Hasil untuk "Electricity and magnetism"

Jiong CHEN, Wenqing WU, Hao LI et al.

Regarding the volatility and uncertainties in the operation of independent microgrid with photovoltaic energy storage, a control strategy based on sliding mode is proposed to enhance the robustness against various disturbances and improve the system dynamic performance. In order to effectively reduce the adverse effect of external solar irradiation, a non-singular fast terminal sliding mode control (NFTSMC) based on front DC/DC converter is proposed, in which incremental conductance method (InC) is implemented , to boost the maximum power point tracking (MPPT) performance by means of adjusting the photovoltaic output voltage tracking reference voltage. In order to alleviate the adverse effect of load change on the system performance, a control scheme based on sliding mode control of full bridge inverter is proposed to achieve low steady state error and rapid dynamic response. Furthermore, in order to maintain the voltage stability of the DC bus, the traditional dual-circuit PI control scheme is used to realize the bidirectional DC/DC converter to ensure the power balance of the system. Finally, simulation tests are carried out in Matlab/simulink environment to verify the effectiveness of the control strategy.

Weichuan Zhao, Gijs Willem Lagerweij, Mohamad Ghaffarian Niasar

ABSTRACT As power‐electronic (PE)‐based systems become increasingly common in the electric power grid, the insulation systems used in medium‐ and high‐voltage (HV) applications will be exposed to high‐frequency (HF) electric fields. Therefore, the insulation materials must be characterised using HF waveforms. However, generating these waveforms presents a significant challenge due to the large reactive power associated with the dv/dt. This paper proposes a resonant test system with a ferrite‐based transformer for HF insulation testing. The resonant circuit is formed by the transformer's leakage inductance and the insulation sample capacitance, with an adjustable frequency tuning capacitor. The system can be driven with an inverter or linear power amplifier. Increasing the test voltage level while maintaining the same test frequency presents several challenges: transformer core grounding, high resonant current and implications for bobbin and insulation design. This paper investigates these challenges and proposes an oil‐insulated resonant transformer, capable of extending the test voltage to 23 kVpk for HF insulation tests at around 40 kHz. High‐frequency breakdown tests are performed on enamelled copper wire in various insulation media using the prototype resonant test system, highlighting the importance of the dielectric's thermal performance.

Yunpeng Liu, Guanyu Chen, Fuseng Xu et al.

Abstract This research introduces an equivalent circuit model and a computational method to address complex mechanical motion issues through electromechanical analogies. The study initially refines core vibration characteristics using single‐ and multi‐degree‐of‐freedom models, subsequently establishing equivalent circuit models for these various degrees of freedom. However, employing high degree‐of‐freedom models for detailed modelling of the core proves overly cumbersome. The research advocates for a distributed equivalent circuit model to more accurately represent the core's layered structure, thus facilitating enhanced core modelling. Moreover, the study formulates a mechanical wave transmission equation pertinent to the vibration of the iron core, which constitutes the foundation of the distributed mechanical vibration model. This model comprehensively assesses the impact of three critical factors on core vibration: the non‐linearity of winding resistance, the electromechanical coupling coefficient, and the dynamic stiffness of the core. A case study elucidates the distinct influences of each factor on vibration characteristics. Furthermore, this study derives vibration calculations from a 60‐day overload ageing test conducted on a 10 kV transformer under 135°C overload conditions. The methodology involves integrating measured compression force values and the calculated dynamic stiffness of the core into an equivalent circuit model. Subsequent analysis compares the results from the equivalent circuit model with experimental measurements. These comparisons indicate an agreement between the calculated and measured values in the time–frequency domain, thereby confirming the accuracy of the equivalent circuit model calculations.

Xin TIAN, Linyu WANG, Xingpei JI et al.

After the modern infrastructure system policy was put forward, new requirements were put forward for the construction of transportation, water conservancy, energy, and new infrastructure represented by information and communications. Starting from the effectiveness of infrastructure, various industries have proposed optimization directions for layout, structure, function, and system integration. This article starts from the study of the functional role of the modern infrastructure system, analyzes the important role of the power grid infrastructure in the modern infrastructure system, and uses Pearson's correlation coefficient to study the relationship between the power grid infrastructure line length and transformer capacity scale and the electricity consumption of the whole society. The article also forecasts the length of transmission lines and transformer capacity scale in the eastern, central, western, northeastern, and other regions in 2025 and 2035. On this basis, the layout, structure, and function of the power grid infrastructure within the framework of the modern infrastructure system are analyzed, and the logic of system integration optimization is given. In addition, the requirements for power grid layout structure function and system integration optimization in building a modern infrastructure system are put forward, providing a reference for the investment and construction of power grid infrastructure.

