Materials Literature
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Semiconductive tapes are applied to the end turn region of high voltage stator coils to reduce corona discharge at the slot exit region. The nonlinear, stress grading tapes are used to even out the voltage stress resulting in a more even distribution which also reduces the maximum stress level. To be able to optimize…
This paper presents a generalized dynamic circuit model of high frequency transformers, which includes all types of core losses and thermal effects on magnetic hysteresis. This transformer model provides accurate core loss prediction and is suitable for the simulation of transformers used in high frequency switching-m…
We present a theory for the van Hove singularity (VHS) in the tunneling density of states (TDOS) of disordered multichannel quantum wires, in particular multiwall carbon nanotubes. We assume close-by gates that screen off electron-electron interactions. Diagrammatic perturbation theory within the noncrossing approxima…
The gas-insulated transmission line (GIL) has been optimised for the needs of the 21st Century, where high-power transmission lines are needed and overhead lines are often not suitable. It will be used as a power feeder into huge metropolitan areas because energy resources are usually far away from the load centre. Al…
The charge carriers that are responsible for propagating current through a material have different behaviours for different applied frequencies, especially for high frequency applications. It is important to understand the role of several contributing factors. In view of the different applications of ferrites at micro…
As IC technology scales, the performance of ULSI chips is increasingly limited by the capacitance of the interconnects. The interconnect capacitance contributes to RC delay, AC power (CV/sub 2/f), and crosstalk. The use of air-gaps formed between metal lines during SiO/sub 2/ deposition has been shown to reduce the ca…
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…