Dynamic physical characteristics of DC arc on arcing horn for HVDC grounding electrode line

The dynamic physical characteristics of a DC arc on an arcing horn for a high voltage direct current(HVDC)grounding electrode line are significantly different from those of the switching device arc,secondary arc,AC fault arc and pantograph-catenary arc.In this work,an experimental platform for the DC arc on the arcing horn was built,and mechanisms of the arc column short circuit and arc root movement were studied.This work further analyzes the characteristics and mechanisms of the arc motion when wind speed and direction,magnetic field and the expansion angle of the electrode are varied.Arc root movement is more likely to occur at the upper electrode.There is a competitive relationship between arc expansion and the transferring effect.The effect of wind on the arc column is greater than the effect on the arc root.The magnetic field has a significant driving effect on both the arc column and the arc root.The research results provide a comprehensive experimental basis for forther probing the method of DC arc suppression,and the improvement of the arcing horn.

Research on the energy consumption mechanism and characteristics of the gallium indium tin liquid metal arcing process

For high-voltage direct current(HVDC)power grid transmission with higher voltages,the energyconsuming branch of the DC circuit breaker is required to dissipate huge energies of more than megajoules in a short time in the case of a fault and short circuit.The requirements for huge volume and weight are difficult to meet with energy-consuming equipment based on ZnO.In this paper,a new energy consumption method is proposed based on gallium indium tin(GaInSn)liquid metal in the arcing process,and a test platform with adjustable short-circuit current is built.The mechanism triggering GaInSn liquid metal arcing energy consumption is studied.It is found that short-circuit current and channel aperture are the key parameters affecting the energy consumption of liquid metal arcing.The characteristics of GaInSn liquid metal energy consumption are investigated,and four stages of liquid metal energy consumption are found:oscillatory shrinkage,arc breakdown,arc burning phase change and arc extinction.The influence of short-circuit current and channel aperture on the energy consumption characteristics of GaInSn liquid metal is investigated.To further explore the physical mechanism of the above phenomena,a magneto-hydrodynamic model of energy consumption in the GaInSn liquid metal arcing process is established.The influence of short-circuit current and channel aperture on the temperature distribution of the liquid metal arc is analyzed.The mechanism of the effect of short-circuit current and channel aperture on peak arc temperature and the temperature diffusion rate is clarified.The research results provide theoretical support for this new liquid metal energy consumption mode DC circuit breaker.

Arcing Model of a Disconnector and its Effect on VFTO

In the computational process of very fast transient over-voltage （VFTO）, it is essen-tial to find an accurate model for a gas insulated substation. The arcing model of the disconnector is particularly important. The general arcing model is not able to give a good description of the arc development process. In this paper, based on the physical process of arcing and existing arc models （the exponential time-varying resistance model and the segmental arcing models）, a dy- namic arcing model is proposed, which is divided into two stages before and after the zero crossing. The dynamic arcing model combines hyperbola time-varying resistance and the Mayr model to describe the dynamic process of arcing. The present paper creates an arc model blockset upon the Matlab/Simulink software platform. Moreover for a specific 1100 kV station, VFTO is simulated in detail based on different arcing models. It is demonstrated that the dynamic arcing model can describe the physical arc process precisely and is useful for improving the accuracy of VFTO simulations.

Critical Length Criterion and the Arc Chain Model for Calculating the Arcing Time of the Secondary Arc Related to AC Transmission Lines

The prompt extinction of the secondary arc is critical to the single-phase reclosing of AC transmission lines, including half-wavelength power transmission lines. In this paper, a low- voltage physical experimental platform was established and the motion process of the secondary arc was recorded by a high-speed camera. It was found that the arcing time of the secondary arc rendered a close relationship with its arc length. Through the input and output power energy analysis of the secondary arc, a new critical length criterion for the arcing time was proposed. The arc chain model was then adopted to calculate the arcing time with both the traditional and the proposed critical length criteria, and the simulation results were compared with the experimental data. The study showed that the arcing time calculated from the new critical length criterion gave more accurate results, which can provide a reliable criterion in term of arcing time for modeling and simulation of the secondary arc related with power transmission lines.

