Vegetable-oil-based dielectric coolants

Electrical transformer insulation systems are evaluated based on economic, safety, and environmental standpoints using total life cycle analysis. Because of the inherent high efficiency of liquid-cooled transformer designs, new developments focus on improving the environmental and safety properties of fire resistant (less-flammable, high fire point) fluids. This article reports the latest findings on dielectric systems using natural ester (vegetable oil) fluids. Because esters naturally have lower oxidation resistance than mineral oils, a novel blend of base oils and additives were developed to overcome this potential handicap. Single- and three-phase prototype field installations using these new dielectric coolants are discussed     

Electrostatic Ignition Hazards with Flammable Liquids

The hazard of spark ignition of flammable vapor/air mixtures is recognized and receives much attention in the petroleum and chemical industries. Bonding and grounding procedures, described in various consensus standards, prevent hazardous differences of potential between conductive objects. These techniques are not adequate, however, to prevent hazardous accumulations of charges in poorly conductive liquids, for which additional precautions are necessary. A lack of consensus concerning the definition of ``static-prone' liquids has hampered progress in this area, and has frequently led to the development of costly protective measures to meet arbitrary requirements. The results of experiments that measure the charge accumulation in liquids during agitation as a function of liquid conductivity are presented. Data are included for the particularly severe static charging that accompanies the mixing of powders in poorly conductive solvents. The degree of static hazard is determined by comparing the measured value of charge accumulation to a calculated value that is sufficient to cause sparking. Techniques for keeping the charge accumulation to safe values are described. Special static hazards of nonconductive containers are discussed.     

Partial discharge. XIII. Acoustic partial dischargedetection-fundamental considerations

An overview of the basic acoustics theory required to understand the finer points of acoustic partial discharge (PD) detection systems is given. PD and acoustic test methods are discussed, and acoustic wave motion, impedance, and intensity are described. Wave propagation and signal absorption, and the velocity of sound are discussed. Acoustic characteristics of media gases, liquids, and solid materials are described     

Novel electrical and optical properties of liquid conductingpolymers and oligomers

A conducting polymer with highly extended conjugated bonds in its main chain becomes fusible and also soluble in common solvents after the introduction of long side chains, such as alkyl, as a substituent. Because these liquid conducting polymers and oligomers have much smaller band gaps than those of conventional organic liquids, they exhibit relatively high electrical conductivity and also interact with visible light. Therefore, these liquid conducting polymers can be used effectively for fundamental research to clarify the electronic state and transport processes in dielectric liquids. Novel anomalies in electrical conductivity, photoconductivity and luminescence also have been observed in these liquids, and are discussed in terms of the fluctuation of electronic band gap and the interchain interaction, which depends on alkyl side chain length and on its conformation, and therefore on temperature. The unique applications of these liquid conducting polymers and solutions are also discussed. Characteristics of the interface between conducting polymer and dielectric liquids are also found and discussed in terms of electron scavenging of CO₂ in liquid and CO₂ fixation     

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     

Bacterial decontamination of liquids with pulsed electric fields

The effect of pulsed electric fields on the viability of microorganisms, mainly bacteria, in liquids has been studied since the 1960's. Experimental results obtained over a large range of electrical and microbiological parameters, point towards an irreversible formation of pores in the cell membrane as the mechanism for lysing. The model of membrane pore formation seems to fail only for ultrashort electrical pulses, where intracellular effects, and possibly resonant effects, might dominate. This paper presents an overview of the effect of pulsed electric fields on the viability of microorganisms in liquids, In particular, the lytic effect of variations in the electrical pulse parameters, such as pulse shape, amplitude, duration, and single shot vs. repetitive operation, is described, A major application of the pulsed electric field method is `cold' bacterial decontamination of liquid food and drinking water. The energy consumption for complete bacterial decontamination is presently 100 to 400 kJ/l. A possible reduction of the required energy by utilizing intracellular electric field interactions and resonance effects is discussed     

