Cable Shield Research Articles

Theoretical analysis of stratum horizontal displacements caused by small radius curve shield tunneling

For small radius curve shield tunneling, over excavation is required on the inner side of the curve to corner the shield machine. Currently, there is no corresponding analytical solution for horizontal displacements. In this paper, using the image method and Mindlin solution and considering four factors: additional thrust on the excavation surface, frictional resistance of the shield shell, ground loss, and grouting pressure at the shield tail, a formula for calculating stratum horizontal displacements caused by small radius curve shield tunneling is derived. Based on the 220 kV Rhinoceros Station cable shield tunnel project in Guangzhou, the stratum horizontal displacement law and influencing factors are analyzed. Through comparison and verification with on-site measured data, the results indicate that the theoretical formula derived is reasonable and reliable, providing a new approach for predicting the stratum horizontal displacements induced by curve shield tunneling. The law of stratum horizontal deformation exhibits that the horizontal displacement caused by the over excavation side of the curve moves toward the tunnel side. The outer side of the curve shifts away from the tunnel. The peak appears near the axis of the shield tunnel. The ground loss has the most significant influence on stratum horizontal displacements. Furthermore, on the same tunnel cross-section, the closer the soil is to the tunnel, the greater the horizontal displacement of the soil, and vice versa. The change in shield shell length profoundly affects horizontal displacements. The friction difference coefficient has a significant impact on the stratum horizontal displacement outside the curve.

Parametric Design of a 3D-Printed Removable Common-Mode Trap for Magnetic Resonance Imaging.

Radiofrequency coils are utilized during transmit and receive of MRI signals. Cable traps remove common-mode current from the coaxial cable shield, which helps improve the image quality and reduces risks of burns to the patient. Traditional cable traps use wounded coaxial cables that limit the flexibility in the design process. Floating cable traps were introduced which eliminated any physical connection between the trap and coaxial cable, allowing complete flexibility in design and placement. However, the design process of floating cable traps is iterative and may take several rounds of 3D modeling. This work seeks to optimize the design process through the use of parametric design methodologies. The proposed methodology allows for 3D printing the floating cable trap after inputting the design parameters. The cable trap was able to attenuate currents in the coaxial shields to -48 dB, highlighting its performance and design robustness.

Reduction of High-Voltage Cable Line Capacity Caused by Implementation of Magnetic Field Shielding Techniques

The paper deals with a capacity of high-voltage cable line made of three single-core cross-linked polyethylene insulated power cables. We consider three cases. First is a single-point bonded cable system when no magnetic field shielding technique is implemented and the capacity achieves maximum values. Second is a solidly bonded cable system when a thermal effect of induced shield currents causes a capacity reduction. The third case under study is a single-point bonded cable system covered by the passive loop. The passive loop mitigates the cable line magnetic field as well as the solidly bonding does, but also the thermal effect of passive loop currents reduces the capacity. The goal of the paper is to evaluate the relative change of cable line capacity when implementing magnetic field shielding techniques comparably to unshielded case. To achieve the goal we use a standard IEC 60287 when calculating the cable line capacity in the first and the second cases, and a thermal field simulation in the third case. The capacity is evaluated by successive approximations. Iterations are stopped when the conductor reaches the maximum operating temperature. We show that the increase in cable spacing does not guarantee the capacity increase when the solid bonding of cable shields or the passive loop is used. The most significant result is the substantiation of the advantages of passive loop, which provides the greater capacity in comparison with solid bonding at equivalent magnetic field shielding efficiencies. The obtained results can be used when choosing the type of bonding and the technique of cable line magnetic field mitigation.

Assessing the Shield Termination Approaches in Aircraft Wiring to Against the Lightning Indirect Effects

Lightning is a natural phenomenon where high voltages and currents suddenly discharge. It can be caused by clouds themselves, clouds between them, or clouds near the earth. Aircraft are also at risk of being struck by lightning and there is currently no way to prevent this from happening. Instead, efforts are being made to protect by reducing the effects of lightning. Metal structures in aircraft form a Faraday cage which helps in preventing lightning currents from entering the aircraft. However, composite structures, which are becoming more prevalent in the aviation sector, are less efficient in doing so compared to metals. Additionally, openings such as windows in the aircraft can break the Faraday cage and allow strong electromagnetic fields to penetrate. Hence, all equipment used on board the aircraft must be adequately qualified and lightning-proof. The most popular technique used to reduce the indirect effects of lightning on electronics is cable shielding. In this study, various shielding termination techniques for their effectiveness against indirect effect of lightning examined and It is found that utilizing a 360˚ backshell termination technique provided to be highly effective, providing protection of nearly 3 dB. The results obtained from the experiments are compared with simulation results and previous studies and it has been observed that the obtained results are consistent with each other.

