Pressboard

About: Pressboard is a research topic. Over the lifetime, 1123 publications have been published within this topic receiving 9089 citations.

Creeping Discharge Characteristics of Nanofluid-Impregnated Pressboards Under AC Stress

Abstract: This paper presents experimental research on creeping discharge characteristics of TiO2 nanofluid-impregnated pressboards (NPs) under sustained ac voltage. It was found that NPs possess higher resistance to creeping discharge than that of pure oil-impregnated pressboard. The results of permittivity and surface charge accumulation and decay characteristics reveal that the modification of nanoparticles can not only make the electric field more uniformly distributed at the interface of nanofluid/pressboard due to a better matching in permittivity but also significantly increase the surface charge decay rate via a trapping and detrapping process in shallower traps. Thus, the creeping discharge characteristics of NPs are greatly improved by the modification of TiO2 nanoparticles.

Using the three-parameter Weibull distribution in assessment of threshold strength of pressboard impregnated by different liquid dielectrics

Abstract: This study presents the results of the measurements of electrical strength of pressboard specimens impregnated with three different liquid dielectrics: mineral oil, natural ester and synthetic ester. In the experiment carried out in accordance with IEC 60243 standard, two types of pressboard specimens of thicknesses 0.5 and 1 mm, respectively, were considered. The data obtained during the measurements in the form of breakdown voltages were used for calculation of the electrical strength. Both standard-based approach where median value was taken into account in calculations and statistical approach using three-parameter Weibull distribution function where location parameter V 0 was considered were applied. The results obtained on the basis of both approaches showed that both the specimens impregnated with mineral oil and ester liquids gave the satisfactory results within the electrical strength determined, which in all cases was higher than minimum required for the impregnated pressboards. The differences indicating slightly better impregnation properties of mineral oil, when the same impregnation conditions are used, are noticeable especially in the case of location parameter of Weibull distribution function. However, these differences are small and in relation to the requirements for the impregnated pressboards may be treated as negligible.

Установка, методика и результаты измерений электрических параметров композита электротехнический картон-трансформаторное масло

Abstract: The paper presents a measuring stand designed and built for testing direct and alternating current properties of power transformers basic insulation component i.e. electrotechnical pressboard impregnated with transformer oil. Measurements of direct and alternating current parameters are performed using the frequency domain spectroscopy and polarization depolarization current methods. The measuring station includes a specially developed climatic chamber which is characterized by high accuracy of temperature stabilization and maintenance during several dozen hours of measurements. The uncertainty of temperature maintaining during several dozen hours of measurements does not exceed ± 0.01 °C. The computer software developed to control the station allows for remote measurements, changes in supply voltage and temperature settings and acquisition of the obtained results. A new type of measuring capacitor was developed and manufactured, the structure of which significantly reduces the chance of samples contamination during measurements. By increasing the accuracy of temperature stabilization during measurements, the resolution of measurement temperatures was increased, at which it is possible to perform measurements with the frequency domain spectroscopy and polarization depolarization current methods. This allowed to reduce the step of measurement temperature change and thus to increase the accuracy of determining the activation energy of the measured parameters. The article also contains basic information on the analysis of the direct and alternating current electrical parameters of the composite electrotechnical pressboard-mineral oil-water nanoparticles. The results of several direct and alternating current parameters measurements of a transformer oil impregnated pressboard sample with a moisture content of (5.2 ± 0.1) % by weight obtained by the use of a measuring stand are presented as examples.

Diffusion coefficient in transformer pressboard insulation part 2: mineral oil impregnated

Abstract: Moisture is one of the most influencing parameters which accelerates solid insulation degradation process in transformers. Correct estimation of the moisture within solid insulation of transformer is still a challenge due to temperature driven complex moisture dynamics between oil and paper insulation. Although some authors have proposed coefficients for Kraft paper as well as for non-impregnated pressboard much less work has been done on oil-impregnated pressboard insulations. In this paper, the determination of the diffusion coefficient of moisture in transformer pressboard impregnated with mineral oil is tackled. Studies were carried out on different samples thickness of pressboard which are typical in power transformer. The experimental conditions were simulated using a mathematical model based on the Fick?s second law and an expression for the diffusion coefficient is proposed and validated experimentally.

Surface treeing on pressboard barriers in synthetic and natural ester liquids under AC stress

Abstract: This paper reports experimental investigations on pressboard surface treeing processes and the accompanying creepage discharge patterns. With the help of fast digital video recorder, wideband discharge current sampling resistor and commercial PD detector, it is found that the liquid impregnated pressboard as composite insulation is susceptible to erosion giving rise to white marks due to intense discharges occurring on/near to the pressboard surface. The white mark is visible after discharges evaporate the liquid and moisture and takes the form of trapped gaseous bubbles within the surface layers of pressboard. Once the white mark is formed, it can continue to grow even under a reduced voltage level until it bridges the gap and finally causes flashover. The white mark appears at a lower voltage and propagates more readily on the ester impregnated pressboard, due to more intense discharges, more gas generation and the higher viscosity of esters than mineral oil.