Study of double-chamber air arc plasma torch and the application in solid-waste disposal

Arc plasma can be applied in hazardous solid waste disposal for higher temperature than common heating methods,but some practical issues exist in practical engineering application.In this study,an air arc plasma torch with double chambers and magnetic controlling is designed to realize wide variable power and long electrode life.The detailed characteristics and laws of the air arc are studied.The condition parameters of arc current(I),air flow rate(G)and the structure parameters of inlet area ratios and electrode diameters influence both the arc voltage and arc root positions.The arc rotating driven by magnetic field effectively lengthens the electrode life.The gasification process and product of organic wastes by air plasma are influenced largely by the waste compositions and the air flow rate.A furnace structure with more even atmosphere and longer residence time should be considered for better gasification.Oxygen-deficient environment is important to suppress NOxformation during the application of air plasma.Inorganic solid wastes can be melt by the air plasma and cooled down to form compact vitreous structures in which heavy metals can be locked and the leaching rates significantly decrease down.

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.

Cathode Erosion of Graphite and Cu/C Materials in Airarcs

Cathode erosion of graphite and Cu/C was studied in direct current arcs, which were ignited between two electrodes comprised of two kinds of carbon materials and a tungsten anode in air. The arced zones on the cathode surface were investigated by a scanning electron microscope. Also, the cathode erosion rates of the investigated materials were measured. The results show that two distinct zone can be seen on both cathodes. The eroded area was located at the zone just opposite to the anode and surrounded by a white zone. The arced surface on the Cu/C containing 9.3 % Cu is rougher than that of the pure graphite. Many particles with various sizes distributed on the Cu/C. The vaporization of Cu can lower the surface temperature and reduce the cathode erosion. Therefore, the cathode erosion rate of the Cu/C is lower than that of the pure graphite.

Resistance Characteristics of Arc in Long Air Gap

Arc resistance is an important parameter for characterizing long arcs in air, and its laboratory testing is of importance for accurate arc modeling of electromagnetic transient caused by short circuit fault. Therefore, we constructed an experimental system to study the cha- racteristics of long AC arc in air. Driven by currents of 10 kA or 40 kA (root mean square value), the system produces arcs with different initial lengths of 1 m, 2 m and 4 m, and the movement of the arcs are captured by a high-speed camera. After performing experiments using the system, we carried out analysis and comparisons of the arc resistance of arcs with different lengths and different currents, as well as a study of the relationship between the macro-morphology and the resistance of the arcs. Conclusions were drawn from the experimental re- sults: the arc voltage had obvious saturation characteristics; the arc resistance increased with the increase of arc length and the decrease of current; the arcs bended or extended significantly in time and the peak arc voltage within a single cycle increased correspondingly; the arcs had voltage and current in the same phase. In the end, a formula of arc resistance based on the experiment results is derived.

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.

高海拔环境下大容量直流空气断路器灭弧性能研究

高原轨道交通和电工产业转型对起关键保护作用的大容量直流空气断路器(LC-DCCB)提出了更高要求,但现有产品在高海拔地区的开断仍存在一定问题。该文以轨道交通用LC-DCCB为研究对象,首先基于磁流体动力学(MHD)理论,考虑湍流效应的影响,对其在高海拔环境下开断18 kA短路电流进行仿真;然后对电弧形态及灭弧室内温度场、电磁场、气流场进行分析,得出高海拔地区空气电弧开断困难的主要原因;最后根据仿真与理论分析,考虑采用合理数量和布局的间插式U型栅片改善电弧开断特性。结果表明:随着海拔的升高,电弧前期运动速度加快,但断路器的灭弧性能降低;在高海拔环境下电弧存在严重的弧根粘滞和弧根拖尾现象,弧根拖尾畸变空间电场,不利于熄弧;同时,在不同海拔环境下,电弧会产生不同程度的反向运动现象,易导致弧后重燃。该研究深入揭示了高海拔环境下LC-DCCB电弧演变过程及复杂开断现象背后的物理本质,可为该类产品研发提供理论指导。

