考虑阴极斑点动态特性的真空灭弧室触头磁场计算方法研究

真空断路器广泛应用于中压电力系统中，利用触头线圈产生的磁场调控真空电弧是提高真空断路器开断能力的重要手段，然而目前的设计方法没有综合考虑阴极斑点动态运动与触头线圈磁场的耦合效应，影响其设计准确性和精度。本文建立了考虑阴极斑点与磁场耦合关系的触头磁场计算模型，根据阴极斑点分布计算触头间隙控制电弧的磁场，并由磁场推进阴极斑点运动。在四分之一匝线圈式触头下，分析了阴极斑点分布对触头磁场的影响，对比了考虑耦合关系对触头磁场计算结果造成的差异。仿真结果表明，在阴极斑点的初始扩散阶段，纵磁变化不明显，而横磁随阴极斑点扩散而变化；稳定燃弧时，考虑耦合关系与否的纵磁最大差值可达纵磁最大值的24.1%。本文所建立的模型以及计算方法为真空灭弧室触头提供了一种新的设计思路与方法。     

一种新型的四极纵磁场触头设计及其特点

纵磁触头已应用于真空灭弧室中，特别是在短路电流较大时，其应用更为普遍。本文介绍了一种新型的、基于四极性磁场结构的纵磁触头及其性能特点。论文首先介绍了这种新型触头结构的基本原理。主要是利用有限元法、通过三维磁场模拟来进行分析，接着主要研究了燃弧期间纵向磁场的磁通密度、电流和磁通密度的相位转换，以及触头上流过的电流。在有大电流流过时，四极性纵磁场对于电弧特性的影响是利用电弧高速摄像及燃弧后触头表面的照片来分析的。这种结构的触头通过短路试验验证，其开断性能已达到12kV／63kA。     

横磁场和纵磁场中真空电弧的离子能量

在真空断路器中，当电流达到几千安时会产生电弧集聚，我们使用两种触头来克服由于这种现象而产生的不良后果。横磁触头产生的横磁场使集聚电弧旋转，电有量均匀地分布在触头表面。纵磁触头可以防止电弧集聚到很高的能量。为了提高这两种真空断路器的开断容量，了解电流零点附近真空电弧等离子体（即真空电弧）的特性和变化过程，如等离子体的密度、等离子体的衰变以及能量就十分重要。在本文中，我们主要是用延迟场分析仪来研究电流过零前最后3ms内电弧电流的有效值达到了7．5kA时真空电弧等离子体中离子能量的分布状况。研究发现：横磁和纵磁触头的电弧离子能量存在着明显的差别。在电流超过5kA时，这两种触头上电弧离子能量的分布接近于麦克期韦（Maxwellian)分布，这是一种由离子碰撞决定的等离子体的特有分布。也就是说，在电流接近零点时，横磁触头中电弧离子的运动具有很强的方向性，而纵磁触头中能量的分布却明显受到离子碰撞的影响。     

杯状纵磁真空灭弧室三维涡流场仿真

对杯状纵磁真空灭弧室触头建立了与实际触头结构完全一致的有限元分析模型，模型中把电弧弧柱处理成圆柱形金属导体。对模型用有限元法进行了三维涡流场仿真。仿真结果表明，考虑电弧以及杯和电弧的涡流效应后，在电流峰值时，触头片中电流密度最大值变大；触头片上槽一侧的纵向磁场比另一侧强；磁感应强度B矢量在触头表面上的分布呈“旋涡”形状，其纵向分量在触头中心较大，越靠近触头边缘越小，而横向分量则增大；电流过零时，与未考虑电弧以及杯和电弧的涡流效应时的计算结果相比，触头间隙中心平面上及触头表面上的纵向磁场分布变为“帐篷”形状，纵向磁感应强度最大值也变大。在触头开距中心处纵向磁场较强且纵向磁场滞后时间也相对较长。     

纵磁结构触头涡流的仿真分析

电弧熄灭后,真空触头间隙中的剩磁是由触头结构中各部分的涡流所产生的,其中主要是触头片中的涡流。本文利用有限元法对1/2匝和1/3匝纵磁结构触头在大开距下的涡流特性进行了仿真研究,对比分析了触头结构、开距以及触头片开槽方式等对涡流、纵向磁场滞后时间的影响。     

