Hasil untuk "Electricity and magnetism"

Qiang Sun, Dengwei Ding, Yanpeng Ge et al.

Abstract During on‐site withstand voltage tests of gas‐insulated switchgears (GIS), once a breakdown occurs, it is hard to locate the breakdown position due to the intricate branch structures and minimal breakdown energy. The existing methods may require the placement of a large number of sensors with unsatisfactory accuracy, which adversely affects the process of inspecting and repairing, as well as the subsequent tests. To address this issue, this paper introduces a novel GIS breakdown location method. This method is predicated on the natural frequency of the transient voltage caused by the breakdown. The relationship between the breakdown position and the natural frequency is first derived, which is referred to as the location equation. Then, the natural frequency characteristics are discussed from both mathematical and energy perspectives. Based on these characteristics, the location method is proposed that utilises the location equation and the frequencies at two measurement points. The results of the laboratory experiments demonstrate the accuracy of the method and certain advantages over the ultrasonic method. Further, the effectiveness of the method in GIS and gas‐insulated transmission lines (GIL) with complex structures and high voltage levels is also confirmed by simulation cases and field experimental data.

Yukun He, Renjie Tang, Ka'nan Wang et al.

ABSTRACT An LC quadrature voltage‐controlled oscillator (LC‐QVCO) with novel compensated coupling networks to achieve both low supply sensitivity and quadrature phase enhancement is proposed. Designed and fabricated in a standard 0.18‐μm CMOS process, the proposed QVCO improves the supply noise rejection by more than 16.72 dB compared with the conventional LC‐QVCO and achieves quadrature phase error of < 0.86° within the frequency tuning range from 3.32 to 3.52 GHz, whereas occupying a core area of 504 × 400 μm2 and consuming 3.2 mA including the bias circuitry, from a 1.8‐V supply voltage. The phase noise is measured to be −110.64 dBc/Hz at 1 MHz offset and −130.49 dBc/Hz at 10 MHz offset from the high‐band carrier frequency at 3.52 GHz.

Qihe LOU, Rongsheng LI, Jie TAN et al.

Current procedures to calculate transient stability limit of interface tie line power transfer, using either time domain simulation method or direct method based on Lyapunov stability theory, are very time-consuming and complex. In view of this problem, a new method to compute transient stability limit of interface power transmission is proposed based on convolutional neural network. Firstly, the system operation data and the experimental simulation data are combined together to formulate the characteristic attributes of the transmission interface. Then certain key features of the transmission interface are selected as the input layer vector of the neural network. And next the nonlinear mapping relationship between the key features of the system and the transient stability limit of interface power transmission is constructed after multiple rounds of training processes. Finally, the reliability and effectiveness of the proposed calculation method are verified by case studies of IEEE14 bus system.

Chongyang Huang, Yongshuai Yin, Shuxin Liu et al.

Abstract A simulation analysis and an experiment are carried out to investigate how the gap difference between the breaks of a direct current vacuum circuit breakers with multi‐breaks (MB‐DC VCB) caused by the mechanism dispersion of the breaker influences the distribution of TRV among the breaks. An interruption model of MB‐DC VCB, combining the continuous transition model, is established to analyse the rising rate of transient recovery voltage and the dielectric strength recovery speed of the breaks for MB‐DC VCB under different gap difference conditions. Based on the experimental platform of dual break DC vacuum circuit breaker breaking, the correctness of the simulation model is verified on a DC VCB with the double‐breaks interruption experimental platform. Moreover, a model is applied to the non‐synchronous interruption simulation of a DC VCB with three‐breaks. The relationship between the TRVs of the breaks under different gap difference conditions is analysed using the comparative analysis method, obtaining the maximum gap difference at the moment of breaking failure. The results of this study show that large‐gap breaks have a higher TRV than small‐gap breaks (the fracture of the action delay module), with double fractures reaching 1.4 times and triple fractures reaching a maximum of 1.52 times; the ability of small‐gap breaks to withstand TRV is weak, giving rise to re‐breakdown or even interruption failure; as the number of fractures increases, the maximum gap difference also increases. Improving the synchronous interruption ability of the MB‐DC VCB is conducive to improving the interruption performance and interruption success rate of this type of a circuit breaker.

