Treeing in mechanically prestressed electrical insulation

The technique of prestressing electrical insulation by the inclusion of fibers in tension during the curing process has been used to establish a region of balancing compressive stress adjacent to the fibers and through which growing electrical trees have to pass. It has been known for many years that compressive stress has a retarding effect on tree growth (and tensile stress has an accelerating effect). The compressive stress, therefore, set up due to prestressing decelerates tree growth and long treeing times have been observed. Room temperature cured epoxy resin readily demonstrates the prestressing phenomenon but, as a result of its relatively low glass transition temperature, it is unable to sustain the prestress at temperatures in excess of 40 /spl deg/C. Post curing at 100 /spl deg/C raises the glass transition temperature and although a greater initial fiber tension is required to produce the same degree of prestress, the prestress is subsequently sustainable at temperatures up to and beyond 80 /spl deg/C. This has been demonstrated by the determination of the remnant stress in the cast-in fibers using Raman spectroscopy and by the enhanced treeing times observed in high temperature cured samples.     

A versatile method to study electrical treeing in polymeric materials

Electrical treeing in high voltage cable insulation has been studied widely as it is one of the major breakdown mechanisms for solid dielectrics subjected to high electrical stresses. The most frequently experimental set-up used to study electrical treeing is utilizing needles to achieve a high divergent field to promote the initiation of electrical trees. In this paper a new type of electrode configuration is described, which will be beneficial when examining electrical treeing in terms of both the capability to follow the course of events in real time and the small amount of insulation material is needed. This new electrode configuration makes use of a thin tungsten wire as electrode to obtain the high divergent electrical stress needed to initiate electrical trees. Multiple electrical trees are at times formed at different points along the wire during the testing, this indicates that the field are homogenous along the wire. This allows for determining the tree initiation field and the rate of tree growth. It is also shown that this electrode configuration is able to distinguish the increased electrical tree inception obtained by the addition of voltage stabilizers.     

Fluorescent lamp model with power and temperature dependence for high-frequency electronic ballasts

The electrical behavior of a fluorescent lamp operating at high frequency can be characterized by a resistance. The lamp equivalent resistance varies with the operating power and ambient temperature. On this basis, an electrical circuit model of the fluorescent lamp for high-frequency steady-state operation is developed. A test system is set up to emulate the dimming operation of fluorescent lamps in a temperature range from -15/spl deg/C to 55/spl deg/C. For a given lamp, the voltage equation can be obtained from few test data. Then, the equations for the arc current and the equivalent resistance can be derived. These lamp equations can be used for predicting the operating characteristics of the dimmable ballast-lamp circuits with considerations on the temperature effects. The verification of the proposed lamp model is illustrated by implementation examples.     

高频下电树老化引起的高密度聚乙烯击穿现象

为了分析高频下电树老化引起的高密度聚乙烯击穿现象,实验研究了冰水淬火高密度聚乙烯(HDPE)薄膜在频率50 Hz~90 kHz范围内的交流电压作用下电树老化引起的破坏现象及电树生长过程中的电树形态特性的变化。观测高频下树老化引起击穿过程中电弧运动发现:不同频率下HDPE薄膜中电树生长过程中存在树枝、树干、丛状和击穿型4种基本电树形态;在高频下不同电树形态存在形态转换的关系,且随着频率和电压的升高,相同条件下电树老化引起的击穿破坏概率大大增加。试验结果表明,在较高频率下树的形态易向击穿型发展。最后从高频电压对材料极化过程的影响及高频所引起的材料疲劳效应、热效应加剧角度出发,对在高频下电树老化易于引发击穿的特性展开了深入的讨论,解释了高频或中频电气设备易发生绝缘老化破坏的现象。     

Barrier effect of treeing in composite insulating materials with heat-adhesive interfaces of different polymers

A polymer/polymer composite system is widely used in high-voltage equipment and power cables. The interface of this composite system plays an important role in the electrical degradation, such as electrical treeing or partial discharge, of the composite system. Therefore, it is important to study the effect of an interface on the electrical treeing of polymer/polymer-composite insulating materials. In this paper, we describe the tree growth and complete breakdown characteristics of specimens with a polymer barrier film layer molded in ethylene vinyl acetate copolymer (EVA), in which the interface of EVA and the barrier film is perpendicular to the electric field under an AC voltage. It is found that with a barrier film, the tree growth is retarded on the barrier film, which then punctures the film, or develops along the edge of the film. It is also found that the pressure of decomposing gas in the tree channels plays an important role in tree propagation.     