Numerical Simulation of Gas Flow During Arcing Process for 252 kV Puffer Circuit Breakers

A numerical simulation model for 252 kV puffer circuit breaker is constructed, by using a proven commercial computational fluid dynamics （CFD） package, PHOENICS. The model takes into account the moving parts in the circuit breaker, turbulence enhanced momentum and energy transport, radiation transport. The arcing process in a SF6 puffer circuit breaker with two hollow contacts is simulated under different conditions, and the simulation results are verified with experimental results. Through simulation, the pressure, temperature and velocity in the arc quenching chamber can be obtained. The simulation model is also capable of predicting the influence of design parameters variations on breaker performance, and can thus help to reduce the number of short-circuit tests during the design stage.

Calculation of Nozzle Ablation During Arcing Period in an SF_6 Auto-Expansion Circuit Breaker

The nozzle ablation process is described as two phases of heat and ablation in the interruption for an SF6 circuit breaker in this paper. Their mathematical models are established with the Fourier heat conduction differential equation respectively. The masses of nozzle ablation with different arc durations and arc currents are calculated through the model of the nozzle abla- tion combined with an MHD （magneto-hydrodynamic） arc model. The time of the temperature rise on the inner surface of the nozzle under a given energy flux and of reaching the pyrolysis temperature under different energy fluxes is respectively analyzed. The relations between the mass of nozzle ablation and breaking current and arc duration are obtained. The result shows that the absorbing energy process before the nozzle ablation can be neglected under the condition of the energy flux entering into nozzle q 〉 10^9 W/m^2. The ablation is the severest during the high-current phase and the ablation mass increases rapidly with the breaking current and with arc duration respectively.

Analysis of the Carbon Nano-Structures Formation in Liquid Arcing

Graphite electrodes were used for the direct current （DC） arc discharge in water. And high-resolution transmission electron microscopy （HRTEM） was used to investigate the products. Based on the experimental phenomena and nano-structure products, arc plasma characteristics in water were analyzed theoretically. Two growth regions and relevant growth modes were proposed to interpret the formation mechanisms of nano-structures by arc discharge in water. Furthermore, liquid nitrogen and cross magnetic field was applied to change the arcing state respectively, and new carbon nano-structures were obtained. Their formation mechanisms were also analyzed correspondingly.

高等教育线上线下混合教学模式探索和实施

根据新工科建设方案及理工科专业课程特色,教学过程以问题前导,以任务驱动,以思政案例贯穿,以多层级路径开展,以学生为中心。本文根据高等理工科专业基础课程特点,给出了基于BOPPPS(Bridge in引导、Objective学习目标、Pre-assessment前测、Participatory learning参与式学习、Post-assessment后测、Summary总结)模型和ARCS(Attention注意、Relevance关联、Confidence信心和Satisfaction满意)模型的混合式教学流程和活动。分析了课程整体设计思路及教学模型、学情分析与目标设定、课程内容设计与资源整合、教学过程与实施方法、学习评价与教学反馈、课程成效等内容,包括教学模型、评价体系、线上线下教学过程及实施办法和效果,通过师生互动和学生反馈意见,不断更新各个平台的教学资源,改进教学方法,持续提升课程教学质量。

高职院校学生ARCS学习动机模型的探索与实践

本研究利用发放调查问卷、查阅文献和现场访谈等方法,结合ARCS学习动机模型,对现阶段高职院校学生学习现状进行调查研究。结合调查分析结果,借助ARCS学习动机模型进行教学设计并实施教学,调动学生学习的积极性,激发学生的学习动机,提高了学生的学习兴趣和学习能力。

