Non-sustained disruptive discharges: test experiences, standardization status and network consequences

In the test practice of KEMA 32% of the vacuum circuit breakers offered for testing in 1999 have shown non-sustained disruptive discharges (NSDD), mostly within 300 ms after interruption. This implies, that although current has been interrupted, very brief periods of conduction occur, which seems to be an accepted inherent property of vacuum switching devices. NSDDs occurred in the complete range of rated voltages (12 kV-50 kV) and short-circuit breaking current (12 kA-40 kA) of the tested devices. No clear correlation of NSDD occurrence with arcing current could be established. In 79% of the cases, less than four NSDD occurrences per test report were counted. It is demonstrated from short-circuit current test data that during the occurrence of NSDD, a much larger part of the circuit is contributing to transient phenomena than just the "local" parasitic in the immediate vicinity of the breaker. This is derived from the measured duration of the conducting period during NSDD and contradicts the general notion that NSDD is just a local phenomenon, the duration of which is entirely determined by the parameters of the switching device itself. The new standard IEC 62271-100 for circuit breakers makes no distinction between (a) capacitive re-strike (late breakdown leading to polarity reversal of the load capacitor) and (b) NSDD in the case of a vacuum switching device breaking down more than half a power frequency cycle after capacitive current interruption. It is demonstrated that over-voltages that accompany such "capacitive NSDDs" certainly can not be neglected.     

Insulation recovery characteristics after current interruption by various vacuum interrupter electrodes

Insulation recovery characteristics after current interruption for a vacuum interrupter were investigated. We used spiral and axial magnetic field electrodes for comparison of the electrode structure, while CuBi and CuCr were also used for comparison of the contact material. This paper describes how the axial magnetic field electrode and CuCr (50%) performed best in our experimental data. In addition, we discussed reasons for the variation in characteristics between electrodes.     

纳米CuCr50触头材料电弧侵蚀特性

近年来,纳米CuCr触头材料在截流水平、耐压能力等方面的表现优于微晶CuCr触头材料。笔者利用真空触点模拟装置和基于虚拟仪器的电器电寿命测试系统,研究了直流低电压、小电流下的纳米CuCr50触头材料的电弧侵蚀量与分断燃弧时间和触头表面形貌之间的关系,同时采用两种微晶CuCr50触头材料作为对比。利用电光分析天平纳米CuCr50触头材料的侵蚀量,利用电子扫描显微镜测量触头表面形貌。结果表明:纳米CuCr50触头材料的平均分断燃弧时间和侵蚀量均高于两种微晶CuCr50触头材料。纳米CuCr50触头表面Cr颗粒细化及均匀分布,有利于分散电弧。纳米CuCr50阴极触头表面电弧烧蚀比较均匀,而两种微晶CuCr50触头阴极表面电弧局部烧蚀严重,出现明显的凹坑侵蚀。     

Dielectric strength of a vacuum interrupter contact gap after making current operations

Experimental results concerning the breakdown voltage and prebreakdown current of a vacuum interrupter contact gap, after making current operations, are presented. The dielectric strength of the contact gap is lowest for a switching sequence during which a making of high current is followed by a no-load contact opening. The breakdown voltage is much lower than after making operation, followed by interruption of a sufficiently high current. The basic process of breakdown initiation appears to be field electron emission from a specific structure on the contact surface, created by weld rupture.     

Recovery of breakdown strength of a vacuum interrupter after extinction of high currents

Relevant phenomena during the period of the recovery of the dielectric strength of vacuum interrupter (VI) are reviewed. Metal vapor, residual charge and the effects of molten contact surfaces reduce the breakdown strength after the interruption of high currents. Metal droplets seem to play only a secondary role during the recovery phase. Instability of liquid protrusions is suspected to initiate breakdown if the electric field strength exceeds 10 kV/mm at the molten contact surfaces (undisturbed field). Key parameters are surface temperature and vapor density. Breakdown during recovery of the dielectric strength depends not only on the value of the voltage applied but also on the duration of the high voltage stress. A spontaneous triggering event in the presence of metal vapor appears to initiate breakdown at conditions below the Paschen breakdown limit. This type of breakdown events limits the interruption performance of VI's.     

