Conductor Configurations Research Articles

Innovative hybrid grey wolf-particle swarm optimization for calculating transmission line parameter

Transmission line (TL) parameters, particularly capacitance, are important for ensuring the efficient and reliable operation of power systems. As power networks become increasingly complex, accurately determining TL parameters faces certain challenges, particularly capacitance, which involves overcoming computational challenges due to bundling configurations. The interconnected nature of modern TL and the use of advanced technologies further add to the complexity. Effective estimation requires advanced measurement techniques and sophisticated computational tools. Recently, optimization techniques have become widely used for TL parameter calculations. However, traditional methods struggle with challenges like limited exploration and slow convergence. To address these issues, this research introduces a hybrid algorithm called HGWPSO, which combines the Grey Wolf Optimizer (GWO) with Particle Swarm Optimization (PSO). The main objective is to enhance the exploitation ability of GWO with the exploration capability of PSO, maximizing the strengths of both variants. Initially, to verify the efficiency of HGWPSO, CEC_19 benchmark functions are utilized to evaluate its performance. Secondly, the main focus of this study is to calculate TL parameters such as capacitance considering two, three, and four-bundle conductors using the HGWPSO algorithm and comparing its performance with other optimization techniques. According to the obtained result, the average percentage reduction for HGWPSO is 0.15 % in test case 1, 4.85 % in test case 2, and 2.84 % in test case 3, compared to others. It shows that the HGWPSO has better performance than other methods regarding convergence speed, and ability to locate the global optimum. Finally, experimental analysis confirms the superiority of the HGWPSO in accurately estimating TL capacitance for different bundle conductor configurations, obtaining lower average values, and effectively addressing the characteristic complexities in the TL parameter.

Impact of temperature asymmetry and small fraction of static positive ions on the relaxed states of a relativistic hot pair plasma

Abstract The relaxed state of a magnetized relativistic hot plasma composed of inertial electrons and positrons having different relativistic temperatures and a fraction of static positive ions is studied. From the steady-state solutions of vortex dynamics equations and the relation for current density, a non-force-free triple Beltrami (TB) relaxed state equation is derived. The TB state is characterized by three scale parameters that consequently provide three different self-organized structures. The analysis of the relaxed state shows that for specific values of generalized helicities, the disparity in relativistic temperature and the existence of a small fraction of static positive ions in pair plasma can transform the nature of scale parameters. Moreover, an analytical solution of the TB state for an axisymmetric cylindrical geometry with an internal conductor configuration demonstrates that due to asymmetries of temperature and density of plasma species, diamagnetic structures can transform into paramagnetic ones and vice versa. The present study will improve our understanding of pair plasmas in trap-based plasma confinement experiments and astrophysical environments.

Performance of low-loss demountable joints between CORC® cable-in-conduit-conductors at magnetic fields up to 8 T developed for fusion magnets

High-temperature superconductors (HTS) are promising candidates for use in the high-field magnets needed in particle accelerators and fusion reactors. HTS conductor on round core (CORC®) cables and wires wound from ReBa2Cu3O7-x (REBCO) coated tapes are being developed for use in high-field magnet applications including fusion magnets operating at currents beyond 80 kA, requiring them to be bundled into cable-in-conduit conductor (CICC) configurations. The use of HTS cables enable demountable superconducting fusion magnets that would allow easier access to the fusion machine for maintenance and parts replacement. Such demountable magnets require practical, low-resistance joints, capable of injecting current uniformly into the many REBCO tapes that make up different cable designs. Optimization steps on CORC® cables have resulted in high-current terminations and joints with a joint resistance measured between a pair of 30-tape CORC® cables of 51 nΩ at 76 K and 1.9 nΩ at 4 K. Demountable joints between CICCs consisting of six CORC® cables arranged in flat and round configurations were also tested and compared to joints between low-temperature superconducting (LTS) CICCs consisting of NbTi Rutherford cables. Samples were paired into two configurations (LTS-to-LTS and HTS-to-HTS) with a demountable joint between them that were each tested in series with currents up to 10 000 A in an applied background magnetic field of up to 8 T. The total loop resistance of the HTS-to-HTS sample, including their terminations and joint, was about 4 nΩ at 4 K in self-field with the resistance of the copper pressed joint being less than 1 nΩ. At 8 T, the total loop resistance increased to 6.9 nΩ with the pressed joint contributing 1.4 nΩ. These initial tests prove the feasibility of producing remountable (dry) joints with low resistance between superconducting magnet windings in future compact fusion machines.