挖掘机液压混合动力系统跟踪控制研究

由于挖掘机混合动力系统参数的不确定性和系统的非线性给挖掘机的跟踪控制带来了巨大的困难。对此,构建了挖掘机液压混合动力系统模型,并采用改进的自适应鲁棒控制(ARC)实现挖掘机液压混合动力系统的跟踪控制。根据挖掘机液压混合动力系统,对液压系统、挖掘机动力学和发动机进行数学建模。利用线性稳定反馈控制规律,采用改进的自适应鲁棒控制,使挖掘机液压混合动力系统具有足够大的反馈增益。最后对斗杆、动臂和铲斗的倾角进行跟踪仿真实验,给出了系统模型位置和速度的跟踪误差,并与PI控制进行比较分析。结果表明:相比于PI控制,ARC控制下的斗杆、动臂和铲斗倾角的最大振幅波动率和倾角的波动范围都有所降低,且回转位置和速度的跟踪误差超调较小。说明采用ARC控制的挖掘机混合动力系统控制方法,能够更好的补偿系统模型的非线性,具有较好的控制稳定性以及跟踪精度。

“1+2+3+4+5”——经贸类课程教学的金字塔型新范式

随着数字经济的迅猛发展和社会的不断进步,高校经贸类课程的教学改革显得尤为迫切。为此,高校需要历经多周期、多人次的实践、改进和完善过程,始终“以学习者为中心”,并以ARCS模型作为理论基础,充分调动学习者的学习动机,进而达到提高学习效果、提升专业素养的目标。通过调研、培训和资料梳理,课题组从分析教与学的动机问题入手,运用混合式(书架)教学方法对独创的教学设计进行深度实施并展开科学评估,形成五个层次分阶段的金字塔型教学新范式。

小花楼织机织造技艺数字化教育设计研究

目的为了缓解小花楼织机织造技艺面临失传的问题,根据ARCS动机理论展开织造技艺数字化教育的设计研究,提升学习者在体验过程中的注意力和理解力,增强其掌握织造技艺的自信和满足感。方法结合ARCS动机理论和小花楼织机的织造技艺知识点,将数字化教育划分为三个教育单元,即小花楼织机的交互及展示设计、小花楼织机结构的模块化设计、实物模型控制及模拟设计,并在Unity平台中展开Arduino开发板以集成设计,由浅入深地构建数字化教育场景。结论对照实验结果表明,基于ARCS动机理论的数字化教育方式具有可行性和实践性,小花楼织机织造技艺的知识可达性和教育互动性有了显著提高,为蜀锦织造技艺的传承和发展提供了一定的参考价值和实践意义。

基于地理探测器和GIS的云南省传统村落空间分布格局及其影响因素研究

以云南省777个传统村落为研究对象,使用Arc GIS10.7工具,综合采用空间自相关、最邻近指数、标准差椭圆、核密度分析和地理探测器等多种方法,从自然、社会和文化三大维度探析云南省传统村落的空间分布特征及其影响因素.结果表明:(1)云南省传统村落空间分布上整体呈现出“滇西密、滇东疏、西北密、东北疏、东南密、西南疏”的分布格局.(2)云南省传统村落空间分布具有显著的指向性和集聚性,全省整体呈现出“三核状”分布格局,表现为集聚与分散相结合的分布形态.其中整体及局部指向性均为“西北至东南指向”.空间分布集聚性上,高密度区主要分布于红河哈尼族彝族自治州(滇南)、保山市(滇西)、大理白族自治州和丽江市(滇西北).(3)自然、人文、社会和政策导向等因素的相互耦合作用形成了云南省传统村落的空间分布特征.水资源储量、人均GDP、道路通车里程、少数民族占比与文化多样性指数等是主要的影响因素.

ARCS动机模型下右玉精神融入高校思政教育探析

右玉精神蕴涵的深厚思想精髓是我国高校思想政治教育的重要资源和优秀教材,能够很好地帮助当代青年学生提升自身政治素养和传承艰苦奋斗的精神。文章基于ARCS动机模型,从“注意、关联、信心、满意”四个环节,归纳总结了右玉精神融入高校思想政治教育过程中面临的现实困境,如学习氛围不浓且教学模式陈旧、学习内容机械生硬、教学手段陈旧单调、学习效果不佳学生满意度不高,尝试提出营造氛围改变教学模式、与时俱进设计教学内容、完善教学评价反馈机制、情景教学并注重成果展示四个解决路径。

A spatiotemporal evolution model of a short-circuit arc to a secondary arc based on the improved charge simulation method

