Dielectric strength of series connected vacuum gaps

A simple procedure to obtain an analytical equation for the distribution function of breakdown voltage in devices containing an arbitrary number of identical elements in series is proposed. The obtained results make possible to analyze an influence of static properties of the elements and their number on the dielectric strength of a device as a whole. The probability of the breakdown of the switching device is calculated using the empirical distribution functions of breakdown voltages of each TVS. The Weibull plots are used to analyze the breakdown test results. The measurement of the dielectric strength performed for AC and DC devices shows a good agreement with the calculated data.     

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.     

Dielectric strength and statistical property of single and triple-break vacuum interrupters in series

The maximum possible improvement factor of vacuum circuit breaker (VCB) with multiple breaks compared with one-break, which had the same total gap length, was deduced. Based on the research on the breakdown weak points in high voltage vacuum gaps, a theoretic model was set up for describing the statistical property of multi-break VCB. Dielectric experiments were carried out on a commercial vacuum interrupter arrangements with single break or triple breaks in series under lightning impulse voltage. It shows that the more numbers in series are, the higher the breakdown voltage improvement factor is. The statistical results show that the triple-break vacuum interrupters in series have lower breakdown probability compared with a single-break one. It can be demonstrated in a preliminary study that the experimental results confirm the previous theoretical studies.     

激光触发开关同步特性的研究

利用高压电容放电开关试验平台,对两个氮气气体开关在266nm脉冲激光触发作用下开关的工作特性进行了研究。实验结果表明:两个开关的延时、抖动随激光能量的增加、欠压比的增大而减小。激光能量5.5mJ时,每个开关电压抖动时间达到了亚纳秒量级,但是两个开关的延时时间差大于1ns;当激光能量大于8mJ时,两开关导通的延时时间差达到了亚纳秒量级,可认为两开关同步导通。     

Dielectric strength of double and single-break vacuum interrupters:experiments with real HV demonstration bottles

This paper describes dielectric experiments on vacuum interrupters for HV applications. The investigations were performed with two different vacuum bottle designs. The difference between these objects is the number of breaker units per bottle and slight deviations in the shielding arrangement. On this basis the dielectric results of one and two interrupter units in one housing are discussed. The experiments show the gain of dielectric strength caused by conditioning effects, and were carried out under ac and lightning impulse voltage (LIV)     

真空开关真空度测试仪的应用

传统判断真空开关真空泡是否漏气的主要方法是通过交流耐压试验，但事实证明，用交流耐压试验并不能完全真正检测到真空开关真空泡漏气与否，最有交的方法是检测真空泡的真空度。为此，介绍一种可检漏方法－利用真空度测试仪检测，并介绍真空度测试仪的原理及其实际应用，实践说明真空度湿度测试仪能更加准确地反映真实泡的运行状况。     

妈湾发电厂F-C真空开关的改造

针对深圳妈湾发电总厂一期工程厂用中压系统的F－C真空开关缺陷较多的情况,对隔离开关解头、开关辅助触头等进行了技术改造,并通过更改绝缘件、防护板的结构和材质,增加小车导轨装置等措施来提高开关的安全性和“五防”功能。改造后开关的质量水平有明显的提高。     

Impulse breakdown voltages of triggered multistage vacuum gap

Several sealed-off triggered vacuum gaps are connected in series to improve hold-off voltage. The characteristics of impulse breakdown voltage of these series-connected gaps are investigated experimentally. The sum hold-off voltage of series-connected gaps decreases to a unit hold-off voltage when the maximum value of voltage division ratio across the gaps increases to unity. Self-breakdown probability of the series-connected gaps is always higher than that of a single gap under the same conditions. Hence, stage efficiency of the multistage gap decreases with increasing number of stages. Its value is 90 percent with 2-stage gap and 75 percent with 5-stage gap, respectively, under the same voltage division ratio and the same gap length (2.0 mm) in each stage. Triggered breakdown voltage of 2- or 3- stage gap is several hundred volts when all gaps are triggered simultaneously at the peak of the main impulse wave and a working voltage range is nearly 100 percent in this case. The working voltage range decreases with number of stages. Its value is 45 percent with 3-stage gap and 15 percent with 5-stage gap, respectively, when one triggered gap is fired for switching.     

浅谈高压真空开关的机械参数及其调试

分析了影响高压真空开关技术的机械参数后,提出机械参数的选择及其调试。     

Design rules for threshold switches based on a field triggered thermal runaway mechanism

We investigate a new type of threshold switching devices, which is based on a purely electronic phenomena. These threshold switches are polarity independent and switch abruptly from a high resistive state to a low resistive state at a threshold voltage. The device stays in this low resistive state as long as a high voltage drops over the device. When the voltage is reduced, the low resistive state is lost and the device switches back to the initial high resistive state. This makes these threshold switches highly interesting as selector elements for resistive switching memory concepts, based on device arrays, which are the prerequisite for new applications like logic-in-memory concepts. The threshold switching considered here is based on a combination of a Poole–Frenkel conduction mechanism and Joule heating. Hence, it is not strongly restricted to specific materials rather it is connected to the physical quantities of the Poole–Frenkel conduction mechanism and the thermal conductance. This enables to design the threshold switch to its application requirements by adjusting the relevant physical material properties or designing the device geometry. Here we present a theoretical study, which tackles the influence of several material properties and the device design. From this simulation model the impact on technical important figures of merits is determined, such as the threshold switching voltage and the selectivity.     

