mlsa-iai-msu-lab/ru_sci_bench_zho_cite_reranking huggingface dataset:
An Olefinic 1,2-α-Boryl Migration Enables 1,2-Bis(boronic esters) via Radical-Polar Crossover Reaction

A radical-induced 1,2-α-boryl migration through radical polar crossover reactions has been described. In this work, in situ formed vinyldiboron "ate" complexes from alkenyl Grignard reagent and diborylalkanes react with commercial radical precursors under light initiation. This three-component process enables diborylation of alkene. This protocol features high atom economy, a broad substrate scope as well as good functional group toleration with mild conditions.
Performance analysis of SBAS ephemeris corrections and integrity algorithms in China region

Satellite Based Augmentation Systems (SBASs) improve the positioning accuracy and integrity by broadcasting to the civil aviation community the corrections and integrity parameters.A snapshot algorithm based on the minimum variance estimation is investigated in this study to calculate the satellite clock and orbit corrections.A chi-square test is performed on the remaining errors in the corrected ephemeris to guarantee the integrity.User Differential Range Error (UDRE) and scaling matrix contained in Message Type 28 are derived using the covariance information based on the assumption that one of the reference stations failed.A software package is developed and applied in the real data collected at 26 stations.International GNSS (Global Navigation Satellite System) Service (IGS) precise clock and orbit products are taken as the references to assess the accuracy of corrections.For both Global Positioning System (GPS) and BeiDou Navigation Satellite System (BDS),the range accuracy of 0.10 m can be achieved with the employment of the derived corrections.No obvious performance difference between GPS and BDS is found.UDREs for all visible satellites are generated with the maximum index of 12 and minimum index of 3.The geometric range differences calculated with IGS precise products and broadcast ephemeris are employed to assess the integrity of UDRE.It is found that the UDRE is able to bound the residuals with 99.9% confidence which meet the requirement of aviation users.With ionospheric delay corrected by Global Ionosphere Map (GIM),the positioning accuracy of 0.98 m with GPS corrections and 0.80 m with multi-constellation augmentation can be achieved which indicates a significant improvement of GPS standalone results.
Binary phase hopping based spreading code authentication technique

Civil receivers of Global Navigation Satellite System (GNSS) are vulnerable to spoofing and jamming attacks due to their signal structures.The Spreading Code Authentication (SCA) technique is one of the GNSS message encryption identity authentication techniques.Its robustness and complexity are in between Navigation Message Authentication (NMA) and Navigation Message Encryption (NME)/Spreading Code Encryption (SCE).A commonly used spreading code authentication technique inserts unpredictable chips into the public spreading code.This method changes the signal structure,degrades the correlation of the spreading code,and causes performance loss.This paper proposes a binary phase hopping based spreading code authentication technique,which can achieve identity authentication without changing the existing signal structure.Analysis shows that this method can reduce the performance loss of the original signal and has good compatibility with the existing receiver architecture.
Steady-state power operation region of a modular multilevel converter connecting to an AC grid

The modular multilevel converter (MMC) has become a widely used topology for voltage source converter-based high-voltage direct current transmission projects.To calculate the power operation region of an MMC directly and efficiently,we propose a novel steady-state phasor model of the MMC.The model is expressed as an equivalent capacitance in series with a voltage source,where parameters are independent of alternating current (AC) electrical quantity.Based on the model,we propose an open-loop approach to determine the operation region boundary of MMC by calculating the envelopes of the P-Q curves.The effect of MMC parameters,the circulating current control,and the short-circuit ratio of the AC grid to the power operation region can be determined by the size and position of the power operation region.The proposed approach and analysis results were verified by an MMC/AC simulation model built in PSCAD/EMTDC.
Partial discharge detection and identification at low air pressure in noisy environment

Increasing demand for electric power in more electric aircraft requires a higher operating voltage for the power system that leads to higher electric stress on the insulation system.Operating at high altitudes where the electrical strength of air is weakened exposes the insulation system to even higher levels of electrical stress.As such,the probability of partial discharges (PD),which result in insulation degradation and failure,is higher.The presence of switching circuits in the power distribution system of the more electric aircraft is capable of producing high levels of noise.This noise in combination with the background noise and parasitic impedances will cause high amplitude ringing in the measured partial discharge signal waveform.Here,a method based on the combination of the wavelet and energy techniques is employed to detect PD pulses in a noisy environment under the low air pressure condition.To verify the technique,a laboratory setup consisting of two separate PD sources mounted in low air pressure (33 kPa) chamber is developed where sine and square waveforms are used as the applied voltage.The obtained results demonstrate that the proposed approach offers low computational complexity,high performance in PD phase localization,and robustness in a noisy environment.
Effect of sinusoidal waveform and frequency on space charge characteristics of polyimide

