Conductor Model Research Articles

Modeling of HTS high-current stacked conductors with defective tapes in different locations

The numerical modeling of HTS stacked conductors was performed with different quantities and locations of defective tapes. The effects of various defective tapes on the overall critical currents, current distributions, and AC losses were studied. Results show the more defective tapes and the higher defect grades were, the larger degradations of critical currents would be. If the quantity of defective tapes was 10, compared with the non-defect case, the AC loss increased by 62% in Scenario A (defective tapes increasing from outside to inside), increased by 24% in Scenario B (defective tapes increasing from inside to outside), and increased by 48% in Scenario C (defective tapes increasing from top to bottom). Therefore, to overcome the issues on current-carrying capability and AC loss, adding reasonable redundancy and safety allowance for HTS tapes, overall critical currents and cryogenic systems is necessary. Overall, this article presents novel analysis and results, which are useful for the future designs of HTS high-current stacked conductors/cables.

Towards a mesoscale physical modeling framework for stereotactic-EEG recordings

Objective. Stereotactic-electroencephalography (SEEG) and scalp EEG recordings can be modeled using mesoscale neural mass population models (NMMs). However, the relationship between those mathematical models and the physics of the measurements is unclear. In addition, it is challenging to represent SEEG data by combining NMMs and volume conductor models due to the intermediate spatial scale represented by these measurements. Approach. We provide a framework combining the multi-compartmental modeling formalism and a detailed geometrical model to simulate the transmembrane currents that appear in layer 3, 5 and 6 pyramidal cells due to a synaptic input. With this approach, it is possible to realistically simulate the current source density (CSD) depth profile inside a cortical patch due to inputs localized into a single cortical layer and the induced voltage measured by two SEEG contacts using a volume conductor model. Based on this approach, we built a framework to connect the activity of a NMM with a volume conductor model and we simulated an example of SEEG signal as a proof of concept. Main results. CSD depends strongly on the distribution of the synaptic inputs onto the different cortical layers and the equivalent current dipole strengths display substantial differences (of up to a factor of four in magnitude in our example). Thus, the inputs coming from different neural populations do not contribute equally to the electrophysiological recordings. A direct consequence of this is that the raw output of NMMs is not a good proxy for electrical recordings. We also show that the simplest CSD model that can accurately reproduce SEEG measurements can be constructed from discrete monopolar sources (one per cortical layer). Significance. Our results highlight the importance of including a physical model in NMMs to represent measurements. We provide a framework connecting microscale neuron models with the neural mass formalism and with physical models of the measurement process that can improve the accuracy of predicted electrophysiological recordings.

Mapping Brain Motor Functions Using Transcranial Magnetic Stimulation with a Volume Conductor Model and Electrophysiological Experiments.

Transcranial magnetic stimulation (TMS) activates brain cells in a noninvasive manner and can be used for mapping brain motor functions. However, the complexity of the brain anatomy prevents the determination of the exact location of the stimulated sites, resulting in the limitation of the spatial resolution of multiple targets. The aim of this study is to map two neighboring muscles in cortical motor areas accurately and quickly. Multiple stimuli were applied to the subject using a TMS stimulator to measure the motor-evoked potentials (MEPs) in the corresponding muscles. For each stimulation condition (coil location and angle), the induced electric field (EF) in the brain was computed using a volume conductor model for an individualized head model of the subject constructed from magnetic resonance images. A post-processing method was implemented to determine a TMS hotspot using EF corresponding to multiple stimuli, considering the amplitude of the measured MEPs. The dependence of the computationally estimated hotspot distribution on two target muscles was evaluated (n = 11). The center of gravity of the first dorsal interosseous cortical representation was lateral to the abductor digiti minimi by a minimum of 2 mm. The localizations were consistent with the putative sites obtained from previous EF-based studies and fMRI studies. The simultaneous cortical mapping of two finger muscles was achieved with only several stimuli, which is one or two orders of magnitude smaller than that in previous studies. Our proposal would be useful in the preoperative mapping of motor or speech areas to plan brain surgery interventions.