The initial shape of the secondary arc considerably influences its subsequent shape.To establish the model for the arcing time of the secondary arc and modify the single-phase reclosing sequence,theoretical and experimental analysis of the evolution process of the short-circuit arc to the secondary arc is critical.In this study,an improved charge simulation method was used to develop the internal-space electric-field model of the short-circuit arc.The intensity of the electric field was used as an independent variable to describe the initial shape of the secondary arc.A secondary arc evolution model was developed based on this model.Moreover,the accuracy of the model was evaluated by comparison with physical experimental results.When the secondary arc current increased,the arcing time and dispersion increased.There is an overall trend of increasing arc length with increasing arcing time.Nevertheless,there is a reduction in arc length during arc ignition due to short circuits between the arc columns.Furthermore,the arcing time decreased in the range of 0°-90°as the angle between the wind direction and the x-axis increased.This work investigated the method by which short-circuit arcs evolve into secondary arcs.The results can be used to develop the secondary arc evolution model and to provide both a technical and theoretical basis for secondary arc suppression.

Geochemistry of island arc assemblage in the Eastern Desert of Egypt and the role of Pan-African magmatism in crustal growth of the Arabian–Nubian Shield:A review

Neoproterozoic island arc assemblage of the Arabian–Nubian Shield(ANS)in the Eastern Desert(ED)of Egypt comprises juvenile suites of metavolcanics(MV),large amounts of meta-sedimentary rocks(MS),and voluminous metagabbros-diorites(MGD)and syn-tectonic intrusions of older granitoids(OG).We report here the updates of these four rock units in terms of classification,distribution,chemical characteristics,geodynamic evolution,metamorphism,and ages.In addition,we discuss these integrated data to elucidate a reasonable and reliable model for crustal evolution in the ANS.The main features of these rock units indicate their relation to each other and the geodynamic environment dominated by early immature oceanic island arcs to primitive continental arcs.Integrated information of the island arc metavolcanic and plutonic rocks(gabbros,diorites,tonalites,and granodiorites)furnish evidence of the genetic relationships.These include proximity and a coeval nature in the field;all protolith magmas are subalkaline in nature following calc-alkaline series with minor tholeiitic affinities;common geochemical signature of the arc rocks and subduction-related magmatism;their similar enrichment in LREEs;and similar major element compositions with mafic melts derived from metasomatized mantle wedge.The volcano-sedimentary and the OG rocks underwent multiphase deformation events whereas the MGD complexes deformed slightly.Based on the magmatic,sedimentological,and metamorphic evolutions constrained by geochronological data as well as the progressive evolutionary trend from extensional to compressional regimes,a possible gradual decrease in the subducted slab dip angle is the most infl uential in any geodynamic model for arc assemblage in the ED of Egypt.

Plasma nitrogen fixation system with dual-loop enhancement for improved energy efficiency and its efficacy for lettuce cultivation

Plasma nitrogen fixation(PNF)has been emerging as a promising technology for greenhouse gasfree and renewable energy-based agriculture.Yet,most PNF studies seldom address practical application-specific issues.In this work,we present the development of a compact and automatic PNF system for on-site agricultural applications.The system utilized a gliding-arc discharge as the plasma source and employed a dual-loop design to generate NO_(x)from air and water under atmospheric conditions.Experimental results showed that the system with a dualloop design performs well in terms of energy costs and production rates.Optimal operational parameters for the system were determined through experimentation,resulting in an energy cost of 13.9 MJ mol^(-1)and an energy efficiency of 16 g kWh^(-1)for NO_(3)^(-)production,respectively.Moreover,the concentration of exhausted NO_(x)was below the emission standards.Soilless lettuce cultivation experiments demonstrated that NO_(x)^(-)produced by the PNF system could serve as liquid nitrate nitrogen fertilizer.Overall,our work demonstrates the potential of the developed PNF system for on-site application in the production of green-leaf vegetables.

