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Showing papers on "Pressboard published in 1999"


Journal ArticleDOI
TL;DR: In this paper, the authors present an overview of several applications of interdigital ω-κ dielectrometry developed during the last few years, including landmine detection using spectroscopy.

37 citations


Patent
31 Aug 1999
TL;DR: A plate-shaped constructional element comprises a perforated plate made of a solid material such as metal, wood, wood chip board, pressboard, synthetic material or gypsum as discussed by the authors.
Abstract: A plate-shaped constructional element comprises a perforated plate made of a solid material such as metal, wood, wood chip board, pressboard, synthetic material or gypsum, and is characterized by the provision that a micro-perforated sheet or thin plate is disposed on one of the plate surfaces of the plate. One variant provides that the holes in the plate are formed in such a manner that they open each into a micro hole on one side of the plate.

21 citations


Proceedings ArticleDOI
01 Jan 1999
TL;DR: In this article, a method of relating tensile strength and degree of polymerization to ageing time is compared to traditional mathematical formulae derived for the ageing of pressboard, previously reported by Moser and Dahinden (1987).
Abstract: The original properties of solid (cellulose) insulation in a transformer deteriorate under thermal stress. Decomposition products (gases and furanic compounds) are released, which can be detected in the oil. The degree of polymerisation (DP) of the paper decreases and with it the tensile strength (TS). In order to predict the life expectancy of paper insulation under working conditions, it is necessary to understand the processes of degradation, and measure parameters of ageing that can be used to calculate the life of the different paper types. This paper presents results for various insulating papers aged under accelerated ageing conditions in the laboratory. A new method of relating tensile strength and degree of polymerisation to ageing time is compared to traditional mathematical formulae derived for the ageing of pressboard, previously reported by Moser and Dahinden (1987).

20 citations


Proceedings ArticleDOI
Katsumi Kato1, Y. Hashiba, Y. Nakagami, M. Miyamoto, Hitoshi Okubo 
20 Jul 1999
TL;DR: In this article, the authors measured the electric field in transformer oil/pressboard composite system, using a Kerr electro-optic method to discuss electric field distribution and charge behavior induced by flow electrification.
Abstract: In this paper, we measured the electric field in transformer oil/pressboard composite system, using a Kerr electro-optic method to discuss the electric field distribution and charge behavior induced by flow electrification. We investigated electric field in both uncharged and charged oil, under different flowing conditions. From the experiments, we could quantitatively estimate and analyze the time transition of electric field by charge accumulation on the pressboard. Finally, we propose a charge behavior model in flowing transformer oil.

13 citations


Proceedings ArticleDOI
20 Jul 1999
TL;DR: In this paper, the most constrained parts in transformer as far as flow electrification is concerned: the insulated pressboards between windings, and the generation process has been investigated with regard to time, temperature and velocity, for different oil samplings (used and new oils) flowing along a used or a new pressboard.
Abstract: Up to now the ECT (Electrostatic Charging Tendency) measurement and, to a smaller extent, the continuous aging test for tan /spl delta/ are the most commonly applied measurements for transformer monitoring. So it is important that the reliability of these two tests involving only the oil should be established for different oil-pressboard couples. As part of the research program of Electricite de France in the field of static electrification in transformers, an experiment has been carried out, at the university of Poitiers, to study the most constrained parts in transformer as far as flow electrification is concerned: the insulated pressboards between windings. So, the generation process has been investigated with regard to time, temperature and velocity, for different oil samplings (used and new oils) flowing along a used or a new pressboard. In the meantime, ECT and tan /spl delta/ tests have been performed for each types of oil. It turns out that those two monitoring measurements and the charge generation in the pressboard are not always directly correlated but that diagnosis requires a deeper analysis taking into account transient kinetics aspects and pressboard state.

13 citations


Proceedings ArticleDOI
20 Jul 1999
TL;DR: In this paper, the propagation aspects of a creepage discharge on a hard glass (thickness: 3 mm) in insulating oil such as transformer oil are observed in detail under an impulse voltage condition in a pointplane electrode geometry, by using a high-speed schlieren method.
Abstract: In relation to the optimum design of internal insulation for HV oil-filled power apparatus, studies of the creepage discharge on the surface of a solid insulator in insulating oil are of practical importance, so much research on this subject has been carried out. In the present paper, the propagation aspects of a creepage discharge on a hard glass (thickness: 3 mm) in insulating oil such as transformer oil are observed in detail under an impulse voltage condition in a point-plane electrode geometry, by using a high-speed schlieren method. In addition, turning our attention to a surface state of a pressboard, the creepage discharge on it is investigated by using a video camera and an image-fiber observation system.