The charge phenomena under sine and half-wave sine voltages within the frequency range of 500 Hz are studied here.Based on the pulsed electro-acoustic method,the traditional circuit design under high-frequency voltages is first analysed.It is found that the selection of a 186 pF protection capacitor and a 333 kΩ protection resistor can ensure that the actual voltage applied to the sample is consistent with the expected input.Based on this design,experimental results show that the polarity of the charge accumulated in the depth of the sample is determined by that of the upper electrode.Comparison results under special voltages with different amplitudes and frequencies indicate that the amount of accumulated charge under sine voltages are larger than those under positive and negative half-wave sine and DC conditions,and the samples under lower-frequency conditions show more charge accumulation.The maximum electric field strengths appear at 90 and 270 degrees of the sine voltage with a frequency of 10 Hz,and their values are 68.55 and 81.82 kV/mm,respectively.Therefore,the charge characteristics are easily affected by the voltage's waveform and frequency parameters.The results obtained here can provide guidance for the application of insulating materials under special voltage environments.
ShuffleNet-based comprehensive diagnosis for insulation and mechanical faults of power equipment

Despite the complicated fault mechanism of power equipment,with the increasing promotion and development of the Ubiquitous Power Internet of Things (UPIoT),the fault information of power equipment can be instantly saved,which makes possible intelligent diagnosis via fault samples.This study proposes a new method to implement comprehensive intelligent diagnosis by adopting the ShuffleNet lightweight convolution neural network (SLCNN).Considering the requirements of the UPIoT intelligent terminal,this study constructs six models,which are measured in terms of recognition accuracy,model storage,and calculation cost when applied to insulation and mechanical datasets.Compared with the existing models,the SLCNN outperforms them significantly in terms of recognition accuracy,with an accuracy of 95.77% and 99.9% in insulation and mechanical fault diagnoses,respectively.The SLCNN also demonstrates obvious advantages in other performance indicators,all of which contribute to its use in the accurate and reliable fault diagnosis of power equipment in the UPIoT context.Furthermore,through comparing feature maps,it is discovered that the aliasing degree and boundary of insulation defects are not as obvious as those of mechanical faults,which means that insulation fault diagnosis is much more difficult than mechanical fault diagnosis.
Design of adaptive bushing based on field grading materials

Electrical bushings, as important power system components, are critical to the reliability of power systems. The capacitance-graded bushing is a type of high voltage bushing that is most commonly used in current power systems. However, the limitations of and problems with capacitance-graded bushings are exposed when the operating voltage level increases. A new direct current wall bushing with adaptive field grading materials is proposed, based on the core features of the problem that the bushing is intended to solve. The main insulation structure of the proposed DC wall bushing with adaptive field grading materials comprises three parts: a field grading layer, a current limiting layer and an electrode extension layer. The proposed bushing has characteristics that include a simple structure, small size and environmental friendliness, and it also meets the requirements of existing power systems. The proposed bushing also conforms to the intended development direction for future power equipment and will aid in the development of power systems for operation at higher voltages.
Calculation of conductive ions distribution in icicle and melting water conductivity

The flashover problem of ice-covered insulators has seriously affected the safe operation of transmission lines. Numerous researches have shown that the high conductivity water film on the surface is determined by the conductive ions distribution in the icicle which is the key factor affecting the flashover voltage of ice-covered insulators. In our previous work, the conductive ions distribution in the icicle has been obtained through experiments and simulation analysis. In order to calculate the conductivity of the water film, the conductive ion-specific content at different positions in the icicle has been calculated mathematically. In addition, based on the simulation of icicle melting process, the icicle melting process is analysed, and the melting water conductivity of the icicle is calculated. Moreover, melting ice test is carried out in artificial climate chamber to verify the validity of the calculation method. The calculated results are in good agreement with the test results. The conclusion obtained here would provide theoretical basis for establishing a flashover model of ice-covered insulators.
Space charge dynamics in epoxy resin under voltage polarity reversal at various temperatures