D. Kakulia, K. Tavzarashvili, I. Noselidze et al.

This paper proposes an idea of the use of Dielectric Resonators (DRs) as concentrators of alternating magnetic fields for plasma density control applications. The study involves numerical simulations using the Method of Auxiliary Sources (MAS) to analyze Dielectric Frequency Selective Surfaces (DFSS) composed of periodic dielectric elements. Materials with variable dielectric permittivities, including E-Glass, Plexiglass, Taconic CER-10, and Teflon are considered, and their resonance properties are investigated. Results indicate that DFSSs can create strong magnetic fields at resonance frequencies, which can be utilized for plasma density regulation in processes like thin film deposition. The results demonstrate that materials with lower dielectric permittivity, such as Plexiglass and Teflon, exhibit higher resonance quality factors, while higher permittivity materials like E-Glass and Taconic CER-10 show poorer quality factors. The study emphasizes the potential of DFSSs in enhancing plasma density and improving industrial applications, highlighting the importance of precise geometric configurations and material properties in designing effective dielectric resonators.

Hui WANG, Kerui ZHOU, Zuohui WU et al.

To improve the renewable energy consumption and low-carbon economic benefits of the integrated energy system (IES), this paper proposes a multi-time scale coordinated optimal scheduling model for IES that combines power-to-gas (P2G) and carbon capture system (CCS). Firstly, a coupling model of P2G and CCS based on a tiered carbon trading mechanism is established, and an electric-thermal-cooling IES is constructed using multiple energy conversion and storage devices. Secondly, based on the multi-time scale optimization scheduling strategy, an optimal scheduling model is established respectively for three stages including day-ahead, intra-day rolling, and real-time adjustment with energy purchasing costs, operation and maintenance cost, carbon trading cost, and wind and solar curtailment cost as objective function. Finally, a simulation was conducted using a case study of an industrial park in Sichuan. The results demonstrate that the proposed model effectively improves the low-carbon economic benefits, energy utilization efficiency, and system stability of the IES.

Wen‐Liang Zhou, Shi‐Wei Qu, Mingyao Xia et al.

Abstract The authors proposed an ultrawideband (UWB) dual‐polarised tightly coupled dipole array (TCDA). A split X‐shaped resistive frequency selective surface (FSS) is utilised, which can get more admirable impedance matching. The proposed antenna can achieve active voltage standing wave ratio (VSWR) below 2.9 when scanning up to ±75° and ±60° in the E and H planes from 2 to 18 GHz, respectively. Furthermore, two rectangular patches served as directors are designed, which can provide stronger forward radiation to reduce the loss of resistive FSS for radiation efficiency. As a result, the average radiation efficiency is above 84% and the lowest radiation efficiency is 70%. Moreover, the overall antenna profile is 15 mm (0.1λ at the largest working wavelength). To validate the design method, a 16 × 16 array prototype is fabricated and measured. Good agreement is achieved between the simulations and measurements.

Guido Menichetti, Matteo Calandra, Marco Polini

Motivated by growing interest in atomically-thin van der Waals magnetic materials, we present an {\it ab initio} theoretical study of the dependence of their magnetic properties on the electron/hole density $ρ$ induced via the electrical field effect. By focusing on the case of monolayer ${\rm Cr}_2{\rm Ge}_2{\rm Te}_6$ (a prototypical 2D Ising ferromagnet) and employing a hybrid functional, we first study the dependence of the gap and effective mass on the carrier concentration $ρ$. We then investigate the robustness of magnetism by studying the dependencies of the exchange couplings and magneto-crystalline anisotropy energy (MAE) on $ρ$. In agreement with experimental results, we find that magnetism displays a bipolar electrically-tunable character, which is, however, much more robust for hole ($ρ>0$) rather than electron ($ρ<0$) doping. Indeed, the MAE vanishes for an electron density $ρ\approx - 7.5 \times 10^{13}~{\rm e} \times {\rm cm}^{-2}$, signalling the failure of a localized description based on a Heisenberg-type anisotropic spin Hamiltonian. This is in agreement with the rapid increase of the coupling between fourth-neighbor atoms with increasing electron density.