An approach of calculating winding pack smeared properties for TF magnets using artificial neural network

Tokamak superconducting TF coils experience severe structural and thermal loads during operation. Hence optimizing the design of the conductor and the coil is crucial, making it inevitable to repeatedly try different conductor and WP configurations, and then perform structural analyses for the magnet. However, due to the fact that the magnet is huge in size, meanwhile the WP constituents are heterogeneous, complex and small in dimension, it is generally unrealistic to perform a global 3D structural analysis on a magnet model with detailed WPs. Smeared WPs with equivalent homogeneous properties are therefore commonly used to build the finite-element model. Usually, the smeared properties of WP are calculated by finite-element analyses, which are time costly and cumbersome. Here the ANN approach is proposed to calculate the WP smeared properties. First, the conductor and WP configurations are summarized, and a universal representative WP model is developed. Then, 4322 training cases are calculated by finite-element analyses with ANSYS. Next, the ANN model is built and the training cases are fed into it, after 298 iterations the ANN achieves convergence with excellent performance. Finally, the effectiveness of the trained ANN is demonstrated. Our results indicate that the ANN approach of calculating the WP smeared properties is reliable and can reduce the calculation time by 5 order of magnitude than the finite-element analysis.

Examination of the Partial Discharge Behaviour Within a Spherical Cavity in Insulation Paper of Transformer

This paper investigates the behaviour of partial discharge (PD) in transformer insulation paper based on the Finite Element Method (FEM). The three-dimensional (3D) FEM model consists of conductor and insulation paper, representing part of a transformer’s high voltage winding. The conductor’s width, height, and length used in this study were 2.4 mm, 11.5 mm, and 16 mm. An insulation paper thickness of 1 mm was modelled around the conductor. An internal cavity with a diameter of 0.5 mm cavity was introduced within the insulation paper. This study introduced two locations of the spherical cavities at the centre and left corner of the insulation paper: Location 1 (L1) and Location 2 (L2). An AC voltage of 33 kV, 50 Hz, was applied to the conductor while the bottom of the insulation paper was grounded. The model was used to study the electric field distribution within the insulation paper and its effect on PD current and charge magnitude. The influence of cavity location on the charge magnitude was also examined. It is found that the electric field distribution is influenced by the conductor configuration as well as the location of the cavity. The electric field in the cavity is the highest at L1 compared to L2. The first PD occurs faster for the cavity with a high electric field. Due to the PD occurrence at the same inception field, the real PD current and charge magnitude is similar at different locations. The apparent PD current and charge magnitude induced at the ground electrode is slightly higher at L1 than at L2.

An Improved Parameter-Free Fault Locator for Untransposed Line With Unsynchronized Terminals

This letter presents a novel parameter-free fault location algorithm for a two-terminal single circuit untransposed line with flat and delta conductor configurations while considering unsynchronized measurements. It improves the existing works by introducing unequal angles of synchronism mismatch in pre-fault and fault conditions. EMTP-RV based simulation results corroborate the validity and accuracy of the developed fault location algorithm. Simulation results are also compared with existing methods to demonstrate improved features of the proposed algorithm. Field test results are also presented to further validate the performance of the proposed algorithm.

ARTIFICIAL NEURAL NETWORK MODELS FOR ESTIMATION OF ELECTRIC FIELD INTENSITY AND MAGNETIC FLUX DENSITY IN THE PROXIMITY OF OVERHEAD TRANSMISSION LINE.