高气压下三维旋转滑动弧放电光谱特性分析

为探究气体压力对滑动弧放电稳定性的影响规律,在高气压放电实验平台上,开展了滑动弧放电光谱特性研究。利用发射光谱法对滑动弧放电过程中的激发态物质进行诊断,并对不同气体压力条件下滑动弧放电的电子密度、振动温度、转动温度进行了计算。在滑动弧放电发射光谱中观测到氮气第二正带系N_(2)(C^(3)Π_(u)→B^(3)Π_(g))和氮气第一负带系N^(+)_(2)(B^(2)Σ^(+)_(u)→X^(2)Σ^(+)_(g))的发射谱线,随着气体压力升高,氮气第二正带系谱线发射强度增强,氮气第一负带系的发射强度变化幅度较小。当气体压力超过0.26 MPa之后,在滑动弧放电发射光谱中发现了氮气Gaydon s Green带系507.4 nm的发射谱线,其发射强度为3508.49 arb,随气体压力升高其谱线发射强度无明显变化。利用Stark展宽法对滑动弧放电过程中的电子密度进行了计算,得到电子密度在1023量级,并且随着气体压力的增加,滑动弧放电的电子密度呈线性增加。针对氮气分子第二正带系的5条谱线,采用玻尔兹曼图解法对滑动弧放电的振动温度进行计算,振动温度随气体压力的变化并非单调变化,在0.3 MPa之前振动温度变化幅度较小,气体压力超过0.3 MPa之后振动温度迅速增加。对氮气分子第一负带系390~391.6 nm处的发射谱线进行拟合计算滑动弧放电的转动温度,结果表明在0.24 MPa之前转动温度随气体压力升高变化幅度较大,气体压力超过0.24 MPa之后转动温度增长幅度变小。

气垫压带输送机凸弧段分析研究

垂直气垫压带输送机的技术要点为压紧力的大小和凹凸弧段气膜的承载力。凹凸弧段气室提供的气膜承载力能否满足输送要求是凹凸弧段能否使用气室替代托辊的关键。文中通过对凸弧段进行受力分析,推导出输送带张力和气膜承载力的公式,改变气孔排数,选择正压区域5排、7排、9排气孔的双圆弧气室进行仿真,比较总压压力云图和正侧压承载力。结果表明:5排气孔的双圆弧气室内流量损失减少,气膜稳定,承载力较大。

大电流空气电弧栅片烧蚀数值模拟与分析

电网输配电容量不断增加对低压断路器的开断性能提出了更高的要求。低压断路器开断大电流时,电弧烧蚀灭弧栅片产生的金属蒸汽会极大的影响断路器开断性能,阻碍断路器发展并且不利于电网安全运行。因此,建立了开断电流为10 kA的栅片烧蚀模型,研究了栅片烧蚀特性。模型考虑了栅片阴极端和阳极端不同的电弧能量注入,栅片材料的熔化、蒸发以及栅片表面形貌变化,并将弧根运动引入模型中。利用此模型计算了铁栅片烧蚀质量以及温度和熔化材料分布。仿真结果表明:栅片阴极端温升大小和范围均小于栅片阳极端的值。栅片表面熔化区域尺寸和位置随着弧根的移动而改变。栅片阳极端熔沸点来临时刻分别是2.19 ms和2.89 ms,烧蚀质量为1.84 mg。而栅片阴极端熔点来临时刻为4.12 ms,温度始终低于栅片材料沸点,烧蚀质量近乎为0。该文得到了单次开断下栅片两端烧蚀形貌,为研究多次开断下栅片烧蚀引起的栅片间短弧长度和移动路径变化对断路器开断性能的影响献力。