Bohao Li, Wen-Xuan Qiu, Fengcheng Wu

We present a theoretical study of an interaction-driven quantum phase diagram of twisted bilayer MoTe$_2$ at hole filling factor $ν_h=1$ as a function of twist angle $θ$ and layer potential difference $V_z$, where $V_z$ is generated by an applied out-of-plane electric field. At $V_z=0$, the phase diagram includes quantum anomalous Hall insulators in the intermediate $θ$ regime and topologically trivial multiferroic states with coexisting ferroelectricity and magnetism in both small and large $θ$ regimes. There can be two transitions from the quantum anomalous Hall insulator phase to topologically trivial out-of-plane ferromagnetic phase, and finally to in-plane 120$^\circ$ antiferromagnetic phase as $|V_z|$ increases, or a single transition without the intervening ferromagnetic phase. We show explicitly that the spin vector chirality of various 120$^\circ$ antiferromagnetic states can be electrically switched. We discuss the connection between the experimentally measured Curie-Weiss temperature and the low-temperature magnetic order based on an effective Heisenberg model with magnetic anisotropy.

Lingling HAO, Yongli ZHU, Yongzheng WANG

In order to make full use of the large number of unlabeled samples generated during transformer fault and improve the accuracy of fault diagnosis, an innovative fault diagnosis method is proposed based on the combination of deep contractive autoencoder (DCAE) and kernel semi-supervised extreme learning machines (KSSELM). First, the unlabeled samples are used to train the DCAE network layer by layer and initialize the network parameters. Then the labeled samples are used to fine-tune the network parameters.Finally, the labeled samples and unlabeled samples are used as the inputs of the hybrid network of DCAE-KSSELM to make the fault diagnosis. The experimental results show that the proposed hybrid model has good stability, high fault diagnosis accuracy and strong robustness.

Dong DOU, Yanyu WANG, Xin LI et al.

Due to the gradual increase in the installed capacity proportion of renewable energy in western Inner Mongolia in recent years, large-scale energy storage needs to be deployed to solve the problems caused by the intermittency and fluctuation of renewable energy to the power system. This paper designs and proposes a techno-economically optimal configuration model for energy storage in western Inner Mongolia to achieve the optimal energy storage configuration in this region. Specifically, the site selection and type selection for energy storage in western Inner Mongolia are studied by taking into account both technical and economic performance. Then, with the goal of suppressing wind and photovoltaic (PV) output fluctuation maximally and maximizing the revenue of energy storage projects, including their external value, a techno-economically optimal configuration model for energy storage is constructed and solved with the NSGA-II algorithm. An empirical study of a wind and PV resource aggregating area in western Inner Mongolia shows that when the suppression rate of wind and PV output fluctuation is controlled within 30% and the ratio of PV installed capacity to wind power installed capacity is low, deploying a certain scale of energy storage can obtain remarkable effects in both the technical and economic aspects. Finally, an energy storage configuration scheme based on the site selection, type selection, and empirical analysis results is proposed for western Inner Mongolia.

Jun Shu, Yueping Zhang

Abstract A novel liquid crystal beam‐steerable antenna is presented. It is a conventional liquid crystal microstrip patch antenna with a bending slot in the middle of the H‐plane. Owing to the introduction of the bending slot, this antenna can work at even mode and odd mode within a frequency band. To obtain the resonant frequencies and radiation characteristics of the two modes, the method of characteristic mode analysis is utilised. It indicates that the resonant frequency of even mode is lower than that of odd mode. Therefore, by choosing liquid crystal as its substrate, this antenna can alter its operating modes by varying the permittivity of liquid crystal. Furthermore, beam steering can be realised since the radiation patterns of the two modes are divergent. An antenna prototype at Ka‐band has been designed, fabricated and measured. The measured results show that the maximum radiation direction can scan from −30° to −2° continuously at 26.5 GHz in the H‐plane.