提高真空灭弧室额定电流下的开断次数

本文述叙真空灭弧室加强型纵向磁场的触头结构。纵向分量磁场的单位感应密度达到１０ＭｒЛ／ｋＡ。从而缩短了收缩型强电弧（１〉１０ｋＡ）变为准扩散型电弧的时间，在电弧由收缩型变为准扩散型之前，电弧在整个触头表面的运动是收缩在磁场横向分量上。控制这两种强电流电弧变态可以降低触头分断速度并且在保持短路电流分断能力的情况下能成倍地提高真空灭弧室的开断次数。     

真空开关管加强型磁场触头

本文描述真空开关管中具有放大了的纵向磁场触头的设计。规定的级向磁场的磁感应达１０ｍＴ／ｋＡ，这是大电流电弧由聚集型向准扩散型转化时间减少的缘故。触头表面的电弧运动由聚集型向准扩散型墨迹的横向磁场来控制。两种大电流电弧模型都可以降低触头分离速度。在单相实验中，直径约７０ｍｍ的触头可分断２５－２７ｋＡ的电流，其分离速度为１．１ｍ／ｓ和０．８ｍ／ｓ，５０Ｈｚ，恢复电压为３５ｋＶ。     

真空灭弧室纵磁场和横磁场触头优化选择的标准

真空中开断大的交流电流时，金属蒸汽形成的电弧会在触头间隙燃烧直到下一个电流零点。然而如果电流达到大约10kA的范围时，电弧将由于自生磁场产生集聚，为了避免局部触头过热，有两种方法：通过械磁场（RMF）使集聚型电板在触头表面运动。通过纵磁场（AMF）阻止电弧集聚。本文对纵磁场和横磁场的功能原理和物理过程做了简要介绍；在低，中，高压范围内，将横磁场与纵磁场从开断能力，电阻，管子尺寸和生产成本等方面做了比较。     

大电流真空断路器的研究

本文研究的目标是测定电流峰值增至１００ｋＡ时要保持扩散型电弧的纵向磁场强度。磁场是由流过真空灭弧室（ＶＩ）外的线圈的电流产生的。用数码像机观察电弧并研究电弧聚集和电弧电压间的关系。１００ｋＡ（峰值）的电弧在５．５ｍＴ／ｋＡ时能保持扩散。然后，分析了触头速度的影响。测定了分闸电流与气体压力和瞬态恢复电压（ＴＲＶ）的关系。     

真空开关管开断能力随触头几何形状变化的关系

真空断路器触头的形状和大小各不相同,关于它们开断能力的系统研究已有报道。各种几何形状的电扳可产生自激的横向或轴向磁场(其强度与电流有关),其开断电流的极限值也因而确定。令人尤感兴趣的是电弧的外观(发散或集中,体现在电弧电压的波形中)、触头的抗腐蚀性能以及电弧运动对灭弧能力的影响。Weil—Dobke 综合试验电路,其最大电流为60kA(有效值),电压状态与20kV 的电力系统相对应。单极开断试验的实验就是应用此线路及一台可拆卸的真空良装置进行的。实验的结果表明:开断能力总的说来随触头直径的增大而提高。横向磁的结构为电弧在整个使用寿命期间保持良好运动状态创造了条件,因而使性能得到改善,但轴向磁场结构的触头所得到的结果最好。     

纵向磁场对真空电弧作用的研究

本文研究了真空电弧与使其保持扩散型的纵向磁场间的关系，并得出了电弧电流与纵向磁场间的关系式。     

Vacuum arc recovery phenomena

The present experimental and theoretical study has been designed to uncover the mechanism underlying the rapid recovery of electrical strength of a short vacuum gap after arcing. In the experiment the contacts were of gas-free silver and the contact area and gap length were varied. Recovery strength was measured following the forced extinction of a 250 amp arc in 0.5 µsec. This rapid cutoff of current has revealed detail in vacuum arc recovery curves which is difficult to observe by other experimental techniques. The experimental results show that the gap recovery times range from 1 to 30 µsec depending on the gap proportions. Recovery is most rapid for large diameter contacts which are closely spaced. In the theoretical analysis, the recovery times for various gap proportions were calculated by following the decay of the metal vapor density in the gap from an initial density, present at arc extinction, to a final critical density characteristic of full gap recovery. The reasonable agreement between the measured and calculated recovery times lends support to a model in which condensation of metal vapor on the contacts plays a decisive role in the rapid recovery of electrical strength in a vacuum gap after arcing.     

