Aleksandr Novozhilov, Zhanat Issabekov, Timofey Novozhilov
et al.
Electrical energy in urban and industrial power supply networks is mainly transmitted through 6–10-kV cable networks with an isolated neutral, where most lines are made as bunches of cables. Up to 75–90% of electrical faults in these cable networks belong to single-phase ground faults (SGFs), which can cause more severe accidents accompanied by significant economic damage. Widely known simple and directional protections against SGFs are relatively selective and, hence, often incapable of properly responding to SGFs in a network with such lines and detecting a cable with SGFs in the bunch of a damaged line. These disadvantages can be eliminated by using new, simple, and inexpensive, absolutely selective protections capable of detecting a cable with SGFs in a damaged line. We suggest the techniques and devices based on zero-sequence current transformers and ring measuring converters for building up such protection systems. The methods for calculating zero-sequence currents in cables of a bunched cable line, depending on the SGF point and the currents in the responding elements, are developed, as well as a procedure for determining a damaged cable and methods for estimating the responding element thresholds and the length of the protection dead zone.
This paper focuses on the determination of and improvement in the energy efficiency of plasma jets. To achieve this goal, an equivalent electrical model of a discharge reactor was developed, incorporating variable electrical parameters. The evolution of these parameters was determined by a mathematical identification method based on the recursive least squares algorithm (RLSA). The good agreement between the measured currents and those calculated using our electrical circuit, as well as the significant shapes of the estimated parameters, confirmed the accuracy of the parameter estimation method. This allowed us to use these parameters to determine the energy delivered to the reactor and that used during the discharge. This made our reactor controllable at the energy level. Thus, the ratio between these two energies allowed us to calculate the energy efficiency of plasma jets at each discharge instant. We also studied the effect of the applied voltage on efficiency. We found that efficiency was increased from 75% to 90% by increasing the voltage from 6 kV to 8 kV. All the results found in this work were interpreted and compared with the discharge behavior. This proposed model will help us to choose the right operating conditions to reach the maximum efficiency.
Rebekah Hermsmeier, Ana Maria Rey, Timur V. Tscherbul
By leveraging the hyperfine interaction between the rotational and nuclear spin degrees of freedom, we demonstrate extensive magnetic control over the electric dipole moments, electric dipolar interactions, and ac Stark shifts of ground-state alkali-dimer molecules such as KRb$(X^1Σ)$. The control is enabled by narrow avoided crossings and the highly ergodic character of molecular eigenstates at low magnetic fields, offering a general and robust way of continuously tuning the intermolecular electric dipolar interaction for applications in quantum simulation and sensing.
Abstract Antennas using the active frequency selective surface (AFSS) can achieve fast beam‐scanning ability at a low cost. In this study, a switched beam antenna with a high gain and 360° coverage in the horizontal plane is proposed. Twelve columns of AFSS form a cylindrical cavity and are transmissive or reflective to the incident electromagnetic waves under the control of PIN diodes. Benefiting from a coaxial continuous transverse stub array placed at the cavity centre and using 4 units to generate a high gain omnidirectional radiation, the proposed antenna can realise a highly directive switched beam. An antenna prototype is designed, fabricated and measured. Results show that it achieves a |S11| < −10 dB bandwidth of 12.9% and is able to sweep its beam around the azimuth plane with a high gain up to 13.6 dBi at 5.8 GHz working frequency.
Ferrine Gianne G. Reyes, Jason P. Licerio, Aian B. Ontoria
et al.
Nitrides of aluminum (Al) and titanium (Ti) mixtures have long been studied and used as commercial coatings because of their high hardness and high oxidation resistance due to the formation of an alumina layer on the coating surface. To fully understand the contribution of Al and Ti to the properties of the film, a combinatorial deposition approach was employed using half-disk targets. Film growth was carried out using a magnetron sputtering system powered by a 13.56 MHz radio frequency power supply with varying argon (Ar) and nitrogen (N<sub>2</sub>) gas ratios. Depending on the location of the substrate relative to the target, atomic percent gradients of 0.60–0.70 Al and 0.30–0.40 Ti across the substrate surface were obtained from energy dispersive X-ray spectral analysis. X-ray diffraction peaks at 43.59°, 74.71° (face-centered cubic), and 50.60° (wurtzite) confirmed the presence of aluminum titanium nitride (AlTiN) mixtures, with an increasing amount of wurtzite phase at higher Al concentrations. For all samples, cauliflower-like nanograins were obtained and samples of the 80:20 Ar:N<sub>2</sub> gas pressure ratio showed the smallest grain size among the three gas ratio combinations. The 80:20 Ar:N<sub>2</sub> films revealed a relatively high hardness compared to the other gas ratios. All thin films exhibited good adhesion to 304 stainless steel substrates.