This paper considers the application of artificial neural network (ANN) models for electric field intensity and magnetic flux density estimation in the proximity of overhead transmission lines. Specifically, two distinct ANN models are used to facilitate independent estimation of electric field intensity and magnetic flux density in the proximity of overhead transmission lines. The considered ANN approach is systematically evaluated under different scenarios. An example of an overhead transmission line with horizontal phase conductor configuration is used to enable a direct comparison of the electric field intensity and magnetic flux density estimates generated by the two ANN models to measurement results obtained over the lateral profile. Further investigation of ANN models involves an extensive study whereby 13 different overhead transmission lines of horizontal configurations are used as the basis for comparing measurement results to estimates provided by the ANN models. In this study, the performance analysis of the ANN models was evaluated using coefficient of determination and root mean square error. The obtained results demonstrate that the considered ANN approach can be used to estimate the electric field intensity and magnetic flux density in the proximity of overhead transmission lines.

High hydrogen storage ability of a decorated g-C3N4 monolayer decorated with both Mg and Li: A density functional theory (DFT) study

In this work, the hydrogen storage properties of a g-C3N4 monolayer decorated with both Mg and Li were thoroughly investigated by performing density functional theory (DFT) calculations. Along these lines, the projected densities of states (PDOS) and the Bader Charge analysis showed that both Mg and Li atoms can transfer their electronic charges to the g-C3N4 monolayer. Interestingly, the latter is transformed from a semiconductor material to a metallic conductor configuration, while a local electric field is formed around it. On top of that, the formed local electric field polarized hydrogen molecules and as a result, led to an enhanced hydrogen adsorption ability. Mg atoms have more outmost electrons, and more charges can be transferred to the monolayer, which leads to the creation of a stronger local electric field to adsorb an elevated number of hydrogen molecules than Li atoms. On the other hand, Li atoms are lighter, more active and easier to lose outmost electrons than Mg atoms. By considering these advantages, a g-C3N4 monolayer decorated with one unit of both Mg and Li was investigated, which has the ability to adsorb 10 hydrogen molecules, leading thus to a high hydrogen storage capacity of 10.01 wt %. Our work paves the way for the development of novel material configurations for improved hydrogen storage applications.

Conductor design and performance analysis for CFETR magnet

The design work of the China Fusion Engineering Test Reactor (CFETR) was carried out in the past years. The magnet system is composed of 16 toroidal field (TF) coils, 8 central solenoid (CS) coils, and 7 poloidal field (PF) coils. The maximum magnetic field on the TF coils is 14.4 T. Three grades of cable-in-conduit conductors (CICCs), including high-Jc Nb3Sn strand, ITER-like Nb3Sn strand, and NbTi strand, have been chosen for the TF WP winding in high, medium, and low magnetic fields. High-Jc Nb3Sn strand will also be applied in the CS conductor considering the maximum magnetic field, which is higher than the TF coil. For the PF coil, the ITER-like Nb3Sn strand will be applied in Conductor PF1 and Conductor PF7, and NbTi will be applied in others. In this paper, conductor designs for the CFETR magnet including design criteria, choice of conductor configurations, and conductor performance analysis are presented.

