Conductor Geometry Research Articles

A topology optimization of on-chip planar inductor based on evolutional on/off method and CMA-ES

PurposeThere are few reports that evolutional topology optimization methods are applied to the conductor geometry design problems. This paper aims to propose an evolutional topology optimization method is applied to the conductor design problems of an on-chip inductor model.Design/methodology/approachThis paper presents a topology optimization method for conductor shape designs. This method is based on the normalized Gaussian network-based evolutional on/off topology optimization method and the covariance matrix adaptation evolution strategy. As a target device, an on-chip planer inductor is used, and single- and multi-objective optimization problems are defined. These optimization problems are solved by the proposed method.FindingsThrough the single- and multi-objective optimizations of the on-chip inductor, it is shown that the conductor shapes of the inductor can be optimized based on the proposed methods.Originality/valueThe proposed topology optimization method is applicable to the conductor design problems in that the connectivity of the shapes is strongly required.

Design study of superconducting coil system for JA DEMO

A fusion demonstration (DEMO) reactor requires toroidal field (TF) coils larger than those used in ITER and can withstand higher electromagnetic forces. This creates significant challenges regarding the manufacturability of the TF coils, the increased electromagnetic forces on the TF inner leg case, and increased fabrication costs. This means that new winding pack designs and superconducting conductors must be designed to meet these requirements, and high-strength cryogenic steel for the coil case must be developed to withstand electromagnetic forces. This paper describes these possible solutions based on the Japanese DEMO (JA DEMO) design. In the layered winding of rectangular conductors, it was found that a new conductor geometry called the hybrid R-shape conductor can significantly reduce the stress on the turn insulation while reducing the superconducting wire to less than half. In addition, a guideline for designing the conductor strand structure was provided for a superconducting conductor subjected to electromagnetic forces 1.5 times greater than those of ITER. Furthermore, the effect of composition on strength was evaluated using several prototype materials based on high-Cr austenitic steels, and the feasibility of increasing the strength of cryogenic steels was confirmed.

Image Analysis Capabilities and Methodologies of Nb3Sn Rutherford Cables

The unique Rutherford cabling facility at the Berkeley Center for Magnet Technology, LBNL, has been leading the production of a range of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn cables for a variety of magnet projects domestically and internationally. Cable fabrication is a critical step in accelerator magnet production: to ensure tight dimensional control of the multi-turn coils, fine tolerances must be kept on the cable width, thickness, keystone angle [1] with minimal degradation to the conductor. In addition to these dimensional measurements, we implemented an in-line image acquisition system that can monitor for critical defects such as cross-overs, as well as track the extent of strand deformation at the cable edges. At LBNL, we have collected a large dataset to establish the association between the cable edge facet dimension and the cross-sectional subelement damages. We thus can use image analysis on the facet as an integral and critical quick turn-around-time quality control monitor. Although such measurements are not direct and require a baseline for a given conductor and cable geometry combination, they are non-destructive. They can be measured across the entire length of the cable, which contrasts with critical current or residual resistance ratio measurements, which are only made at the point and tail of the cable and require a lengthy heat-treatment. Moreover, the high frequency of image acquisition coupled with Fast Fourier Transform analysis can give us insights into the key components of the cabling machine as they tend to produce periodic variations within the cable. Such analysis can help find potential faults and inform maintenance planning. This work describes our setup of in-line imaging of Rutherford cables during manufacture, the subsequent image analysis, and data processing. Several case studies illustrate typical usage of the system and lessons learned.

Circulating and Eddy Current Losses in Coreless Axial Flux PM Machine Stators With PCB Windings

Printed circuit board (PCB) stators in coreless axial flux permanent magnet (AFPM) machines have been proposed, designed, and studied for use in multiple industries due to their design flexibility and reduction of manufacturing costs, volume, and weight compared to conventional stators. This paper investigates mechanisms and methods of approximating open circuit losses in PCB stators within example wave and spiral winding topologies for a dual rotor, single stator configuration using 3D FEA, analytical hybrid techniques and experiments. The effect of rotor magnet shape, end winding, and active conductor geometry on eddy currents is studied, and some mitigation techniques are proposed. Through stator equivalent circuit analysis, circulating current losses caused by mechanical abnormalities and magnetic circuit asymmetry are assessed. Possible strategies and schemes to minimize circulating current losses are also described. The trade-off between stator loss components and some practical design considerations are outlined in detail. The open circuit power losses of a prototype coreless AFPM motor were experimentally tested using multiple example PCB stators and emulated rotor asymmetries, with the findings being comparable to the FEA and hybrid analytical methods results.