Partial discharge. V. PD in polymer-type line insulators

For pt.IV see ibid., vol.7, no.1, p.20 (1991). Some of the problems related to corona and partial discharge damage to polymer insulators are outlined. The basic construction of polymer insulators for overhead lines, which consist of a core, weathersheds, and metal end fittings, is described. Two types in common use are suspension/dead-end type, which is used where line loads subject the insulator core to tension forces, and the post type, which is used where line loads subject the core to appreciable bending forces in addition to tension forces. The partial discharge performance of polymer insulators, which depends on the choice of material, design, and construction of the insulators, is discussed. A factor common to all designs is poor partial discharge detection sensitivity, in the sense that a partial-discharge-producing defect along the insulator has very small capacitive coupling to the insulator terminals as a result of the large dimensions of the insulator and the small size of the terminals. Sources of cavity discharges are discussed. These can occur in the fiberglass core or in the weathersheds. External discharges, which can take place on the weathersheds or the hardware ends, are also examined     

Bubble formation in synthetic insulating liquids in a pulseddivergent electric field

This is a study of high field conduction phenomena in two aromatic insulating liquids (monobenzyltoluene and dibenzyltoluene) in a point-plane electrode geometry. These liquids behave qualitatively like saturated hydrocarbons; current instability (electron avalanche) for high enough fields near the negative point giving rise to a current pulse regime, which causes the formation of bubbles by local heating. The generation and dynamics of these bubbles as a function of various parameters (injected energy, hydrostatic pressure and the nature of the liquid) are presented and discussed     

HVDC's increasing popularity

The economic performance, and environmental advantages that are responsible for the growing use of high-voltage DC (HVDC) power transmission are examined. To gain the advantages of a DC system, measures must be taken to properly integrate the DC and AC systems. The various interactions between two systems, which need to be evaluated, are described. These are reactive power support, dynamic overvoltages migration, and harmonics. Insulation coordination is also necessary. Current HVDC applications and areas of HVDC expansion are discussed     

MOCVD of BaSrTiO3 for ulsi drams

Abstract

The CVD of high permittivity materials such as BaSrTiO₃ presents new challenges to the semiconductor equipment and materials industries. The electrical properties of the material are a strong function of composition, microstructure and dopant concentration (electronic and ionic). However, the source reagents are typically low vapor pressure liquids, solids or solids dissolved in liquids which are challenging to manufacture with ultra-high purity and difficult to deliver with high accuracy and precision. Reactor walls must be heated to avoid condensation of the source materials and deposition temperatures are high where radiative heat transfer becomes significant. Reaction products are difficult to remove by standard dry chemical etching techniques because the halides of many of the metals are involatile inorganic salts. Design strategies to overcome these challenges and the resulting properties of BaSrTiO₃ films will be discussed.     

Cryogenic liquids - a prospective insulation basis for future powerequipment

Cryogenic liquids are claimed to have an impact on the concept of improved future power equipment. The low boiling temperature of liquid helium or liquid nitrogen offers the use of superconducting materials which eliminate ohmic losses in the conductors. This yields a high overall current density in the equipment. The liquids seem to be interesting basic insulators with reasonable dielectric performance in the medium high voltage domain. The liquids are chemically inert, and no irreversible compound within the insulation system must be anticipated. Hazards such as fire risk in case of faults can be ruled out. Thermal aging of the insulation system can also be disregarded because no excess temperature must be taken into account during service, even in the case of temporary overload operation. Dielectric aging due to partial discharges may be of little concern because the liquids can be easily fully reprocessed by vaporizing and recondensing. Finally, the liquids are produced from gases which are found in open atmosphere. Thus, the disposal of insulation systems at the end of operational life is straightforward     

Small Bubble Formation by Using Strong Nonuniform Electric Field

An experimental study on a small bubble formation was carried out to examine the effect of electric field on it. The nitrogen bubble in insulating liquids was divided easily into small ones by means of a strong nonuniform electric field. It has been recognized that a strong electrical pressure arises at the tip of the capillary electrode where almost all the line of electric force concentrates and that it increases with increasing applied voltage, while bubble size decreases markedly depending on the electrical properties of the liquids. The efficiency of the small bubble formation also depends on the electrical properties of the liquids, and it reaches a few percent for good insulating liquids. An additional experiment was performed to observe the generation of an electrohydrodynamic (EHD) flow of liquid and to discuss its contribution to the small bubble formation.     