Systematic modeling of electrostatic radiation shields for deep space flight

Astronauts are exposed to a unique radiation environment during space missions. This environment is dominated by high charge and energy (HZE) ions with sources that include solar energetic particles (SEPs), galactic cosmic rays (GCRs), and trapped electrons and protons around planetary bodies with substantial magnetic fields. Traditional shielding strategies aim to reduce astronaut radiation exposure by increasing vehicle mass, but this is ineffective for the extremely penetrating GCRs. Use of electromagnetic fields has been investigated previously, but these studies have been limited to single point designs. The NASA Active Shielding project has instead developed a workflow that includes a fast and accurate particle propagation code (Active Shielding Particle Pusher), which can be used to rapidly evaluate the shielding efficacy of many different permutations of electromagnetic shielding designs. While some validation of the code has been previously done, additional validation is needed to increase user confidence in simulation results involving more complicated electrostatic conductor configurations. In the present study, we evaluated shielding properties of spherical electrode arrays and planar grid structures against 2 MeV or 6 MeV H+ and 22.5 MeV Fe6+ ions using ASPP, SIMION, and COMSOL, and compared these results to laboratory-based measurements. Many numerical experiments were conducted to reproduce experimental ion beam tests that measure the consequential particle reduction rate in a safe zone compared to the initial number of ions. The experimental visualizations were also compared with the present numerical results and found to be in close agreement with each other for all considered voltage combinations applied to electrode structures. This comparison allows us to use numerical models to predict the behavior of complex shielding structures at much larger scales not feasible in a laboratory environment.

The effect of decarburization on the fatigue life of overhead line hardware

Altering the microstructure in order to improve the tensile properties of bow shackles resulted in inconsistency in the fatigue performance. This raises the question whether the inconsistency in fatigue life can be attributed to microstructural changes along the profile of the shackle or to decarburization at the surface. Bow shackles forged from 080M40 (EN8) material were subjected to different heat treatments in order to alter the microstructure. The shackles were subjected to five different fatigue load cases, which represented typical loads experienced at termination points for an overhead power line with a span length of 400 m, with changes in conductor type, configuration, wind, and ice loading. Although the change in microstructure does improve both the tensile and fatigue performance, we found that the depth of the decarburization layer has a greater effect on the high cycle fatigue life of bow shackles than the non-homogeneous microstructure.

Robust REBCO Insert Coil for Upgrade of 25 T Cryogen-Free Superconducting Magnet

The upgrade project of the 25T-CSM to 30 T is on-going at HFLSM, IMR, Tohoku University. The goal is to obtain 30 T in a 32 mm warm bore by replacing the present Bi2223 insert coil with one wound using REBCO. In order to develop a robust REBCO high field insert, we adopt a two-tape bundle conductor with a face-to-back configuration. We confirmed that this conductor configuration mitigates effectively the risk posed by local defects in an R&D coil: a stable operation was achieved with negligible degradation in coil I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> even with a severe local defect on one of the two tapes. Quench protection from possible hotspot in the REBCO insert using an early detection method is made possible by the two-tape bundle configuration and the thick Cu stabilizer. Other R&D coils using such conductor were tested with large hoop stresses up to 460 MPa with no degradation. On the basis of these R&D studies, a robust REBCO insert is designed for the upgrade. The designed REBCO insert has a capability to achieve 35 T with enough I <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> margin if we accept a maximum hoop stress of 500 MPa.

Structural Analysis of Steel Transmission Towers for Large River Crossing of Overhead Transmission Lines

This study aims to investigate the structural behavior of steel transmission towers used for large river crossings. Design standards usually applied to analyze these structures don’t consider situations in which the transmission towers are used in river crossings. In Brazil, due to the fact that it is necessary to cross large areas owing to the rivers’ size, these towers assume great heights. It should be noted that the towers can weigh up to 24,500kN and exceed 300m in height. The current study develops an analysis that surpasses the existing standard methodologies, aiming for a structural optimization compatible with vast crossings and new materials, aiming to resolve this design challenge regarding power transmission lines. To do this, a river crossing spanning 2,300m, situated in the northern region of Brazil, was studied based on the use of three different conductor configurations, electrically equivalent, commonly used wind design standards, and structural solutions utilizing tubular and angle profiles.