The method of calculating the design parameters of a collinear serial antenna using the dispersion characteristics of the retarding system

The paper presents a technique for analyzing the electrical characteristics of series-type collinear antennas made according to the Franklin scheme, which are intended for use in radio communication systems with moving objects as basic or subscriber antenna-feeder devices. Collinear antennas belong to omnidirectional type antennas and allow to significantly increase the amplification factor in comparison with already existing types of antennas of a similar type, which is what attracts antenna technology developers today. The main element of a series-type collinear antenna is a phase-shifting device that determines both the performance of the antenna and its electrical characteristics. The most widely used phase-shifting devices were inductive chokes – a section of conductor of a certain length rolled into a spiral. The proposed engineering method of calculating the parameters of the inductive choke allows you to quickly and accurately adjust its characteristics with the calculation of the necessary phase shift. This approach takes into account the physical parameters of the conductor material and the geometry of the spiral conductor, which greatly simplifies the engineering process of developing collinear antennas. The obtained results of simulation of electrical characteristics confirm the effectiveness of the proposed method. A significant increase in the amplification factor compared to the existing types of antennas and compliance of the electrical characteristics with the specified parameters was revealed. The work has an important contribution to the development of antenna technology and has practical application in radio communication systems with moving objects. The proposed method of calculating the parameters of the inductive choke can be used by antenna developers to increase the productivity and efficiency of their radio communication system.

Biophysical modeling of the electric field magnitude and distribution induced by electrical stimulation with intracerebral electrodes

Intracranial electrodes are used clinically for diagnostic or therapeutic purposes, notably in drug-refractory epilepsy (DRE) among others. Visualization and quantification of the energy delivered through such electrodes is key to understanding how the resulting electric fields modulate neuronal excitability, i.e. the ratio between excitation and inhibition. Quantifying the electric field induced by electrical stimulation in a patient-specific manner is challenging, because these electric fields depend on a number of factors: electrode trajectory with respect to folded brain anatomy, biophysical (electrical conductivity / permittivity) properties of brain tissue and stimulation parameters such as electrode contacts position and intensity. Here, we aimed to evaluate various biophysical models for characterizing the electric fields induced by electrical stimulation in DRE patients undergoing stereoelectroencephalography (SEEG) recordings in the context of pre-surgical evaluation. This stimulation was performed with multiple-contact intracranial electrodes used in routine clinical practice. We introduced realistic 3D models of electrode geometry and trajectory in the neocortex. For the electrodes, we compared point (0D) and line (1D) sources approximations. For brain tissue, we considered three configurations of increasing complexity: a 6-layer spherical model, a toy model with a sulcus representation, replicating results from previous approaches; and went beyond the state-of-the-art by using a realistic head model geometry. Electrode geometry influenced the electric field distribution at close distances (∼3 mm) from the electrode axis. For larger distances, the volume conductor geometry and electrical conductivity dominated electric field distribution. These results are the first step towards accurate and computationally tractable patient-specific models of electric fields induced by neuromodulation and neurostimulation procedures.