9 citations


Proceedings ArticleDOI
01 Jan 1999
TL;DR: In this article, an experimental validation has been performed on a transformer insulation model using an acoustic PD detector, and it is observed that the signal gets attenuated significantly when it passes through pressboard barriers.
Abstract: Acoustic partial discharge (PD) measurement is a useful method of identifying and locating PD in a power transformer in service. In this paper an experimental validation has been performed on a transformer insulation model using an acoustic PD detector. While the efficacy of the method is proved, it is observed that the signal gets attenuated significantly when it passes through pressboard barriers. Even though acoustic PD values can be correlated with the maximum discharge magnitude for a single discharge activity in the laboratory simulations, this relationship could not be established during actual PD measurements in a transformer at site, as the acoustic PD signal depends upon many factors.

5 citations


Patent
31 Aug 1999
TL;DR: In this article, a plate-shaped component comprised of a perforated plate made of a solid material such as metal, wood, compregnated wood, pressboard, plastic or plaster is described.
Abstract: The invention relates to a plate-shaped component comprised of a perforated plate made of a solid material such as metal, wood, compregnated wood, pressboard, plastic or plaster. The invention is characterized in that a micro-perforated film or thin plate (3) is arranged on one of the plate surfaces of the plate (2). A variant of the invention provides that the holes (1a) are formed in the plate such that they open into a micro-hole on one side of the plate (1).

3 citations


Proceedings ArticleDOI
20 Jul 1999
TL;DR: In this paper, a model transformer insulation system consisting of pressboard and transformer oil with uniform field electrode arrangement was tested for its behaviour under partial discharges and the system was allowed to age until failure of the sample occurred in the form of a puncture.
Abstract: Partial discharges cause degradation of insulation systems and a study of their behaviour can give useful information regarding the state of the insulation system. Partial discharge tests are therefore, carried out as quality checks for the insulation system. A model transformer insulation system consisting of pressboard and transformer oil with uniform field electrode arrangement was tested for its behaviour under partial discharges. The system was allowed to age until failure of the sample occurred in the form of a puncture. Records of partial discharge distributions were acquired along with oscillograms. Oscillograms help in the traceability of the measurement when compared with distributions. A comparative study of the effect of amplifier setting and the pulse repetition rate on the partial discharge distributions and the oscillograms acquired during ageing of the sample has been presented. It is shown that by appropriate threshold on the distribution, distinctive features can be extracted.

3 citations


Proceedings ArticleDOI
17 Oct 1999
TL;DR: In this article, the authors measured and compared the convected space charge density value obtained with a brand new pressboard sample and with a pressboard coming from a damaged power transformer, and analyzed the influence of an additive (BTA benzotriazol 1-2-3) in oil.
Abstract: In high power transformers, pressboard and oil are required for electrical insulation On the other hand, the oil is also used as a coolant of the system The flow electrification process occurring at oil-pressboard interface seems to be initiating on electrical discharge incidents Our recent investigations of electrification generated by an oil flow through different pressboards showed an influence of the pressboard degradation by artificial electrical discharges Consequently the goal of this experimental study is to measure and to compare the convected space charge density value obtained with a brand new pressboard sample and with a pressboard coming from a damaged power transformer The influence of an additive (BTA benzotriazol 1-2-3) in oil is also analyzed The results show that the pressboard sample obtained from the damaged power transformer induces a high increase of flow electrification due to a modification of the exchange process at the pressboard-oil interface On the other hand, an addition of BTA permits to reduce significantly flow electrification

2 citations


Proceedings ArticleDOI
01 Jan 1999
TL;DR: In this article, a model insulation system consisting of oil impregnated pressboard with uniform field electrode arrangement has been tested for its behaviour under partial discharge (PD) pulses and it is shown that by defining a modified scale parameter for the Weibull distribution it is possible to take into account the effect of both smaller and larger magnitude PD pulses.
Abstract: Partial discharge (PD) measurement and interpretation is one of the most useful diagnostic tools for quality assurance testing during the design, manufacture and life assessment of electrical equipment. Pressboard-oil insulation continues to be a major component in the insulation design of EHV transformers. As tests on practical systems are not always feasible due to cost and time factors, model systems tests are gaining importance. In the present work a model insulation system consisting of oil impregnated pressboard with uniform field electrode arrangement has been tested for its behaviour under PDs. It is shown that by defining a modified scale parameter for the Weibull distribution it is possible to take into account the effect of both smaller and larger magnitude PD pulses. The modified scale parameter serves as a good index for characterising PD behaviour in the oil impregnated pressboard insulation system studied.

Proceedings ArticleDOI
17 Oct 1999
TL;DR: In this article, an automatic setup has been performed in order to make long term experiments on oil impregnated pressboard sample submitted to both electric field and temperature gradient and the evolution in terms of time of the potential distribution is measured inside a sample at the application of an electric field for different temperature gradients.
Abstract: An automatic experimental setup has been performed in order to make long term experiments on oil impregnated pressboard sample submitted to both electric field and temperature gradient. The evolution, in terms of time, of the potential distribution is measured inside the impregnated pressboard sample at the application of an electric field for different temperature gradients. Four temperature gradients have been tested and three different electric fields. The space charge evolution is measured during around two hours after each temperature gradient application for a given electric field. The analyze of the charge development can then be used to understand the charge accumulation in pressboard due to flow electrification in transformer during temperature stabilization.