A New TDR-Based Sensing Cable for Improving Performance of Bridge Scour Monitoring

The use of time domain reflectometry (TDR) for real-time monitoring of bridge scour process has gone through several stages of development. The recently-proposed concept of bundled TDR sensing cable, in which two sets of insulated steel strands are twisted around and connected to a central coaxial cable to form a compact sensing cable, is a major change that has several advantages including the bottom-up sensing mechanism. Nevertheless, there is big room for improving its measurement sensitivity and signal to noise ratio (SNR). Changes in waveguide configuration also need to be made to avoid the adverse effect of insulation abrasion observed in field implementation. This study evaluated three new conductor and insulator configurations for constructing the sensing waveguide, including a balanced two-conductor waveguide (Type I), an unbalanced three-conductor waveguide with insulation coating on the middle conductor (Type II) and an unbalanced three-conductor with insulation coating on the two outer conductors (Type III). In all cases, the spacing between the two sets of steel strands (i.e., the waveguide conductors) was especially enlarged by replacing some steel strands with non-conductor wires to increases measurement sensitivity and avoid shorted conditions due to insulation abrasion. Experimental results show that Type III has the best performance on all counts. A new improved TDR sensing cable was hence proposed based on Type III configuration. Its performance was further evaluated by a full-scale experiment to take into consideration the long range of measurement in most field conditions. Detailed discussions on improvements of measurement sensitivity and SNR, limitation of sensing range, and mitigating the adverse effect of insulation abrasion are presented.

DC corona characteristics derived from corona cage tests and simulations

This study presents experimental and simulation studies on DC corona characteristics to investigate the behavior of high voltage direct current transmission (HVDC) lines. Experimental studies are performed using an indoor corona cage and various conductor configurations, which are the scaled models of the prospective HVDC line in Turkey. Following the preliminary tests with single line models of aluminum rods and stranded conductors, DC corona inception voltages (CIVs) of prospective bundled conductor configurations are measured by using a daylight UV corona camera and a high-sensitive micro ammeter. Measurements include three different sub-conductor spacing both for the positive and for the negative DC voltages. Corona currents are measured for the voltages above the CIV levels. Experimental studies are varied by complementary simulations using a FEM based software, COMSOL Multyphysics. Following the development of 3D models of the corona cage and the prospective conductor configurations, electric field distribution along the conductor surfaces are determined. CIV measurements and simulation results are used to compute the corona inception electric field strengths of the aforementioned configurations. Radio interference voltages and audible noise levels of the configurations are finally calculated at a constant test voltage using the empirical formulations and the field simulation results. The results are discussed at the end to guide the design of intended HVDC line in Turkey.

Casimir forces and high- Tc superconductors

We investigate the Casimir forces between high-$T_c$ superconductors as function of the distance and temperature, focusing on optimally-doped YBa$_2$Cu$_3$O$_{6.95}$. We consider formerly studied configurations in normal metals lying in the short-distance (50 nm - 600 nm), and long-distance (600 nm - 10 microns) regimes. The dielectric properties of the material are described in terms of weakly-interacting, short-correlated conducting pairs transported along quasi-2D layers. In the short-range regime, a continuous behavior of the Casimir forces arises, with no significant discontinuity at the transition temperature. This behavior also follows in the equivalent the normal conductor configuration. In the long-range regime, the forces show an abrupt increment at the critical temperature. Simultaneously, the Casimir entropy and the specific heat develop a strong discontinuous behavior, characteristic of the SC-normal phase transition. In every situation, the entropy vanishes at extremely low temperatures.