Epoxy resin has been used to cast the core of the dry-type high voltage direct current bushings and can accumulate space charge under high electric fields at high temperatures,which is believed to be a potential threat to the safe operation of dry bushings,especially under polarity reversal.In this study,results of a study of the evolution of space charge and electric field distribution in epoxy resin,under polarity reversal at 10 and 20 kV/mm,and at temperatures between 40 and 100°C,are presented.The results show that the space charge dynamics in epoxy resin during the test were different at various temperatures.At temperatures no more than 60°C,space charge accumulation within the samples was not obvious.Instead,a low-frequency dielectric relaxation process maybe occurs during the polarity reversal,which made the charge peaks on the electrodes after the reversal were slightly smaller than those before the reversal.At temperatures no less than 80°C,considering that the applied electric field has little effect on the barrier reductions of the traps within the samples,the space charge dynamics were mainly governed by a thermally activated process,and the depths of the deepest occupied traps were obtain by analysing the transient processes.
Ionization waves in nanosecond pulsed atmospheric pressure plasma jets in argon

Typical ionization waves(IWs)are observed during the propagation of nanosecond pulsed atmospheric pressure plasma jets(APPJs)with argon flow, combining both the measurement of the axial electric field(E_z)and the temporal resolved optical imaging. The movement of the luminous APPJ head is recognized as the development of the IW front, accompanied with the propagation of the peak electric field. Especially, the radial distribution of E_z transits from a central peak profile before the IW front arrives to a hollow profile after the pass of the IW front. As for the temporal E_z trend, there is a mode transition from the single-peak feature under a low peak voltage to the double-peak feature under a higher peak voltage, indicating the existence of both primary and secondary IWs. The effect of target conditions on the IWs in APPJs is also explored. With a metal target, no residual electric field is observed before imposing the high-voltage pulses. However, with a dielectric target, the residual surface charges generate a background electric field in the opposite direction to that during IW propagation. In the free APPJ(with no target), on the voltage falling edge, a negative electric field drives the electron flow to compensate the positive ions left over during the forward IW propagation on the voltage rising edge.
Application of multi-source information fusion based on D-S evidence theory in insulation defect identification of DC XLPE cable

During the installation and laying process of cross-linked polyethylene(XLPE)cable, it is difficult to avoid the influence of external harsh environment, which leads to insulation deterioration and failure. The partial discharge and leakage current play an important role in formation mechanism, characteristic law and identification technology of DC XLPE cable defect. However, the defect identification accuracy of single source data is limited. The correlation between partial discharge and leakage current of typical defect is analysed here. Based on the shape characteristic parameters of typical DC partial discharge spectrum and the energy characteristic parameters of leakage current wavelet decomposition node, a weighted Dempster-Shafer(D-S)evidence theory is used to fuse and identify different information sources. The results show that the classification rate of the proposed method can reach 88%, which can effectively identify insulation defects.
Review of the decomposition characteristics of eco-friendly insulation gas

As one of the major concerns of climate change,identifying a proper eco-friendly insulation gas for replacing sulphur hexafluoride (SF6) becomes a prominent research topic in recent years.c-C_4F_8,CF_3I,C_5F_(10)O,C_6F_(12)O and C_4F_7N are some potential alternatives that are proved to have excellent characteristics,including high insulation strengths and low Global Warming Potentials (GWPs).Beyond these key factors,the decomposition products of these alternatives are closely related to the gases' insulation performance,as well as the safety of operators and the compatibility with other materials.In addition,the type and content of decomposition products can be used for fault diagnosis.Therefore,a number of studies were carried out to reveal the decomposition mechanism of these alternative gases,and then to explore the gases' application feasibility and strategy.The recent advances obtained in these studies,including theoretical calculation methods,detection of gas decomposition products,decomposition mechanism are reviewed,and some perspectives for future works are proposed.It is concluded that the phenomenon of solid matter precipitation in c-C_4F_8 and CF_3I gas decomposition cannot be ignored and that more research is needed to reveal the influence of buffer gases,micro-aerobic,micro-water and other impurities on the gas decomposition process.
Review of surface transient charge measurement on solid insulating materials via the Pockels technique