Abstract In this work, electrical tree inception and ageing experiments were conducted to investigate the initiation, growth characteristics and structural characteristics of electrical trees of nano‐SiO2 doped epoxy resin at different temperatures. Electrical tree inception and ageing experiments were conducted using power frequency voltage of 15 kV at 20, 40, 60, 80 and 100°C. Electrical breakdown properties of epoxy resin were investigated by applying AC and DC voltages at 20, 40, 80 and 120°C. There are two major observations based on the experimental results. With the increase of temperature, the morphological structure of the electrical trees changes from dendritic to plexiform, the tree inception voltage decreases and the growth rate of the electrical trees increases obviously. Either under DC or AC voltage, the breakdown strength of the nano‐SiO2 doped epoxy resin decreases as the temperature increases. Finally, based on the space charge and the trap level measurement, the mechanism of the electrical tree propagation and breakdown in nano‐SiO2 doped epoxy resin was analysed.
This study numerically examines the pulse radiating capacities of a novel cylindrically slotted cloaked antenna. The performance of the cloaks for the proposed structure is investigated using the scattering cancellation principle. Furthermore, the pulse radiating performance of the proposed antenna is extensively evaluated by employing a figure of merit. The results show that the proposed antenna exhibits a maximum pulse radiating capacity at 67.5° for the theta-polarized angle, while its pulse radiating performance is independent on the phi-polarized angles.
Electrical engineering. Electronics. Nuclear engineering, Electricity and magnetism
We developed a resistance measurement using radio frequency reflection to investigate the electrical transport characteristics under destructive pulsed magnetic fields above 100 T. A homemade flexible printed circuit for a sample stage reduced the noise caused by the induced voltage from the pulsed magnetic fields, improving the accuracy of the measurements of the reflected waves. From the obtained reflectance data, the absolute value of the magnetoresistance was successfully determined by using a phase analysis with admittance charts. These developments enable more accurate and comprehensive measurements of electrical resistance in pulsed magnetic fields.
Abstract Besides a typical high‐density plasma source, electrical explosion of conductors is also indispensable in switches, nanomaterial synthesis, shock‐wave sources, etc. In this paper, an experimental study regarding plasma dynamics of electrical wire explosions (μs‐timescale) is presented, with spatiotemporal resolved diagnostics. Pure Cu/Ni wire and Cu‐Ni alloy wire were used and compared. The alloy wire usually has a higher resistivity, resulting in a higher initial energy deposition (heating) rate. Abel inverse transformation indicated that the plasma radiation focussed on the outer region of the discharge channel for the alloy wire. In addition, the metallic vapour determined by the material properties had a considerable influence on the plasma process and resulting nanomaterials. In particular, both transverse and axial‐layered structures were observed in alloy wire vapour. In addition, for the first time, the expanding arc‐like plasma of explosion products was understood and examined from aspects of material properties and energy relaxation. The later stage of wire explosion resembled the state of regular metal vapour arcs under 1 MPa pressure. Finally, the core factor for the fast energy deposition stage of wire explosion was ascertained. Correlations between pre‐exposition circuit parameters and post‐explosion dynamic effects were found, which is significant for practical applications.
For the problem of medium and high frequency oscillations in flexible HVDC projects, the existing solution is to add a filter in the voltage feedforward path to suppress high frequency oscillations, which, however, increases the risk of medium frequency oscillations. For this reason, a method is proposed to avoid medium-high frequency oscillations by adjusting the control link delay based on the south channel of the Chongqing-Hubei flexible HVDC transmission project. Firstly, a impedance model of MMC converter station is established based on the principle of multi-harmonic linearization, and a comprehensive analysis is made on the influence of control link delay and grid voltage feedforward strategy on the impedance characteristics of MMC converter station and system stability. And then, the feasibility of adjusting the delay of the control link to avoid the medium-high frequency oscillation is discussed, and the method for selecting the time delay of the control link is given. Finally, based on PSCAD/EMTDC electromagnetic transient simulation, it is verified that the proposed method can achieve the suppression of the medium-high frequency oscillations in both the Hubei-side and Chongqing-side systems. Meanwhile, the proposed method has minor effect on the dynamic characteristics of the system.
