| 1. |
- Girlanda, Orlando, et al.
(author)
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Analysis of the Micromechanical Deformation in Pressboard performed by X-ray Microtomography
- 2015
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In: IEEE Electrical Insulation Conference (EIC). - Piscataway, NJ : IEEE Communications Society. - 9781479973545 ; , s. 89-92
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Conference paper (peer-reviewed)abstract
- A large number of electrical insulation components are produced in paper-based materials. Paper combines good insulating properties with the necessary mechanical and chemical stability. Paper consists of a system of fibers binding to each other creating a strong network. The presence of large open pores allows for impregnability of the material but also causes mechanical weakness in particular in the out-of-plane direction of the material. This aspect is important for pressboard components, where the resistance to compression stress is relevant for e.g. transformer windings. It is therefore relevant to understand the mechanisms that underlay the out-of-plane deformation of pressboard. In order to get a clear picture of the deformation patterns within the material, X-ray micro-computed tomography was used. Pressboard test pieces were subjected to in-situ out-of-plane compressive loading. 3D images of the sample could be captured before, during and after the loading sequence. Image analysis allowed for the definition of strain fields. The results revealed a strong correlation between the density variation within the sample and the strain calculated from the 3D images.
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| 2. |
- Kubyshkina, Elena, et al.
(author)
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Ab-initio Modeling of Interfacial Region in Nanocomposite Dielectrics
- 2015
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In: 2015 Electrical Insulation Conference (EIC). - : IEEE. - 9781479973545 ; , s. 618-620
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Conference paper (peer-reviewed)abstract
- The interfacial region between a base matrix and nanoparticles in nanocomposite dielectrics is often referred to as the main cause of good performance of nanocomposites as insulating materials. In the present work we compare electronic structure of the interfacial region in the polyethylene magnesium oxide nanocomposite with the electronic structures of its bulk constituents. The calculations were performed with density functional theory, the LDA and AM05 functionals were used. Hydroxylated, silanol-terminated (-SiOH) MgO surfaces and an interface (a surface with grafted through Si alkane chains) were studied. Investigation has shown the presence of surface states in untreated (hydroxylated) MgO (111) surface, while for both silanized surfaces these states are removed. It results in 1.7 eV higher band gap energy compared to the untreated case. Untreated regions present in treated nanoparticle are proposed to behave as traps for electrons.
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| 3. |
- Nikjoo, Roya, et al.
(author)
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Effect of High Voltage Transients on Surface Discharge Characteristics of Oil-Paper Insulation
- 2015
-
In: 2015 IEEE Electrical Insulation Conference (EIC). - : IEEE. - 9781479973545 ; , s. 69-72
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Conference paper (peer-reviewed)abstract
- Condition assessment of power components such as power transformers and their bushings depends on the interpretation of data obtained from the monitoring systems. Various defects in their insulation would behave differently under electrical stresses. Surface discharge on the oil-paper interface is one of the defects which can be responsible for the failure of those components. Power system transients can impose stresses on the insulation of the power transformers and their bushings. This study investigates the effect of transients such as lightning impulses on the surface discharge characteristics of oil-impregnated paper. Two configurations, needle and rod (IEC-b), are used here. Two distinctive situations occur on paper due to these different configurations. The corresponding effect is shown in the form of variation in the partial discharge numbers and phase-resolved patterns. In the needle electrode configuration, the paper remains un-aged and the applied impulses cause a prompt change in the total number of discharges which decays fast. However, with the rod electrode, the paper gets carbonized and the applied impulses cause a decrease in the total number of discharges. The influence of moisture content in oil-impregnated paper was also studied. For this case, the total number of discharges considerably increase after applying impulse.
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