频率对高密度聚乙烯电树老化特性的影响

为了解频率对高密度聚乙烯电树老化特性的影响,在50Hz~90kHz较宽频率范围的交流电压作用下,研究了冰水淬火高密度聚乙烯(HDPE)薄膜的电树老化特性。结果表明,频率对电树起始形态具有重要的影响,随着电压频率的升高,树枝型电树的起始几率逐渐降低,丛状型电树的起始几率逐渐升高,电树逐渐由树枝型起始为主向丛状型起始为主转变,树干型和直击型为高频下所特有的电树起始形态。随着电树的生长,电树形态存在转换的可能,低频下,起始占主导的树枝型电树向丛状和树干型转变;高频下,起始占主导的丛状型电树则极易转变为树干和击穿型,导致绝缘的破坏。电树的发展可分为起始、滞长、生长和击穿期4个阶段。频率的提高加快了电树的发展速度且减少了电树的发展阶段,使发生击穿的几率大为增加。     

Single-mode 1.27-/spl mu/m InGaAs:Sb-GaAs-GaAsP quantum well vertical cavity surface emitting lasers

The 1.27-/spl mu/m InGaAs:Sb-GaAs-GaAsP vertical cavity surface emitting lasers (VCSELs) were grown by metalorganic chemical vapor deposition and exhibited excellent performance and temperature stability. The threshold current varies from 1.8 to 1.1 mA and the slope efficiency falls less than /spl sim/35% from 0.17 to 0.11 mW/mA as the temperature is raised from room temperature to 75/spl deg/C. The VCSELs continuously operate up to 105/spl deg/C with a slope efficiency of 0.023 mW/mA. With a bias current of only 5 mA, the 3-dB modulation frequency response was measured to be 8.36 GHz, which is appropriate for 10-Gb/s operation. The maximal bandwidth is estimated to be 10.7 GHz with modulation current efficiency factor of /spl sim/5.25GHz/(mA)/sup 1/2/. These VCSELs also demonstrate high-speed modulation up to 10 Gb/s from 25/spl deg/C to 70/spl deg/C. We also accumulated life test data up to 1000 h at 70/spl deg/C/10 mA.     

Electrical characterization of benzocyclobutene polymers for electric micromachines

An approach using interdigitated capacitors for electrical characterization of CYCLOTENE, a spin-on low-k benzocyclobutene (BCB)-based polymer is introduced and the effect of moisture uptake is investigated. The dielectric constant of CYCLOTENE is extracted from capacitance measurements with a systematic error less than 0.1%, giving an average value of 2.49 with a standard deviation of 1.5%. The dielectric constant increases by 1.2% after a humidity stress of 85% RH at 85/spl deg/C. The I-V characteristics of CYCLOTENE show a dependency of breakdown strength and leakage current on the geometrical dimensions of the device under test. A breakdown strength of 225V//spl mu/m and 320 V//spl mu/m for 2-/spl mu/m and 3-/spl mu/m finger spacing, respectively, and a leakage current of a few to tens of pA are measured. The I-V characteristics degrade drastically after the humidity stress, showing a breakdown strength of 100 V//spl mu/m and 180 V//spl mu/m for 2-/spl mu/m and 3-/spl mu/m finger spacing, respectively, and a maximum increase in the leakage current as large as one order of magnitude. The maximum performance and long-term reliability of an electric micromachine are adversely affected by the degradation of the breakdown voltage and the leakage current after moisture absorption. It is expected, however, that the electrical efficiency is improved using BCB-based polymers with negligible dependency on moisture absorption.     

Vacuum electrical breakdown characteristics and surface condition of Ti electrodes with oxidation conditions

Outgassing from an electrode surface is regarded as a major factor leading to electrical breakdowns in vacuum. Recently oxidation treatment at 200/spl deg/C was reported as an effective means of reducing Ti outgassing. In this paper, we report our measurement and comparison of the electrical breakdown characteristics of Ti electrodes with different oxidation conditions (without oxidation, oxidation at 200/spl deg/C, oxidation at 450/spl deg/C). In addition, we analyzed electrode surfaces before and after breakdown experiments in situ with X-ray photoelectron spectroscopy (XPS). Before oxidation, we machined the electrode's surfaces to the roughness of 0.8 /spl mu/m Rmax with diamond turning. Breakdown experiments demonstrated that the breakdown field is highest at the first application of voltage to electrodes with oxidized at 200/spl deg/C. Before breakdown experiment, surface analysis revealed that all the sample electrodes had a large amount of carbon originating from the hydrocarbons of contaminants, and after the experiments, they revealed that the carbons had disappeared. To obtain breakdown characteristics of electrodes with smoother surfaces, we conducted experiments on electrodes with a surface roughness of 0.05 /spl mu/m Ra. For these electrodes, the breakdown field was higher at first breakdown; the repetitions required to achieve saturated breakdown fields were significantly fewer, and the amount of carbon on electrode surfaces before breakdown was less.     