Ear-EEG sensitivity modeling for neural sources and ocular artifacts.

The ear-EEG has emerged as a promising candidate for real-world wearable brain monitoring. While experimental studies have validated several applications of ear-EEG, the source-sensor relationship for neural sources from across the brain surface has not yet been established. In addition, modeling of the ear-EEG sensitivity to sources of artifacts is still missing. Through volume conductor modeling, the sensitivity of various configurations of ear-EEG is established for a range of neural sources, in addition to ocular artifact sources for the blink, vertical saccade, and horizontal saccade eye movements. Results conclusively support the introduction of ear-EEG into conventional EEG paradigms for monitoring neural activity that originates from within the temporal lobes, while also revealing the extent to which ear-EEG can be used for sources further away from these regions. The use of ear-EEG in scenarios prone to ocular artifacts is also supported, through the demonstration of proportional scaling of artifacts and neural signals in various configurations of ear-EEG. The results from this study can be used to support both existing and prospective experimental ear-EEG studies and applications in the context of sensitivity to both neural sources and ocular artifacts.

Design and dimensioning of a test bench for investigating the relationship between critical temperature and axial mechanical stress of GdBaCuO tape conductors

PurposeSuperconductors offer several advantages compared with conventional conductors. However, it is not clear at this stage whether these types of conductors provide the same durability. For this reason, tape conductors under mechanical forces need to be studied in detail. The purpose of this paper is to investigate the relationship between critical temperature and axial mechanical stress of GdBaCuO tape conductors.Design/methodology/approachThe paper investigates the influence of axial mechanical stresses on the critical temperature of superconductors. For these investigations, a multi-physical test rig was developed, which makes it possible to perform these types of investigations. With the presented measurement methodology, the influence of mechanical stresses on the tape conductor can be determined.FindingsThe investigations show a correlation between the critical temperature and the acting mechanical stresses. The analytically presented approach to describe the transition temperature is valid for the investigated samples. In addition, it is determined that the effects are not reversible, and therefore, permanent damage to the tape conductor is observed.Originality/valueThe presented investigations make it possible to create more accurate models of GdBaCuO tape conductors. This enables to extend the superconducting state space, which so far depends on three critical quantities, by the quantity of the axial stress.

Inflection point temperature characteristics of carbon fiber composite core conductors

Carbon fiber composite core conductor is a new construction, which is new overhead transmission times the capacity of the conductor. Transmission line times the capacity of the transformation project has great potential for exploration, but due to the short time put into actual operation, the research is relatively weak, and cannot accurately assess its characteristics, therefor resulting in the further promotion of carbon fiber conductor application is limited. In this paper, based on the geographical characteristics of carbon fiber conductors in actual operation, a set of" inflection point temperature" model for carbon fiber conductors is built, measuring the stall distance L, height difference angle β and initial temperature t0 of carbon fiber composite core conductor. So based on the stall distance L, height difference angle β and initial temperature t0 to calculate the carbon fiber composite core conductors, the theoretical basis at the inflection point temperature, which is for the further study of the arc sag characteristics of the multi-capacity conductor can be made.

GA-CSM based optimized clearances for the reduction of occupational exposure in EHV substation

• Multi-objective GA-CSM based algorithm is proposed, for the first time, to identify the optimal ground clearances of EHV substation conductors for adherence to the ICNIRP guidelines. • CSM models are developed as per the actual layout of the substation and E-fields are computed in view of occupational exposure. • Modified ground clearances are obtained for the existing conductor arrangement and for the best topology among the transposed topologies. • Novel substation layout with reduced inner bay heights is proposed. The magnitude of the electric field (E-field) in a 765 kV substation is reduced by altering the conductor clearances in view of the occupational exposure limits. Multi-objective genetic algorithm (GA) along with the charge simulation method (CSM) is utilized in arriving at the optimal clearances of the substation conductors. An EHV substation is modeled with the dimensions and the clearances as in the actual layout of a substation. The E-field results obtained using the finite-line based modeling and infinite-line based modeling of conductors, are compared in terms of the model accuracy and the computational time. The advantages of using the infinite-line based CSM model in view of the occupational exposure is detailed. With the proposed GA-CSM routine, the maximum value of the E-field in the substation is reduced to 10 kV/m (from the existing value of 13 kV/m). The proposed method is used with the existing topology and the best possible transposed topology to obtain the modified layouts. A novel EHV substation layout with different ground clearances for the inner bays and the outer bays is presented. The GA-CSM routine proposed in this work is applicable to any EHV substation with the multiple conductor arrangements.

