Fluid-chemical modeling of the near-cathode sheath formation process in a high current broken in DC air circuit breaker

When the contacts of a medium-voltage DC air circuit breaker(DCCB) are separated, the energy distribution of the arc is determined by the formation process of the near-electrode sheath. Therefore, the voltage drop through the near-electrode sheath is an important means to build up the arc voltage, which directly determines the current-limiting performance of the DCCB. A numerical model to describe the near-electrode sheath formation process can provide insight into the physical mechanism of the arc formation, and thus provide a method for arc energy regulation. In this work, we establish a two-dimensional axisymmetric time-varying model of a medium-voltage DCCB arc when interrupted by high current based on a fluid-chemical model involving 16 kinds of species and 46 collision reactions. The transient distributions of electron number density, positive and negative ion number density, net space charge density, axial electric field, axial potential between electrodes, and near-cathode sheath are obtained from the numerical model. The computational results show that the electron density in the arc column increases, then decreases, and then stabilizes during the near-cathode sheath formation process, and the arc column's diameter gradually becomes wider. The 11.14 V–12.33 V drops along the17 μm space charge layer away from the cathode(65.5 k V/m–72.5 k V/m) when the current varies from 20 k A–80 k A.The homogeneous external magnetic field has little effect on the distribution of particles in the near-cathode sheath core,but the electron number density at the near-cathode sheath periphery can increase as the magnetic field increases and the homogeneous external magnetic field will lead to arc diffusion. The validity of the numerical model can be proven by comparison with the experiment.

Simulation and Experimental Analysis of Arc Motion Characteristics in Air Circuit Breaker

In this paper, to simulate the arc motion in an air circuit breaker （ACB）, a three- dimensional magneto-hydrodynamic （MHD） model is developed, considering the influence of ther- mal radiation, the change of physical parameters of arc plasma and the nonlinear characteristic of ferromagnetic material. The distributions of pressure, temperature, gas flow and current density of arc plasma in the arc region are calculated. The simulation results show some phenomena which discourage arc interruption, such as back commutation and arc burning at the back of the splitter plate. To verify the simulation model, the arc motion is studied experimentally. The influences of the material and position of the innermost barrier plate are analyzed mainly. It proved that the model developed in this paper can efficiently simulate the arc motion. The results indicate that the insulation barrier plate close to the top of the splitter plate is conducive to the arc splitting, which leads to the significant increase of the arc voltage, so it is better for arc interruption. The research can provide methods and references to the optimization of ACB design.

The Influence of Contact Space on Arc Commutation Process in Air Circuit Breaker

In this paper, a 3D magneto-hydrodynamic （MHD） arc simulation model is applied to analyze the arc motion during current interruption in a certain air circuit breaker （ACB）. The distributions of pressure, temperature, gas flow and current density of the arc plasma in the arc region are calculated, and the factors influencing the commutation process are analyzed according to the calculated results. Based on the airflow in the arc chamber, the causes of arc commutation asynchrony and the back commutation are investigated. It indicates that a reasonable contact space design is crucial to a successful arc commutation process. To verify the simulation results, the influence of contact space on arc voltage and arc commutation is tested. This research can provide methods and references to the optimization of ACB design.

Yaxi Brand Lowvolt Frame-type Air Circuit Breaker

The Yaxi brand DW18 series tow-volt frame-type air circuit breakers are made by the Xian Yaxi Electric Appliance Company, using advanced technology. Their technical performance has reached the world advanced level and they have been designated by the State Science and Technology Commission as national key products.

NaOH-NaNO_3-Air体系低温碱性熔炼处理废弃电路板多金属粉末

研究Na OH-Na NO3-Air体系低温碱性熔炼处理废弃电路板多金属粉末的工艺流程,在熔炼过程中对各因素对两性金属的影响进行系统研究,优化得到较为适宜的熔体组成与工艺条件:Na NO3,Na OH和多金属粉末质量比为0.6:2.5:1.0,温度为350℃,空气流量为1.5 L/min,熔炼时间为30 min。研究结果表明:在此条件下Sn,Pb,Al和Sn的转化率分别为100%,83.99%,93.26%和91.97%。针对含两性金属的碱性浸出液,设计Ca(OH)2沉锡和Na2S·9H2O沉铅锌的分离工艺,得到纯度(质量分数)98%以上的Sn O2及Pb S-Zn O混合物。

Research on arc root stagnation when small current is interrupted in self-excited circuit breaker

The self-excited DC air circuit breaker(SE-DCCB)has been widely used in urban rail transit due to its excellent stability.It can realize forward and reverse interruption,but has difficulty interrupting small currents due to the phenomenon of arc root sticking at the entrance of the arc chamber in the splitting process,which is known as arc root stagnation.A coupling model of the self-excited magnetic field and magnetohydrodynamics is established for the SE-DCCB with the traditional structure.The magnetic field,temperature and airflow distribution in the arc chamber are investigated with an interrupting current of 150 A.The simulation results show that the direction and magnitude of the magnetic blowout force are the dominant factors in the arc root stagnation.The local high temperature of the arc chamber due to arc root stagnation increases the obstruction effect of the airflow vortex on the arc root movement,which significantly increases the arc duration time of small current interruption.Based on the research,the structure of the magnetic conductance plate of the actual product is improved,which can improve the direction and magnitude of the magnetic blowout force at the arc root so as to restrain the development of the airflow vortex effectively and solve the problem of arc root stagnation when the small current is interrupted.The simulation results show that the circuit breaker with improved structure has a better performance for a small current interruption range from 100 A to 350 A.

