Thermally and electrically induced bubbles in liquid argon andnitrogen

An experimental study of high field conduction phenomena in liquid argon and liquid nitrogen in a point-plane electrode geometry is reported. These liquids behave qualitatively like saturated hydrocarbons except when they are studied close to their normal boiling point. The generation and dynamics of microscopic bubbles (thermally and electrically induced) as a function of various parameters (nature of the liquid, injected energy, hydrostatic pressure) are presented and discussed. Possible influences of these phenomena on the electrical insulation at cryogenic temperatures is also discussed     

Influence of liquid temperature and electrode size on insulated breakdown characteristics in saturated superfluid helium

The dc breakdown strength and pulsed breakdown time lag of saturated superfluid liquid helium (HeII) at 1.4 and 1.85 K are measured over a wide range of electrode sizes and applied field strengths. The results of the measurements are statistically analyzed by using Weibull distribution functions. It is found that the area effect is dominant for dc and pulsed breakdown rather than the volume effect as in the case of liquid helium of 4.2 K (HeI). The shape parameter in the Weibull distribution function for dc breakdown strengths of HeII is smaller than that of HeI. As a result, dc breakdown in superfluid helium can take place in a wider electrode area than in normal liquid helium, while no remarkable differences in breakdown areas are observed between 1.85 and 1.4 K. On the other hand, the statistical time lag in HeII becomes shorter with a decrease in temperature. According to the Fowler‐Nordheim theory, it is suggested that a higher electron mobility in HeII may increase the field‐emitted electron kinetic energy to trigger liquid breakdown with a higher probability. © 1999 Scripta Technica, Electr Eng Jpn, 128(3): 16–23, 1999     

DC breakdown voltage characteristics of saturated liquid helium in the presence of metallic particles

This paper deals with the breakdown voltage characteristics of saturated liquid helium in the presence of a needle-shaped or spherical metallic particle to obtain insulation design data for pool-cooled, low-temperature superconducting coils and to find the predominant factor affecting the breakdown voltage of liquid helium at a given state. The results show the following. (1) The generation of bubbles at the instant of collision of a particle with an electrode is caused mainly by the kinetic energy released from the moving particle to the liquid helium, while the electrostatic energy accompanying the microdischarge between the particle and the electrode has a lesser effect on it. (2) The lowest breakdown voltage at different particle conditions appears in the case of a free needle particle. The low breakdown voltage is caused by the bubble triggered by the particle collision, the high electric field at the tip of the needle particle, and the rich initial electrons supplied by the microdischarge.     

Surface charge accumulation and decay on a spacer stressed with DC voltages at atmospheric conditions

Contents Surface charge accumulation and its decay at a GIS spacer are studied at atmospheric conditions employing a two step-calibration method. The results show that the accumulation saturates within 30 minutes; the dominant mechanism of surface charge accumulation is the drift of charged particles via air, while that of the decay is surface conduction. The characteristics are similar at both polarities.

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Sättigungskonzentration und Abklingverhalten der Oberflächenladung an einem mit Gleichspannung beanspruchten Abstandshalter unter atmosphärischen Bedingungen

Übersicht Die Konzentration und das Abklingen von Oberflächenladungen an einem GIS Abstandshalter wurden unter atmosphärischen Bedingungen mit Hilfe eines zweistufigen Kalibrierungsverfahrens untersucht. Die Ergebnisse zeigen eine Sättigung der Ladungskonzentration innerhalb von 30 Minuten. Als Hauptursache der Ladungskonzentration ist die Drift geladener Teilchen in Luft anzusehen, während das Abklingen auf die Oberflächenleitung zurückzuführen ist. Ähnliche Charakteristiken ergeben sich mit beiden Polaritäten.

     

Detection of possible voltage collapse buses in stressed power systems based on information from multiple solutions in load flow calculations

Conventionally, most voltage stability indices, including the voltage instability proximity index (VIPI), have been formulated for the overall system. Voltage instability phenomena, however, can occur locally and then cause cascade collapses throughout the system. Therefore, it is of some importance to establish an index that can locate the possible voltage collapse buses in power systems efficiently. In this paper, we describe the local properties of the information of multiple solutions in load flow calculation and their use in voltage instability assessment. It should be noted that this kind of information is formatted in the voltage space rather than in the specified value space. Therefore, it is difficult to obtain information in the specified value space, and the qualitative property in a simple one-machine one-load (two-bus) power system may not be generalized for multimachine multiload power systems. We present our investigation by considering several model systems and quantitatively comparing them with the two-bus power system. Taking advantage of the power flow formulation, it can be concluded that the localization of the voltage variation vector that indicates the initial direction of the voltage collapse will provide exact information for identifying problem buses in the system. The nose curves of problem buses can be obtained for monitoring purposes at the same time. With the application of these results and VIPI, an emergency countermeasure is suggested for monitoring and delaying possible voltage collapse in stressed power systems. © 1997 Scripta Technica, Inc. Electr Eng Jpn 119(1): 45–54, 1997     