Influence of busbar trunking system design on thermal performance operating with non-sinusoidal currents

The selection of busbar trunking systems is crucial for operational safety and reliability in electrical power systems. However, harmonic currents created by semiconductor-based converters reduce the current carrying capacity of busbar trunking systems, especially in electric vehicle charging stations, energy storage systems, microgrids, and data centers. In this case, busbar trunking systems with two neutrals or increased cross-section could be used for operating conditions with harmonic currents. Therefore, this study examines the thermal performance of the busbar trunking systems with different design parameters when loaded with harmonic currents. For this purpose, coupled electromagnetic field and thermal analyses were carried out using the finite element method. As expected, the results show that the maximum temperature in the temperature distributions increases significantly when busbar trunking systems are loaded with non-sinusoidal currents. Furthermore, the analysis studies determined the loading limits of busbar trunking systems within the thermal restriction when operating with non-sinusoidal currents. Accordingly, depending on the conductor’s phase sequences, the busbar trunking system model with one neutral conductor can be loaded with between 20% and 25%, two neutral conductors model can be loaded with between 22% and 39%, and the busbar trunking system model with 25% increased conductor cross-sections can be loaded with between 39% and 44% harmonic current. The results show that in the case of loading with non-sinusoidal currents, especially at a high portion of third harmonic components, choosing a busbar trunking system with a high cross-section area is advantageous compared to using two neutral conductors. This information is crucial to system reliability in electrical power system design. Therefore, it has become necessary to conduct these evaluations according to the equipment used while designing the electrical power system. • The proper selection of BTS is crucial for safety and reliability in power systems. • Magnetic and thermal analyses were carried out with the FEA for different BTS models. • Increasing the conductor cross-sectional area gives lower temperature rises. • These analyses are especially crucial for electric vehicle charging stations.

MODEL OF THERMOMECHANICAL VIBRATIONS OF CURRENT-CARRYING CONDUCTORS

In the operation practice of overhead power transmission lines (OHL), the phenomenon of "galloping" of conductors is well known – vibrations with frequencies of ~ 1 Hz and with amplitudes of the order of the static sag [1, 2]. This phenomenon is observed, as a rule, when the symmetry of the conductor section is violated due to icy deposits, which gives the conductor some aerodynamic efficiency. However, this model does not explain all the observed cases of galloping. In this regard, it is advisable to pay attention to the little-known experience of Academician Abram F. Ioffe, who experimentally discovered the self-excitation of a current-carrying conductor – a stretched string that heats up when connected to an electrical circuit. Solving this issue can significantly expand the understanding of the nature of conductor galloping and open up new ways to fend off this phenomenon, which poses a danger to the stability of the functioning of energy systems. This requires a mathematical model of the OHL conductor describing the interaction of mechanical and thermal processes. The purpose of this work is to construct the simplest version of this model, on the basis of which the condition of self-excitation of thermomechanical self-excitation of real OHL conductors can be justified.

Data-driven sparse identification of galloping model of iced quad bundle conductors

The galloping of iced conductors is a serious threat to the safe operation of power systems. Establishing an accurate galloping model of iced conductors has always been a difficult point in galloping research. Therefore, the sparse identification of nonlinear dynamics (SINDy) algorithm is used to identify the galloping model from noise measurement data. A theoretical model of galloping of iced quad bundle conductors is established. Meanwhile, the algorithm is used to identify the simulated data of the theoretical model. The parameter identification ability of the algorithm under noisy velocity measurement is analyzed. An excellent denoising method was selected for data preprocessing, and then the model identification effect of the algorithm after data preprocessing is studied. Besides, the accuracy of the prediction model based on this algorithm and the support vector regression (SVR) prediction model under different training data lengths are compared. The results show that the model identified by the SINDy algorithm in the noise measurement data after data preprocessing has high accuracy and robustness. Moreover, the amount of data used is small. The model identified by this algorithm plays an important role in the rapid investigation, prediction and early warning of galloping phenomena.