Jon Håvard H. Eriksrød, Kristian G. Kjelgård, Tor S. Lande

Abstract In this paper, we present a new microstrip to waveguide transition design for interfacing printed circuit board (PCB) microstrip transmission lines with 3‐D printed metallised‐plastic waveguide components. Compared with traditional metal waveguides, interfacing with plastic‐based waveguides are challenging due to thermal and mechanical constraints. Despite the development of 3‐D printing technology, the precision of 3‐D printed waveguides is not as good as the machined metal counterparts. This is critical for microwave components and must be considered in the design process. To minimise the effect of non‐ideal waveguide components, a design methodology minimising sensitivity to geometrical variations in the 3‐D printed parts is proposed. By sandwiching the PCB between two waveguide sections and optimising the waveguide impedance transformation geometry, the design shows very low insertion loss. It is mechanically robust, cost effective and simple to manufacture. In full system integration, this transition design eliminates the need for expensive microwave cabling and connectors by directly mounting the waveguide to the microwave transceiver PCB. The proof‐of‐concept transition structure presented in this paper is suitable for microwave applications where low cost and low weight are critical, for example, drone‐based radars for remote sensing and space‐born satellites. The fabricated structure is characterised using two sets of waveguide components manufactured with different 3‐D printing technology and metallisation process': conductive spray painted Fused Deposition Modelling—Polylactic Acid (PLA Painted) and copper electroplated Stereolithography (SLA Plated). Scattering parameters for both types are measured in a short and back‐to‐back configuration, obtaining the reflection coefficient and insertion loss. Measurements indicate good agreement with modelling and measured performance exceeding prior art. The measured operation band of the Copper‐SLA version is 2.9–7.2 GHz with <−10 dB reflection coefficient (S11) and with an insertion loss (S21) of <0.7 dB. With the reduced metallisation and surface quality of the Spray‐PLA model, the band is shifted to 3.0–8.0 GHz with an increased S21 of <1.8 dB. The results demonstrate the importance of adopting new transition structures for 3‐D printed microwave components where the surface roughness, metallisation quality, and mechanical properties are less optimal. By combining the proposed design with 3‐D printed metallised microwave components, very light weight and cost‐effective antenna systems can be implemented. Radiation measurements of a 3‐D printed double ridge horn antenna connected to the waveguide and used as a feed are also presented, where the operation band is measured to 3–10 GHz with a gain of 5–10 dBi.

P. Pelupessy

<p>In this work, it is experimentally shown that the weak oscillating magnetic field (known as the “radiation damping” field) caused by the inductive coupling between the transverse magnetization of nuclei and the radio frequency circuit perturbs remote resonances when homonuclear total correlation mixing is applied. Numerical simulations are used to rationalize this effect.</p>

Vyacheslav Klyukhin

The Compact Muon Solenoid (CMS) detector is a general-purpose experimental setup at the Large Hadron Collider (LHC) at CERN to investigate the production of new particles in the proton-proton collisions at a centre of mass energy 13 TeV. The third run of the data taken is started in April 2022 and will continue till the end of 2025. Then, during a long shutdown time, the existing CMS hadron endcap calorimeter will be replaced with a new high granularity calorimeter (HGCal) designed for the higher LHC luminosity. The HGCal contains the stainless-steel absorber plates with a relative permeability limited by a value of 1.05 from estimation of the electromagnetic forces acting on this slightly magnetic material. To exclude the surprises with possible perturbation of the inner magnetic flux density in the region of the charged particle tracking system, an influence of this additional material onto the quality of the magnetic field inside the inner tracker volume is investigated at this limited value of the permeability of stainless steel . The three-dimensional model of the CMS magnet is used for this purpose. The method of the magnetic field double integrals characterizing the charged particle momentum resolution the first time is applied to the CMS detector and the first time is described in the journal publication. The results obtained with this method are presented in detail and discussed.