Influence of the gassing materials on the dielectric properties of air

Influence of the gassing materials, such as PA6, PMMA, and POM on the dielectric properties of air are investigated. In this work, the fundamental electron collision cross section data were carefully selected and validated. Then the species compositions of the air–organic vapor mixtures were calculated based on the Gibbs free energy minimization. Finally, the Townsend ionization coefficient, the Townsend electron attachment coefficient and the critical reduced electric field strength were derived from the calculated electron energy distribution function by solving the Boltzmann transport equation. The calculation results indicated that H;O with large attachment cross sections has a great impact on the critical reduced electric field strength of the air–organic vapor mixtures. On the other hand, the vaporization of gassing materials can help to increase the dielectric properties of air circuit breakers to some degree.

延迟焦化装置密闭除焦系统S-CCHS技术应用总结

安全环保型延迟焦化密闭除焦、输送及存储成套技术(S-CCHS)的投用,实现了石油焦处理全过程密闭清洁化操作。运行过程暴露出冷切焦水系统中焦粉含量明显增加、各输送带尾部溜料、输送带清扫效果不佳、装车过程中产生焦粉弥漫、设备故障率高等问题,影响装置的安全平稳运行,对环保产生不利影响。通过优化冷切焦水系统流程,系统中焦粉质量浓度从200 mg/L降至20~40 mg/L,下降明显;通过对传输带、定量料仓的全密闭改造,从根本上解决了焦粉向大气中弥漫的问题;通过对高故障率设备进行更新并制定预防性维修计划,有效降低了密闭除焦现场设备故障率。为延迟焦化装置密闭除焦同类技术的应用提供了参考。

端部结构三大梁焊缝气孔原因分析及解决措施

气孔是铝合金焊接中常见的缺陷之一,其会降低焊缝的致密性,削弱焊缝的有效截面积,从而降低焊缝的力学性能。本文通过分析环境温湿度、焊接工艺、自动焊接设备等因素,找出了造成铝合金车体底架端部结构三大梁焊缝密集型气孔的原因。通过逐一排查和试验分析,发现此密集型气孔是由于悬臂MIG自动焊接专机的气路系统密封性问题所导致的。由于自动焊专机焊接系统焊枪喷嘴处的保护气体流量过小,气体保护不足,致使焊缝产生密集型气孔。经测量发现,从气瓶到焊枪喷嘴的保护气流量发生了严重的衰减,衰减值高达13 L/min。针对此问题,改造自动焊专机原有气路系统,确保焊枪喷嘴处保护气体流量到达22 L/min,保护了电弧、金属熔滴、熔池和焊接区,有效控制了焊接气孔的产生。

地铁车辆空调系统变频改造及谐波抑制方案技术研究

随着城市轨道交通行业的飞速发展和国家对“节能减排”的重视,地铁列车空调系统的节能性变得尤为重要。早期地铁空调系统基本为定频空调,在不改变原有定频空调主体结构的前提下,通过换型为变频压缩机、增加变频器,以及开展相关的电路及结构改造可升级为变频空调,从而降低能源消耗。文章以某地铁公司变频空调改造项目为例,分析地铁车辆空调变频改造技术,针对变频改造中线性负载变为非线性负载时谐波电流注入导致谐波电压畸变超标,衍生出的SIV与空调匹配性问题,设计谐波抑制方案,通过在空调输入侧增加电感降低谐波分量,并叠加LC谐振回路对含量相对较高的5次方和7次方谐波进行反向振荡削减其谐波含量,有效将谐波电压降低在设计标准5%范围内。

锚杆钻车冷却系统分析及优化

基于煤矿井下锚杆钻车液压系统工作原理,分析了液压系统压力损失和热平衡,绘制了系统热能循环图,根据能量守恒、热平衡原理得出了该锚杆钻车发热总功率计算公式。针对目前锚杆钻车冷却系统存在的问题,提出了强制循环冷却的冷却方法。实验表明,锚杆钻车液压油温与液压系统总效率和工作回路等因素有关;通过强制循环冷却可解决锚杆钻车油温过高的问题;该冷却系统的设计为同类型锚杆钻车液压系统的设计提供了参考。

