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This paper presents results of a comparative study of the behavior of electrical tree partial discharges (PD) in clean epoxy and a MgO/epoxy resin nanocomposite. It was found that the PD phase-resolved patterns (PDPRP) of tree discharges in both clean epoxy and nanocomposite epoxy exhibited two distinct categories of small and big discharge pulses. In nanocomposite epoxy however, the average PD magnitude...
A nanofluid is a fluid containing nano-sized materials. It exhibits more efficient heat transfer abilities compared to the host fluid. However the precise effect on the electrical properties of the host fluid is still uncertain. The purpose of the present study is to analyze the AC breakdown strength and viscosity of mineral oil based SiO2 nanofluids. The host fluid used in this paper is Shell Diala...
Electroactive polymers, or EAP, are a class of materials that change their shape when excited by an electric field. Main focus of research is currently the application of EAP as artificial muscles, where they convert electrical energy into motion. Conversely, they can also be used to convert mechanical energy into electrical energy. This paper describes the concept of a prototype wave energy converter,...
Polymeric insulation materials have not been used in HVDC cable systems until recently because of the tendency of polymers to deplete accumulated charges very slowly. Research on space charge injection, conduction and trapping mechanisms can reveal information about which new materials are the best candidates for HVDC cable insulation. In this paper, the space charge accumulation processes are evaluated...
In non-hermetically sealed medium voltage oil switchgear (MV OIS), insulating oil will absorb water from the ambient air. Humidity influenced by the acidity of the oil affects the breakdown voltage. Moreover, switching actions causes copper particles from the switching contacts to be released in the oil. To assess and consequently reduce the risk of failures due to breakdown of oil, parameters such...
The oil-impregnated (OI) insulation has been chosen as the insulating medium of high voltage transformers, power cables and capacitors. When the OI insulation is installed in the component it is expected to withstand operational stresses without breakdown in order to provide reliable operation during whole life-time of the component, i.e. 30–40 years. The chief disadvantage of the OI insulation is...
The thermal conductivity of polymer-based microcomposites has been investigated for a long time. The existing theories predict the thermal conductivity of the polymers filled with conventional sized microparticles quite well. Significant effort has been made in studying and developing of the thermal conductivity behavior of a relatively new class of composites, which contain nanosized filler. A considerable...
Present work addresses the dielectric spectroscopy investigation of epoxy-based composites, filled with magnesium oxide (MgO) nanoparticles with a fillgrade of up to 10 percent by weight. An even distribution of the nanoparticles was realized via ultrasonic vibration and high shear mixing. Dielectric spectroscopy measurement was performed on samples which were cured for 4 hours. Further measurement...
Four important models for explaining the properties that are observed in polymer based nanocomposites are the multi-core model, the intensity model, the interphase volume model and the double layer model. This paper outlines a new model, based on those four, which aims to explain certain properties that are considered unique to nanocomposites. The idea behind the polymer chain alignment model is that...
Delivery of energy in areas with a large population density and little space for high voltage equipment is an issue for utility companies in metropolises. Gas insulated switchgear is an alternative to conventional cable systems, enabling higher energy densities. However, the sulfur hexafluoride used in GIS causes environmental problems, which may not be acceptable anymore in a society with emphasis...
The transformers are very complex devices, consisting of different subcomponents e.g. winding, tap changer, bushing etc. During operation, all of the subcomponents are stressed and subjected to aging. When the aging reaches certain level, the subcomponent may fail. By application of statistical tools it is possible to investigate the failure occurrence in transformers. That means, that by fitting...
Epoxy resin is one of the most widely used thermosetting polymers and commonly applied in electrical power engineering. The intrinsic properties of epoxy can be improved by the introduction of inorganic filler, thus fabricating a composite material. In this study we investigate the influence of the filler size and its concentration on the complex permittivity and thermal conductivity of epoxy. The...
Various samples based on bisphenol-A type epoxy resin were prepared. Composites were produced containing various amounts of aluminum oxide, aluminum nitride and magnesium oxide, using ex-situ polymerization of surface functionalized particles. The average particle size of the used filler material ranged between 22 nm (magnesium oxide) and 60 nm (aluminum nitride). Synthesis of the samples is described...
Specific properties of insulation systems based on thermosetting and thermoplastic polymers can be enhanced by adding different types of inorganic fillers. The focus of this paper is on the effect of the filler size and modifications of the crystallinity of aluminum oxide (Al2O3) nanoparticles on the dielectric and thermal properties of epoxy-based composites. Nanoalumina in the α, γ and δ phases...
This paper reports electric properties calculation of a composite housed SF6 insulated bushing based on the finite element method. After introducing different stages of electric field distribution under DC voltage, the finite element method and boundary conditions are described. The electric field distribution, time constant of transmission from conductive distribution to resistive distribution are...
Electrical insulation based on epoxy resin is commonly used in high voltage applications. Examples are transformers, terminations, plugs or connectors. But, it is also used in high voltage applications where energy transportation or distribution is not the main purpose, e.g. in medical and industrial X-ray systems, or radar. This paper addresses the changes in the structure due to the introduction...
The dielectric spectroscopy of an impregnated paper and a type of vegetable oil was measured in the frequency domain. In order to investigate the effect of aging on the dielectric response, accelerated thermal aging was conducted on the paper samples and oils samples, respectively. Their dielectric responses were measured at intervals throughout the aging process. Since moisture has a great influence...
The aging of the epoxy-paper insulation of an oil-impregnated transformer was studied through partial discharge analysis. Accelerated electrical aging tests were carried out on samples of transformers windings, with and without paper insulation. Partial discharge (PD) measurements according to standard IEC 60270 were performed periodically during aging, and partial discharge phase patterns were recorded...
This investigation aims to perform a probabilistic prediction of the lifetime of epoxy resin insulation of transformer windings. To support the prediction, several accelerated electrical aging tests were conducted at different voltage levels on epoxy resin insulated transformer winding specimens. The lifetimes achieved from the tests show a “flat z-shaped” V-t (voltage vs. lifetime) curve and indicate...
Nanocomposites have been known in the field of electrical engineering for more than a decade, albeit there are still uncertainties of how the filler properties influence the properties of the composite material. Filler size, shape, aspect ratio and the surface modification, which consequently leads to even dispersion or clusters of particles, are all suspected to influence the dielectric behaviour...
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