility the low computational cost of the proposed approach allows for large parameter sweeps, which may be required in a design phase, without requiring commercial software.

Electromagnetic Interference in a Buried Multiconductor Cable Due to a Dynamic Wireless Power Transfer System

The aim of this study is to predict the electromagnetic interference (EMI) effect produced by a dynamic wireless power transfer (DWPT) system on a buried multiconductor signal cable. The short-track DWPT system architecture is here considered with an operating frequency of 85 kHz and maximum power transferred to an EV equal to 10 kW. The EMI source is the DWPT transmitting coil which is activated when a vehicle passes over it. The electric and magnetic fields in the earth produced by the DWPT coil currents are calculated numerically using the finite elements method (FEM). These fields are then used to derive the voltage and current sources that appear in the field-excited multiconductor transmission line (MTL) model, used for the buried shielded cable. The MTL is analyzed considering the first ten harmonics of the current. The currents and voltages at the terminal ends are calculated considering the wireless charging of a single electric vehicle (EV) first, and then the simultaneous charging of 10 EVs which absorb a total power of 100 kW. The preliminary results reveal possible EMI problems in underground cables.

Mapping the Buried Cable by Ground Penetrating Radar and Gaussian-Process Regression

With the rapid expansion of urban areas and the increasingly use of electricity, the need for locating buried cables is becoming urgent. In this paper, a noval method to locate underground cables based on Ground Penetrating Radar (GPR) and Gaussian-process regression is proposed. Firstly, the coordinate system of the detected area is conducted, and the input and output of locating buried cables are determined. The GPR is moved along the established parallel detection lines, and the hyperbolic signatures generated by buried cables are identified and fitted, thus the positions and depths of some points on the cable could be derived. On the basis of the established coordinate system and the derived points on the cable, the clustering method and cable fitting algorithm based on Gaussian-process regression are proposed to find the most likely locations of the underground cables. Furthermore, the confidence intervals of the cable's locations are also obtained. Both the position and depth noises are taken into account in our method, ensuring the robustness and feasibility in different environments and equipments. Experiments on real-world datasets are conducted, and the obtained results demonstrate the effectiveness of the proposed method.

Effect of elevated temperature on geotechnical properties of soils – A review

Land used for construction purposes should have large bearing capability and less squeezability. Soft soils such as clayey soil have low bearing capacity and high compressibility which must be converted or treated before the construction process to meet the requirements. The presence of oil and gas pipe lines, buried high voltage cables, fire accidents, storage of high-level waste could limit the use of conventional methods such as deep cement mixing. Hence, alternate methods are required, heat treatment has been considered to be the efficient technique, if the need of enhancement in characteristics are required. This paper discusses the literature available on thermal treatment. The effect of temperature on various properties of soil like Atterberg limits, free swell, porewater pressure, swelling, shear strength, stress strain behavior of soil and mineralogy is included in this paper. This review paper summarizes the effectiveness of thermal treatment on soft soil.

Long-term Thermo-hydraulic Response of the Shallow Subsurface soil in the Vicinity of a Buried Horizontal Heat Source

Heat and mass transfer in the shallow subsurface and in the vicinity of buried heat sources has been often studied based on rather simplifying assumptions, such as the Equilibrium Phase Change (EPC), disregarding film flow, and adsorptive soil-water characteristics. In this study, a fully coupled non-isothermal multiphase flow model is developed that utilizes the Non-equilibrium Phase Change (NEPC) approach. First, the performance of the EPC and NEPC approaches is assessed and validated against the in-field experimental data. The second and main objective of this study is to analyze the thermo-hydraulic response of granular soil close to a buried horizontal heat source (e.g., electrical cables) for one year under real meteorological conditions. Numerical results indicate that the NEPC model has higher robustness in predicting the volumetric water content in the soil close to the soil-atmospheric boundary. However, NEPC and EPC approaches estimate the same temperature variations in the soil. In the case of precipitation (e.g., rainfall), the NEPC model predicts higher degrees of saturation in deeper soil in which the infiltrated water reaches 150 cm below the surface, while, in the EPC model, the infiltrated water barely reaches the 100 cm depth. The increase in moisture content close to the heat source facilitates the heat transfer in the medium and thus results in a 40% to 50% reduction in soil temperature close to the heat source. An accurate prediction of the soil moisture content in the medium is needed to evaluate the performance and thermal capacity of buried electrical cables. Furthermore, the heating/cooling cycles contribute to gradually drying the soil in the vicinity of the heater until the hydraulically equilibrated condition is attained.