Lumbar trans-spinal direct current stimulation: A modeling-experimental approach to dorsal root ganglia stimulation.

The excitability of spinal motor neurons (MN) can be altered through subthreshold currents, such as transcutaneous spinal direct-current stimulation (tsDCS). Current evidence shows that tsDCS can interfere with ascending somatosensory pathways and lower motor neurons' (LMN) excitability, which points to its therapeutic potential for repairing altered spinal responses. We aim to define the best tsDCS montage for maximizing the electric field (E-field) in the lumbar spinal cord (L-SC) by computer modeling; and to apply this montage to measure the effect on LMN excitability and somatosensory evoked potentials (SSEP). A human volume conductor model was obtained from an available database. The E-field distribution was calculated considering three different electrode settings aiming at maximizing the field at L-SC and right dorsal root ganglia (DRG). The best electrode setting was then selected and applied in a blind crossover pseudo-randomized study including 14 subjects. tsDCS was delivered for 15 min (cathodal vs. sham) over L2 vertebra level (4 mA, 144 mC/cm2), and its effect on F-waves, H-reflex (including homosynaptic depression, HD) and SSEPs was investigated in the lower limbs. All simulated montages showed higher current density and E-field magnitudes between the electrodes (>0.15 V/m), with a major longitudinal component and with rostral-caudal direction. The induced E-field involved the sensory ganglia and was maximum in the right T8-left L2 montage, which was the one selected for the experimental protocol. We disclosed a statistically significant increase of the H-reflex amplitude at 0.1 Hz, after cathodal tsDCS (c-tsDCS) on both sides. No other significant change was observed. Our results can suggest the c-tsDCS applied to the L-SC and DRG can modulate synaptic efficiency increasing lower motor neurons response to Ia fibers excitation. The possible implications of our findings for treating clinical conditions will be addressed in future studies.

Coupling model for time-domain analysis of nonparallel overhead wires and buried conductors in the presence of lossy ground

Buried conductors crossing paths with overhead transmission lines is a common occurrence. Interference caused by overhead lines has been found capable of affecting the safe, sustainable operation of the buried conductors. Such occurrences introduce an electromagnetic problem of a nonparallel structure with conductors present in both air and ground half-spaces. Electromagnetic transient (EMT) simulations of such structures are vital in predicting the behaviour of modern power networks. This paper develops a novel EMT compatible time-domain model for nonparallel overhead wires and conductors that are buried in a frequency-dependent lossy (finitely-conducting) ground. Analytical expressions are derived for the per-unit-length (PUL) impedance and admittance matrices based on thin-wire electromagnetic scattering theory. The closed-form formulations derived in this work can be easily incorporated in an EMT simulator to calculate the coupling effect between nonparallel overhead lines and buried conductors. The validity of the proposed approach is examined for various values of the ground conductivity, the radius of the buried conductor, the crossing angle, and burial depth of the conductor by comparing with results with those obtained using a full-wave approach. A case study on the induced voltage in buried conductors due to typical lightning transients in overhead lines has also been performed. • A novel closed-form formulation has been obtained for the mutual coupling of a nonparallel overhead and buried conductors. • Results obtained using the proposed model has been compared with those calculated using a commercial full-wave solver. • Case studies on the induced voltage in buried conductors due to typical lightning and switching transients in overhead lines have also been performed. • Results indicate that hazardous voltages might be induced in buried conductors at such occurrences.