直流开断中触头边缘弧根停滞现象及影响因素研究

弧根演化过程对直流空气断路器的开关效率有显著影响。基于空气电弧磁流体动力学(MHD)模型,对触头边缘弧根停滞的根本原因进行仿真分析,得出外磁场大小和开断速度对触头边缘弧根停滞的影响。结果表明,弧根从触头转移至跑弧道是通过击穿完成的,触头边缘弧根停滞是弧根转移前跑弧道未达到击穿条件导致的。触头边缘弧根停滞时间随磁感应强度的增大而减少,并减少速度变慢,最后趋于稳定;燃弧初期,一定范围内提高触头开断速度有利于减少弧根停滞时间,但受洛伦兹力和气流场的双重影响,过高的开断速度对减少电弧停滞时间的效果减弱。

空气电弧射流表面改性提高硅橡胶电缆抗印字污染性能

硅橡胶电缆经常发生印字污染,影响使用。大气压等离子体表面改性技术广泛用于材料表面性能提升,但解决印字污染问题的相关条件、方法和效果等尚需研究。本工作利用高频交流电源驱动空气电弧射流对硅橡胶进行表面改性,通过发光图像、电学特性和光谱谱线强度表征射流的放电特性,并通过热成像仪获得射流处理下硅橡胶表面温升情况。模拟实际处理工艺,以不同移动速率处理硅橡胶表面。结果表明,射流处理能够有效解决硅橡胶表面印字污染问题,同时使硅橡胶表面的水接触角下降。在低速处理条件下,由于电弧的烧蚀作用,闪络电压和击穿场强均会降低。扫描电子显微镜(SEM)和X射线能谱仪(EDS)检测结果表明,处理后的硅橡胶表面交联聚合程度提高,抑制硅橡胶界面分子的扩散运动,从而提高了其抗印字污染性能。

微振动环境下空调系统减振降噪技术应用研究

为降低某地下厂房空调系统运行时产生的振动与噪声对精密仪器测试平台的影响,提出了一种空调系统减振降噪综合治理方法,应用低频气囊隔振装置及肘形挠性接管、弹性马脚等隔振元件,使空调机组隔振量达到45dB,应用阵列式消声器、双层微穿孔吸声板等降噪元件,使测试厂房空气噪声降低22dB(A)。综合治理后,测试平台基座线性加速度降低13.55dB,满足了该厂房测试平台微振动环境要求。

多翼离心风机叶片参数优化设计对壁挂式空调新风部件的气动性能研究

随着城市化的发展,舒适健康以及审美需求逐年提升,新风空调的销量越来越大,新风量、新风噪声都越来越受到用户关注,新风带来的困扰越来越凸显。为改善多翼离心风机的气动性能和噪声值,基于CFD数值摸拟与实验测试相结合的方式对单圆弧叶轮进行全参数优化设计。通过响应面设计方法对叶片进口安装角βb_(1)、出口安装角βb_(2)、叶片内径D_(2)、叶片数Z几个参数进行参数化设计。经过多组方案计算,获得叶片参数与风量和功率的关系。研究发现通过调整叶轮参数,改善叶片流道内的流场分布,能够有效提高叶片的做功能力并且降低风机噪声性能。与原型相比,实测同风量噪声降低0.8dB(A),功率降低11.8%。

小电流下弧根运动对空气直流电弧的影响

阴极弧根为电子发射的主要区域,弧根的运动对空气直流电弧等离子体特性有重要意义。通过电极旋转驱动阴极弧根运动,实验观测得到电极旋转情况下空气直流电弧拉弧过程电极表面烧蚀情况、扭曲的弧柱形态,同时提取并对比了直线拉弧和旋转拉弧的电弧电压上升曲线。参照临界电流试验条件,建立小电流下平行电极间三维电弧仿真模型,探究在小电流情况下,自由燃烧态电弧的演变过程。仿真结果表明:阴极弧根运动使得发射后极间带电粒子空间分布变化,间隙放电通道改变,电弧的最大温度值降低;当电弧放电通道不稳定时,极间电弧电压出现波动,电弧能量包络空间相对变小,间隙中高能粒子较少,有利于电弧能量的空间逸散。

Temporal and spatial evolution of air-spark switch plasma investigated by the Mach–Zehnder interferometer

An air-spark switch plasma was diagnosed by the Mach–Zehnder laser interferometer with ultra-high spatial and temporal resolution. The interferograms containing plasma phase shift information at different time were obtained. The phase shift distributions of the plasma were extracted by numerically processing the interferograms. The three-dimensional(3 D) electron density distributions of the air-spark switch plasma were then obtained. The working process of the air-spark switch was described by analyzing the temporal and spatial evolution of the plasma electron density.

