mlsa-iai-msu-lab/ru_sci_bench_zho_cite_reranking huggingface dataset:
Surface discharge imaging in presence of deposited space charges in non-uniform DC electric field

An investigation is made of the influence of an accumulated charge sprinkled on the surface of an epoxy resin plate in corona mode on partial discharge inception and its forms as analyzed by optical imaging at DC voltage. The effects of the polarities of both the deposited hetero-and homocharges were investigated. The occurrence of first streamer discharges was detected electrically and observed by optical imaging. The various forms of streamers were acquired by optical imaging and associated with the polarity and intensity of the accumulated surface charges. Surface charge sprinkling on the epoxy specimen surface was quantitatively evaluated by surface charge mapping. In addition, the effect of the subsequent discharges occurring in a heterocharge configuration above the inception voltage was observed. In terms of their directions and lengths, the kinetics of the streamer filaments revealed a strong dependence on both the polarity and the intensity of an accumulated charge. Compared with the reference charge-free surface, the strongest drop in dielectric strength in the interelectrode space with a sprinkled charge was obtained for the heterocharge configuration. The presented results provide a contribution to the assessment of streamer behaviour in the presence of accumulated surface charges, including its polarity and intensity.
Study on the erosion characteristics of copper-carbon electrode pairs by DC air arc

As common electric contact materials, copper-carbon electrode pairs are widely used in the field of electric contact such as in high-speed railways, motor collector rings and grounding brushes. They play a key role in energy transmission in the above-mentioned systems. Arc erosion has become a key issue threatening system safety. In this work, a dedicated arc erosion platform was built to study the polarity effect of copper-carbon electrode pairs. It was found that arc dynamics and electrodes erosion behaviours were significantly different under different polarities, which could be understood from the mechanism of heat transfer, cooling and electron emission of the electrode. Then, when the carbon material was used as an anode, the arc caused carbon transfer: the carbon material sublimated quickly due to electron condensation and thermal conduction and quickly condensed on the low-temperature metal electrode, while the carbon material transfer could partly inhibit the oxidation of the cathode metal electrode. In addition, the rapid sublimation of the carbon material produced high-temperature airflow, which would make the arc impedance fluctuate and cause the arc voltage to jump. Finally, the anode heat transfer and cathode cooling mechanism directly affected the material state, and the erosion of the anode material was more serious.
Effect of magnetic field on double layer in argon helicon plasma

The electric double layer in argon helicon plasma by using floating electrostatic probe and local optical emission spectroscopy under different external magnetic field was investigated. Results show that electrons generated in the plasma source can be magnetized by the magnetic field and transported by the gradient of diverging magnetic field in the diffusion chamber, giving rise to the hollowed distribution of electron temperature. The electron temperature on axis has a sudden decrease, leading to the sudden decrease of plasma density as well as the plasma potential, forming a double layer structure. The position of double layer moves along with the position of diverging magnetic field, and the potential drop increases along with the strength of magnetic field. The structure of the external magnetic field plays the decisive factor for the double layer in helicon plasma.
Mechanical defect identification for gas-insulated switchgear equipment based on time-frequency vibration signal analysis

Mechanical defect is an important reason for the failure of gas-insulated switchgear(GIS)equipment. Based on the time-frequency characteristic vibration signal analysis on five kinds of mechanical defects, a novel intelligent algorithm model combining complementary ensemble empirical mode decomposition(CEEMD)and genetic algorithm improved kernel fuzzy mean clustering(GAKFCM)was proposed to identify the mechanical defect type. First, the mechanical defect platform and detection system were built. Then CEEMD and IMF sensitivity factors were used to analyse the time-frequency signal of five kinds of vibration defects, and the feature extraction was performed on the processed vibration signals. Finally, the mechanical vibration defect recognition model was established based on the GAKFCM algorithm and its validity was verified. Results show that the developed detection system can detect mechanical vibration signals sensitively. Singular values, frequency band lines and entropy can reflect the energy attenuation and distribution differences for different type of mechanical defect vibration signals. The proposed GAKFCM clustering model combining the above vibration feature parameters can effectively find and diagnose the mechanical defect of GIS equipment. Its recognition accuracy reaches 96.74%, especially for the loose contact seat bolts and poor contact failures of the disconnector.
Micro-mechanism study on synergistic degradation of the oil-paper insulation with dibenzyl disulfide, hexadecyl mercaptan and benzothiophene