Fault Location Method for Three-Core Cable Using Amplitude Ratio of Shield-Grounding Wire Currents

With significant technological advancements in power grids, three-core cables are widely employed for their safety and other benefits. In general, three-core cables in medium-voltage distribution systems are laid underground during operation. As a result, the harsh working environment and complex fault conditions can bring massive challenges to fault location issues. To address the problem, the distinctive cable features are extensively considered in this article, including relatively larger capacitance, cable shield effects, and shield bonding methods. Initially, an equivalent cable model is developed to analyze the relationship between shield-grounding wire currents and the fault point. A single-phase grounding fault location method is then formulated based on the ratio of shield-grounding wire currents at both terminals. In PSCAD/EMTDC, a range of fault scenarios are simulated to verify the proposed method. In comparison to conventional similar approaches, the proposed method exhibits higher accuracy and robustness to fault resistance and diverse fault conditions. Finally, the effectiveness of the proposed method is validated on a real 10 kV distribution network experimental platform under several fault scenarios.

Triaxial Cell for Determining Shielded Cable Transfer Impedance During Environmental Stress

Transfer impedance is a main characteristic to describe the shielding performance of shielded cables at least up to 1 GHz. Traditionally, methods, such as line-injection and triaxial cell, have been used to characterize it at ambient laboratory conditions. While the ambient laboratory conditions might represent appropriate environmental conditions for some industries, in others, such as automotive, they are only a small subset of the real conditions. Thus, there is a need to characterize the transfer impedance over different environmental conditions. In this article, the authors present and verify a new triaxial cell design that is aimed to provide reliable measurements during high thermal and mechanical stresses. First, the cell performance is compared with a commercial cell at laboratory ambient conditions. Then, measurements are performed with the new cell at highly accelerated life testing conditions. Under these high thermal and mechanical stress conditions, the cell performance is verified, and results on typical shielded cable performance under the same conditions are given.

Three-Dimensional FDTD-Based Simulation of Lightning-Induced Surges in Secondary Circuits With Shielded Control Cables Over Grounding Grids in Substations

Nowadays, plenty of sensitive electronic devices are installed in secondary circuits in substations. When lightning strikes a substation and transmission line, lightning currents flow into the grounding structure of the substation through shield wires and lightning surge arresters in the primary circuit, and lightning overvoltages are induced on control cables in the secondary circuit owing to the effect of transient ground potential rises of the grounding structure and electromagnetic coupling. Shielded control cables are one of the countermeasures against lightning overvoltage induced on control cables; thus, it is useful to evaluate the effectiveness of shielded control cables for designing protection measures properly. Recently, the finite-difference time-domain (FDTD) method, which is one of the full-wave numerical approaches, has been commonly used for simulating electromagnetic transient phenomena in grounding structures, such as the grounding grids of substations. In this work, first, we studied the modeling of tape-type shielded control cables used in substations for FDTD-based electromagnetic transient analyses. Then, using the control cable model, we simulated a test platform of primary and secondary circuits in a substation and calculated the transient response of a grounding grid and voltages induced on the control cable when a lightning impulse current was injected into the grounding grid. We then compared the calculated results with the measured waveforms for validation.