Surface charges accumulated on solid insulating materials in electrical apparatuses and electronic devices could distort the initial electric field and severely damage the insulation performance. Accurate transient surface charge measurement is critical to determine the mechanisms of charge transport and flashover occurrence, and estimate surface insulation strength under high voltage. The measurement technique based on the Pockels electro-optic effect is considered as the only approach for 2-D dynamic charge distribution behaviour so far, and it has good capability to avoid original electric field distortion caused by conventional methods featured by metal probes. This paper reviews recent progress of the noninvasive dynamic surface charge measurement systems on the Pockels technique. We focus especially on typical systems with transmitting and reflecting configurations and the frequently used fast inversion algorithms. It can be inferred that higher spatial-temporal resolution, higher signal-to-noise ratio,and better compatibility for both transparent and opaque materials are the future development trends, which greatly depend on multiple technological breakthroughs at impact-resistant electro-optic crystals, advanced high-speed photography and high-performance inversion algorithms. In addition, the recent studies on transient behaviour of surface discharge, together with the present limitation and future prospects are discussed. It is expected that more ideas will be inspired in transient surface charge measurement by the Pockels technique and other relevant electro-optic methods.
Effect of DC electric field on moisture migration characteristics in oil-pressboard

The moisture content has a great influence on the electric insulation strength of oil-pressboard. Therefore, it is very important to assess the moisture content in power transformers. There is lack of research about the effect of DC electric field on moisture migration. Here, the authors analyse the moisture migration characteristics of oil-pressboard under DC electric field. The DC electric field has a greater influence on the moisture content in the oil. Compared with no DC electric field, the moisture content in oil is reduced by 22.91 mg/L at 50°C, while it is reduced by 17.63 mg/L at 70°C. Under the same moisture content in the oil, the moisture content in the pressboard which affected by the DC electric field is higher than the Oommen curve, the maximum difference is 0.88% at 50°C, and 0.05% at 70°C. This result can provide a reference for the revision of existing moisture assessment methods.
Exploiting buck-boost duality in dual active bridge modular multilevel converters to achieve high DC step ratios

A previously unidentified duality between buck and boost configured dc-ac modular multilevel converters(MMCs)is firstly revealed. Armed with this insight, a new dualactive-bridge(DAB)-MMC is proposed for high-voltage dc(HVDC)-to-medium-voltage dc(MVDC)power conversion that utilizes cascaded buck and boost dc-ac stages to obtain high dc step ratios. Single-phase and three-phase variants are presented. When compared with the conventional DAB-MMC solution for the same dc step ratio, both the single-phase and three-phase topologies offer reduced MVDC side transformer winding current stresses, while the three-phase topology also yields reduced MVDC side MMC submodule current stresses. The former is achieved by having the freedom to design the transformer with a lower turns ratio, and the latter is achieved due to the inherent paralleling of submodules on the MVDC side of the converter. Analysis of the three-phase topology reveals its low-voltage side transformer winding current stresses can be reduced by a factor of 3.27. A generalized mathematical model of the proposed buck-boost DABMMC is derived and used to propose a dynamic controller for both the single-phase and three-phase topologies. Real-time simulations obtained from a real-time digital simulator system that incorporates an FPGA-based controller for the valve firing controls validate the proposed buck-boost DAB-MMC operation and dynamic controls.
Method of GIL partial discharge localization based on natural neighbour interpolation and ECOC-MLP-SVM using optical simulation technology

Partial discharge(PD)is one of the main causes rendering the deterioration of the insulation state in gas-insulated transmission line(GIL). Accurate and timely localization of the PD source is essential to ensure the safe and stable operation of the GIL. At present, optical PD detection technology shows advantages in terms of high sensitivity and strong anti-interference performance. Therefore, an optical PD localization method based on optical simulation fingerprint database is proposed. The introduction of simulation conquers the difficulty of obtaining a PD fingerprint database in field experiments. This method constructs a simulation fingerprint database by performing PD simulation in a GIL simulation model of the same size as the actual GIL. The natural neighbour interpolation algorithm is applied to expand the simulation fingerprint database to cover all locations in the GIL. The two-level localization method proposed is to match the PD fingerprint to be tested with the expanded fingerprint database, which can reduce the amount of calculation while maintaining the localization accuracy. The experimental results show that the average localization error of this method is only 9.7 mm, and the localization time is reduced by about 11 times compared with the normal one-level localization method.
Performance of silicone rubber composites using boron nitride to replace alumina tri-hydrate

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 trimethoxysilane(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.