Pallavi Kalikotay, Snigdha Ghosh, Nilanjan Chaudhuri et al.

We evaluate the electrical conductivity and shear viscosity of a interacting pion gas in a thermo-magnetic medium using the kinetic theory. The collision term of the relativistic Boltzmann transport equation in presence of background magnetic field is solved using the relaxation time approximation. The medium modified relaxation time is obtained from the corresponding in-medium $ππ\rightarrow ππ$ scattering cross-section calculated using the thermo-magnetic $ρ$ propagator. It is observed that the average relaxation time shows a $1/T^4$ variation with temperature for a fixed value of magnetic field. The relaxation time shows a mild oscillatory variation with respect to the magnetic field. It is also observed that the medium dependent scattering cross-section causes a considerable amount of influence on the electrical conductivity and shear viscosity compared to its vacuum counterpart.

Viviane Pierrard, Maximilien Péters de Bonhome, Jasper Halekas et al.

In the present work, the kinetic exospheric model of the solar wind is improved by considering regularized Kappa distributions that have no diverging moments through consideration of a cut-off at relativistic velocities. The model becomes valid even for kappa indices lower than 2, which is important since low values of kappa are observed in the fast solar wind. The exospheric model shows that the electric potential accelerates the wind to supersonic velocities. The presence of suprathermal Strahl electrons at the exobase can further increase the velocity to higher values, leading to profiles comparable to the observations in the fast and slow wind at all radial distances. The kappa index is not the only parameter that influences the acceleration of the wind: the difference in the altitude of the exobase also makes a significant difference between the fast and slow wind. The exobase is located at lower altitudes in the coronal holes where the density is smaller than in the other regions of the corona, allowing the wind originating from the holes to be accelerated to higher velocities. The new observations of Parker Solar Probe are used to constrain the model. The observations at low radial distances show suprathermal electrons already well present in the Strahl in the antisunward direction and a deficit in the sunward direction, confirming the exospheric feature of almost no incoming particles. For proton distributions, we observe that the proton tail parallel to the magnetic field is already present at 17.2 Rs.

Jean-Marcel Rax, Renaud Gueroult, Nathaniel J. Fisch

Very large DC and AC electric fields cannot be sustained between conducting electrodes because of volume gas breakdown and/or surface field emission. However, very large potential fields are now routinely generated in plasma structures such as laser generated wake in unmagnetized plasmas. In magnetized plasmas, large DC fields can also be sustained and controlled perpendicular to the magnetic field, but the metallic end plates limiting the plasma, terminating the magnetic field lines and usually providing the voltage drop feed between the field lines, impose severe restrictions on the maximum field. However, it is shown that very large radial DC voltage drops can be sustained by injecting waves of predetermined frequencies and wave vectors, traveling along the azimuthal direction of an axially magnetized plasma cylinder, or by injecting fast neutral particles beams along this azimuthal direction. The large conductivity along the magnetic field lines and the small conductivity between the field lines then distribute this voltage drop. The global power balance and control parameters of wave and beam generated large DC electric fields in magnetized plasmas are identified, described and analyzed.

Jie Wu

Abstract A low‐cost phased array antenna, consisting of waveguide radiators, dielectric phase shifters and a cooperated feeding network, is proposed and experimentally validated in this paper. The required progressive phases are obtained by controlling the loading depths of dielectric laminas, which are axially inserted into the rectangular channels. The phase difference among channels is determined by the lamina length, the loading depth and the dielectric constant. Theoretically arbitrary phases can be achieved with these design freedoms. A validation prototype of a 1 × 4 array antenna operating around 10 GHz with an element spacing of 0.735λ0 demonstrates a continuous beam steering range of ±23°, which is consistent with theoretical predictions.

Lang Liu, Sang Pyo Kim

The Einstein-Maxwell theory has black hole solutions with electric and magnetic charges. In the standard model for particle physics, dyons with electric and magnetic charges would have been formed in the early universe. We derive the equations of motion of black hole binaries with electric and magnetic charges and explore some features of static orbits. We calculate the total emission rates of energy and angular momentum due to gravitational and electromagnetic radiations from dyonic binary black holes in different cases. It is shown that the emission rates of energy and angular momentum due to gravitational and electromagnetic radiations have the same dependence on the conic angle for different orbits. Moreover, we obtain the evolutions of orbits and find that a circular orbit remains circular while an elliptic orbit becomes quasi-circular due to electromagnetic and gravitational radiations. Our results provide rich information about black hole binaries with electric and magnetic charges and can be used to test black holes with magnetic charges.

Xin Chen, Jiaqi Wang, Chong Zhang et al.