In recent years, there have been many cases of transformer failures caused by corrosive sulfides. At present, research mainly focuses on the single sulfide dibenzyl disulphide, but few research on multiple sulphur or the oil-paper hybrid insulation. In this study, three typical sulfides dibenzyl disulfide, hexadecyl mercaptan and benzothiophene were selected to form seven sul fide-oil-paper models. Then relaxation calculations were carried out, and through molecular dynamics simulation, the synergistic effect of different sulfides on the properties of insulating paper and insulating oil was discussed. Results show that the coexistence of the three sulfides has the most severe weakening on the mechanical properties of cellulose, and it also causes great damage to hydrogen bonds. Hexadecyl mercaptan has a weaker effect on hydrogen bond destruction, but it will greatly aggravate the cellulose chain movement. The viscosity of insulating oil is generally increased by the influence of sulfide. Hexadecyl mercaptan is the main factor affecting the viscosity. Thiophene has little effect on the viscosity, cttive protection technology on sulphur corrosion.
Equipotential shielding voltage sensor for contact measurement of transient voltage in EHV/UHV power grids

In this study, an equipotential shielding voltage sensor is proposed to achieve contact measurement of transient voltage in extra-high voltage(EHV)/ultra-high voltage(UHV)power grids. Two design versions of the voltage sensor for engineering application are described. One version of the sensor is designed as a miniaturized sensor for non-disturbing measurement of potential distribution along power electronic equipment under transient voltage. The other version is designed for online measurement and monitoring in alternating current EHV/UHV power grids. Based on the design parameters, the performance of the sensor is evaluated, including stability of measurement, shielding effect against the interference from adjacent objects and frequency bandwidth. In order to verify the performance of this sensor, an experimental comparison between this sensor and a standard capacittive voltage divider used in high voltage laboratory was carried out and the results of comparison are presented. The results show that the difference of measured peak voltage between the two devices is no more than ±5%, and the difference of measured time parameters between the two devices is no more than ±15%.
Optical sensors for power transformer monitoring: A review

Power transformers play a vital role in power transmission systems from the energy source to the consumption center. In situ diagnostics of the performance of power transformers provides a variety of benefits to ensure reliable electricity transmission. Immunity to electromagnetic interference, high sensitivity, high insulation as well as small dimensions of optical sensing make it very attractive for applications in power transformer monitoring. This paper presents a critical review of various diagnostic methods for power transformers such as partial discharge, dissolved gases, temperature and other important sensing, and optical detection. The advantages and disadvantages of different monitoring methods are carefully discussed and assessed. Finally, the existing technical barriers and future prospects of optical monitoring methods for power transformers are presented.
Characterization of magnetic field waveforms from triggered lightning attached on transmission line at 18 m, 130 m and 1.55 km

The authors present a statistical analysis of characteristics of magnetic fields at different distances from triggered lightning experiments on Transmission Line at Guangdong Comprehensive Observation Experiment on Lightning Discharge during the summer of 2019. The histograms and parameters of statistical distributions for the following 22 waveform characteristics are presented, including current peak, 10%-90% risetime, halfpeak width and steepness, leader magnetic field peak, return-stroke magnetic field peak, magnetic field peak, 10%-90% risetime, half-peak width and steepness at 15 m, 130 m and 1.55 km. The arithmetic mean of 48 return stroke current peaks is 18.3 kA and the geometric mean is 17.0 kA. The arithmetic and geometric means of the current 10%-90% risetime are 0.6 and 0.6 µs,respectively. The leader magnetic field, return-stroke magnetic field and magnetic field peak at 18 m, 130 m and 1.55 km are shown linear relationship with current peak values. With increasing the distance(r), the magnetic field peak value decrease, combining the magnetic field characteristics reported by previous studies, the analysis of all magnetic field peaks in different distances suggest linear relationship with r~(0.90). The magnetic field 10%-90% risetime shows linear relationship with ln(r)and half-peak width did not show significant correlation with distance.
Ageing characteristics and lifetime model of oil-paper insulation for oil-immersed paper condenser bushing