Influence of switching on dielectric properties of vacuuminterrupters

This paper deals with the influence of switching operations `closing without current/breaking without current', `closing without current/breaking with rated current', and `closing without current/breaking of rated short-circuit current' on vacuum interrupter dielectric strength. Two types of commercially available vacuum interrupter with transverse magnetic field CuCr contacts were tested. Breakdown voltages and emission currents, which appear before and after switching operations, were determined experimentally. The corresponding characteristics were determined after conditioning. The voltage shapes, dc, lightning impulse voltage (1.2/50 μs), and 50 Hz ac were applied. The obtained results were statistically treated. After taking into account theoretical considerations, it was concluded which physical mechanisms determine the influence of switching operations on the dielectric strength. It was found that in interrupters with poor contact material, the dielectric strength can deteriorate below the limits required by standards     

Study on Restrike Phenomena for 40.5-kV Vacuum Circuit Breakers

Introduction Modern vacuum circuit breakers with vacuum interrupters have been used widely to switch and protect distribution cir- cuits[1]. Vacuum circuit breakers, in contrast to other circuit breakers, possess the following features[2].1) They provide …     

Influence of switching operations on the vacuum interrupterdielectric strength

The influence of switching operations on dielectric strength of vacuum interrupters is described. Detailed experimental procedure and numerical processing of experimental results are presented. The breakdown voltage and emission current before and after switching operations were experimentally determined for closing without current/breaking without current, closing without current/breaking with rated current, and closing without current/breaking of rated short-circuit current. The interconnect gap was varied, and DC lightning impulse voltage (1.2/50 μs) and AC 50 Hz voltages were applied. Three types of commercially available vacuum interrupter were tested, two with transverse and one with axial magnetic field and all having CuCr contacts. It was found which physical mechanisms determine the influence of switching operations     

Contact behavior in vacuum under capacitive switching duty

According to the relevant IEC standards vacuum circuit-breakers have to meet various needs, e.g. the interruption capability, making operations, and dielectric strength. Besides the interruption of short-circuit currents, switching of capacitive currents causes high stress of the circuit-breaker. Switching of capacitor banks, overhead lines, or cables leads to very small currents in comparison with short circuit currents. After current interruption the circuit-breaker must withstand twice the peak value of the system voltage. Furthermore, restrikes can lead to voltage multiplication. This conjunction of relatively small breaking currents with high voltage stress must be considered in detail. This work introduces a test arrangement for combined tests of making operation, current interruption, and dielectric stress of a vacuum gap under capacitive switching condition. A test vessel permits investigations of various contact materials and designs. It is connected to a synthetic test circuit which provides the appropriate test currents and capacitive voltage. During the test sequence the contacts are stressed by inrush-currents up to 4.5 kA peak, followed by a breaking operation at 500 A peak and a subsequent capacitive voltage up to 50 kV peak. Both the appearance of pre-ignitions at contact closing and the behavior under capacitive voltage stress after breaking are indications of the contact surface conditions.     

1000kV同塔双回输电线路绝缘子串污秽特性

为了研究1000kV同塔双回输电线路绝缘子串的污耐压特性,按照真型布置,依据GB/T4585-2004采用升降法求取绝缘子串的50%污秽闪络电压。内容包括不同型式、不同串形绝缘子的污耐压特性,附灰密度(ρNSDD)、上下表面不均匀积污对污耐压的影响等。指出单V串污耐压特性优于I串污耐压特性;ρNSDD的增加使得绝缘子的U50%下降;上下表面不均匀积污时的U50%高于均匀积污时的U50%等。研究结果对1000kV特高压同塔双回线路绝缘子串的选型及污秽外绝缘配置具有重要指导意义。     