The Effect of Geometry on the Fatigue Life of Overhead Line Hardware

Bow shackle failures, over the years, raised the question whether these failures are attributed to microstructural changes along the profile of the shackle or due to the geometry of the shackle. Bow shackles forged from 080M40 (EN8) material were subjected to different heat treatments in order to alter the microstructure thereof. The shackles were 3D-scanned prior to fatigue testing, and the data points were imported into engineering simulation software (ANSYS), to build a finite element model of each shackle tested. The shackles were subjected to five different fatigue load cases, which represented typical loads experienced at termination points for an overhead line with a span length of 400 m, with changes in conductor type, configuration, wind and ice loading. The fatigue tests revealed that the improvement in fatigue performance with an increase in hardness was limited to the lower load levels. In addition, the finite element model indicated that the misalignment of the bolt holes results in unequal load distribution between the two legs, with a considerable increase in the bending stress experienced by the leg carrying the higher loading. The influence of the bow shape of the shackle was confirmed by testing straight-leg shackles also manufactured from 080M40 material, which outperformed the fatigue performance of the bow shackles. Furthermore, misalignment of the bolt holes for the straight shackles did not have the same detrimental effect compared to the bow shackle. Although the change in microstructure does influence the fatigue performance, this investigation concludes that the combined influences of the curved leg and misalignment of the bolt holes pose a greater impact on the fatigue performance of bow shackles than microstructure. Furthermore, the fatigue performance of line hardware shackles is significantly improved by changing the geometry of the shackle from a curved leg to a straight leg.

Theoretical Investigation of Current-Sharing Properties of Three-Strand Parallel Conductors Composed of REBa2Cu3O&lt;italic&gt; &lt;sub&gt;y&lt;/sub&gt; &lt;/italic&gt; Superconducting Tapes

For nuclear magnetic resonance superconducting magnets wound with REBa2Cu3O y (REBCO, where RE = rare earth elements such as Y, Gd, Eu, and so on) superconducting tapes, the current capacity of the tapes needs to be enhanced from the viewpoint of magnet protection. Thus, the introduction of the configuration of parallel conductors was proposed. The constituent tapes should be insulated and transposed for low ac loss and uniform current sharing among the tapes. However, when the tapes have different values of critical current, I c, and their n -values, the tapes will not have uniform transport currents. In this paper, the current-sharing properties of three-strand parallel conductors composed of REBCO tapes, which were wound into coils, were theoretically investigated by accounting for the spatial distribution of the magnetic field, i.e., magnetic field and field angular dependences of I c. Here, it was assumed that the I – V characteristics are expressed by the n -value model. Equivalent circuit equations were derived and numerically solved. As a result, it was revealed that at a frequency higher than 0.01 Hz, the current flow is almost uniform even if there is a variation of 10% in I c and the n -value among the tapes. On the other hand, in the case of dc, the current sharing depends on the dispersion of I c and the n -value. In this paper, a simple solution for the control of the contact resistance at the terminals among the strands was proposed.

Direct Current Injection Test Devices on Metal Cylinder: Experiment and Numerical Simulation

In order to study the lightning indirect effects on the metal cylinder, the direct current injection test devices on the metal cylinder were studied in this paper based on experiment and simulation. The return conductor configuration was designed. A giant magneto resistive (GMR) sensor was calibrated to measure the intensity of the magnetic field inside and outside the metal cylinder. The impulse current injection test system similar to coaxial transmission line was established and the injection experiment was carried out. In order to verify the experimental results, a numerical simulation using the CST Microwave Studio was given. The magnetic field intensity inside and outside the metal cylinder is discussed by comparing the experimental and computational results. Moreover, the space distribution of the magnetic field is also simulated. The results show the feasibility of the test devices. The conclusions provide a foundation for further lightning indirect effect test on cylindrical ordnance.

Simulation analysis on return conductor configuration for lightning indirect effect test of metal cylinder

Objectives In order to study the lightning indirect effect of metal cylindrical ordnance, a method for constructing the tester for lightning indirect effect of the metal cylindrical flying object is studied, and a cage type frame similar to coaxial line is designed as the coupling device. Methods Firstly, the current resonance of system is analyzed by observing the current waveform of different terminators. Then, through the electromagnetic simulation software CST, the surface current distribution of the metal cylinder is simulated, and the influences of different load impedance and different return conductor arrangement on the uniformity of surface current distribution are analyzed. Finally, according to the simulation results, the surface current intensity of cylinder and the instantaneous electromagnetic field distribution inside and outside the cylinder are analyzed. Results The simulation results show that the cage type injection device similar to coaxial line can be used for indirect lightning effect test of metal cylinders. Conclusions The simulation results provide a basis for the further test.