Numerical Investigation on the Dynamic Response and Fatigue Analysis of the Tension Insulator String Under Stochastic Wind

The tension insulator string is an important component for transferring the load of the conductor to the transmission tower. The damage of tension insulator strings may dramatically affect the operation safety of the grid power. In this paper, the dynamic response and fatigue life of the tension insulator strings under stochastic wind were systematically studied. Firstly, finite element models of conductors and the tension insulator string upon the actual transmission lines were established. The effects of height difference ratios on the dynamic tension of conductors and the dynamic response of tension insulator strings under a 10 m/s stochastic wind were investigated, respectively. Secondly, a simplified calculation method of stress time history is proposed to simplify the fatigue life analysis for tension insulator strings. Finally, based on the Rayleigh distribution, wind farms with the annual mean wind speed of 7 m/s were established to evaluate the fatigue life of tension insulator strings. The stress results revealed the at-risk parts in tension insulator strings and their failure modes. The fatigue life results showed 17.1 and 33.4 years for the GD (Guan Dian)-fittings and the upper U-shackles, respectively. This study can provide a useful guideline for optimization and safety evaluation of fittings.

Abnormal Seebeck Effect in Vertically Stacked 2D/2D PtSe2 /PtSe2 Homostructure.

When a thermoelectric (TE) material is deposited with a secondary TE material, the total Seebeck coefficient of the stacked layer is generally represented by a parallel conductor model. Accordingly, when TE material layers of the same thickness are stacked vertically, the total Seebeck coefficient in the transverse direction may change in a single layer. Here, an abnormal Seebeck effect in a stacked two-dimensional (2D) PtSe2 /PtSe2 homostructure film, i.e., an extra in-plane Seebeck voltage is produced by wet-transfer stacking at the interface between the PtSe2 layers under a transverse temperature gradient is reported. This abnormal Seebeck effect is referred to as the interfacial Seebeck effect in stacked PtSe2 /PtSe2 homostructures. This effect is attributed to the carrier-interface interaction, and has independent characteristics in relation to carrier concentration. It is confirmed that the in-plane Seebeck coefficient increases as the number of stacked PtSe2 layers increase and observed a high Seebeck coefficient exceeding ≈188 µV K-1 at 300 K in a four-layer-stacked PtSe2 /PtSe2 homostructure.

Ideal Conductor Model: An Analytical Finite-Size Correction for Nonequilibrium Molecular Dynamics Simulations of Ion Transport through Nanoporous Membranes.

Modulating ion transport through nanoporous membranes is critical to many important chemical and biological separation processes. The corresponding transport timescales, however, are often too long to capture accurately using conventional molecular dynamics (MD). Recently, path sampling techniques, such as forward-flux sampling (FFS), have emerged as attractive alternatives for efficiently and accurately estimating arbitrarily long ionic passage times. Here, we use non-equilibrium MD and FFS to explore how the kinetics and mechanisms of pressure-driven chloride transport through a nanoporous graphitic membrane are affected by its lateral dimensions. We not only find ionic passage times and free energy barriers to decrease dramatically upon increasing the membrane surface area but also observe an abrupt and discontinuous change in the locus of the transition state. These strong finite size effects arise due to the cumulative effect of the periodic images of the leading ion entering the pore on the distribution of the induced excess charge at the membrane surface in the feed. By assuming that the feed is an ideal conductor, we analytically derive a finite size correction term that can be computed from the information obtained from a single simulation and successfully use it to obtain corrected free energy profiles with no dependence on the system size. We then estimate ionic passage times in the thermodynamic limit by assuming an Eyring-type dependence of rates on barriers with a size-independent prefactor. This approach constitutes a universal framework for removing finite size artifacts in molecular simulations of ion transport through nanoporous membranes and biological channel proteins.

An Alternative in H-Formulation to the Critical Current Model of HTS Conductors

A new concept of H-formulation is introduced to reformulate the self-consistent static current model which has been devised to evaluate the critical current of high-temperature superconducting conductors. On the certain collection of known ideas, the attempt is carried out playing to its strength of the vectorial field quantity as directly obtained from the discretized elements. Equipped with the free boundary method, the formulation is implemented not only for efficient modeling by reducing the air region, but also by enabling the background magnetic field to be an explicit term. To prove such an efficacy, a practical case is brought for benchmark test. Then, the result is discussed, in comparison with the previous method, supporting the idea as a potential measure to improve the numerical model of high-temperature superconductors.