Optical Xerography

After a review of standard xerography, it is shown that optical techniques can be used to perform all the xerographic functions (charging, exposure, transfer, fusing and cleaning) except development. ``Photoelectric charging' and ``induction charging' are described in detail, and the complicated and subtle phenomena which occur at the photoconductor interfaces are clarified. ``Persistent internal polarization (PIP)' is also discussed, and the role of the photoconductor interfaces and the bulk traps in the photoconductor are clarified. The spectral considerations necessary to optimize machine performance are discussed in terms of the crucial components (lamps, documents, optics and photoconductors). The new concept of ``optical transfer' and the use of light to aid in ``cleaning' are described. The use of radiation to perform xerographic fusing is described for both ``flash' fusing and ``radiant' fusing. The essential concepts necessary for achieving ``selective fusing' are discussed.     

Arcing resistance of high fire point dielectric liquids

High fire point (HFP) dielectric liquids have been in use since the demise of Askarels (PCB/TCB) in the mid 1970s. Having fire points of at least 300°C, their main application has been in the role of transformer impregnants particularly in units located in, on, or near buildings. This study was aimed at evaluating the suitability of such liquids for application in arcing environments. At present, most HFP liquids are produced from one of three different chemical bases. These are: (a) polyol ester; (b) high molecular weight hydrocarbon (HMWH); and (c) dimethyl silicone. Samples of these liquids were evaluated in a typical oil switch primarily utilized in capacitor switching applications. Although not an HFP liquid, transformer oil was included in the test matrix to provide a base line to which the other liquids could be compared. Each liquid was exposed to 250 cycles of switching 8000 V at 50 A. The results show that both polyol ester and HMWHs compare favorably to transformer oil in this application. However, the dielectric breakdown value of dimethyl silicone was so rapidly degraded that its use under such conditions requires considerable caution. Further analysis of the particulate arc by-products formed in the dimethyl silicone revealed that this material had an extremely high dielectric constant. Through computer modeling, it was shown that the great disparity in dielectric constants between the fluid and the particulate would greatly intensify the electrical stress on the fluid and cause dielectric breakdown     

Using Digital Measurement in Raw Mill Control Systems

Digital measurement is described, and its importance to the raw mill operation is discussed. The systems that can make use of digital measurement are also considered.     

Silicon micromachined hollow optical waveguides for sensingapplications

Novel micromachined optical waveguides useful for sensing applications are proposed. The waveguide is designed as hollow-core antiresonant reflecting optical waveguide (ARROW) and can be easily fabricated using standard silicon micromachining techniques. The hollow structure permits to use the core to confine simultaneously the light and the substance to be probed, leading to an increase of the interaction efficiency. Numerical simulations, performed using finite element method technique, show that with a suitable design these waveguides can be used in sensing applications, where the substances under test can be gases or liquids     

离子液体在锂离子电池中的应用

对应用于锂离子电池电解质的离子液体按照阳离子的类型进行分类,并介绍了它们的性质.综述了近年来离子液体作为电解质的应用方式,包括单一的离子液体、离子液体与传统有机电解质混合、离子液体聚合物和离子液体中引入功能基团.讨论了阴、阳离子结构对离子液体性质的影响,离子液体与电极的匹配性.     

The mind matters: artificial intelligence and its societalimplications

The advent of machine intelligence and the social and ethical issues it raises are examined. The concept of the silicon mind is discussed and landmarks in artificial intelligence (AI) are reviewed. The problem of knowledge representation is considered. The use of artificial intelligence by the military is described. The possible effects of AI on society are also discussed     

Partial discharge. VIII. PD testing of solid dielectric cable

For pt.VII see ibid., vol.7, no.4, p.9 (1991). The development of solid dielectric cable is discussed and its potential defects are described. Limitations to partial discharge (PD) measurement and testing are discussed, and its use for detecting cavities (also referred to as voids), which are probably the most common defect in solid dielectric cable and the primary defect detected by PD test, is discussed. PD test standards for solid dielectric cable are reviewed. Practical aspects of PD testing are addressed. Alternative, nonelectrical test methods are briefly described and assessed