The effect of the electrode gap on breakdown in liquid dielectrics

It is a well known fact that the breakdown voltage of an insulating liquid increases nonlinearly with increasing electrode gap. Under nonuniform field dc conditions two breakdown voltages are determined depending on the electrode polarity. Using point-plane geometries, with gaps of 5 mm or larger, one finds that typical transformer oils have higher breakdown voltages when the point is negative than when it is positive. Recently, perfluorinated polyethers have been found to produce opposite results when using average gap sizes of 5 to 10 mm. To elucidate this situation a study of the effect of gap size on breakdown voltage has been undertaken. The results show that for the polyethers at larger gaps the sequence is reversed. These observations are explained in terms of the respective streamer developments in these liquids and the relative stability of their negative ions. In the case of the conventional hydrocarbon type oils, the positive streamer usually grows slightly faster than the negative one, but the streamer inception voltages of both are rather similar. In the case of perfluorinated polyethers the positive streamers move at least 10× faster than the negative ones, but they require much higher inception voltages than negative ones. At gaps ≳12 mm and the associated higher applied voltages this breakdown at negative polarity occurs at higher voltages than at the positive one. The negative ions of the perfluoro compounds are much more stable than those of conventional hydrocarbons. The discharge of the negatively charged perfluoro ions requires much higher fields than do those of conventional hydrocarbons. The implications of these observations are discussed in some detail     

不同添加剂在离子液体中对锂电极形貌的影响

在金属锂的沉积过程中,由于锂枝晶的产生,严重阻碍了锂作为阳极应用于金属锂二次电池之中。电解液的组成在金属锂的沉积、溶解过程中发挥着重要的作用,采用电化学沉积的方法探究了8种不同添加剂在离子液体1-丁基-3-甲基咪唑四氟硼酸盐中沉积金属锂形貌的影响。实验结果表明:碳酸乙烯酯作为添加剂时能有效抑制金属锂枝晶的生长,形成较为紧密的锂金属层,为开发一种新型的锂离子电池电解液提供了可能。     

咪唑离子液体中氧在MnO_2电极上的电化学性能

以N-甲基咪唑和不同链长的卤代烷烃为原料,合成了三种咪唑类的双(三氟甲基磺酰)亚胺根(TFSI―)离子液体。测定了它们的电导率与电化学窗口;并通过循环伏安、计时电流和交流阻抗等电化学方法,对三种离子液体在涂覆MnO2玻碳电极上的氧还原性能进行了研究。实验结果表明:咪唑环上侧链的链长越长其电导率越小,但对电化学窗口影响不大。分析了氧在三种离子液体中的氧还原电催化机理,比较其电化学性能,均发现咪唑环上侧链链长越短其电化学性能越好。     

The impact of electrode dielectric coating on the insulationintegrity of GIS/GITL with metallic particle contaminants

Coating the inside surface of gas insulated switchgear (GIS) enclosures with a dielectric film reduces the deleterious effect of electrode surface roughness, impedes the development of metallic particle initiated microdischarges, increases the field required to lift particles, and reduces the charge acquired by particles, all of which help alleviate the adverse effect of contaminating metallic particles on insulation withstand. The performance of particle-contaminated compressed gas systems with dielectric coated electrodes is analyzed. Two mechanisms for the transfer of charge from electrodes to contaminating particles are considered, namely, conduction through the coating layer and microdischarges in the surrounding gas. The paper presents an electrostatic study of the particle lifting fields with dielectric covered electrodes. The overall breakdown strength of the system is evaluated and the results are discussed in the light of experimental findings     

风电模拟装置风机模拟直流电机调速控制的研究

介绍了一种采用转速、电流双闭环控制的基于西门子直流调速器6RA70的直流电机(DCM)模拟风机装置,包括硬件系统的设计和软件程序的编写.在此基础上利用Citect SCADA软件建立风力发电监控平台,并与可编程逻辑控制器(PLC)联网,通过PLC与直流调速器6RA70通信控制DCM模拟风机运行.在搭建的DCM -双馈发电机(DFIG)风力发电系统模拟试验平台上运行后,表明该装置可根据用户要求和控制指令实现任意风速下DCM模拟风机输出,具有安全可靠、精确度高,且可远程控制的特性.     