Identifying aspects of complex and technological systems in the mental models of students who constructed computational models of electric circuits

AbstractElectricity, especially the flow of current, is a challenging topic for students of all ages. This study conceptualizes students' explanation of electric current as a cluster of knowledge elements. These clusters, in turn, represent students' mental models of electric circuits. Thus, this study aims to identify and characterize students' mental models of electric circuits and to determine, through these mental models, how the students' perception of electric circuits changed as they constructed and explored micro‐level computational models. Using clustering methods, we identified five mental models, ranging between a naive technology perspective model and a more advanced complex systems perspective model. We employed a quasi‐experimental, pretest‐intervention‐posttest‐comparison‐group design, comparing the mental model development of 33 students who constructed models of electric conductors using the Much.Matter.in.Motion (MMM) modeling platform, with that of 23 students who learned in a normative curriculum. Both groups completed identical pre‐ and posttest questionnaires, and three students from the experimental group were interviewed before and after the intervention. As expected, we found that students who learned by constructing computational models with the MMM platform exhibited greater shifts in the sophistication of their mental models compared with students who experienced the normative teaching approach.

Mechanical Analysis of Full-Scale Nb3Sn CICC Designs for Tokamaks

Several designs of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn Cable-In-Conduit Conductors (CICCs) have been proposed so far for high-performance tokamak magnets. The Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn strands composing the conductors are subjected to mechanical stresses of electromagnetic (EM) and thermal origin, inducing local deformations and affecting the strands critical current carrying capability. In the last ten years a numerical tool based on a finite element (FE) code has been developed to simulate the mechanical behavior of the CICCs subjected to operating loads. The main goal of this tool is to predict the electro-mechanical performance of the conductor in operation as a function of the design parameters such as the void fraction, the twist pitches and the conductor shape. In this work, a detailed model of a full-cable ITER TF CICC is presented. This model proves useful for a deeper understanding of the mechanical phenomena occurring among the sub-cables during the conductor operation. Moreover, the numerical modelling of different conductors from the ITER, DTT and JT60 projects is also presented to highlight the versatility of the code.

Building a surrogate model of a perfect electric conductor using polynomial chaos expansion and the characteristic mode analysis

A surrogate model for a perfect electric conductor plate is built by using the polynomial chaos expansion method. The plate is excited via four capacitive coupling elements for which the locations are determined by the analysis of the current distribution for each mode provided by the characteristic mode analysis. A numerical model based on the method of moments is then created to generate a database needed to build the surrogate model. Radiation patterns calculated by the surrogate model are compared with those given by the numerical model. The results show that the surrogate model can mimic the numerical model and it can be used to replace complex numerical models to save computation time and to alleviate the burden on the computation resources. Then, a sensitivity analysis is conducted to exhibit the effect of the parameter deviations on the overall antenna performance and to reveal the influential input parameters. The results of sensitivity analysis are used to reduce the complexity of the overall structure.

基于最速降线的T型槽开沟装置导种管设计与试验

The disorder flow of seeds caused by the collision in the seed-guiding tube is one of the important reasons for the reduction of seeding uniformity. For this problem, a seed-guiding tube with brachistochrone considering the influence of friction was presented in this paper. By analyzing kinetics and rotating the equation coordinate system, brachistochrone under the condition of friction was obtained and applied to the design of the structural parameters of the grain conductor of T-groove furrowing device, and a discrete element model of the grain conductor and wheat was established, thus single-factor simulation analysis and quadratic regression orthogonal rotation combination simulation tests were conducted to explore the optimal combination of parameters. The test results showed that the seed-guiding tube had a brachistochrone radius of 14.708 mm, a linear length of 500 mm and a working speed of 4 km/h, and the seed spacing offset dispersion degree and the seed lateral offset dispersion degree were 12.26 and 8.53 respectively, which had a high seeding uniformity. The results of the bench validation test showed that the coefficients of variation of the two test evaluation indexes between the bench test results and the virtual simulation results were 10.20% and 8.62% respectively, therefore the simulation results could be used for the optimization of the seed guide tube.