Особенности моделирования воздушных и кабельных участков линий электропередачи 110–750 кВ при использовании фазного координатного базиса

Power system steady state and transient analysis require correct modeling of overhead transmission lines and cables operating at 110–750 kV. The key difficulties to model sections of overhead and cable lines are caused by complex conductor geometry, their transposition, as well as grounding schemes of ground wires of overhead lines and screens of underground cables. The paper covers various aspects of 110–750 overhead line and cable modeling that must be taken into consideration to obtain a reliable mathematical model in a phase domain. Modern software does not provide a universal solution to determine line parameters. The 110–500 kV cable line modeling issues have not been worked out properly and require careful analysis of specialized foreign literature. Thus, the task to develop the algorithms of calculating the parameters of overhead and cable power lines is relevant, taking into account the various configuration options of these lines which are possible in operational practice. To derive overhead transmission line and cable line models, electric circuit theory and matrix algebra methods have been used. The ATP/ATPDraw and MATLAB/Simulink software environment has been used to investigate what tools are available to determine line parameters, as well as to verify some of the calculation results. Analysis has been carried out to reveal the options available in the ATP/ATPDraw and MATLAB/Simulink software to compute line parameters in a phase domain. An algorithm has been developed and verified to calculate overhead line parameters regardless of the number of parallel circuits. The key features of the calculation of the matrix of linear resistances of overhead power transmission lines are outlined. The main features of modern cable lines operating at 110–500 kV are also described. The paper presents various cable layouts possible in real-field conditions, as well as provides expressions that allow obtaining correct impedances and admittances for a system of cable line conductors. Study of the options of various software tools dedicated to overhead line parameter calculation in a phase domain has revealed that these tools cannot be deemed universal to represent an overhead line of whatever configuration. However, the developed algorithm is universal as it allows computing line parameters regardless the ground wire grounding approach. The expressions presented in this paper consider various layouts of 110–500 kV cable lines that could be encountered in the Russian power system.

Determining the Transmission Capacity of Existing Transmission Lines Under High Wind Generation Conditions

Determining the transmission capacity of existing transmission lines is determine by the conductor current. Transmission line can withstand current below thermal standpoint limit to avoid irreparable damage to conductor. The maximum value of current can be determined with static approach (STR – Static Thermal Rating) and dynamic approach (DTR - Dynamic Thermal Rating). STR is defined by simple calculations and does not change often throughout the year where the DTR is calculated for in time conditions taking into account atmospheric conditions, conductor geometry and conductor current. Most common approach to calculate conductor temperature is done by applying IEEE standard (IEEE 738, 2012) or CIGRE (TB601, 2014). Most congestion in the transmission network occurs during the higher production from wind farms when the wind have significant speed. It is to be expected that similar meteorological conditions (wind speed and direction) will occur on transmission lines in the immediate geographical area of wind power plants. In this paper, analysis of relations between atmospheric parameters (wind speed and direction, ambient temperature and solar radiation) and ampacity is described as functional dependence. Taking historical weather data from meteorological stations, atmospheric conditions on transmission line corridors and taking account the frequency of occurrence of individual meteorological variations ampacity of conductor will be determined. For such determined conditions that are influenced by a certain parameters variation of ampacity have a different rating scales. The obtained results will provide an insight into the current ampacity and the possibilities of the transmission line capacity during the high engagement of wind power plants.

Advancing OHL Rating Calculations: Modeling Mixed-Convective Cooling and Conductor Geometry

The existing standard current-temperature calculations for overhead line (OHL) conductors have been adequate for conventional conductors and their operating temperatures. However, these calculations make assumptions and include simplifications about conductor geometry and aero-thermal-dynamics, introducing an error in the High-Temperature Low-Sag conductors operating temperatures. To quantify the error introduced by the shape of strands, the paper employs a Multi-Physics Finite Element Modeling approach that calculates the conjugate heat transfer for trapezoidal stranded OHL conductors. Furthermore, it proposes corrective equations to improve the accuracy of existing methods. The equations incorporate a new Nusselt number correlation for mixed convection and capture the surface area ignored by current calculations. The outer conductor geometry assumptions and the combined natural and forced convective cooling omission in the IEEE and CIGRE methods introduce an error at low (below 0.12 m/s) cross-flow wind speeds suggesting an underestimation of conductor temperature by up to 4%. In medium wind speeds, typically at 0.5 m/s–0.61 m/s, the standard methods overestimate the conductor temperature limiting its current-carrying capability. A 5% uprating for existing OHLs is potentially feasible, particularly for the trapezoidal stranded conductors, when removing the assumptions made in existing methods.

