There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

2005년 대한 생화학·분자생물학회 하계학술대회를 다녀와서

The present review article represents a comprehensive study on polymer micro/nanocomposites that are used in high-voltage applications. Particular focus is on the structure-property relationship of composite materials used in power engineering, by exploiting fundamental theory as well as numerical/analytical models and the influence of material design on electrical, mechanical and thermal properties. In addition to describing the scientific development of micro/nanocomposites electrical features desired in power engineering, the study is mainly focused on the electrical properties of insulating materials, particularly cross-linked polyethylene (XLPE) and epoxy resins, unfilled and filled with different types of filler. Polymer micro/nanocomposites based on XLPE and epoxy resins are usually used as insulating systems for high-voltage applications, such as: cables, generators, motors, cast resin dry-type transformers, etc. Furthermore, this paper includes ample discussions regarding the advantages and disadvantages resulting in the electrical, mechanical and thermal properties by the addition of micro- and nanofillers into the base polymer. The study goals are to determine the impact of filler size, type and distribution of the particles into the polymer matrix on the electrical, mechanical and thermal properties of the polymer micro/nanocomposites compared to the neat polymer and traditionally materials used as insulation systems in high-voltage engineering. Properties such as electrical conductivity, relative permittivity, dielectric losses, partial discharges, erosion resistance, space charge behavior, electric breakdown, tracking and electrical tree resistance, thermal conductivity, tensile strength and modulus, elongation at break of micro- and nanocomposites based on epoxy resin and XLPE are analyzed. Finally, it was concluded that the use of polymer micro/nanocomposites in electrical engineering is very promising and further research work must be accomplished in order to diversify the polymer composites matrices and to improve their properties.

Properties of Polymer Composites Used in High-Voltage Applications.

Recent progress in the development of polyethylene/metal-oxide nanocomposites for extruded high-voltage direct-current (HVDC) cables with ultrahigh electric insulation properties is presented. This is a promising technology with the potential of raising the upper voltage limit in today's underground/submarine cables, based on pristine polyethylene, to levels where the loss of energy during electric power transmission becomes low enough to ensure intercontinental electric power transmission. The development of HVDC insulating materials together with the impact of the interface between the particles and the polymer on the nanocomposites electric properties are shown. Important parameters from the atomic to the microlevel, such as interfacial chemistry, interfacial area, and degree of particle dispersion/aggregation, are discussed. This work is placed in perspective with important work by others, and suggested mechanisms for improved insulation using nanoparticles, such as increased charge trap density, adsorption of impurities/ions, and induced particle dipole moments are considered. The effects of the nanoparticles and of their interfacial structures on the mechanical properties and the implications of cavitation on the electric properties are also discussed. Although the main interest in improving the properties of insulating polymers has been on the use of nanoparticles, leading to nanodielectrics, it is pointed out here that larger microscopic hierarchical metal-oxide particles with high surface porosity also impart good insulation properties. The impact of the type of particle and its inherent properties (purity and conductivity) on the nanocomposite dielectric and insulating properties are also discussed based on data obtained by a newly developed technique to directly observe the charge distribution on a nanometer scale in the nanocomposite.

The Role of Interfaces in Polyethylene/Metal-Oxide Nanocomposites for Ultrahigh-Voltage Insulating Materials.

The problem of corrosive sulfur is extremely well documented in the electrical power industry and to some extent remains a global problem. The presence of corrosive sulfur in transformers is widely reported as a cause of sudden and unexpected failure. Regeneration of transformer oil using a reactivating sorbent in the form of bauxite clays has proven effective in removal of oxidation products in transformer oils. Unfortunately, in some cases, increased levels of silver corrosion have been observed shortly after oil reclamation. It is, therefore, important to understand fully the chemistry occurring both during the oil reclamation and during silver corrosion. Once a fuller understanding of the causes of increased oil corrosivity is obtained, effective precautions can be taken to limit the formation of corrosive species, whilst minimizing the volume of oil wastage during reclamation. In this paper, the problem of silver corrosion is discussed. Initial results from corrosion tests using transformer oils are described, with particular attention paid to the analytical methods used. Scanning electron microscopy coupled with energy-dispersive x-ray spectroscopy (SEM-EDX) was found to be a good method of characterizing the topology and elemental composition of the corroded silver surface. In terms of the oil composition, x-ray fluorescence spectroscopy is a very effective method for monitoring total sulfur and copper content. It is anticipated that once corrosive species are identified from the buffer tank samples, it will be possible to target such species in future analyses, allowing the detection of corrosive species at very low concentrations.