This study extensively investigated the ageing characteristics and lifetime model of oilpaper insulation for oil-immersed paper condenser bushing. The accelerated thermal and electrothermal ageing experiments of oil-immersed paper condenser bushing were conducted respectively. The properties of oil-paper insulation during the ageing process were investigated. Results showed that descending speed of degree of polymerization of the innermost and the outermost layer paper was higher than that of middle layer paper, the difference in water content on different paper layers caused varying deterioration speeds. The aluminium foil contributed to a surge in aluminium dissolution in oil, further accelerating the ageing of insulation. Based on the obtained degree of polymerization data under thermal ageing at 90°C, 100°C and 130°C, the lifetime model of oil-paper insulation for condenser bushing model was established. In addition, the surface breakdown of the scale model of bushing occurred after 133 days ageing, the properties of bushing decreased gradually during the ageing process and sharply after the breakdown. Degree of polymerization deviation of different paper layers in bushing between calculated value according to the above lifetime model and actual value of bushing after the breakdown was less than 6%, further verifying the validity of lifetime model.
Research on 3-D total electric field of crossing high voltage direct current transmission lines based on upstream finite element method

The ongoing large-scale construction of ultra high voltage direct current projects in China makes the crossing of two high voltage direct current(HVDC)lines inevitable. It is critical to study the characteristics and calculation method of 3-D total electric fields of crossing HVDC lines. The problems encountered when applying the 3-D upstream finite element method to calculate total electric field of crossing HVDC lines and the solutions are studied in this study. In view of the surface electric field varying greatly along longitudinal direction of conductors, the calculation method adopting the Davidon-Fletcher-Powell optimization algorithm is introduced to realize the fast computation of 3-D space-charge-free field. Considering the distinct corona intensity at different positions of conductors, a new formula for initializing charge density is studied to ensure the convergence of calculation process. Considering the large computation amount of total electric field, an adaptive iteration strategy is put forward to effectively speed up the calculation. The measurement of ground total electric field underneath a crossing HVDC test line is conducted to verify the validity of the proposed calculation method. The distribution characteristics of electric fields of crossing HVDC lines are calculated and analysed. The research results will provide technical support for the design and environmental impact assessment of crossing HVDC transmission lines.
Contamination degree prediction of insulator surface based on exploratory factor analysis-least square support vector machine combined model

This study presents a combined model based on the exploratory factor analysis(EFA)and the least square support vector machine(LSSVM)to predict the contamination degree of insulator surface. Firstly, EFA method is utilised to reduce numerous influence factor variables of the insulator contamination into a few factor variables, which could decrease the complexity of the model. Then, regarding the above factor variables as new input variables, LSSVM model is established to predict the insulator contamination degree. In order to obtain the optimal predictive value, the non-dominated sorting genetic algorithm II is applied on the optimization of LSSVM model parameters. The proposed EFA-LSSVM combined model is compared with the models of LSSVM, back propagation neural network, and multiple linear regression on the model performance. Results indicate that the EFA-LSSVM combined model in this study effectively overcomes the shortcomings of the other three models mentioned above in computational time, prediction accuracy and generalization ability. Finally, the feasibility of the proposed model in predicting contamination degree of insulator surface is verified by adopting the radar map of the evaluation indexes of model performance.
Testing cable system reliability after commissioning and during operation life: in medio stat virtus?

Quality control, commissioning and diagnostic tests on insulation systems of electrical apparatus are necessary to reduce the failure risk under operation, eliminate infant mortality failures and reduce the impact of ageing on insulation system reliability. This study tries to establish a path which, based on the statistical-phenomenological modelling of the hazard rate, or bathtub curve, drives in the choice of test overvoltage and procedures. The choice of the test voltage and its waveform should be made carefully to improve reliability(reduce failure hazard)in any section of the bathtub curve. This may require, however, different choices depending on the section which corresponds to the planned test. For example, large overvoltages could be acceptable to remove the infant mortality to ensure the highest reliability of newly commissioned apparatus, but they can incept highly energetic, and, thus, fast degradation mechanisms on apparatus operating on the field for a period of time,that can worsen, rather than improving, the insulation system reliability. Resorting to partial discharge measurement during any overvoltage test seems to be the optimal solution to find the most appropriate overvoltage for any type of testing need, leveraging the Latin concept that 'in medio stat virtus'.
Enhanced voltage distribution and breakdown strength performances of oil-paper composite insulation by adding TiO_2 nanoparticles

