Materials Literature
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It is well known that the physical, mechanical, optical and electrical properties are affected by the sample morphology. The aim of the work was to gain knowledge and basic understanding of the morphology of polyethylene materials used for power cable insulation. A permanganic etching procedure with subsequent TEM mic…
The understanding of degradation processes in transmission-class cable joints is very important to the reliability of the operating system. Degradation caused by partial discharges (PD) and their associated characteristics were investigated in model "pre-fabricated" cable joints. Time to breakdown and PD pulse paramet…
The study of the additives-induced modification of structure and morphology of polyethylene, and the correlation between additives used and the properties of the LDPE product, were the aim of our research project.
A new macromodel for general-purpose analysis programs is proposed. This model is suitable for simulation of partial discharges in solid inhomogeneous dielectrics with a large number of voids. It incorporates the classic equivalent parameters of the void, and as a part of a complex electrical scheme, acts automaticall…
This paper handles the practical application of the ultra high frequency (UHF) partial discharge (PD) measuring technique in on-site tests using a resonant test set-up. Application during the service life of gas-insulated switchgear (GIS) is also addressed (on-line monitoring). Tests made during commissioning proved t…
In order to reconstruct the 3D patterns of real electrical trees, we investigated the applicability of computerized tomography method (CTM) and the serial sectioning method (SSM). We also investigated the relationship between the fractal dimension of the reconstructed 3D patterns and that of projected 2D patterns of r…
We have shown that there is a direct relationship between the state (glassy or flexible) of the epoxy resin and its tree growth and space charge behaviour. At this stage it is not possible to relate directly the tree growth behaviour to the space charge properties of the epoxy resin. The main problem is that the tree…
Room Temperature Vulcanizing Silicone Rubber (RTV SR) coatings are used for improving the contamination performance of ceramic insulators, especially in substations. Recently, some concern has been expressed regarding the electrical performance of RTV SR coatings under acid rain conditions. In the present study, four…
Though paper-oil insulation is extensively used for EHV applications, there are many associated problems relating to the presence of dc component. The insulation is subjected to a dc component in addition to the average ac stresses that exist in the system. Under the combined ac/dc stresses, the behaviour of paper-oil…
A simple in-house experimental setup based on impedance measurement for determining the core loss of ferrimagnetic materials under sinusoidal excitation is proposed. The magnetic cores used in high frequency transformers are made of materials having very low core loss. The accuracy of the core loss constructed by the…
This paper deals with the influence of water immersion on the hydrophobicity loss process of different silicone rubbers. The advancing and receding angles (AA and RA) of thin rubber plates were measured. The presented results show that water immersion had only a small effect on the wettability (AA) of the silicone rub…
The effect of poling on the piezoelectric properties of sol-gel derived PbZr/sub 0.45/Ti/sub 0.55/O/sub 3/ (PZT) thin films is investigated by laser interferometry. Poling conditions are varied in order to optimize the longitudinal piezoelectric coefficient (d/sub 33/) of the films. Short-term aging of d/sub 33/ is al…
We report a $150--2000{\mathrm{cm}}^{\ensuremath{-}1}$ Raman study of the single-molecule magnets ${\mathrm{Mn}}_{12}{\mathrm{O}}_{12}$-acetate $({\mathrm{Mn}}_{12}\ensuremath{-}\mathrm{Ac}),$ deuterated ${\mathrm{Mn}}_{12}\ensuremath{-}\mathrm{Ac},$ ${\mathrm{Fe}}_{8}{\mathrm{Br}}_{8},$ ${\mathrm{O}}^{17}$-labeled ${…
Transformer oil and oil-impregnated pressboard are major insulating materials in a HVDC (high voltage direct current) converter transformer which provides electrical power transformation between an AC and a DC system. However, the dc component on the valve side of a HVDC converter transformer gives rise to special con…
A density functional plane-wave pseudopotential method is used to study various Σ = 5 (001) twist boundary models for strontium titanate. Results concerning the atom-level geometries and electronic structures are reported. The structures have varying SrO/TiO 2 ratios and their relative stabilities are discussed in ter…
Photoluminescence (PL) spectra of TlInSeS layered single crystals were investigated in the wavelength region 460–800 nm and in the temperature range 10–65 K. We observed one wide PL band centred at 584 nm (2.122 eV) at T = 10 K and an excitation intensity of 7.5 W cm −2 . We have also studied the variation of the PL i…
Phonon modes and Raman intensities of Ge quantum dots (QDs) with two different types of surfaces, a free standing surface or a fixed surface, in a size range from five atoms to 7 nm in diameter, are calculated by using a microscopic valence force field model. The results are compared, and the effects of surfaces on ph…
A space charge distribution and an external circuit current were simultaneously measured up to electrical breakdown in a 100 /spl mu/m thick low-density polyethylene (LDPE) film with a semi-conducting electrode under dc voltage by using pulse electro-acoustic (PEA) method. We estimated an electric field distribution a…
Methods of locating defects in overhead high voltage and extra-high voltage transmission lines are described and evaluated. Included is a technology which utilizes corona partial discharge detection to find faulty conditions while simultaneously performing routine visual inspections from a helicopter. The corona inspe…
Nearterm industrial applications require pressure sensors and acceleration sensors which are able to operate at elevated temperatures and in harsh environments where conventional silicon devices do not work. Many properties of diamond (e.g. its physical hardness, high Young's modulus, high tensile yield strength, chem…