Shielding Grounding Optimization Method for Spaceborne Multi-Cable

The coupling relationship between space electronics systems is complex, and the signals of optoelectronic load cables are susceptible to interference, especially the early anomalous weak signals on a ground surface used for immediate remote sensing, which are more susceptible to coupling interference between cables. Ensuring a good grounding state for the cable shield is vital for reducing the interference suffered by cables and increasing the electromagnetic compatibility of the system. In this paper, we propose a shielding grounding optimization method for a spaceborne multi-cable shield, including a cable model and parameter extremization and parameter scanning simulation performed using CST, data processing and truth table transformation conducted using MATLAB, and logic expression extraction carried out using Multisim. The method can sort and classify the shielding effects of all the grounding states of multi-cable shields in batches, and ultimately output logical expressions specifying the mapping relationship between the shield grounding state and shielding effect, allowing the optimal shield grounding state to be quickly identified. Finally, the method was applied to a satellite-borne scanning mirror drive control system, and the effectiveness and accuracy of the method were verified by experimental tests.

Review of Typical Interference Suppression Measures for Industrial Control Systems

Interference suppression is one of the core issues in the research of industrial control systems, and the research of interference suppression methods is an essential technology to ensure the reliable and stable operation of control systems. In this paper, from the conductive coupling, common impedance coupling, capacitive coupling, inductive coupling and electromagnetic field coupling, and other propagation paths to start, a comprehensive and systematic description and analysis of all types of interference suppression, including magnetic loop suppression, cable shielding, surge suppression and isolation of interference and other related methods and measures, the basic principle of suppression, the implementation of the method and the characteristics of the analysis and summary of the choice of interference suppression methods for industrial control systems. The basic suppression principles, implementation methods, and characteristics are analyzed and summarized to provide a reference for the selection of interference suppression methods for industrial control systems.

Far-Field Radiation Prediction and Analysis of a Power Converter With V-Shaped Flat Cables Based on PEEC

The far-field radiation generated by a power electronic converter with V-shaped cables is a key theoretical problem with engineering application significance. The irregular V-shaped antenna is very difficult to calculate analytically, making a precise prediction of the power converter's far-field radiation very challenging. In this work, the far-field radiation of a power converter with flat shielded cables is modeled and predicted using the retarded partial element equivalent circuit ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${\mathbf{\tau}}$</tex-math></inline-formula> PEEC) theory. The τPEEC modified node analysis circuit model of a metal radiator is introduced first, and then the radiator's input impedance formula is deduced. The τPEEC computation model of the V-shaped radiator, which includes the ground plane reflection effect, is developed for the typical far-field radiation test configuration, and the numerical calculation of the far-field radiation transfer function is obtained using the field strength sensor method. To test the suggested τPEEC approach, a 30-MHz low-side buck converter with flat shielded cables is built, and its 10-m far-field radiation strength is predicted. The V-shaped radiator's radiation characteristics are also investigated, and a design for suppression is proposed and demonstrated.

Research on Interferences of VFTO to Irregular Distributions of Secondary Side Cables

In the digital era, the secondary equipment of power system is becoming more and more sensitive to electromagnetic interference. Gas insulated switchgear (GIS) in substations will generate very fast transient overvoltage (VFTO) after switching action. The VFTO will generate transient electromagnetic fields and cause interferences to the secondary side cables. In recent years, the anti-interference measures for cable protection have been greatly improved. However, in the current cable trenches of some substations, there are still many irregular cable arrangements. It may have some influences on the electromagnetic interference to the cable generated by VFTO. This paper expresses a method for finding the exact interference areas of the cable and standardizing the wiring standard of the cable. Firstly, the relationship between the cable position variation and parameters is analyzed. Then, simulation experiments based on speculation are conducted to observe the effect of irregular cable arrangement on port voltage, and computer software simulation is performed for comparison. After that, an irregular cable is simulated and an interval type Ⅱ fuzzy neural network is used to predict the parameters of the shielding layer of the cable at each irregularly arranged point. Finally, the voltage and current at each point of the cable shield are calculated through the finite-difference time-domain (FDTD) algorithm. In this manner, the actual position of the higher interference voltage can be determined, which can provide a reference standard for cable arrangement.

Defect Diagnosis Method of Cable Shielding Layer Based on Frequency Domain Reflection Coefficient Spectrum

In this article, the genetic algorithm-variational mode decomposition-reflection coefficient spectrum (RCS) method is proposed based on frequency domain RCS to detect and locate the weak defects of the cable shielding layer more precisely. In this method, variational mode decomposition (VMD) algorithm is applied on the RCS to extract defect information, and genetic algorithm based on envelope entropy and kurtosis is adopted to optimize the number of decomposed intrinsic mode functions and penalty factor of the VMD. In addition, with 40 groups of data, support vector machine algorithm is engaged to identify the types of different shielding layer defects. The experimental results show that the proposed method can detect and locate weak defects, such as one-strand fractures and holes, and meanwhile identify the types of defects accurately.

