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.

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。

直流空气断路器高海拔环境下电弧重燃现象及其抑制措施

高海拔环境下直流空气断路器(DC ACB)在电弧开断过程中易发生重燃,导致开断失败的概率增加。为了抑制DC ACB高海拔开断时的电弧重燃,以轨道交通用车载DC ACB为研究对象,建立了二维磁流体动力学(MHD)仿真模型,分析了不同海拔下DC ACB中的电弧演变过程,通过增大横向磁场及设置“C”形栅片对其高海拔开断性能进行优化。结果表明增大横向磁场,2 km、3 km海拔下DC ACB不发生电弧重燃,但4 km、5 km海拔下发生电弧重燃。4 km、5 km海拔下,在增大横向磁场的基础上采用含“C”形栅片的改进灭弧室结构,能够使DC ACB在高海拔环境下成功开断。

基于有限元法的主断路器断口缺陷分析

为减小产品尺寸,机车车辆主断路器断口间常采用灌封硅凝胶来改善绝缘性能。当灌封胶与灭弧室外壳及外支撑绝缘子间的粘接出现问题时,两个复合界面上将出现缺陷,形成由空气填充的气隙缝。文章针对该现象,预估气隙缝位置及大小并建立仿真模型,计算峰值为138 kV的标准操作过电压(250/2500µs)下该模型电场强度的数值大小和电场分布,着重分析了气隙缝周围的电场畸变。仿真结果表明:灭弧室瓷壳表面较外支撑绝缘子内表面气隙缝的电场强度大,畸变更严重。

LW25-252型断路器气动阀体密封圈检修(检验)方法

某220 kV站内进口设备LW25-252型断路器为单台供气式气动机构,内部气动阀由于存在运行时间较长,密封圈老化导致出现气动阀频繁漏气。文章通过研究该站LW25-252型断路器中VA133、VA134型气动阀,经过对气动阀的拆接、工作原理分析以及各部位密封垫作用,确定阀体内活塞杆密封圈为气动阀漏气根源,根据阀体活塞杆结构研制专用工具供拆解、组装阀体,并进一步模拟集中供气模式设计气动阀体检测平台,对修后气动阀进行自测自检,实现对该厂家VA133、VA134型气动阀自拆自修自检,降低对外部厂家援助依赖。

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.

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。

极地气垫破冰船发动机余热利用数值研究

为了有效利用极地气垫破冰船的发动机余热,需要研究相应的数值模拟方法。本文基于计算流体力学方法及混合物多相流模型,对包括舱室和垫升风机在内的内外部流场,进行与热交换相关的流场和温度场数值模拟。结果表明,加热对于改善垫升风机的推进效率有利,可使舱室平均温度上升41.13℃,垫升风机内平均温度上升34.16℃,对于极地气垫破冰船舱室及垫升风机内平均气温的提升有显著效果。混合物多相流模型用于数值求解此类热交换问题的有效性得到了验证。

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。

一起35 kV SF_(6)断路器气压低频繁告警的故障分析

SF_(6)气体绝缘高压断路器,其气压会因为泄漏和温度等原因而发生变化,对变电站安全运行造成影响。文章针对案例进行具体分析,在气压低频繁告警的故障发生时,应对断路器进行检漏检查,快速定位故障点,并加强在日常运维和检修过程中的防范。

电力机车用22CB系列真空断路器典型漏风故障分析

真空断路器用于接通及断开25 kV接触网与电力机车间的电路,它是机车电源的总开关和保护设备,研究分析真空断路器故障现象及产生原因能够对生产商制造工艺和机务段使用维护提供宝贵的指导经验。漏风故障是真空断路器主要的故障类型,文中通过对电力机车用22CB系列真空主断路器4起典型的漏风故障进行分析,对现有的真空断路器生产检修工艺及管理提供改善建议,从而降低产品故障率,提升可靠性,保障电力机车安全稳定运行。

地铁车辆司机室送风单元常见电气故障及对策分析

测试地铁车辆司机室送风单元电气故障件,分析故障原因,并提出相应对策。结果表明:空气断路器合闸时,变压器原边侧磁通量瞬变产生励磁电流从而导致故障发生;变压器的损坏多数是由于继电器触点粘连导致,需要注意变压器短路以防绝缘纸烧损;电机热继电器的整定值设定应将负载波动和电源波动考虑在内,减少保护故障的发生;中间继电器自身的灭弧能力对场景应用尤为关键;转换开关控制中间继电器切换时,触点间隔应大于继电器的切换时间。最后对送风单元中的空气断路器、电机热继电器、变压器、中间继电器、转换开关的选型设计要点进行总结。

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。

用三维有限元方法研究影响框架断路器电动斥力的因素

触头系统上电动斥力的计算对框架断路器(ACB)的设计有重要意义。为克服传统定性分析的缺点,提出一种定量分析的方法来研究影响框架断路器电动斥力的因素。该方法基于电流-磁场-电动斥力之间的方程,并考虑了铁磁物质的影响,应用三维有限元分析,首先研究了框架断路器通过恒定电流各动触头片电动斥力的大小及分布特点,然后分析了动触头并联支路数及转轴位置对电动斥力的影响,同时还研究了软联接对电动斥力的影响。计算结果可为ACB新触头系统的设计提供参考。

舰用框架断路器抗冲击动力学建模与仿真

舰用框架断路器受冲击载荷作用后的冲击响应特性对舰船电力系统能否可靠运作起着重要作用。本文建立舰用框架断路器冲击系统的数学模型,然后对冲击载荷作用下框架断路器进行了有限元建模和动力学仿真,分析了施加不同方向冲击载荷和施加不同大小冲击载荷时框架断路器机构的位移、加速度、应力历程、能量变化等动态响应特性,探讨了研究舰用框架断路器机构冲击响应的新思路和方法。最后,对舰用框架断路器抗冲击设计提出了一些建议。

考虑空间形位偏差的万能式断路器 关键零件断裂失效研究

在万能式断路器合闸时,弹簧所储存的能量以撞击的形式经打击杆传递给连杆机构。由工艺因素引起的打击杆形位偏差对打击杆的断裂过程产生影响,使操作机构的使用寿命远低于设计指标。该文根据多体动力学理论,建立操作机构的虚拟样机模型。通过试验采集储能杠杆和联动轴的运动状态,对虚拟样机的准确性进行验证。然后使用实际产品的测量数据,获得打击杆端点相对滚子的空间形位偏差范围。再使用虚拟样机参数建模表现偏差情况,分析打击杆载荷峰值和裂纹萌生周期的变化。最后假设打击杆上已存在椭圆形裂纹,研究偏差对裂纹尖端应力强度因子的影响。该文给出打击杆空间形位偏差对其断裂过程的影响,可以为设计及工艺改进提供理论指导。