三种CuCr触头材料对真空灭弧室投切背靠背电容器组性能的影响

为研究三种不同触头材料(真空熔渗CuCr50、真空熔铸CuCr40Te0.005、电弧熔炼CuCr50)对真空灭弧室投切背靠背电容器组性能的影响,将采用三种不同材料制备的触头各装配在三只相同的12kV等级真空灭弧室中,每只真空灭弧室经过80次背靠背电容器组合分操作,高频涌流设定为幅值8 kA、频率3.8 kHz。结果表明:真空熔渗CuCr50、真空熔铸CuCr40Te0.005以及电弧熔炼CuCr50的平均重击穿概率分别为6.7%、5.8%、8.3%,重击穿现象主要发生于恢复电压持续时间的1/4T与10T之间(T表示恢复电压周期20 ms);复燃现象多次出现,真空熔铸CuCr40Te0.005(1次)电弧熔炼CuCr50(9次)真空熔渗CuCr50(10次)。     

两种铜基触头材料的电弧侵蚀性能研究

电接触材料在工作过程中会受到机械磨损、环境腐蚀及电弧侵蚀,其中,电弧侵蚀对电接触材料影响最大,它是影响接触材料的电寿命和可靠性的最重要因素。笔者对采用熔渗法制备的CuCr50与电弧法制备的CuCr45电接触材料分别进行DC 50 V,20、30、40、50 A的电接触试验,并通过扫描电镜观察材料在电弧侵蚀后的形貌,对这两种材料在直流、阻性负载条件下的电弧侵蚀特征进行对比研究。结果表明,CuCr45与CurCr50在DC 50 V,20、30、40、50 A条件下,材料都由阳极向阴极转移;之后归纳出电弧侵蚀后两种材料的表面形貌特征,最后分析了两种材料的燃弧能量与熔焊力。     

盐密和灰密对110kV复合绝缘子闪络电压的影响

合成绝缘子具有很好的防污闪特性,但也会发生污秽闪络,这与常规的人工污秽试验仅考虑盐密的影响不无关系。文中选择110kV合成绝缘子为试品,在人工雾室中研究了灰密(NSDD)和盐密(ESDD)对合成绝缘子污闪特性的影响,分析了NSDD影响的原因,并采用2种方法对试验数据进行了分析和拟合。结果表明:人工污秽试验中,合成绝缘子污闪电压Uf与ESDD和NSDD均有关,但二者的影响是彼此独立的;随着ESDD或NSDD的增加,其Uf均按幂函数规律降低;ESDD和NSDD对Uf影响的特征指数分别为0.106、0.140,即对于合成绝缘子,灰密的影响大于盐密,这与瓷绝缘子相反;灰密对污闪电压影响的原因之一是吸收更多的水分,二是破坏合成绝缘子的憎水性。     

纳米触头材料电性能研究进展

分析了纳米材料与常规材料在热学性能和机械性能上的差异,综述了纳米触头材料在截流水平、抗电弧侵蚀和耐压能力等电性能研究上取得的进展,并对已有研究成果进行了概括和总结。结果表明:相对于同种配比的常规触头材料,纳米CuCr和AgFe触头材料的截流水平低于常规触头材料;纳米CuCr和AgFe的直流电弧稳定性高于常规触头材料,直流电弧寿命大于常规触头材料;纳米CuCr触头材料的耐压能力高于常规触头材料;纳米AgSnO2和AgNi触头材料的抗电弧侵蚀性能优于常规触头材料。因此,在今后对纳米触头材料的研究和开发过程中,加强纳米触头材料制备工艺研究和纳米触头材料的理论研究,有利于提高纳米触头材料电性能。     

Compact high-voltage vacuum circuit breaker, a feasibility study

This study focuses on a compact vacuum circuit breaker (CB) for nominal voltage of 72.5 kV, nominal current of 2000 A and short circuit current of 31.5 kA. The dielectric conception of the vacuum interrupter (VI) is based on a multiple floating shield configuration which reduces the risk of total breakdown due to partial breakdown between the contacts and shield. An optimised electrical field distribution on the contact surface with the maximum field pointing towards the floating shield is arranged and hence reducing the breakdown effective area of the contacts facing each. All tests have been performed on a specially designed single-phase circuit breaker pole-unit equipped with a low energy spring type mechanism. Interruption performance was confirmed in direct tests. The circuit-breaker pole was proved to be restrike-free with respect to cable charging class C2. Dielectric tests in new condition and after interruption tests confirmed the announced ratings. These tests confirm the feasibility of this HV-CB with 25% more compact VTs based on the outlined dielectric conception.     