Dielectric surface flashover in vacuum at 100 K

Cryogenic components in high power electrical systems and in power electronics gain more and more importance. The behavior of insulators for cryogenic conditions, however, is virtually unknown. In a fast coaxial setup, dielectric test sample and electrodes in vacuum are cooled to <100 K and flashover is characterized using fast electrical and optical diagnostics. Three consecutive development stages for flashover in self-breakdown mode with a gap distance of 0.5 cm can be distinguished: (1) a fast current rise to mA amplitudes within ~2 ns, probably associated with field emission, followed by, (2) a slow current rise to ~5 to 10 A amplitude with duration of 40 ns to 1 μs, associated with secondary emission avalanche saturation, and (3) a transition to a rapid gaseous ionization above the sample caused by electron induced outgassing, leading to impedance-limited current amplitudes of ⩽300 A. Phase (1) shows a higher final current at lower temperature, which is probably due to a higher initial velocity of the secondary electrons, the duration of phase (2) is a decreasing function of breakdown voltage and only slightly dependent on temperature, which points to a weak temperature dependence of the outgassing process. Flashover potentials show a slight increase at lower temperature     

Dielectric surface flashover in vacuum. Experimental design issues

In order to determine the influence of intrinsic material properties of dielectric materials on high field surface flashover characteristics in vacuum, it is important that we minimize or eliminate the influence of the experimental test structure on the high field processes. In this paper we shall examine the flashover characteristics of polycrystalline alumina insulators, using a lateral test structure similar to the one used in semiconductor devices. A significant improvement in surface flashover strengths (~200%) was found using a metalized contact electrode system compared with a classical solid electrode system. The results indicate that, using a metalized film cathode, the scatter in the flashover data is significantly reduced compared with the solid electrode system, implying that the electron-dielectric interaction processes that lead to flashover occur in a more predictable fashion. The new metal contact electrode system reveals the dependence of flashover strength on the surface preparation and the grain size of the dielectric material. The average flashover strength increases and the scatter in the flashover data decrease with a decrease in the average grain size of the particles composing the alumina ceramic. Thus the surface flashover processes in vacuum are related to the dielectric surface microstructure, specifically the surface and sub-surface microdamage and grain-boundary defects     

Dielectric strength of transformer insulation at DC polarityreversal

Among special insulation tests for DC power converter transformers, polarity reversal tests can be substituted by applied AC voltage tests from a stress similarity in oil ducts. In order to investigate equivalent levels of other insulation tests to polarity reversal tests, the dielectric strength of a transformer at polarity reversals was examined by use of a model of typical oil/paper composite insulation. From the comparison of polarity reversal and other insulation tests, it was found that dielectric strength of transformer insulation at polarity reversals is phenomenally similar to that under switching impulse stresses. Equivalent AC test voltage to polarity reversal test was also estimated from the experimental results. The breakdown characteristics of polarity reversal tests showed that partial discharges at polarity reversals impose less harmful stress on insulation barriers than those at usual AC or impulse tests     

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     

Electric strength of vacuum systems with Co-Mo alloy coated Cuelectrodes

The paper presents the results of investigations of the electric strength at 50 Hz AC voltage of vacuum insulation systems that were not subjected to conditioning. The experiments have shown that a Co-Mo alloy coating electrolytically deposited on the surface of copper electrodes causes, at the pressure 2 mPa, >25% increase of electric strength of unconditioned vacuum insulation systems. This breakdown strength decreases with increasing gap spacing between the electrodes, and amounts ~17 kV/mm for systems with Cu electrodes at the electrode gap of 1 mm, and ~9 kV/mm at a gap of 6 mm. Plane electrodes with rounded-off edges of Rogowski's profile were used in the investigations. The electrodes with 50 mm diameter, were made of OFHC Cu. The paper shows the influence of the value of pressure from ~1 mPa to 1 Pa and at constant pressure of ~1 mPa, the length of vacuum gap, and the presence of a Co-Mo alloy layer coating the electrodes     

The irreversibility of dielectric strength of vacuum interruptersafter short-circuit current interruption

The irreversibility of dielectric strength of commercial vacuum interrupters after a large number of consecutive short-circuit current interruptions is investigated in order to find out how dielectric performance of a vacuum interrupter degrades during its service life. Breakdown voltage data were measured in appropriate experiments in which the types of tested interrupters and arcing conditions were varied. It was found that for interrupters with poor contact material the dielectric strength can deteriorate severely, falling below limits required by standards. It is concluded that the most important for the irreversible decrease in the dielectric strength is the contact material, i.e. its erosion properties. It appears that contacts with axial magnetic field are less susceptible to irreversible changes in dielectric strength after short-circuit current interruption than contacts with transverse magnetic field     

Dielectric breakdown strength correlation with time-to-failureduring wet aging of XLPE-insulated cables

This paper reviews two sets of failure information, the GMTF (a parameter obtained from time-to-failure results) and GMBD stress (a parameter that is calculated from AC breakdown test results), and suggests a correlation. The test results were obtained from accelerated aging experiments on full-sized medium voltage cables in carefully controlled and monitored water-filled tanks. Results show that the ambient temperature AC breakdown strength for equivalently aged cables is influenced primarily by voltage stress during aging-not by the aging temperature. The AC breakdown strength on equivalently aged cables was also shown to decrease with reductions in the aging voltage at all aging temperatures