Plasma Parameters in the Reactor with Simultaneous Magnetron Discharge and Inductive Radio-Frequency Discharge in the Presence of External Magnetic Field

A plasma reactor that contains vacuum–arc and magnetron sputtering sources and radio-frequency discharge that generates high-density plasma in the presence of external magnetic field is developed, constructed, and optimized. The reactor can be used for deposition of various functional coatings with ion stimulation. The parameters of the inductive radio-frequency discharge generated in the presence of external magnetic field that serves as a source of assisting ions are optimized. It is shown that the working interval of the induction of external magnetic field corresponds to the resonant excitation of the coupled helicon and Trivelpiece–Gold waves. The effect of magnitude and configuration of magnetic field on the parameters of gas-discharge plasma and ion current in the substrate region is studied in the presence of separately and simultaneously initiated magnetron and inductive discharges. The effect of ion flux that is incident on the films in the course of growth on the structure of functional coatings is analyzed.     

The unusual electrical erosion of high tungsten content, tungstencopper contacts switching load current in vacuum

The electrical erosion of high tungsten content, tungsten-copper (7-10 wt.% Cu) was investigated. The contacts were placed in a vacuum interrupter envelope with a background pressure of about 10^-6 torr. The contacts switched one half cycle of 60 Hz current per operation. The polarity of the current was changed on each operation. Six contact pairs were investigated. Each pair was subjected to an ever-increasing number of operations: 1 K, 5 K, 10 K, 20 K, 40 K, 50 K, and 60 K. The contact erosion was inferred by measuring the linear position of the moving contact terminal. On completing the electrical testing, the vacuum interrupters were dismantled and the contact surfaces were observed. Unlike the previous work on Ag-WC (50 wt.% Ag) and Cu-Cr (75 wt.% Cu), the W-Cu contacts showed a localized build up of erosion products on the contact surfaces even beginning at 1 K operations. The experiments were repeated switching a unidirectional current i.e., the contacts remained at the same polarity throughout the experiments. Here an anode pip and a cathode crater were formed immediately. The difference in the topographies of these contacts is discussed in terms of the metallographic analysis of the deposits on the contacts, the erosion deposits on the shields surrounding the contacts and the expansion of the vacuum arc     

Magnetic field measurements with a novel surface micromachinedmagnetic-field sensor

The surface micromachining process of Robert Bosch GmbH has been used to fabricate a novel type of magnetic-field sensor. The Lorentz force, caused by the interaction of a current and an external magnetic field in a suspended surface micromachined conducting beam, laterally displaces the suspended structure. The displacement of the structure is converted into a capacitance change by comb-electrodes, which form a differential capacitor. An appropriate electronic circuitry measures the magnetic field by quantifying the displacement of the conducting beam. In order to increase sensitivity to magnetic fields, the magnitude of the deflection is increased by resonant operation in a vacuum ambient. The sensor obtains its vacuum environment by encapsulation with a new wafer bonding process. Prototype sensors with resonant frequencies in the range around 1300 Hz show Q-factors above 30. With these samples, relative magnetic sensitivities of 900 000 (V/A·T) with a detection limit in the sub μT-range are reported     

Arc stability characteristics of vacuum switches

The surface layer of a newly manufactured vacuum switch with two-phase composition contacts, e.g., Cu+2-percent Bi or Cu+2-percent Te, exhibits a strong arc stability behavior, which tends to decrease with the erosion of the surface layer. In comparison, unalloyed metals, Cu or W, and single-phase compositions, Cu2Te, show a homogeneous arc stability behavior.     

真空断路器灭弧系统的解析

本文介绍了真空电弧的灭弧机理,在此基础上分析灭弧系统中电极结构、电极材料、屏蔽罩和真空度等对真空断路器灭弧性能的影响.     

Magnetically controlled vacuum-arc on-off switch

A vacuum spark gap is demonstrated which attains high-power switch-off capability by a magnetic control field applied to the anode in a Penning-type discharge geometry. Applying the magnetic field raises the arc voltage and excites oscillations. Circuit interruption results if the arc current is reduced to the current chopping level of the cathode material. Shunt capacitance raises the interruption ability. Currents up to 9 kA were interrupted. Transient recovery voltages ranged up to 20 kV.     

真空灭弧室向高电压大容量发展的关键问题

讨论大开距下纵向磁场与真空电弧的相互作用，测试了高电压真空灭弧室的耐压特性，分析了长行程高速运动波纹管的运动特性，指出国内高电压大容量真空灭弧室生产工艺中的关键问题。