Coexistence of Dirac and Weyl points in non-centrosymmetric semimetal NbIrTe_(4)

Using angle-resolved photoemission spectroscopy and density functional theory calculations methods,we investigate the electronic structures and topological properties of ternary tellurides NbIrTe_(4),a candidate for type-II Weyl semimetal.We demonstrate the presence of several Fermi arcs connecting their corresponding Weyl points on both termination surfaces of the topological material.Our analysis reveals the existence of Dirac points,in addition to Weyl points,giving both theoretical and experimental evidences of the coexistence of Dirac and Weyl points in a single material.These findings not only confirm NbIrTe_(4) as a unique topological semimetal but also open avenues for exploring novel electronic devices based on its coexisting Dirac and Weyl fermions.

An Overview on the Composition and Age of Upper Crust of Proto-Tethyan Lajishan Intra-oceanic Arc,NE Tibet Plateau

Identification and anatomy of oceanic arcs within ancient orogenic belt are significant for better understanding the tectonic framework and closure process of paleo-ocean basin.This article summarizes the geological,geochemical,and geochronological characteristics of upper crust of Proto-Tethyan Lajishan intra-oceanic arc and provides new data to constrain the subduction evolution of the South Qilian Ocean.The intra-oceanic arc volcanic rocks,including intermediate-mafic lava,breccia,tuff,and minor felsic rocks,are distributed along southern part of the Lajishan ophiolite belt.Geochemical and isotopic compositions indicate that the intermediate-mafic lava were originated from depleted mantle contaminated by sediment melts or hydrous fluids,whereas the felsic rocks were likely generated by partial melting of juvenile mafic crust in intra-oceanic arc setting.Zircons from felsic rocks yield consistent and concordant ages ranging from 506 to 523 Ma,suggesting these volcanic rocks represent the relicts of upper crust of the Cambrian intra-oceanic arc.Combined with the Cambrian forearc ophiolite and accretionary complex,we suggest that the Cambrian intra-oceanic arc in the Lajishan ophiolite belt is belonging to the intra-oceanic arc system which was generated by south-directed subduction in the South Qilian Ocean at a relatively short interval between approximately 530 and 480 Ma.

Mafic and felsic magmatism in the Wadi Kalalat area, South Eastern Desert, Egypt: mineralogy, geochemistry and geodynamic evolution during the Neoproterozoic in the Nubian Shield

In the south Eastern Desert of Egypt,two contrasting types of magmatism(mafic and felsic) are recorded in the Wadi Kalalat area,and form the Gabal El Motaghiarat and Gabal Batuga intrusions,respectively.The two intrusions post-dates ophiolitic and arc associations represented by serpentinite and metagabbro-diorite,respectively.The mafic intrusion has a basal ultramafic member represented by fresh peridotite,which is followed upward by olivine gabbro and anorthositic or leucogabbro.This mafic intrusion pertains to the Alaskan-type mafic-ultramafic intrusions in the Arabian-Nubian Shield(ANS)being of tholeiitic nature and emplaced in a typical arc setting.On the other hand,the Gabal Batuga intrusion comprises three varieties of fresh A-type granites of high K-calc alkaline nature,which is peraluminous and garnetbearing in parts.A narrow thermal aureole in the olivine gabbro of the mafic intrusion was developed due to the intrusion of the Batuga granites.This results in the development of a hornfelsic melagabbro variety in which the composition changed from tholeiitic to a calc-alkaline composition due to the addition of S_(i)O_(2),Al_(2)O_(3),alkalis,lithosphile elements(LILEs) such as Rb(70 ppm) and Y(28 ppm) from the felsic intrusion.Outside the thermal aureole,Rb amounts 2-8 ppm and Y lies in the range <2-6ppm.It is believed that the Gabal Batuga felsic intrusion started to emplace during the waning stage of an arc system,with transition from the pre-collisional(i.e.,arc setting) to post-collisional and within plate settings.Magma from which the Gabal Batuga granites were fractionated is high-K calc-alkaline giving rise to a typical post-collisional A-type granite(A_(2)-subtype) indicating an origin from an underplating crustal source.Accordingly,it is stressed here that the younger granites in the ANS are not exclusively post-collisional and within-plate but most likely they started to develop before closure of the arc system.The possible source(s) of mafic magmas that resulted in the formation of the two intrusions are discussed.Mineralogical and geochemical data of the post-intrusion dykes(mafic and felsic) suggest typical active continental rift/within-plate settings.