Oil-paper composite insulation(OPCI)is used as the main insulation material in the converter transformer. However, the dielectric properties of insulating oil and oil-impregnated paper are markedly mismatched under direct current(DC)voltage, resulting in an unbalanced distribution of voltage, which is considered to be a major cause of large insulation margin but frequent failures. Therefore, it is necessary to adjust the voltage distribution in OPCI to enhance its breakdown strength. In this work, surface-treated TiO_2 nanoparticles were employed to modify OPCI. The polarisation current tests revealed that by changing the additive amount of nanoparticles, the polarisation intensities of both oil and oil-impregnated paper could be adjusted. Based on this, a model taking relaxation polarisations into full consideration was established to analyse the voltage distribution in OPCI and predict the optimal concentration. The prepared OPCI with the concentration of 0.02 g/L has desired balanced voltage distribution due to the influence of nanoparticles on interface charge, and therefore high breakdown strengths under both DC voltage and polarity reversal voltage, which can be increased by 22.6% at most. This work puts forward a novel idea to improve insulation property of OPCI and provides a reference for broader application of nanomaterial in power equipment.
Exponentially reduced carrier mobility of natural ester via blocking effect of 2D hexagonal boron nitride nanosheets

In this work, the boron nitride(BN)nanosheets were dispersed in natural esters to fabricate the dielectric nanofluid. Microstructures and chemical compositions of the nanosized BN are determined. The stability, viscosity, and thermal conductivity of the BN nanofluid, were obtained. And the dissipation factor, electrical conductivity,and relative permittivity of the BN nanofluid, were measured. The ion mobilities and migrating times of the nanofluid were measured under different volumetric fractions of BN nanosheets and temperatures. Results show that the electrical conductivity and dissipation factor of the nanofluid decreased by 54% and 48% with the addition of only 0.1% of BN nanosheets under 110°C. Both the half-reduced carrier mobility of the nanofluid and the declined ion concentration by blocking of BN nanosheet contributed to the exponentially reduced electrical conductivity and enhanced dielectric performances of the BN nanofluid. The suppression coefficient k is proposed to quantitatively describe the hinder effect of ion migration in nanofluids by 2D BN nanosheet. Results provide a strategy to design and develop advanced nanofluids with low-dielectric loss by aids of surface adsorption of ion and steric hindrance of 2D nanosheets.
Effects of ambient humidity and thermal aging on properties of Nomex insulation in mining dry-type transformer

Temperature and humidity are the main factors that cause the decomposition of Nomex paper widely used as turn-to-turn insulation material of mining dry-type transformers. In this study, for understanding the effect of ambient humidity and thermal aging on the properties of Nomex paper, specimens with the initial moisture content of 7% were aged in the oven for 168, 504,672 h at 180°C, respectively. After thermal aging, corona discharge experiments of unaged and aged specimens with different aging degrees were carried out at different relative humidity(RH)levels from 10 to 70%. The characteristic parameters of corona discharge, such as the average discharge amplitude and the number of discharges, were measured. Then, the surface conductivity and the surface potential decay rate were measured. The morphology and attenuated total internal reflectance Fourier transform infrared spectroscopy were also analysed for explaining the difference of properties between unaged and aged specimens. The experiment results indicate that the average discharge amplitude decreases with the increase of RH or the deepening of the aging degree of specimens, but the number of discharges shows the reversal tendency. The changes in the physical structure and chemical composition, which is induced by the hydrolysis reaction of Nomex paper, accelerate the surface potential decay and increase the surface conductivity.
Intelligent fault detection and location scheme for modular multi-level converter multi-terminal high-voltage direct current

In order to overcome the drawbacks of the conventional protection methods in high-voltage direct current transmission lines, a deep learning approach is proposed that directly learn the fault conditions based on unsupervised feature extraction to the detection and location decision by leveraging the hidden layer activations of recurrent neural network. The deep-recurrent neural network boosting with the gated recurrent unit compared with the long short-term memory unit is used by analysing both the signal presented in time domain and frequency domain. The proposed method is tested based on a modular multilevel converter based four-terminal high-voltage direct current system. Various faults under different conditions were simulated against fault resistance, external faults and small disturbance immunity with the validity, and the simulation verified a high accuracy, robustness and fast results because of the utilization of characteristic feature extraction.
解决我国核医学诊疗一体化药物发展关键问题的思考