Effects of manufacturing technology on electrical breakdown and morphology of thin films of low density polyethylene blended with polypropylene copolymer

Extruded films prepared from blends of low-density polyethylene (LDPE) and random copolymer of ethylene and propylene (EP) with the T-die method were studied with respect to electrical properties and morphology. Comparisons with data on blown films are made. These blends are of interest as improved LDPE for making XLPE for insulated power cable. In the high temperature region (90/spl deg/C), a specimen with a slightly higher EP content had higher impulse breakdown strength than that with a lower EP content, but no improvement of DC breakdown strength by blending could be found. The improvement of impulse breakdown strength (90/spl deg/C) is explained in terms of morphological changes by blending such as the orientation of chains in a film and the size of spherulites on the assumption of the thermal breakdown. In comparison, a T-die film had higher impulse breakdown strength than that of a blown film for the same composition. The impulse breakdown strength also increased with the use of the higher density LDPE. In the current versus electric field characteristics at 30/spl deg/C, the blend polymer with EP content of 5-10% showed a transition from LDPE behavior at low field region to EP behavior at high field region. However, no appreciable difference in current behavior among the specimens was observed at 90/spl deg/C, which suggests an incompatibility between the two materials that exists at 30/spl deg/C but not at 90/spl deg/C.     

针尖曲率半径对硅橡胶电树枝老化特性的影响

针对硅橡胶材料电树枝老化特性展开了试验研究。采用针板电极结构,测量了不同针尖曲率半径的起树电压和电树枝形态。结果表明,硅橡胶的起树电压较低,抗电树枝老化性能较差,导致了硅橡胶预制式电缆附件故障频发;硅橡胶中的起始电树枝多以单枝状的通道形成为标志,随后发展为4种不同的电树枝形态。进而提出了硅橡胶电树枝形态发展模型,并以此讨论了不同形态的电树枝老化特性。研究还发现,现场实际运行的硅橡胶预制式电缆附件故障解体后发现了单枝通道起始电树枝,其在运行电压作用下容易发展为细枝型形态,但同样会引发电缆附件的击穿。试验结果为现场故障分析提供了参考依据。     

高温下交联聚乙烯电缆绝缘中电树枝测试系统设计

设计了高温下交联聚乙烯(XLPE)电缆绝缘中电树枝化的实验系统,在外施工频电压有效值为13 kV下,对不同温度下高压XLPE电缆绝缘中电树枝生长及其局部放电特性进行研究,结果表明,温度对电树枝的生长具有重要影响,整个系统可以用于高温下电树枝生长过程的实时观测与局部放电连续测量,为研究高温下XLPE电缆绝缘中电树枝引发与生长机理及其局部放电特性分析提供了实验研究平台。     

乙烯-丙烯酸共聚物改性聚乙烯的空间电荷对电树和水树的影响

通过添加不同含量的乙烯 -丙烯酸共聚物 (EAA)改善了聚乙烯 (PE)的电气性能。用电声脉冲法测量了样品中的空间电荷分布。测出了在直流预压电压下的短路电树枝的起始电压。对交流电压下抑制水树枝的产生和成长也做了研究。试验发现 ,不同EAA含量的试样中空间电荷的累积、短路 50 %电树枝的起始电压以及水树枝的形成有一定关系。空间电荷的测量可作为衡量改善试样耐电树枝和水树枝能力的手段     

Performance of high-speed PWM control chips at cryogenic temperatures

Planetary exploration missions and deep space probes require electronics capable of low-temperature operation. Such electronics will not only improve circuit performance and reliability, but also increase system efficiency, and reduce development and launch costs. DC/DC converters are an essential part of most aerospace power management distribution systems. Therefore, DC/DC converters that can operate at cryogenic temperatures are crucial for space missions where low temperatures are encountered. An important component of a DC/DC converter is the pulsewidth modulation (PWM) chip that provides the control to the converter main switches. In the process of designing low-temperature DC/DC converters, experimental investigations were carried out to evaluate the performance of a number of high-speed PWM chips as a function of temperature in the range of 25/spl deg/C to -190/spl deg/C. These IC chips ranged in their electrical characteristics, modes of control, packaging options, and applications. This paper presents and discusses the experimental procedures along with the experimental data obtained on the investigated chips.     