Abstract Boron nitride (BN) has attracted increasing attention as a filler using in insulating materials. In this work, by using an equal amount of BN to replace alumina tri‐hydrate (ATH), various SR/BN/ATH composites were prepared, and for comparison, vinyl tri‐methoxysilane (VTMS) was added to prepare SR/BN/ATH‐VTMS composites. With the increasing BN content, Shore A hardness, breakdown strength and thermal conductivity of the silicone rubber (SR) composites increased despite the tensile strength slightly reduced. By replacing all the ATH with BN, the SR composite showed a ∼47% increase in breakdown strength, reaching 33.8 kV mm−1. The lower dielectric constant and dielectric loss were found for the SR composites with higher BN content, while the decreased dielectric loss and increased dielectric constant were achieved by the introduction of VTMS. Owing to the improved filler‐rubber interfacial interactions by adding VTMS, with the same BN content, all the SR/BN/ATH‐VTMS composites exhibited better property than the SR/BN/ATH composites. The best thermal conductivity of the SR composite reached 0.448 Wm−1 K−1, ∼156% higher than that of the ATH filled SR composite.

Sang Gi Hong, Hakjune Lee, Hoesung Yang et al.

In this letter, we show the experimental results of microwave attenuation characteristics for representative communication frequencies (UHF, public safety long-term evolution [PSLTE], LoRa, Wi-Fi, and LTE) in a compartment fire. We used kerosene, lumber, and urethane foam as fuels, which can be easily found in homes, and measured the signal intensity with three antenna heights to investigate the effect of the flame and smoke. In the compartment environment, the ionized particles were the dominant attenuation factor of the signals. Furthermore, measurements revealed that the attenuation depends on frequencies and fuel types. In particular, large attenuation was observed at particular frequencies when burning lumber and urethane foam.

Alexander V. Zakharov, Eugene V. Rosenfeld

Dust particles on a nonconductive surface are known to acquire electric charge and detach from the surface under plasma conditions and/or when affected by ultraviolet radiation. Similar phenomena occur as a result of electrostatic surface cleaning (shedding) as well as in nature, e.g., when observing levitation of dust particles above the lunar surface. A detachment of dust particles from the surface should occur when the electrostatic forces of their repulsion <i>F_c</i> exceed the sum of the gravitation <i>F_g</i> forces and the adhesive van der Waals <i>F_vdW</i> forces acting on the particle on a nonconducting surface. However, a paradoxical situation usually arises: the three primary forces of different nature <i>F_c, F_g,</i> and <i>F_vdW</i>, acting on a speck of dust with a characteristic size of the order of hundreds or thousands of nanometers, are completely incomparable in magnitude, herewith <i>F_c</i> << <i>F_g << F_vdW.</i> In the last decade, numerous attempts have been made to explain how a particle on a nonconducting surface can acquire a charge sufficient for the electrostatic forces that arise to approach the adhesive forces’ values. However, despite some successes, many questions remain unanswered. This article presents a brief analysis of the charge appearance process on a solitary dust speck and a speck lying on the surface. To explain the detachment of dust particles from the surface caused by electrostatic forces and the accumulation of a charge on those particles sufficient for levitation, one should take into account the charge density fluctuations on the surface.

Yichao Zhao, Yi Su

Abstract The micro‐Doppler (m‐D) effect depends on the rotation of rotor blades in addition to the translation of the platform. Thus it is a characteristic for identifying small unmanned aerial vehicles (UAVs). However, compared with the Doppler signal induced by the translation of the platform, the m‐D signal is weak. In this article, a highly localised data‐association method, intrinsic synchrosqueezing analysis (ISA), is proposed for estimating m‐D characteristics from the returned signal of small UAVs with a dual‐channel radar. Employing synchrosqueezing transform on intrinsic mode functions derived from noise‐assisted multivariate empirical mode decomposition, the proposed ISA method separates the Doppler signal and enables denoising and sharpening time‐frequency representation of the m‐D signal. Simulation results confirm the theoretical analysis, showing the feasibility of estimating m‐D features in a noisy environment. Applications on field data illustrate brighter prospects for identifying small UAVs.

Xin CHEN, Ying-yi FU, Bin YUE et al.

Solid-state nuclear magnetic resonance (NMR) is an important technique to study the acidity and basicity of solid catalysts. Here we review some research works carried out in our laboratory, including studies on the acidity of metal oxides under different water contents, the acidity and basicity characterization of metal oxides by using acidic and basic probe molecules simultaneously. The investigations extend solid-state NMR technique in qualitative and quantitative studies on the acidity and basicity of solid catalysts.

Marc Barbar, Dharik Mallapragada, Meia Alsup et al.

