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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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Proceedings ArticleDOI
08 Jun 2014
TL;DR: Wang et al. as discussed by the authors used pure water and three kinds of sodium chloride solutions with conductivities of 100 μS/cm, 500 μS /cm and 1000 μS 1 cm respectively to prepare presspaper samples.
Abstract: Developments of ultra-high voltage grid in China require better insulation materials, and that forces the transformer presspaper and pressboard manufactures to pay more attention to the papermaking process to enhance their product qualities. In this study, pure water and three kinds of sodium chloride solutions with conductivities of 100 μS/cm, 500 μS/cm and 1000 μS/cm were respectively used to prepare presspaper samples. By vacuum impregnation, four kinds of oil-paper samples were acquired. Test results showed that relative permittivity and tand of oil-paper specimens first varied little then increased a lot with the increasing of water conductivity; DC breakdown field decreased while AC breakdown field changed little. To confirm the differences were due to water conductivity, ion chromatography was used to determine the sodium and chloride ion contents of the presspaper samples, we found that the ion contents increased with electrical conductivity. This indicates that water conductivity does have effects on most electrical properties of oil-paper insulation and lower conductivity can bring better insulation performances.

5 citations

Proceedings ArticleDOI
01 Sep 2016
TL;DR: In this article, the micro surface appearance and mechanical strength of insulating pressboard under different aging time are studied, and the results indicate that long cellulose chain in the surface of pressboard is broken into the shorter one or shed directly with the aging time becoming longer.
Abstract: Oil-impregnated paper is generally used as insulation material in power transformer, which consists of transformer oil and insulating paper (pressboard). And the pressboard made of cellulose is one of important components in transformer insulating system. Oil-impregnated pressboard stays in the environment with high temperature during normal operation of transformer. It is generally recognized that the hot-spot temperature may be the chief factor determining the lifespan of transformer. Furthermore, the inner temperature of transformer will also influence both electrical and mechanical performances of oil- impregnated pressboard. In this paper, the micro surface appearance and mechanical strength of insulating pressboard under different aging time are studied. The sample preparation includes the following steps: vacuum drying for pressboard and transformer oil, impregnating pressboard with transformer oil, and taking oil-impregnated pressboard into vacuum drying oven for thermal aging. When the aging time of oil-immersed pressboard reaches 100h, 200h, 400h and 800h, the pressboard will be taken out of the oven as specimens respectively. After all the specimens under different aging time are obtained, the micro surface appearance of them was observed by scanning electron microscope (SEM) and confocal laser scanning microscope (CLSM). Then the tensile strength of them was tested by tensile strength tester. The results indicate that long cellulose chain in the surface of pressboard is broken into the shorter one or shed directly with the aging time becoming longer, meanwhile the mechanical strength of pressboard becomes weaker.

5 citations

Journal ArticleDOI
TL;DR: In this article, the effect of casein and polyvinyl-based adhesives used in winding cylinders was investigated through standard PD measurements, and the results indicated that pressboards bonded with casein-based adhesive exhibit PD values 20-25 pC lower than those bonded with polyvinel-based AA at identical applied voltages (7.5-25 kV or 3-10 kV/mm).
Abstract: In this study, 238 power transformers (PTs) with operating voltages between 150­500 kV and capacities in the range of 60–167 MVA are tested for partial discharge (PD). Thirty-eight of the PTs exceeded the pre-determined value of 70 pC at 1.5 maximum voltage of the PT. Failure analysis of the failed 38 PTs showed that 21% of the PD sources originate from the winding cylinder, which is formed by bonding the edges of a pressboard with an adhesive. Therefore, in this study, the effect of casein- and polyvinyl-based adhesives used in winding cylinders was investigated through standard PD measurements. The results indicate that pressboards bonded with casein-based adhesives exhibit PD values 20–25 pC lower than those bonded with polyvinyl-based adhesives (50–400 pC) at identical applied voltages (7.5–25 kV or 3–10 kV/mm). The excellent performance of casein-based adhesives is mainly attributed to its porous structure, which accelerates the impregnation of oil into the adhesive and pressboard, as revealed by scanning electron microscopy observations. This practical study will be beneficial in the process of designing and manufacturing PTs and highlight materials for producing PTs with low PD values.

5 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

Journal ArticleDOI
TL;DR: In this paper, a multilayer sensor with two identical rectangular oil ducts constructed by pressboard paper and separated by a middle copper plane electrode is used to measure the ground current from this middle electrode.
Abstract: Streaming electrification dynamics is experimentally investigated by using a multilayer sensor in a closed loop and fresh transformer oil. This sensor consists of two identical rectangular oil ducts constructed by pressboard paper and separated by a middle copper plane electrode. The ground current from this middle electrode is measured. Two outer steel plane electrodes are connected together and used to measure the capacitive “accumulation” current. The leakage currents at the sensor inlet and outlet, as well as the streaming current are also measured. The waveforms of these five currents together and oil temperature at the sensor inlet are simultaneously recorded for laminar flow and at controlled operating conditions; namely, oil temperature, mean flow velocity, humidity, and pressure. The results reveal that the all-recorded currents nonlinearly augment with oil temperature and linearly with oil-flow velocity. These results are interpreted in terms of shear stress, physicochemical reaction, the effect of streaming/floating potential on the electrical double layer (EDL), temperature-dependent oil properties, and introducing an expression of the streaming current. Calculations of accumulated charges on steel electrodes and the loating potential of the copper electrode at different oil-flow velocities, and the fully developed wall space-charge density and physicochemical reaction coefficient are presented.

5 citations


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