Measurement and analysis of dielectric response in oil-paper insulation systems /

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Diss. no. 12832 techn. sc. SFIT Zurich. Literaturverz.

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    • "In order to minimize the weight loss of these samples, short term charging and discharging current measurements [6] are recorded. According to the superposition principle the sum of the charging current i c (t) and the discharging current i d (t) with opposite polarity corresponds to the steady-state direct current i DC for long charging and discharging periods [3], [7] [8] "
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    ABSTRACT: Water absorption behavior of disk-like mineral filled epoxy resin insulators is determined by measuring the change of weight at different relative air humidity. Bulk current measurements with epoxy resin samples which have reached their absorption equilibrium during storage at various relative humidity are carried out and a significant decrease of the volume resistivity is observed with increasing water content. Water absorption into the epoxy samples follows Fick's Diffusion Law (diffusion coefficient D = (5±3)·10<sup>-9</sup> cm<sup>2</sup>S<sup>-1</sup>). A model based on Fickian diffusion has been developed which allows for the simulation of the dynamic degradation of the volume resistivity during humidity storage. The results of simulation are verified by periodic volume resistivity measurements with epoxy resin samples during 99% relative humidity storage.
    Solid Dielectrics (ICSD), 2010 10th IEEE International Conference on; 08/2010
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    • "For the RVM technique, the old interpretation-based only on a simple relationship between the dominant time constant of the polarization spectrum and the water content in cellulose-is not correct. The PDC measurement however, can provide several additional advantages [7] [8] [29] [36] such as – information about dc conductivities containing information about moisture, oilquality and ageing and these time domain signals can be clearly described and explained by physical models (ion movement in oil). When ageing is related to depolymerization of cellulose molecules, it is important for the mechanical strength of the paper but not for the dielectric properties. "
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    ABSTRACT: Properties of oil and paper in a transformer degrade primarily due to thermal ageing and moisture ingress. Dielectric diagnostic tests, such as Recovery Voltage (RV), and Polarizations and Depolarization Current (PDC) measurement are currently being explored as potential tools for insulation condition assessment. A modern chemical analysis tool for paper molecular weight (MW) measurement, Gel Permeation Chromatography (GPC) or the more accurately described Size Exclusion Chromatography (SEC) promises to be useful in assessing ageing condition. However, the issue of separately assessing the impacts of ageing and moisture on oil and paper has been a key issue for many years. In the current research project, a series of experiments have been performed under controlled laboratory conditions with preset moisture content, and at controlled high temperature ageing. Whereas RV and PDC measurement results were found to be more sensitive to the moisture content of the oil and paper insulation, the MW distribution measurement by SEC provided a trend of insulation thermal ageing. This paper first provides a brief description of RVM, PDC and SEC procedures followed by a description of the experimental techniques adopted. Results are then analysed with the view of separately understanding the impacts of thermal ageing and moisture on the condition of oil and paper insulation in a transformer.
    IEEE Transactions on Dielectrics and Electrical Insulation 04/2008; 15(2). DOI:10.1109/TDEI.2008.4483479 · 1.28 Impact Factor
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    • "ISBN 80-8073-477-1. [8] Muht, M: Development in Diagnostics of HV Apparatrus. Proc ISH2007. "

    10/2007; 2(2).
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