Radiofrequency Coils for Low-Field (0.18–0.55 T) Magnetic Resonance Scanners: Experience from a Research Lab–Manufacturing Companies Cooperation

Low-field magnetic resonance imaging (MRI) has become increasingly popular due to cost reduction, artifact minimization, use for interventional radiology, and a better safety profile. The different applications of low-field systems are particularly wide (muscle–skeletal, cardiac, neuro, small animals, food science, as a hybrid scanner for hyperthermia, in interventional radiology and in radiotherapy). The low-field scanners produce lower signal-to-noise ratio (SNR) images with respect to medium- and high-field scanners. Thus, particular attention must be paid in the minimization of the radiofrequency (RF) coil losses compared to the sample noise. Following a short description of the coil design and simulation methods (magnetostatic and full-wave), in this paper we will describe how the choice of electrical parameters (such as conductor geometry and capacitor quality) affects the coil’s overall performance in terms of the quality factor Q, ratio between unloaded and loaded Q, and coil sensitivity. Subsequently, we will summarize the work carried out at our electromagnetic laboratory in collaboration with MR-manufacturing companies in the field of RF coil design, building, and testing for 0.18–0.55 T magnetic resonance (MR) clinical scanners by classifying them between surface-, volume-, and phased-array coils.

PARAMETERS AFFECTING THE TRANSIENT RESPONSE OF VERTICAL PIPE ELECTRODES TO IMPULSE EXCITATION

In this article, an application of the transmission line theory is presented for analyzing various parameters that affect the transient response of ground electrodes. In order to simplify the presentation and the interpretation of the results obtained, a vertical buried pipe electrode was chosen as the ground electrode. The ground electrode is connected to a grounding conductor, the upper part of which is connected to an ideal current source. The impact of the overhead geometry of the grounding conductor upon the transient response of the ground electrode is analyzed by varying the length of the grounding conductor. The ideal current source generates a normalized wave shape current impulse, a so-called double exponential impulse. The effect of the time to peak of the impulse (steepness of the rising edge of the peak current) on the transient response of the ground electrode is analyzed by varying the current wave shape parameters. The impact of soil parameters on the transient response of the ground electrode is also analyzed. The soil is modeled as a single-layer homogeneous isotropic semispace. The soil-air boundary is represented by a plane. The results obtained are presented graphically and discussed.

Construction and Test of the Enhanced Racetrack Model Coil, First CERN R&amp;D Magnet for the FCC

Racetrack model coils (RMC) have been built at CERN during the past decade, as an R&D tool to qualify conductors and technologies developed for high field superconducting accelerator magnets (Perez <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> , 2016). RMC, assembled in a dipole magnet configuration, proved to be an efficient instrument reducing cost and feed-back time while developing new magnets. In a similar way, as for the High-Luminosity Large Hadron Collider (HL-LHC) project, CERN has designed the enhanced RMC (eRMC) made of two flat coils using 40 (1 mm diameter) Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strand cable produced with Rod Restack Process (RRP) technology. This conductor geometry, originally designed and produced to build the block coil dipole magnet FRESCA2 (Rochepault <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">et al.</i> , 2019), was chosen to reduce the production time and shorten the road towards the feasibility demonstration to reach 16–18 T magnetic fields in a dipolar configuration. Like previous model coils built at CERN (Short model coils (SMC) & RMC), eRMC1a has been built using the “bladders and keys” type mechanical structure. This paper describes the main construction steps and the powering test results. At 1.9 K the magnet produced 16.5 T peak field in the conductor, the highest ever for a dipole magnet of this configuration.