Огляд систем контурного екранування для нормалізації магнітного поля кабельних ліній високої напруги

The paper is devoted to the review of known passive loop systems that can be used to normalize the high-voltage cable line magnetic field. The purpose is to identify the most promising systems. We review the most cited scientific papers and patents about the reduction of the power line magnetic field. We identify the top research groups engaged in the design of passive loop systems. The two groups are from Italy, the one each is from Spain and Ukraine. The passive loop systems developed by each group have their own features. We classify the systems according to the following characteristics: the number of passive loops in the shielding system, the shape of passive loops used in the shielding system, and the way to increase the shielding efficiency of cable line magnetic field. According to the number of passive loops, the systems can be divided into three types: single-element, double-element and multi-element. According to the shape of passive loops, two types of shielding systems can be distinguished, namely, the systems using rectangular passive loops and the systems using passive loops made of three cables connected in parallel. According to the method of the shielding efficiency increasing, the system can be divided into four types: the first use ferromagnetic cores covering power and shield cables, the second use additional capacitors connected to shield cables, the third use a unique arrangement of loops between the cable line and the shielding area, the fourth use an increase in the cross-section of shield cables, respectively, an increase in the quantity of metal. The review shows the most promising passive loop systems for normalizing the high-voltage cable line magnetic field are single-element systems with additional cores, namely «High Magnetic Coupling Passive Loop» and «Single-loop shield with ferromagnetic cores and asymmetric magnetic coupling». Keywords: magnetic field, shielding, cable line, reference level, power frequency

Live test technology for metal shielding of medium and low voltage power cables in continuous state

Live test technology for metal shielding of medium and low voltage power cables in continuous state

Comparison of Shielding Effectiveness of Different Shielding Methods for Multi-Core Cable on Lightning Surge Current

Appropriate shielding methods can reduce the lightning induced voltage and current of cables. In this article, different lightning surge currents (8/20 and 5/320 <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">μ</i> s) are coupled to the tested multi-core cable with single shielding layer and double shielding layers. The shielding effectiveness (SE) on the lightning surge current is compared for different cable shielding methods. The experimental results show that the cable induced current is effectively reduced when the shielding layer, the shielding spare core wire or the metal tube are grounded at two ends. A better shielding effect for the cable with double shielding layers is achieved by grounding both ends of the outer shielding layer and one end of the inner shielding layer, reducing the induced current to about 5% when the shielding layer is not grounded. Moreover, the SE of the spare core wire, used as the shielding wire in the multi-core cable, is better than that of the external shielding wire of the cable. The SE of the metal tube increases more and more slowly with the increase of the tube coverage percentage. Furthermore, the descending order of the SE of shielding methods involved here are grounding both ends of double shielding layers, grounding both ends of single shielding layer, spare core wire shielding and metal tube shielding. Finally, some engineering recommendations are proposed through the comparison between the shielding methods in this article and relevant works.

A flexible MRI coil based on a cable conductor and applied to knee imaging

Flexible radiofrequency coils for magnetic resonance imaging (MRI) have garnered attention in research and industrial communities because they provide improved accessibility and performance and can accommodate a range of anatomic postures. Most recent flexible coil developments involve customized conductors or substrate materials and/or target applications at 3 T or above. In contrast, we set out to design a flexible coil based on an off-the-shelf conductor that is suitable for operation at 0.55 T (23.55 MHz). Signal-to-noise ratio (SNR) degradation can occur in such an environment because the resistance of the coil conductor can be significant with respect to the sample. We found that resonating a commercially available RG-223 coaxial cable shield with a lumped capacitor while the inner conductor remained electrically floating gave rise to a highly effective “cable coil.” A 10-cm diameter cable coil was flexible enough to wrap around the knee, an application that can benefit from flexible coils, and had similar conductor loss and SNR as a standard-of-reference rigid copper coil. A two-channel cable coil array also provided good SNR robustness against geometric variability, outperforming a two-channel coaxial coil array by 26 and 16% when the elements were overlapped by 20–40% or gapped by 30–50%, respectively. A 6-channel cable coil array was constructed for 0.55 T knee imaging. Incidental cartilage and bone pathologies were clearly delineated in T1- and T2-weighted turbo spin echo images acquired in 3–4 min with the proposed coil, suggesting that clinical quality knee imaging is feasible in an acceptable examination timeframe. Correcting for T1, the SNR measured with the cable coil was approximately threefold lower than that measured with a 1.5 T state-of-the-art 18-channel coil, which is expected given the threefold difference in main magnetic field strength. This result suggests that the 0.55 T cable coil conductor loss does not deleteriously impact SNR, which might be anticipated at low field.