An initial study into silver corrosion in transformers following oil reclamation

Currently there are no standard techniques to detect copper sulphide deposits in transformers to act as an early warning system. This paper develops and tests a procedure using X-Ray Fluorescence (XRF) spectroscopy to tackle this problem and to monitor dissolved copper in oil, which can have a major impact on the dielectric properties of insulating oil. Initially calibration curves for sulphur and copper demonstrate the XRF’s limits of quantitation. Subsequently, a laboratory scale sample preparation procedure is developed to demonstrate that corrosive sulphur depletion trends may indirectly monitor copper sulphide formation. To confirm depleting sulphur species are corroding copper samples are analysed with Energy Dispersive XRay spectroscopy. Finally XRF demonstrates that corrosive oil has a low impact on the long term concentration of copper in oil. An XRF condition monitoring technique feasibility study is conducted and recommendations are given in how to implement it in the field.

X-ray fluorescence as a condition monitoring tool for copper and corrosive sulphur species in insulating oil

In recent years a significant volume of research has been undertaken in order to understand the latest failures in oil insulated power apparatus due to deposition of copper sulfide on the conductors and in the insulation paper. Dibenzyl Disulfide (DBDS) has been found to be the leading corrosive sulfur compound in the insulation oil. As there are currently no nondestructive techniques available to analyze the degree of damage from sulfur corrosion, electrical plant operators are faced with a choice of either replacing an asset which might still have several years of operational life or keeping a transformer operational with an increased risk of failure. This paper investigates permittivity and loss factor curves of transformer oil impregnated insulation paper, at different corrosive sulfur degradation stages. Three types of transformer conductors are investigated; new, artificially aged and service aged. To increase the understanding of the electrical behavior of Cu2S this paper demonstrates how the electrical properties change with moisture content. Dielectric spectroscopy is used to demonstrate some of the electrical changes across a wide frequency range, from 1mHz to 1MHz.

Impact of corrosive sulfur in transformer insulation paper

Corrosive sulfur in the last decade has been recognized as a major risk to high voltage transformers. An initial study undertaken by CIGRE on copper sulfide in transformer insulation investigated possible sources, i.e. Dibenzyl Disulfide (DBDS), it also looked at possible mitigating techniques, i.e. passivation, environmental influences, i.e. temperature, and improvement to oil corrosion standards, i.e. EN 62535. Although there was significant volume of research undertaken the high voltage industry still felt there is a lack of understanding in the process of copper sulfide formation and long-term effects of mitigation techniques. Hence a new CIGRE transformer working group, A2.40, was created. The identification of techniques with the ability to track the mechanism of copper sulfide (Cu2S) formation is fundamental to the current research objectives. The technique suggested in this paper involves the use of X-ray fluorescence (XRF), which is used for elemental analysis, to track the quantity of sulfur in the oil. As the deposits of Cu2S form in the conductors and paper insulation the amount of sulfur in the oil decreases. By using a series of laboratory experiments is possible to investigate how the rate of formation of Cu2S changes with time, suggesting that there is an initial chemical reaction needed for the Cu2S deposits to form. Scanning Electron Microscopy with Energy-dispersive X-ray spectroscopy (SEM-EDX) has been used to investigate the surface of copper at several different stages of the copper sulfide formation. By manipulating variables, i.e. temperature, it is possible to map their influence and provide a more precise risk assessment of transformer with corrosive oil to electrical utility companies. The experimental results suggest the possibility of developing a method to indirectly measure Cu2S deposition on conductors and insulation paper by tracking sulfur concentration changes in the transformer oil.

Tracking copper sulfide formation in corrosive transformer oil

The effects of functionalizer chain length and water content were explored in a series of polyethylene/silica nanocomposites. Silane molecules with differing chain lengths (propyl, octyl and octadecyl) were used to vary the nanoparticle surface chemistry, while vacuum drying and water immersion were used to extract water from or add water to samples previously equilibrated under ambient conditions. Electrical conductivity was found to be highly dependent upon water content as were the space charge distributions. Both interfacial conditions and the overall charge transport through the sample were strongly dependent on absorbed water and, as such, were found to vary with time through exchange of water with the sample's environment. Changes to charge transport dynamics due to the functionalizer chain length were, however, subtle. The removal of surface hydroxyl groups appears to be the primary mechanism by which functionalization influences electrical behavior; this reduces water uptake and, as a consequence, modifies charge transport behavior.

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A. F. Holt

Papers

An initial study into silver corrosion in transformers following oil reclamation

X-ray fluorescence as a condition monitoring tool for copper and corrosive sulphur species in insulating oil

Impact of corrosive sulfur in transformer insulation paper

Tracking copper sulfide formation in corrosive transformer oil

On the effect of functionalizer chain length and water content in polyethylene/silica nanocomposites: Part II — Charge transport