磁吹直流空气断路器弧根跃迁及对开断特性的影响研究

直流空气断路器的弧根跃迁与其开断特性有着密切的关系。该文搭建实验平台,采用高速摄像机拍摄电弧演变过程,得到清晰的弧根跃迁图像,观测弧根跃迁过程中的“双弧根”现象。基于磁流体动力学理论,建立二维磁吹直流空气电弧模型。模型中赋入鞘层条件,通过耦合外电路模块模拟实验工况,对开断过程中电弧温度场、气流场及弧根跃迁现象进行分析。在此基础上,完成磁场、烧蚀金属蒸气浓度变化对弧根跃迁及开断特性影响的仿真研究。结果表明:磁场强弱会改变弧柱高温区的运动轨迹,影响前后侧的气流场分布,改变局部区域电导率,产生弧根的停滞与跃迁现象,显著影响断路器的开断性能。外施50m T磁场会发生弧根跃迁现象,弧根跃迁可以减少烧蚀,加速开断,其本质成因是通过“双弧根”完成的。“双弧根”现象是由于引弧板表面电导率增大,在其表面形成新的导电斑点形成的。烧蚀产生的金属蒸气不总是阻碍熄弧,当灭弧室中铜蒸气浓度达到50%~60%时,出现弧根跃迁,减少燃弧时间,有利于开断。

中压直流空气断路器短路分断电弧特性研究

基于磁流体动力学理论,考虑空间湍流影响,搭建多物理场耦合中压直流空气断路器大空间、全动态电弧模型,对中压直流空气断路器短路开断电弧进行仿真研究。结果表明:中压直流空气断路器在短路开断电弧过程中,弧根转移会导致弧压、弧流及功率出现波动,电弧弧根出现黏滞现象;栅片间弧柱区会产生电弧反向现象;电弧熄灭速度与外施磁场大小成正相关,但变化趋势并不呈现线性关系。为解决中压直流空气断路器短路电流开断困难问题,提供理论依据。

电弧作用下触头烧蚀特性的仿真研究

开断电弧对断路器触头的烧蚀会影响其使用寿命和可靠性。针对空气电弧作用下的断路器触头烧蚀行为进行了仿真研究。将电弧等效为正态分布的热源,基于传热学和流体学,分析了触头材料的温度变化过程和相变过程;此外,研究了熔池受力对熔池流动及温度的影响;最后,考虑触头材料的蒸发,模拟了触头表面的形貌及温度变化。仿真结果表明:触头温度由表面向内以半圆弧的形式扩散,熔池会先逐渐增大,在电弧作用消失一段时间后才逐渐减小;表面张力对熔池区域内的流动起主导作用,电磁力和浮力依次;考虑触头材料的蒸发时,触头表面会形成烧蚀凹坑,凹坑处的温度最高,凹坑随燃弧时间持续增大。

爆炸气流灭弧防雷装置试验研究与应用

为了提高高压架空线路的耐雷水平,解决电网防雷难题,基于“疏导式”防雷技术基础上研制了一种利用高速气流熄灭电弧的爆炸气流灭弧防雷装置。该装置允许空气间隙击穿形成电弧通道,并同时利用雷电脉冲信号在电弧形成瞬间同步触发灭弧气丸,以产生高速气流在工频电弧建弧初期就将其完全熄灭,并且强气流能快速恢复空气介质强度,防止电弧重燃。文中对该装置的灭弧原理进行了详细论述;通过雷电冲击试验、测试装置触发响应时间试验和工频大电流灭弧试验,检验了该装置的电气性能和灭弧效果,经试验发现其均满足试验要求;根据实际运行效果发现该装置在线路上运行工况良好,防雷效果十分优异。