India is expected to witness rapid growth in electricity use over the next two decades. Here, we introduce a custom regression model to project electricity consumption in India over the coming decades, which includes a bottom-up estimate of electricity consumption for two major growth drivers, air conditioning, and vehicle electrification. The model projections are available at a customizable level of spatial aggregation at an hourly temporal resolution, which makes them useful as inputs to long-term electricity infrastructure planning studies. The approach is used to develop electricity consumption data sets spanning various technology adoption and growth scenarios up to the year 2050 in five-year increments. The aim of the data is to provide a range of scenarios for India's demand growth given new technology adoption. With long-term hourly demand projections serving as an essential input for electricity infrastructure modeling, this data publication enables further work on energy efficiency, generation, and transmission expansion planning for a fast-growing and increasingly important region from a global climate mitigation perspective.

Željko Rapljenović, Nikolina Novosel, Damir Dominko et al.

In this work we present frequency-dependent magnetic susceptibility and dc electric transport properties of three different compositions of hexaferrite Ba$_{1-x}$Pb$_{x}$Fe$_{12-y}$Al$_{y}$O$_{19}$. We find a correlation between activation energies of dc electric transport and ac magnetic susceptibility which persists in the whole researched range of aluminium substitution $x=0$ to $3.3$. This result is discussed in the context of charged magnetic domain walls, the pinning of which is determined by charge carriers activated over the transport gap. Our work points toward a general relaxational mechanism in ferrimagnetic semiconductors which directly affects dynamic magnetic properties via electric transport.

Somyot Tantipattarakul, Alun S. Vaughan, Thomas Andritsch

The properties of novel cable insulation systems will rely critically upon the morphology of the material. Here, a blend of high and low-density polyethylene (PE) was processed in order to generate three sets of samples with different morphologies. The influence of thermo-oxidative ageing at 120°C was then considered. The resulting chemical changes included the introduction of unsaturation and oxygen-containing groups and were determined by antioxidant consumption and oxygen permeability. Such chemical defects were found to be concentrated in the fraction of each system that was molten at 120°C and, consequently, served to inhibit recrystallisation following ageing. The resulting spatial distribution of charge trapping sites was therefore strongly dependent on morphology. The electrical conductivity of each system varied non-monotonically with ageing: short times reduced the conductivity; a rapid increase in conductivity over five orders of magnitude occurred beyond a critical ageing threshold. Despite the pronounced structural differences between the morphologically distinct sets of samples, all exhibited comparable conductivity values beyond this threshold, implying that while charge transport is strongly influenced by chemical factors, crystallinity is relatively unimportant. This experimental finding appears at odds with theoretical studies of the electronic states in crystalline and amorphous PE.

Arcadio Perilla, Jose Luis Rueda Torres, Jose Luis Rueda Torres et al.

This study presents an investigation of the impact of the quasi-stationary voltage support provided by a voltage source converter (VSC) connected to a single point of a power system. Based on the directional derivative concept, an analytical method is developed to quantify the sensitivities of the AC bus voltage with respect to the VSC reactive power control modes. Based on a real case study, it is shown that the method applies to VSC units that are part of VSC-HVDC systems, which can operate in a point-to-point or multi-terminal configuration. Time-domain simulations are performed to verify the findings from the application of the analytical method on a reduced size power system.

Yanzhen ZHOU, Xianyu ZHA, Jian LAN et al.

In traditional data-driven power system transient stability assessment methods, the impact of noise in the collected data and the information missing problems are rarely considered for the transient stability prediction. To deal with these problems, this paper presents a method for transient stability prediction based on data augmentation and deep residual network (ResNet). Firstly, the original training data is extended with consideration of the noise data and data-missing conditions. Then, the real-time data of the disturbed generator is used as input features. Considering the similarity between high-dimensional time series data and images, the deep residual network, which is an improved algorithm based on convolutional neural networks, is used to build transient stability assessment model. The case studies show that the proposed method can improve the generalization ability of the model, and has better robustness in dealing with noise data or data missing problems.

Fan QIU, Lanlan CHEN, Nan LIN et al.

In order to ensure the information security in smart distribution network, more and more cryptographic algorithms are applied in the communication process. by SM2-based Modbus message security of distribution network was analyzed to find out such defects as its vulnerability to replay attack and tampering attack, and several other description errors. In order to improve this method, the authors in this paper propose a SM9-based protocol of identification algorithm suitable for Modbus TCP (transmission control protocol) message. At first, the process of SM9 digital signature is introduced, and then it is applied to Modbus TCP message communication added with the timestamp mechanism. And the security of the improved protocol is analyzed. Finally, the C language is used to realize the signature scheme, and its efficiency is compared with several other signature schemes. The results show that the improved protocol can not only resist replay attacks and tamper attacks, and ensure the data integrity and source reliability in the process of message communication, but also have a good advantage in running efficiency.