An Investigation of Magnetic Field Influence in Underground High Voltage Cable Shields

Magnetic fields and the shielding efficiency of the shields of underground high voltage cables are studied in this paper regarding several shielding configurations and materials. Shielding efficiency and magnetic fields are computed for shields with the same mesh but from different shielding materials, such as aluminum, ferrite, metal, and steel. In order to get the best shield configuration depending on the source characteristics and the material, a conducting ferromagnetic region with various thickness values is considered as shielding. A finite element model is introduced to investigate the influence of the parameters of magnetic fields and the shielding efficiency of underground high voltage cables. Furthermore, the reduction of the magnetic fields with or without shieldings is also presented. The developed method is performed with the magnetic vector potential formulations and validated on a practical problem.

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.

Study on Induced Voltage and Circulation Current of Metal Layer in Single-Core Cable of High-Speed Railway Power Transmission Line

The metal shield and metal armor layers of single-core cables on high-speed railroad power penetration lines are usually grounded by common equipment protectors. This grounding method brings a continuous circulating current between the metal shield and metal armor layer compared to the subequipment protection grounding. In order to quantitatively study the circulating current condition of the through line and its influence on the reliability of the railroad power through line, the induced electric potential and circulating current generation mechanism of the single-core cable of the through line and its influencing factors were firstly analyzed in depth. Then, based on the cross-sectional structure of the single-core cable and the location of the traction network and cable in the roadbed section, a traction power supply model was established and simulated for the interlayer-induced potentials and circulating currents due to the two grounding protection methods under no load, single train operation, and heavy load four-train operation of the line. Finally, three actual sections of the Shanghai–Kunming and Nan–Kunming high-speed railroads in China were selected to collect and analyze the loop flow data with no load and with vehicles passing through, and finally the loop flow law of single-core cable for railroad electric through traffic was derived. The analysis shows that when the metal sheath of a single-core cable is grounded by ordinary equipment, the circulating current generated does not exceed 1% of the core current, which meets the relevant safety standards, but the induced voltage in the case of large loads will exceed 50 V safety voltage.

Investigation on Current Ripple and Electromagnetic Interference in High Voltage Powertrain Systems for Electric Vehicles by Using Crosslinked Polyolefin Insulation Shielded Cable

At this moment, the powertrain system of Electric Vehicles (EVs) tends to use high voltages and high currents when the EVs operate at High Power (HP) mode. The Electromagnetic Interference (EMI) is caused by Electromagnetic Field (EF), high voltage, and current ripple. EMI affects EVs, whereas the Shielding Effectiveness (SE), and the proportional inverse of the transfer impedance prevent the effect of EMI. This research aims to investigate the current ripple the EMI in high voltage powertrain systems for EVs by using the developed crosslinked polyolefin insulation shielded cable, 50 mm2 single-core HP XLPO shielded cable with 0.15 mm annealed tinned-copper wire braid material. The experiment consists of three parts. The first one investigates the tendency of SE and current ripple. The second part shows the analysis of the effect of HP mode to the cable. The third part is an additional study that compares and analyzes the transfer impedance. The results indicate that the cable operates properly in the frequency above 200 Hz, transfer impedance decreasing between 11.5% to 15.25%, induces the SE and reduces the current ripple in the higher frequency range. The results obtained from this research represent a preliminary investigation guideline in decreasing the effect of EMI in EVs by using 50mm2 single-core HP XLPO shielded cable with 0.15 mm annealed tinned-copper wire braid material in a high-power range.