Weibull分布在真空断路器容性关合预击穿特性研究中的应用

当前选相合闸技术在断路器的容性开合工况中应用越来越广泛,而预击穿开距的分散性严重制约着选相关合策略。文中的研究目标是采用熔铸法制备灭弧室触头的40.5 kV真空断路器在容性开合运行工况下的预击穿开距分布情况。试验中采用熔铸法制备的直径为50 mm的CuCr40触头作为试品,通过L-C振荡回路产生了幅值6.48 kA、频率207 Hz的关合涌流,考虑35 kV三相不接地系统中容性系数为1.4的情况,关合过程中的外施电压设为46.3 kV。试验结果表明,预击穿开距dpre的余补累积概率满足三参数Weibull分布,并且3只灭弧室试品总是发生预击穿的预击穿开距基本相同,均为约1.6~1.9 mm,而预击穿开距的分散性则各不相同,约为3.4~6.0 mm。这意味着随着关合操作次数的增加,灭弧室的预击穿开距分布会显著变化,因而对于在真空断路器进行容性开合时考虑采用选相合闸技术而言,预击穿开距的分布是至关重要的。     

Capacitance switching with vacuum circuit breakers-a comparativeevaluation

A statistical approach for determining the probability of reignition during capacitance switching by vacuum circuit breakers is described, wherein the dielectric recovery following current interruption is probed by overstressing the contact gap. It is found that the breakdown data can be quite well described by the Weibull distribution. The method is used to compare the capacitance switching performance of vacuum interrupters having copper/chromium and copper/bismuth contacts. Results imply a reignition rate for copper/bismuth almost two orders of magnitude higher than that for copper/chromium. Reignitions tend to occur when the arc angle (the period of arcing before current zero) is short, regardless of the contact material. The gap between CuCr contacts recovers more quickly than that between CuBi contacts. Very few reignitions after 2.5 ms were observed with CuCr contacts, whereas for CuBi reignitions persisted from 6 to 7 ms. This increases the likelihood of an overvoltage accompanying a reignition     

Optical investigation of AC preflashover of alumina ceramic in vacuum

Optical phenomena accompanying the preflashover along a planar metal-alumina-metal structure were investigated under stepped AC voltage in vacuum. Two kinds of electrode contacts with and without sputtered gold films were employed. For sputtered alumina, the luminescence became observable at /spl sim/1 kV/sub peak/, and revealed two stages depending on the amplitude of applied voltage. For non-sputtered alumina the optical emission appeared at a much higher voltage and presented irregular and discrete light pulses. The energy band at the metal-alumina interface for the two kinds of electrode contacts is responsible for the relevant optical mechanisms. For non-sputtered contact, the light emission was initiated by field electron emission from the triple junction. While for the sputtered contact, prior to the electron emission, electrons/holes could be injected from electrodes into the surface layer of alumina and electroluminescence phenomena occur due to the radiative electron-hole recombination. Injected electrons form a long-term negative space charge region away from each electrode and hence at a critical applied voltage, the trapped electrons are detrapped resulting in intense light emission. These processes play a significant role in the development of flashover.     

合金元素对CuCr触头材料不同温度下真空耐电压强度的影响

研究了合金元素W、Co对真空中CuCr触头材料在不同温度下的真空耐电压强度的影响。研究结果表明,高温时CuCr材料的耐电压能力比室温耐电压能力有所降低,合金元素W、Co通过弥散强化、固溶强化和增大了CuCr的表面张力而提高了CuCr材料室温及高温时的耐电压能力。     

户外高压隔离开关电触头温升机理研究

针对110 kV以上电压等级隔离开关电触头易发热的现象,以具有代表性的GW4A-126型高压隔离开关为对象,研究电触头的温度特性。在简化电触头结构后,应用有限元分析软件ANSYS 建立触指部分的三维模型,在不同接触电阻、接触面积和负载电流的条件下对模型施加载荷,根据得到的温度场分析触指最高温度的变化情况。仿真结果表明：接触压力、接触电阻、接触面积、负载电流和触点材料是影响电触头温度的主要因素;接触电阻和负载电流越大,电触头温升幅度越明显;增大接触面积可以提高电触头的热稳定性。