An investigation into the influence of stator tooth and conductor geometry on AC winding losses in a 365kW permanent magnet machine equipped with rectangular bar conductors

Rectangular bar conductors located in parallel stator slots with a matched geometry offer a potentially attractive solution for permanent magnet machines as they can provide an improved slot fill factor with consequent reduced loss and enhanced heat transfer compared to random wound mush type coils. However, in addition to the manufacturing challenges posed by precisely forming coils from large cross-section bar conductors, the adoption of bar conductors is often constrained by consideration of additional AC losses which are a result of induced eddy currents in the conductors. These induced currents are a result of exposure to time varying fields both from armature reaction fields and incident permanent magnet flux passing through slot opening. In this paper, a 365kW 6000rpm 6-pole permanent magnet machine equipped with various arrangements of solid bar conductors is analysed to understand and illustrate the significance of AC losses in bar conductors and to quantitatively assess the influence of various design changes to the stator. The magnitude of AC losses in a baseline model with a single series wound bar is evaluated by 2D FEA simulations and shown to be prohibitive. In order to reduce AC losses, several design features including using multiple parallel transposed conductors and further optimization of tooth and conductor geometry are considered in this paper. Simulation results show that with optimized stator tooth geometry and multiple parallel transposed conductors, AC losses can be reduced by an order of magnitude compared to a machine designed on purely static considerations.

Intelligent Contactless Current Measurement for Overhead Transmission Lines

Traditional current monitoring devices (e.g. current transformers) for transmission and distribution (T&D) networks are mostly installed at substations, so real-time and accurate information on current is almost unavailable for on-site load current monitoring, imbalance assessment, and equipment maintenance. This increases the fault risk in T&D networks and degrades the reliability and quality of the power supply. To address such a situation, this study proposes an intelligent and contactless current measurement method. The proposed method uses only a small number of magnetic-field sensors and the conductor geometry specification of an overhead line obtained from utilities. The simulation results show that the proposed method can accurately calculate each phase current using only three magnetic field sensors. In addition, a scaled-down overhead line measurement system was built to test the proposed method. The experimental results verify the feasibility of the proposed contactless method for overhead-line current measurement with less than 10 % maximum measurement error.

A Practical Guide to Estimating Coil Inductance for Magnetic Resonance Applications

Radiofrequency (RF) coils are employed to transmit and/or receive signals in Magnetic Resonance (MR) systems. The design of home-made, organ-specific RF coils with optimized homogeneity and/or Signal-to-Noise Ratio (SNR) can be a plus in many research projects. The first step requires accurate inductance calculation, this depending on the conductor’s geometry, to later define the tuning capacitor necessary to obtain the desired resonance frequency. To fulfil such a need it is very useful to perform a priori inductance estimation rather than relying on the time-consuming trial-and-error approach. This paper describes and compares two different procedures for coil inductance estimation to allow for a fast coil-prototyping process. The first method, based on calculations in the quasi-static approximation, permits an investigation on how the cross-sectional geometry of the RF coil conductors affects the total inductance and can be easily computed for a wide variety of coil geometries. The second approach uses a numerical full-wave method based on the Finite-Difference Time-Domain (FDTD) algorithm, and permits the simulation of RF coils with any complex geometry, including the case of multi-element phased array. Comparison with workbench measurements validates both the analytical and numerical results for RF coils operating within a wide field range (0.18–7 T).

Methodology for Minimizing Electric Field at Ground Level from Transmission Lines Using Sensitivity Analysis

In this paper, a new methodology is applied to optimize the geometry of conductors of overhead transmission lines (TL) with high precision and low computational cost. This methodology is based on the sensitivity analysis of the electrical charge of the transmission lines using the adjoint method. This information is used with the gradient method and the golden section algorithm to minimize the electric field at the ground level of three-phase TL with two cables per phase. The approximation using central finite differences to obtain sensitivity is adopted for validation and comparisons. The TL's with high surge impedance loading is obtained after the optimization process.

A nine-channel transmit/receive array for spine imaging at 10.5 T: Introduction to a nonuniform dielectric substrate antenna.