L. Sellies, R. L. E. G. Aspers, M. Tessari

<p>Non-hydrogenative para-hydrogen-induced polarization (PHIP) is a fast, efficient and relatively inexpensive approach to enhance nuclear magnetic resonance (NMR) signals of small molecules in solution. The efficiency of this technique depends on the interplay of NMR relaxation and kinetic processes, which, at high concentrations, can be characterized by selective inversion experiments. However, in the case of dilute solutions this approach is clearly not viable. Here, we present alternative PHIP-based NMR experiments to determine hydrogen and hydride relaxation parameters as well as the rate constants for para-hydrogen association with and dissociation from asymmetric PHIP complexes at micromolar concentrations. Access to these parameters is necessary to understand and improve the PHIP enhancements of (dilute) substrates present in, for instance, biofluids and natural extracts.</p>

Kangyong YIN, Wei LIANG, Jibin YANG et al.

In complex environments such as electric power operation scenes, the performance of ultra wideband (UWB) positioning is seriously degraded due to non line of sight (NLOS) scenarios. The integration of UWB and inertial measurement unit (IMU) can improve the positioning accuracy, but there is error accumulation in IMU measurement, which requires accurate UWB measurement correction. Accurate identification and utilization of NLOS conditions is helpful to improve the positioning accuracy. In this paper, a UWB/IMU fusion algorithm based on extended Kalman filter (EKF) is proposed, which uses the distribution of UWB measurements in electric power operation scenes to determine NLOS conditions and mitigate errors, thus effectively improving the positioning accuracy under NLOS conditions. The proposed algorithm has good usability since it does not need prior knowledge of the environment and IMU correction. Theoretical and practical experimental results show that the performance of the proposed algorithm is superior to other baseline systems.

B. Blümich, J. Anders

<p>Change is inherent to time being transient. With the NMR-MOUSE (MObile Universal Surface Explorer) having matured into an established NMR tool for nondestructive testing of materials, this forward-looking retrospective assesses the challenges the NMR-MOUSE faced when deployed outside a protected laboratory and how its performance quality can be maintained and improved when operated under adverse conditions in foreign environments. This work is dedicated to my dear colleague and friend Geoffrey Bodenhausen on the occasion of his crossing an honorable timeline in appreciation of his ever-continuing success of fueling the dynamics of magnetic resonance.</p>

Yong-xiang WANG, Qiang WANG, Jun XU et al.

In this study, solid-state nuclear magnetic resonance (NMR) spectroscopy was used to probe the changes of acidity of H-ZSM-5 zeolite caused by ammonium hexafluorosilicate (AHFS) washing-related changes of aluminium species. It was observed that the four-coordinate framework aluminum species with Brønsted acidity were partially reduced, while the tri-coordinated framework aluminum with Lewis acidity was slightly decreased after the AHFS treatment. However, AHFS washing was also found to induce mild dealumination and a significant reduction of aluminum species with Lewis acidity containing Al-OH group on zeolites, thus resulting in a remarkable change in the overall acidity of the zeolites.

Malte Tschentscher, David Graber, David Graber et al.

Humidity has been considered as one of the main influencing factors that determine the conduction processes and electric strength of gas-insulated systems. Whereas in the past, various studies focused on the change in the partial discharge inception voltages, breakdown strength of homogeneous and inhomogeneous field arrangements, and insulator flashover voltage, recent studies have investigated the changes in ion currents measured through different gas gaps. In the framework of this contribution, a highly precise humidity control circuit has been developed to analyse the significance of humidity in the range from −25 to −5°C frost-point, which is fully applicable to operating gas-insulated devices. Using sulphur hexafluoride (SF(6)) as the insulation gas at 0.45 MPa, Al(2)O(3)-filled epoxy resin insulators, and technically rough electrodes, the humidity was found to significantly influence the intensity of microdischarges at interfaces. Charge generation from microdischarges at the interfaces substantially increased with increasing humidity. For an electric field of 5 kV/mm that were applicable to the dimensioning of gas-insulated devices, humidity strongly influences the charge provision from technically rough interfaces and potentially contributes to the surface-charge accumulation at insulator surfaces. On the other hand, for low-field conduction phenomena, no increase in the ion currents from natural ionisation or electrophoretic conduction was observed. For the investigated range of parameters, humidity is expected to be highly relevant for the design of gas-insulated devices.