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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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Journal ArticleDOI
TL;DR: In this paper, a 6-pulse DC voltage generator and PD detection and analysis of oil-pressboard insulation under pulsating DC voltage waveform is analyzed through computer simulation.
Abstract: HVDC transmission has been adopted widely for its large energy transport capacity, high stability and more economical in long-distance power transmission. Converter transformer is the key equipment in HVDC transmission system. The insulation of converter transformer valve side endures a composite voltage including AC, DC and pulsating component etc. Partial discharge (PD) occurring in a void surrounded by insulating material is believed to be one of the main causes of insulation breakdown and it is the main factor of electrical aging of materials. Therefore, it is important to recognize the prebreakdown phenomena and to evaluate the lifetime of insulating materials. Much research has been carried out to study the partial discharge characteristics under pure AC or DC voltage. Only a few investigations were focused on composite voltage. In order to obtain more understanding of PD characteristics under composite voltage, the PD detection and analysis of oil-pressboard insulation under pulsating DC voltage waveform are studied in this paper. The voltage waveform of converter transformer is analyzed through computer simulation. A 6-pulse DC voltage generator and PD detection system are set up. Influence of the DC component and pulsating component to the PD characteristics is studied in lab test. The experimental results show the DC component and pulsating component affect the PD inception voltage, but the pulsating component has more significant influence to PD characteristics than DC component. The study provides an experimental foundation for the converter transformer insulation breakdown mechanism analysis.

18 citations

Proceedings ArticleDOI
01 Dec 2012
TL;DR: In this article, the results of practically applicable methods in oil sampling (KFT and capacitance sensors), paper sampling (Dean-Stark method) and also dielectric response (RVM, PDC, FDS) are examined in determining insulation system humidity.
Abstract: Transformer is one of the crucial equipments in electric power network. Moisture in paper insulation acts as a catalyst in transformer insulation aging. Experience has shown that humidity will affect electrical strength of paper and pressboard as well as other insulation system materials by reducing degree of polymerization and accelerated aging. Thus, it is essential to determine the extent of moisture content within insulation system before exciting the transformer and also during normal operation. In this regard, chemical tests on oil have been carried out for many years. Also, electrical tests for assessing the transformer condition have been developed and improved in recent years while most introduced methods aim to extract moisture from transformer insulation system. In this study, the results of practically applicable methods in oil sampling (KFT and capacitance sensors), paper sampling (Dean-Stark method) and also dielectric response (RVM, PDC, FDS) are examined in determining insulation system humidity. Test results through various methods are compared to analyze the sensitivity of different approaches. Crucial practical recommendations as well as advantages and disadvantages of each method are discussed. At last, to recommend an accurate and reliable method for practical implementations, practical tests have been performed simultaneously on three distribution transformers and the results of them are discussed.

18 citations

Proceedings ArticleDOI
15 Jul 1996
TL;DR: In this paper, a cylindrical electrode apparatus with EHV-Weidmann Hi-Val pressboard on the inner cylinder and transformer oil filling the gap was used to measure the time and space distributions of moisture diffusion into oil-impregnated pressboard.
Abstract: Sinusoidal steady state and transient decay measurement techniques were used to monitor the dielectric properties of electrical insulation. Impedance measurements of an air-gap capacitor, immersed in Shell Diala A transformer oil and driven with a 1 V peak sinusoidal signal (5 mHz-10 kHz), showed that the oil conductivity increased with temperature (15-70/spl deg/C) and aging in air but was independent of the oil moisture content (2-30 ppm). Interfacial double layer effects were also observed. Surface charge effects were studied in a cylindrical electrode apparatus with EHV-Weidmann Hi-Val pressboard on the inner cylinder and transformer oil filling the gap. The pressboard dielectric properties were obtained from time transient decay measurements of the open-circuit voltage after disconnecting a DC voltage source from across the cylinders. These measurements indicate that the conduction mechanism through the pressboard follows a drift dominated unipolar conduction law rather than ohmic conduction. Further frequency sweep dielectrometry measurements using a three-wavelength interdigital electrode sensor confirm the dispersive properties of oil-impregnated pressboard. This sensor was also used to measure the time and space distributions of moisture diffusion into oil-impregnated pressboard.

18 citations

Journal ArticleDOI
TL;DR: In this article, the static electrification phenomenon of insulating materials used in power transformers is investigated through two devices, one is a cell with a rotating disk covered on both sides with a given pressboard and immersed in a metallic tank containing /spl sim/41 of oil; and the second device enables us to measure the electrostatic charge tendency of oils.
Abstract: The static electrification phenomenon of insulating materials used in power transformers is investigated through two devices. The first is a cell with a rotating disk covered on both sides with a given pressboard and immersed in a metallic tank containing /spl sim/41 of oil; and second device enables us to measure the electrostatic charge tendency of oils. The electrostatic charge tendency (ECT) of insulating oils and the leakage current generated by the charge concentration gradient at the oil/pressboard interface are analyzed as function of temperature, water content and aging of oils, the nature of the pressboard, and the rotating speed of the disk. The influence of the surface roughness of the pressboard and antistatic additives on the aging and ECT also are considered. A correlation between ECT and the physico-chemical and electrical characteristics of the oil is established. It is shown that the temperature gradients and the water migration phenomena at the oil/pressboard interface play an important role in the charge separation. Transient currents are strongly affected by the presence of air in the pressboard and the aging of the oil.

18 citations

Book ChapterDOI
01 May 2004
TL;DR: In this paper, a prototype of a new sensor dedicated to characterization of the phenomenon, when pressboard-oil insulation is present, has been developed with the University of Poitiers.
Abstract: As far as Static Electrification diagnosis in transformers is concerned, previous works have shown that the commonly applied measurements (leakage currents, Electrostatic Charging Tendency or ageing test for tan˜) were not completely reliable. As part of the research program of Electricite de France, a prototype of a new sensor dedicated to characterization of the phenomenon, when pressboard-oil insulation is present, has been developed with the University of Poitiers. To simulate the pressboard-made channels inside transformer, this device consists in a small pressboard with facilities for measuring reliable parameters related to the generation (accumulated charge) and leakage (leakage current) phases of the phenomenon. As it was likely to be installed on a real transformer, the sensor has been inserted, for its development, in a loop representing at a small- scale the oil path in a transformer with "on line" conductivity and moisture content monitoring. This complete setup has made it possible to investigate the parameters behaviour with regard to oil temperature and velocity during transient and steady states with and without flow. A first electrical model for the electro-kinetics of the sensor has been deduced from the analysis of the results. This device seems a promising tool to predict electrostatic hazards and to derive criteria for Static Electrification diagnosis in transformers.

18 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
202321
202266
202140
202059
201966
201882