Pressboard

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

Измерение скорости просачивания трансформаторного масла через электротехнический картон

Abstract: The paper presents a new test stand for ivestigating the rate of penetration of transformer oil through electrotechnical pressboard. The stand consists of a pipe, to the lower end of which is glued a pressboard plate. The pipe is filled with insulating oil. A mirror is placed under the plate, which directs its image to the lens of the camera, which takes a series of photographs at a given time interval. After being saturated with the insulating oil, the pressboard changes colour from light to dark yellow. The absorbing time is defined as the time in which a dark yellow spot appears on the lower light surface of the pressboard after the pipe is filled with oil. A new way of determining capillary diameters has been developed when the number of capillaries is unknown and the volume of liquid flowing through them is not measurable. The distribution of the times of penetration of transformer oil through 2 mm thick electrotechnical pressboard was determined, the values of which range from about 220 min to about 550 min. It was found that the radii of capillaries through which the insulating oil penetrates are within the range from about 45 nm to about 70 nm. Due to the structure of the pressboard, which consists of cellulose fibres, arranged more or less tightly, there are capillaries in the structure of the board, each of which has sections of varying lengths of radii. This means that short sections of a single capillary can have radii both smaller than 45 nm and larger than 70 nm. The developed stand and the new analysis method can be used for testing various porous materials for penetration by various liquids.

Thermal aging of paper and pressboard in mineral and ester oils under air and nitrogen atmospheres

Abstract: The purpose of this paper is to simulate an accelerated ageing of paper and high density pressboard type B.3.1 in three different liquids (mineral oil MO, natural ester VO and synthetic ester SE) for different periods of ageing at 130°C. The materials were aged in sealed vessels under two different atmospheres: air and nitrogen gaps. The effects of aging on physicochemical properties of oil and cellulose are analyzed and compared. It is shown that ageing rate of pressboard and paper are comparable in each type of oil. Nevertheless, it can be underlined that cellulosic materials are less affected after aging in ester oils evidencing a higher degree of polymerization (DPv). The use of 2-FAL in ester oils remains questionable. The reduction of oxygen content in mineral oil minimizes ageing of oil more than solid insulating materials.

Analysis of the micromechanical deformation in pressboard performed by X-ray microtomography

Abstract: A large number of electrical insulation components are produced in paper-based materials. Paper combines good insulating properties with the necessary mechanical and chemical stability. Paper consists of a system of fibers binding to each other creating a strong network. The presence of large open pores allows for impregnability of the material but also causes mechanical weakness in particular in the out-of-plane direction of the material. This aspect is important for pressboard components, where the resistance to compression stress is relevant for e.g. transformer windings. It is therefore relevant to understand the mechanisms that underlay the out-of-plane deformation of pressboard. In order to get a clear picture of the deformation patterns within the material, X-ray micro-computed tomography was used. Pressboard test pieces were subjected to in-situ out-of-plane compressive loading. 3D images of the sample could be captured before, during and after the loading sequence. Image analysis allowed for the definition of strain fields. The results revealed a strong correlation between the density variation within the sample and the strain calculated from the 3D images.

Research on some related mechanisms of corrosive sulfur problems in mineral oils

Abstract: Since a number of failures have happened on transformers and reactors due to the corrosive sulfur problem, especially for Dibenzyle-disulfide (DBDS) in mineral insulation oils, many researchers have carried out a series of studies on such issue. In this paper, some related mechanisms of corrosive sulfur problems in mineral insulation oils are introduced in detail. Such as the mechanism of DBDS how to change into copper sulfide (Cu 2 S), and which results are proved and checked by gas chromatography equipped with mass spectrometry (GC-MS), when there is copper sulfide deposited, what the surface color and microstructure of copper and insulation paper would be change are shown via scanning electron microscope (SEM), and the mechanism of Cu2S how to influence the dielectric properties of oil immersed insulation pressboard, together with the changing tendency of dissipation factor, permittivity and breakdown strength etc are introduced. Besides, the mechanism that how oxygen in oil to influence the Cu2S migrating from the copper surface into oil or insulation paper is given, and the activation energy of DBDS reacting with copper is obtained by Arrhenius equation, which is about 43.73 kJ/mol in air condition and 98.61 kJ/mol in nitrogen condition, at last, the mechanisms that how to inhibit such corrosive phenomena in mineral insulation oil via adding some passivators are introduced as well.

Analysis of ageing characteristics of solid insulation in mixed insulating fluids

Abstract: The practical stability of solid insulation used in the transformer depends on liquid insulation, where periodic assessment of solid and liquid insulation is mandatory. The usage of mineral oil in the transformer system cause rapid deterioration of solid insulation and which in turn weakens the strength of liquid insulation. Instead of traditional mineral oil, combinations of natural esters and mineral oil have been formed and these mixed natural ester insulating fluid samples are compared against the commercial mineral oil. The ageing tendency of Kraft paper and Pressboard are evaluated by treating the test pieces with samples of mixed insulating fluid groups `A', `B', `C' and `D' by accelerated thermal ageing test. Samples and test piece (Kraft paper and Pressboard) were subjected to acidity and water content test before and after accelerated thermal ageing test as per IEC and IEEE standards. By visual observation, it is agreed that the solid insulation in the 100% composition of natural esters samples ages at a much slower rate than sample of 100% mineral oil. Also the ageing rate increases rapidly with the increasing proportion of mineral oil in the samples.