通风冷却系统对YBXKK防爆电机绕组温升的影响

电机稳态温升是关系到电机使用寿命和运行可靠性的重要因素,其各主要部位的温度分布和定子绕组平均温升均受到通风冷却系统的制约。为了揭示电机温升与风路结构的关系,通过FLUENT分析软件,分别对单侧风路结构和对称风路结构两种不同结构进行整机温度场模拟计算。研究结果表明,对称风路结构较之单侧风路结构绕组温升降低了16 K,效果显著。该研究成果对YBXKK防爆电机的通风系统设计提供了一定参考。

基于梯形图的全气动系统快速设计方法研究

本文所介绍的基于梯形图的全气动系统快速设计方法是日本SMC公司提出的一种快速设计全气动系统回路的方法。它借助于电气系统设计中的概念,将气动元件抽象出类似电气系统的符号,并引入了梯形图的概念,采用分区设计的方法,可以在较短时间内完成比较复杂的全气动回路的设计。

船舶直流电力系统选择性保护方法研究

为了解决船舶直流电力系统保护快速性与选择性矛盾的难题,提出了基于瞬时保护的选择性保护方法及基于差动保护的选择性保护方法。利用数字仿真对2种选择性保护方法进行了性能评估。评估结果表明,基于差动保护的选择性保护方法具有更优的整体保护性能,能有效提高船舶电力系统的安全水平。

万能式断路器综合性能检测系统研制

介绍了一套基于虚拟仪器技术的万能式断路器综合性能检测系统设计方案。系统以工控机为控制核心,配置数据采集卡、信号调理电路和三相大电流发生器、气动夹具等组成系统硬件平台,利用LabVIEW软件开发相关测试及数据处理软件,实现数据采集和处理,满足了万能式断路器综合性能检测的需要。实际运行表明,该系统具有稳定可靠、操作方便、维护简单的特点。

基于ZigBee的汽车空调控制系统

针对汽车空调系统的实时性要求,提出了一种基于ZigBee技术的汽车空调控制系统,给出了控制系统的网络结构、传感器节点和系统主节点电路,设计了控制系统的网络协议和传感器节点以及主控制节点的程序流程。为汽车空调控制提供了一种新的技术。

万能式断路器触头主回路系统的设计与应用

研究和分析了万能式断路器触头主回路系统。对触头系统与桥型触头进行计算分析,开发了新型结构,并在新一代万能式断路器的设计中进行应用,提高了万能式断路器的整机性能,降低电动斥力,提高了触头回路系统的电动及热稳定性。

中央空调控制系统的二线制湿度传感变送器设计

介绍了所研制的二线制湿度传感变送器的电路原理及设计计算。该变送器将湿度信号经C／V和V／I转换电路变成电流信号，送入中央空调控制系统，完成对生产车间的湿度控制。变送器触发源电路保证产生的脉冲串具有改善的波形，单稳态电路实现输出波形的稳定。设计的无源积分器有较好线性度，放大电路的高输入阻抗和高共模抑制比保证了可靠测量远距离小信号。给出了4～20mA二线制湿度传感变送器的电路原理图，实例说明，中央空调控制系统使用的湿度传感变送器具有测量范围宽，精度高，抗干扰能力强等特点。

一种新型芯片冷却构思的实验研究——利用蒸汽压缩空调系统降低计算机机箱环境温度以冷却芯片(英文)

提出通过降低计算机机箱内整体冷却空气温度达到热管理.类似日常生活用的普通空调,提出一种整体式中尺度空调系统来调节计算机内温度,并在实验原型上做了大量概念性的实验.结果表明,计算机机箱内环境空气温度可以从54.7℃降低到32.7℃.说明此种方法可以在不改变计算机任何部件的情况下大大提高计算机系统的冷却效果,为热管理设计的这一特定中尺度空调机非常经济且易操作,在计算机产业上将会得到广泛的应用.如同空调系统的末端一样,此整体式空调机可同时拥有多个蒸发器以带走多个发热元件产生的热量;蒸发器还可以直接扣在中央处理器(CPU)和显卡等芯片的表面以冷却芯片.本文提出的主动冷却系统在调节局部热环境时可灵活调整.例如如果空气冷却系统中有两个蒸发器时,就可用一个冷却机箱内环境温度,另一个直接扣在CPU上.本文提供的概念有望为个人笔记本电脑、台式机和大型计算机提供一种高效的冷却方法,也可应用在其他产热率较高的很多场合.

气动程序气控系统干扰信号处理研究

针对复杂气动程序气控系统干扰信号消除困难,提出了干扰信号处理方案。通过全功能图判断干扰信号的类型,利用单向滚轮杠杆阀将复现长信号变为短信号,然后再将不同步序线上的复现信号与各步序线上处于发信状态的其他控制信号相"与",组合出不同的新信号来消除复现信号干扰;采用双压阀相"与"消除覆盖信号干扰。通过实验验证,提出的干扰信号消除方法确实可行。