The purpose of this study is to introduce a new antenna element with improved transmit performance, named the nonuniform dielectric substrate (NODES) antenna, for building transmit arrays at ultrahigh-field. We optimized a dipole antenna at 10.5 Tesla by maximizing the -SAR efficiency in a phantom for a human spine target. The optimization parameters included permittivity variation in the substrate, substrate thickness, antenna length, and conductor geometry. We conducted electromagnetic simulations as well as phantom experiments to compare the transmit/receive performance of the proposed NODES antenna design with existing coil elements from the literature. Single NODES element showed up to 18% and 30% higher -SAR efficiency than the fractionated dipole and loop elements, respectively. The new element is substantially shorter than a commonly used dipole, which enables z-stacked array formation; it is additionally capable of providing a relatively uniform current distribution along its conductors. The nine-channel transmit/receive NODES array achieved 7.5% higher homogeneity than a loop array with the same number of elements. Excitation with the NODES array resulted in 33% lower peak 10g-averaged SAR and required 34% lower input power than the loop array for the target anatomy of the spine. In this study, we introduced a new RF coil element: the NODES antenna. NODES antenna outperformed the widely used loop and dipole elements and may provide improved transmit/receive performance for future ultrahigh field MRI applications.

Tri-Band, Stable and Compact Patch Frequency Selective Surface Optimized via Hybrid Bioinspired Computing for Applications at 2.4, 3.5 and 5.8 GHz

This work addresses the synthesis of a multi-band frequency selective surface (FSS) through bioinspired computing and a general regression neural network (GRNN). This hybrid computational method, which utilizes the multi-objective cuckoo search algorithm combined to a GRNN, determine the best physical dimensions of the FSS in order to achieve a multi-band filtering at the 2.4, 3.5 and 5.8 GHz spectrums. Therefore, the results are to be applied to aid the propagation of Wi-Fi, WLAN, WiMAX and future sub-6 GHz 5G systems. The resonant frequencies were measured and a -10 dB cutoff value has been considered for the transmission coefficient. The triple rectangular loop conductor geometry of the device is printed upon a glass epoxy (FR-4) substrate. Measurements were made for different wave incidence angles, from 0° up to 45°, to demonstrate how signal incidence would affect the device’s functioning. The agreement between simulated and measured data display satisfactory results.

Broadband finite-element impedance computation for parasitic extraction

Parasitic extraction is a powerful tool in the design process of electromechanical devices, specifically as part of workflows that check electromagnetic compatibility. A novel scheme to extract impedances from CAD device models, suitable for a finite element implementation, is derived from Maxwell’s equations in differential form. It provides a foundation for parasitic extraction across a broad frequency range and is able to handle inhomogeneous permittivities and permeabilities, making it more flexible than existing integral equation approaches. The approach allows for the automatic treatment of multi-port models of arbitrary conductor geometry without requiring any significant manual user interaction. This is achieved by computing a connecting source current density that supplies current to the model’s terminals, whatever their location in the model, subsequently using this current density to compute the electric field, and finally calculating the impedance via a scalar potential. A mandatory low-frequency stabilization scheme is outlined, ensuring a stable evaluation of the model at low frequencies as well. Two quasistatic approximations and the special case of perfect electric conductors are treated theoretically. The magnetoquasistatic approximation is validated against an analytical model in a numerical experiment. Moreover, the intrinsic capability of the method to treat inhomogeneous permittivities and permeabilities is demonstrated with a simple capacitor-coil model including dielectric insulation and magnetic core materials. Finally, the method’s practicality is exemplified with a common mode choke model in a comparison of simulated and measured results.

Advanced Power Line Diagnostics Using Point Cloud Data—Possible Applications and Limits

The advance in remote sensing techniques, especially the development of LiDAR scanning systems, allowed the development of new methods for power line corridor surveys using a digital model of the powerline and its surroundings. The advanced diagnostic techniques based on the acquired conductor geometry recalculation to extreme operating and climatic conditions were proposed using this digital model. Although the recalculation process is relatively easy and straightforward, the uncertainties of input parameters used for the recalculation can significantly compromise such recalculation accuracy. This paper presents a systematic analysis of the accuracy of the recalculation affected by the inaccuracies of the conductor state equation input variables. The sensitivity of the recalculation to the inaccuracy of five basic input parameters was tested (initial temperature and mechanical tension, elasticity modulus, specific gravity load and tower span) by comparing the conductor sag values when input parameters were affected by a specific inaccuracy with an ideal sag-tension table. The presented tests clearly showed that the sag recalculation inaccuracy must be taken into account during the safety assessment process, as the sag deviation can, in some cases, reach values comparable to the minimal clearance distances specified in the technical standards.