Long-wavelength vertical-cavity surface-emitting lasers on InP with lattice matched AlGaInAs-InP DBR grown by MOCVD

1.3- and 1.55-/spl mu/m vertical-cavity surface-emitting lasers (VCSELs) on InP have been realized. High-reflectivity AlGaInAs-InP lattice matched distributed Bragg reflectors (DBRs) were grown on InP substrates. 1.7 (for 1.3 /spl mu/m) and 2.0 (for 1.55 /spl mu/m) mW single mode power at 25/spl deg/C, 0.6 mW single mode power at 85/spl deg/C and lasing operation at >100/spl deg/C have been achieved. 10 Gbit/s error free transmissions through 10 km standard single mode fiber for 1.3-/spl mu/m VCSELs, and through 15 km nonzero dispersion shift fiber for 1.55-/spl mu/m VCSELs, have been demonstrated. With the addition of an SOA, 100 km error free transmission at 10 Gbit/s also has been demonstrated through a negative dispersion fiber. No degradation has been observed after over 2500-h aging test.     

交联聚乙烯绝缘中树状放电的试验研究

本文旨在阐述用快速宽频带测量系统及影视技术对交联聚乙烯绝缘材料中树状放电的试验方法。证明有丛状放电和枝状放电两种形式。给出两种放电形式的不同特征。通过测量放电脉冲参数的变化，研究树状放电的机理。从而提供探索固体有机绝缘材料老化过程检测的新途径。     

Unleash the military super power

Power systems for military aircraft must tolerate extreme conditions: temperatures as low as -40/spl deg/C or as high as 70/spl deg/C, as well as short-term fluctuations from -55/spl deg/C to 180/spl deg/C; relative humidity as high as 100%; impacts reaching 60G. Difficult conditions can be tackled by using suitable materials and enclosure designs, but a system or unit's weight, size and shape are often governed by its location. These challenges are just the beginning. System reliability and availability are paramount as failures must be minimised at all times. To provide a reliable and safe power system for today's military aviators, many design teams are needed to tackle the architectural, electrical, mechanical and chemical parameters of power units. Exploiting emerging technical innovations, such as high-performance FETs, can only make life easier for designers of the future.     

Electric charge transport and trapping in dielectrics deduced from isothermal and nonisothermal measurements

By sequential use of the isothermal charging, the isothermal discharging, the final thermally stimulated discharge current and the final isothermal discharging current techniques, the charge dynamics in highly insulating materials may be investigated. The method is demonstrated for polyethylene terephthalate. The injected charge for a field of 20 MV m/sup -/1 and polarization temperatures up to 110/spl deg/C is almost totally trapped in the material and is released during the heating of the sample at 180/spl deg/C for a sufficiently long time. A significant current at high temperatures, about 90/spl deg/C above the poling temperature, was observed proving that it originates from charge detrapping. The final thermally stimulated discharge current peaks shift to higher temperature when the polarization temperature increases, and are characterized by activation energies in the range from 1.03 to 1.56 eV. They allowed the identification of the glass transition around 114/spl deg/C. The relaxation time of the trapped charge, at 180/spl deg/C, was determined to be about 3780 s, explaining the very good stability of trapped charge.     

1.3-/spl mu/m AlGaInAs strain compensated MQW-buried-heterostructure lasers for uncooled 10-gb/s operation

We have successfully fabricated 1.3-/spl mu/m AlGaInAs strain-compensated multiple-quantum-well (MQW) buried-heterostructure (BH) lasers by narrow-stripe selective metalorganic vapor-phase epitaxy. Based on the optimization of AlGaInAs strain compensated MQW and the Al-oxidation-free BH process, we obtained a low-threshold current of 12.5 mA and a relaxation frequency of more than 10 GHz at 85/spl deg/C for Fabry-Perot lasers. For distributed feedback lasers, we demonstrated a 10-Gb/s operation and transmission of over 16 Km for a single mode fiber at 100/spl deg/C. Furthermore, a record-low 25.8-mA/sub p-p/ modulation current for a 10-Gb/s modulation at 100/spl deg/C was demonstrated with shorter cavity and high grating-coupling coefficient. A median life of more than 1/spl times/10/sup 5/ h at 85/spl deg/C was estimated after an aging test of over 5000 h for these lasers. These superior characteristics at high temperatures were achieved by the combination of the high differential gain of AlGaInAs strain compensated MQW and the BH structure.     

交流叠加冲击电压下XLPE绝缘中电树起始特性

ＸＬＰＥ绝缘在交流叠加冲击电压作用下电树起始特性的试验研究表明,电树的冲击起始场强不仅与预加的交流电压的大小有关,还与冲击电压与交流电压的相对极性有关,并有明显的累积效应,起晕也有明显的时延现象。