单相高频化UPS中DC/DC、AC/DC与DC/AC的设计

介绍了新型单相高频化UPS中的DC/DC变换器、AC/DC整流器、DC/AC逆变器的设计 ,探讨了实际设计中应考虑的问题     

DC pre-breakdown phenomena and breakdown characteristics in thepresence of conducting particles in liquid nitrogen

DC pre-breakdown phenomena and breakdown characteristics in the presence of free conducting particles in liquid nitrogen are studied experimentally. The results show that a microdischarge occurs when a charged particle is approaching an oppositely charged electrode. An intense microdischarge can trigger a complete breakdown of the gap. The breakdown voltage of a uniform field gap with a free metallic particle of mm size might be reduced well below that of a point-to-plane gap without a particle in liquid nitrogen. Heavy contamination by a metallic powder produces a large reduction in the breakdown voltage with a horizontal spacer surface. However carbon powder is less hazardous compared to metallic powder     

ADSS与导线在风偏时鞭击问题的探讨

以35kV、66kV输电线路及其典型铁塔为例，对ADSS与导线在风偏时的鞭击问题进行了分析。文中还介绍了一种校验二者鞭击情况的方法。     

Charging and behavior of a spherically conducting particle on a dielectrically coated electrode in the presence of electrical gradient force in atmospheric air

This paper discusses the charging and behavior of a spherically conducting particle on a dielectrically coated electrode in non-uniform dc and ac electric fields between non-parallel plane electrodes in atmospheric air. The charging mechanism of a particle resting on a dielectrically coated electrode is investigated by observing light emissions from partial discharges and by utilizing the dust figure technique. The charge acquired by a particle is estimated from the results of particle motion onset voltage measurement and direct measurement with a Faraday cage. The basic particle movement as well as particle-triggered breakdown characteristics under non-uniform electric field distribution along the electrode surface is also investigated. The results suggest that the effect of the electrical gradient force/dielectro-phoretic force on particle motion on a dielectrically coated electrode should be adequately considered in the design of gas insulated systems (GIS). This is because a particle can move laterally on the coated electrode toward increasing electric field regions by the action of the electrical gradient force which is independent of the charge on the particle. Also the possibility of the particle charging and lifting at high field regions or reaching and adhering onto an insulating spacer further increases the risk of breakdown.     

现场椭圆偏振方法对铜电极腐蚀及缓蚀的研究

应用现场反射式椭圆偏振技术和循环伏安法研究氯离子以及苯并三氮唑对铜电极腐蚀性能的影响,探索铜电极的腐蚀及缓蚀机理,为铜材料在含有氯离子的腐蚀介质（如一次锌锰干电池）中的使用和保护提供依据。研究结果表明：电解液中氯离子的存在将明显加速铜电极的腐蚀,在电解液中添加苯并三氮唑能够抑制铜的腐蚀,即使电解液中没有氯离子存在,苯并三氮唑也能够阻止铜的氧化;与电化学研究方法比较,椭圆偏振测量技术对于检测表面层的微小变化有其独特的优点,在研究抑制铜腐蚀时能弥补电化学研究方法灵敏度不足的缺陷;文中还提出了苯并三氮唑和氯离子参与形成铜表面保护膜层的模型,并结合该模型对铜腐蚀性能和缓蚀机制进行了解释。     

Impact of DC 48 V on Automotive Power Supply Systems: Comparison with DC 42 V and Future View under DC 60 V

In the twenty‐first century, rapid advances are being made in the electric propulsion of vehicles as a countermeasure of global warming. In addition, CO₂ emissions from all vehicles are to be stringently regulated to 95 g/km by 2020. Thus, most automakers around the world have had to develop not only hybrid electric vehicles, but also conventional internal combustion engine with energy‐saving technology. Battery technology (Li‐ion) and semiconductor technology (SiC and GaN) for automotive power supply systems have proceeded to the mass‐production stage. In 2011, Verband der Automobilindustrie (German OEMs and suppliers) announced the adoption of DC 48 V for the market of 2020. In this paper, we analyze the needs and impact of DC 48 V and compare it with DC 42 V (current technology). We also try to portray the future view under DC 60 V for automotive power supply systems.     

Effects of arc current and electrode size on electrode erosion in ac plasma torches

Heavy erosion of the electrode is a problem in using ac plasma torches. In a series of our studies, the effects of electrode stem size (diameter and length) and tip shape on the electrode erosion were clarified at a low current of 200 A. In this paper, on the basis of the 200-A data, in order to reduce the electrode erosion with the current increased, the effects of current and electrode size on electrode erosion were clarified experimentally and analytically between 100 and 550 A. The electrode used was of solid type and the material was tungsten containing 2 wt% of lanthanum oxide. The plasma gas was argon. Main results are as follows. (1) As the current increased, the electrode erosion increased linearly. In the case of thin electrodes (8 mm ø), between 450 and 550 A, the electrode tip was molten partially and the electrode erosion increased rapidly over 5 mg/h. However, for thick electrodes (13 mm ø), the electrode erosion did not increase rapidly. (2) The temperature distribution along the electrode axis was calculated. As a result, a good correlation was obtained between the calculated temperature of electrode tip and the measured electrode erosion. As the tip temperature decreased to 3000 K (cf. tungsten melting point: 3660 K), the electrode erosion decreased below 5 mg/h of the linearly increasing range.     

燃料电池汽车用DC/DC变换器的控制策略及仿真

结合燃料电池汽车的特殊应用场合，提出了一种结构简单、转换效率高的DC／DC变换器，针对这种特殊的DC／DC变换器及应用控制要求，得出一种旨在完成功率流分配的基本控制方法。