本期重点号文章,从治疗核素~(161)Tb和~(213)Bi的生产、制备与提纯,到显像药物~(68)Ga-DOTATATE备案质量检测方法研究等方面,展示了我国临床核医学工作者围绕目前核医学诊疗一体化发展热点,为解决"卡脖子"关键问题所做的工作。当然,放射性药物的发展还包括提升自主创新药物研发能力、发现更多有效靶点、拓宽核素治疗临床应用领域、改善辐射安全管理过度等诸多问题,因此需要更多的部门关注核医学,从多个维度共同促进我国核医学的发展。
光电直读光谱法测定铝及铝合金中硅含量时的方法验证

基于原子发射光谱技术的光电直读光谱法主要用于金属材料的理化分析,具有制样简单、操作简便、分析快速、准确度高、可多元素同时检测等优点,在金属行业中应用广泛。实验室在开展检测工作前,必须对使用的标准方法进行方法验证,对于非标准方法、实验室制定的方法、超出预定测量范围使用的标准方法或其他扩充和修改过的标准方法进行全面的方法确认。方法验证不仅要识别标准方法的规定要求,还要通过试验证明测定结果的准确度和可靠性,这是对实验室检测能力的重要评价。
无陪护护理模式在手部软组织缺损皮瓣移植修复住院患者中的应用

目的观察无陪护护理模式对手部软组织缺损皮瓣移植修复住院患者的应用效果。方法选取2019年1月-2020年1月接受治疗的500例手部软组织缺损皮瓣移植修复住院患者为研究对象,并根据随机数字表法将其分为对照组和观察组各250例,其中对照组给予常规陪护护理模式,观察组采用无陪护护理模式。采用SPSS 20.0软件进行统计学处理,比较两组患者手部功能恢复、焦虑抑郁情绪、并发症发生率和住院满意度的差异,P<0.05为差异有统计学意义。结果两组患者干预前手部活动功能差异无统计学意义(P>0.05),两组患者治疗后疼痛、全手功能、工作性能等手部活动功能评分均较治疗前增高,两组间比较差异无统计学意义(P>0.05);两组患者干预前焦虑自评量表(SAS)得分和抑郁自评量表(SDS)得分差异无统计学意义(P>0.05),干预后,两组患者的SAS得分和SDS得分均较干预前降低,且观察组得分均低于对照组,差异有统计学意义(P<0.05);观察组患者肺部感染和切口感染的总发生率低于对照组,差异均有统计学意义(X~2=4.703,P<0.05)。观察组和对照组患者住院期间满意度分别为96.00%和91.60%,差异有统计学意义(X~2=4.161,P=0.041)。结论无陪护护理模式在手部软组织缺损皮瓣修复住院患者中的应用效果尚可,与传统陪护护理模式相比,同样可以促进患者手部功能恢复、降低并发症发生率和提高住院满意度,且利于医院环境的管理。
基于康复评定的加速康复外科干预对髋膝关节置换功能恢复的影响

加速康复外科(enhanced recovery after surgery,ERAS)是指改善围手术期多种处理举措,减少术后并发症,缩短住院周期,达到患者的快速康复。但ERAS理念不管在评估还是康复干预方面都有许多不足之处。我们是否可以在关节置换术前综合运用生物力学等精确评估手段,准确地发现及分析这些患者的康复问题,针对问题采取相应的康复干预策略至关重要。本研究旨在建立精准评估下的EARS理念,探讨髋膝关节置换术前基于精准评估下的康复干预对下肢功能恢复影响以及精准评估对于预后的判断,为髋膝关节置换围手术期的康复评估和康复干预提供依据。本次研究的创新点在于基于ERAS理念下,全面分析髋膝置换术前康复患者存在的康复问题,以及术前康复干预对功能改善的影响。采用术前综合康复干预手段(肌力训练、关节活动度训练、物理因子治疗、手法治疗、支具治疗、运动贴扎)缓解患者局部疼痛、肿胀及功能活动受限,提高日常生活活动能力。
玫瑰痤疮的治疗进展

玫瑰痤疮是皮肤科常见病之一,病因复杂,治疗仍面临挑战。近年来,光电技术在玫瑰痤疮的治疗中逐渐扮演了重要角色。一些新兴药物及治疗如微滴注射肉毒素、光动力疗法及外用米诺环素泡沫等,为临床治疗提供了新的思路。该文对近年来玫瑰痤疮治疗的最新研究进展作一综述。