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Pressboard
About: Pressboard is a research topic. Over the lifetime, 1123 publications have been published within this topic receiving 9089 citations.
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TL;DR: In this paper, a study on the characterization of aging of transformer oil-pressboard insulation is presented, where traditional and modern diagnostic tools and techniques were used to investigate aging of oil-paper insulation under controlled laboratory conditions.
Abstract: This paper presents a study on the characterization of aging of transformer oil–pressboard insulation. Traditional and modern diagnostic tools and techniques were used to investigate aging of oil–paper insulation under controlled laboratory conditions. Insulation condition testing includes common chemical diagnostics such as acidity tests and new chemical techniques: determination of relative content of dissolved decay products by spectrophotometry, solid suspension by turbidimetry, Fourier Transform Infrared (FTIR) spectroscopy and electrical diagnostic techniques that have gained exceptional importance for utility professionals: polarisation/depolarisation current, recovery voltage measurement and frequency domain dielectric spectroscopy measurements. From the obtained results it is found that chemical tests depicted more sensitivity to insulation degradation. Also, different oil–pressboard insulation ratios were investigated to assess the influence of the relative amount of cellulosic materials on aged mineral oil decay products and vice versa. Emphasize is laid on the potentialities/avenues offered by FTIR to assess oil insulation condition. Notable experimental results have been reported, which could be valuable to researchers and practicing engineers in this field. Copyright © 2010 John Wiley & Sons, Ltd.
62 citations
TL;DR: In this article, the degradation processes observed in the insulation from aged power transformers were investigated using short-term accelerated ageing experiments on paper-wrapped insulated conductors and on pressboard samples.
Abstract: This paper describes the analysis of accelerated aged insulation samples to investigate the degradation processes observed in the insulation from aged power transformers. Short-term accelerated ageing experiments were performed on paper-wrapped insulated conductors and on pressboard samples. The condition of aged insulation samples was investigated by two relatively new diagnostic techniques: (a) measurements of interfacial polarization spectra by a DC method; and (b) measurements of molecular weight and its distribution by gel permeation chromatography (GPC). Several other electrical properties of the paper/pressboard samples were also studied. Possible correlations have been investigated among the different measured properties. The GPC results have been used to predict how power transformer insulation molecular weights change with temperature and time.
60 citations
TL;DR: In this paper, a rotating cylindrical electrode apparatus was used to simulate now electrification in an electric power transformer, and extensive experiments characterized the time transient and steady state behaviour of the electrification through measurements of the volume charge density, the terminal voltage, and the terminal current as the system was driven out of equilibrium by changes in the flow rate.
Abstract: A rotating cylindrical electrode apparatus, which provided cylindrical Couette flow, was used to simulate now electrification in an electric power transformer. The apparatus had Shell Diala A transformer oil filling the annulus between coaxial cylindrical stainless steel electrodes that were either bare metal, or covered by a thin copper sheet and/or EHV-Weidmann HiVal pressboard insulation. Extensive experiments characterized the time transient and steady state behaviour of the electrification through measurements of the volume charge density, the terminal voltage, and the terminal current as the system was driven out of equilibrium by changes in the flow rate (inner cylinder rotation rates of 100 to 1400 rpm, Reynolds numbers of 5/spl times/10/sup 3/ to 5/spl times/10/sup 5/), temperature (15 to 70/spl deg/C), insulation moisture content (0.5 to 20 ppm in the oil), applied voltage (0 to 2 kV dc), and concentration of the non-ionizable antistatic additive 1,2,3 benzotriazole (BTA, 0 to 60 ppm). Generally, the electrification increased with flow rate and temperature but the BTA appeared to cause competing effects: it decreased the volume charge density on the liquid side of the interface by a factor of 4, which reduces the electrification, but also decreased the oil conductivity by a factor of 10, which enhances the electrification. A critical oil BTA concentration of 5 to 8 ppm minimized the electrification. The volume charge density was sensitive to the current flowing through the interface and surface charge accumulation. With pressboard covering the cylinders, the electrification effects of the temperature and moisture were decoupled during the transient following step reductions in the temperature. The oil moisture content did not affect the oil conductivity significantly, but the volume charge density varied inversely with the moisture content during an initial equilibration period just after the oil had been added to the system. The highest electrification was observed during this equilibration period.
60 citations
TL;DR: In this paper, the DC conductivity of moist pressboard impregnated with insulating oil and its dependence on the moisture and temperature of the samples was investigated. But the transfer of charges was found to take place because of electron hopping between potential wells produced by water nanodrops.
Abstract: This article presents results on the DC conductivity of moist pressboard impregnated with insulating oil and its dependence on the moisture and temperature of the samples. The transfer of charges was found to take place because of electron hopping between potential wells produced by water nanodrops. The average dimension of the nanodrops was around 2.32 nm, forming approximately 220 water molecules.
59 citations
TL;DR: In this paper, the characteristics of the impregnation of cellulose insulation by ester oils are assessed and compared with mineral oil, and it is shown that the factors governing the imprognation processes with ester and mineral oils are very similar, i.e. mainly viscosities and surface tensions.
Abstract: Ester oils have been successfully used in distribution transformers for many years as satisfactory substitutes for mineral oil. In high voltage transformers however their application has been much slower partly due to the fact that the high viscosity of ester oil and hence uncertainties in efficient impregnation of cellulose insulation. In this paper the characteristics of the impregnation of cellulose insulation by ester oils are assessed and compared with mineral oil. Studies are carried out on thick laminated pressboard blocks, typical of support insulation structures in high voltage transformers. The degree of oil impregnation with time at various temperatures is examined. It is shown that the factors governing the impregnation processes with ester and mineral oils are very similar, i.e. mainly viscosities and surface tensions, and if a higher impregnation temperature is used for ester oils the same degree of oil impregnation can be achieved as with mineral oils.
59 citations