Electricity, Production of electric energy or power. Powerplants. Central stations
This paper explains a unified approach for teaching the electrical model of power transformers to undergraduate students using magnetic circuits. The commonly used approach for explaining the electrical model of power transformers is a hybrid approach in which magnetic circuits are used to explain the presence of series inductances. However, the presence of shunt inductance and resistance in the model is explained using alternative approaches. In contrary, this paper explains how both series and shunt elements can be described by using magnetic circuits. Moreover, three real-world examples and Matlab/Simulink results are provided to demonstrate how the presented explanations can be used to describe the responses of power transformers in real-world applications.
Experiments dedicated to the measurement of the electric dipole moment of the neutron require outstanding control of the magnetic field uniformity. The neutron electric dipole moment (nEDM) experiment at the Paul Scherrer Institute uses a 199Hg co-magnetometer to precisely monitor magnetic field variations. This co-magnetometer, in the presence of field non-uniformity, is responsible for the largest systematic effect of this measurement. To evaluate and correct that effect, offline measurements of the field non-uniformity were performed during mapping campaigns in 2013, 2014 and 2017. We present the results of these campaigns, and the improvement the correction of this effect brings to the neutron electric dipole moment measurement.
With the worsening of global environmental pollution problems and the increasing need for energy structure adjustment, hydrogen energy has become a research hotspot across the world as a highly clean and renewable energy. Effective usage of hydrogen energy is an efficient way to solve energy crisis and environmental problems. This paper considers the application of wind power hydrogen production equipment in integrated energy system, discusses different control methods of hydrogen production equipment, and proposes an integrated energy system optimization model for electric hydrogen production equipment. Through the mutual conversion between multiple types of energy sources, the demands of electricity, hydrogen and heat load are satisfied simultaneously. From the simulation results the effectiveness of the proposed model is verified, and the important role of wind power hydrogen production equipment is analyzed in reducing system operation cost and improving clean energy consumption. The simulation results also compare the operation of system under different hydrogen load requirements, which indicate that reasonable arrangement of hydrogen load is conducive to further promoting the green and economic operation of the system.
Electricity, Production of electric energy or power. Powerplants. Central stations
The flooded area detection method based on the fusion of optical and Synthetic Aperture Radar (SAR) images is applicable for all weather conditions and times. However, due to the large number of randomly distributed intensive speckle noise in SAR images, the conventional methods of detection often trigger high false alarm rates at flood-stricken zones. Inspired by the Fuzzy C-Means (FCM) clustering method, a hierarchical clustering algorithm (Hierarchical Fuzzy C-Means, H-FCM) is proposed in this paper. This method fuses the SAR image captured after the flood with the optical image captured before the flood. Based on the fused image, this method uses the proposed hierarchical clustering model to obtain the preliminary detection results of the flooded area. Additionally, the algorithm uses the proposed region-growing algorithm to obtain the river location before the flood and uses it as a spatial constraint for the preliminary detection results to further screen out suspected flooded areas and significantly improve detection performance. The experimental data used in this paper include the remote sensing images captured before and after the Gloucester floods in the United Kingdom in 1999, as well as the remote sensing images captured before and after the Nanchang floods in China in 2019. The effectiveness and validity of the H-FCM algorithm are also supported by comparison experiments.
A new air-stable and easy-to-handle 1-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-3-butyl-imidazol-2-ylidene] Pd(pyridine)Br2 (complex 2) was synthesized from the imidazolium halide salts 1-(2,3,4,6-tetra-O-acetyl-β-D-glucopyranosyl)-3-butyl-midazolium bromide (compound 1) by reaction with Pd(OAc)2 in pyridine. Complex 2 contains multiple chiral centers on the sugar ring. The molecular structures of complex 2 were determined with elemental analysis and liquid-state nuclear magnetic resonance (NMR) spectra. 1H and 13C chemical shifts of complex 2 were fully assigned. It was found that the effects of the carbon and proton chemical environment on the sugar ring is more obvious than that on the butyl chain after formation of N-heterocyclic carbene-palladium(II)-pyridine (NHCs-Pd(II)-Py)-metal bond in the presence of multiple weakly coordinated oxygen.