Pressboard

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

Electric Field Characteristic Calculation on Typical Oil-paper Combination Insulation Under Polarity Reversal

Abstract: Polarity reversal (PR) is a special working condition occurring during the operation of a converter transformer. Due to the action of spatial charge under polarity reversal an extremely high dangerous electric filed will appear in the insulation oil. By use of ANSYS10.0 finite element method (FEM), the electric field strengths of several typical oil-paper combination insulations, such as plate-plate oil-paper insulation, coaxial oil-paper insulation, rod-plate oil-paper insulation and local model of converter transformer’s winding end at valve side, are calculated while polarity reversal occurs, and the relation curves of the maximum filed strength in insulation oil vs. the parameters such as the thickness of insulation pressboard, conductivity ratio of oil to pressboard, the time of polarity reversal and so on, are plotted. In plate-plate oil-paper combination insulation, increasing the thickness of insulation pressboard can reduce the field strength in oil and pressboard. However, in coaxial oil-paper combination insulation when the thickness of insulation exceeds a certain value the field strength within the pressboard under polarity reversal will increase instead. In rod-plate oil-paper combination insulation, more indeterminacy exists in the relation among the field strength under polarity reversal, the size and position of pressboard. Elongating the time of polarity reversal can reduce the field strength under polarity reversal. Field strength under polarity reversal increases with the increasing of the conductivity ratio of oil to pressboard and the field strength in oil and pressboard under polarity reversal will be saturated finally.

Drying process of super thick insulated pressboard

Abstract: The invention belongs to a drying process of a super thick insulated pressboard. In the process, 0.5-0.7 percent pulp is prepared by insulation pulp through conventional treatment, enters a pulp stabilization box and is sent into a wet ground paper forming device through a pulp pump, a prepared wet ground paper is sent into a die which is sleeved with an inner net and is sent into a pressurizer with the die together for water extrusion with the pressure of 0.7-0.9MPa, a vacuum pump assists with water suction and absorption, the wet ground paper is taken out when the moisture achieves 40-50 percent, is sent into a micorwave drying box to be dried through a conveyor belt and is pulled out and sent into a hot press to be dried with the temperature of 115-125 DEG C when being dried with the water content of 25-35 percent, the drying time is determined by the thickness, the wet ground paper is dried until the pressboard water content achieves 4-6 percent and enters a half finished chamber to be in balance treatment for 3-5 days after board disassembly, the paper is treated by edge trimming and finishing and is packaged to be put into a storage after passing the inspections.

Experimental Study of the Aged States Effects on Pressboard PDC Characteristics

Abstract: To investigate the effect of pressboard aged states on its polarization and depolarization currents(PDC) characteristics,the oil-impregnated pressboard samples were accelerated thermally aged for different time intervals.The pressboard samples of different aged states were sequentially put into petroleum ether as de-oiling solvent for residual oil removal,and dried in a vacuum oven to remove the petroleum ether and moisture.To characterize the aging status of different samples,the degree of polymerization(DP) was measured by viscosimetry and the scanning electron microscope(SEM) was also implemented to observe the surface microstructure.Then PDC tests were performed on each water-removed pressboard sample in vacuum and new oil impregnated ambient,respectively.Experimental results show that,with the aging status heavier and decreasing DP values,microstructure of cellulose fiber is significantly destroyed.Aged samples exhibit higher polarization and depolarization currents,lower insulation resistance and smaller absorptance in both ambient.It is confirmed that,for oil-paper insulation,besides the influence of water induced by aging,the deterioration of cellulose itself also causes the increasing of pressboard conductivity,and hence greatly affects the PDC test results.

Effect of the Thickness on the Water Mobility Inside Transformer Cellulosic Insulation

Abstract: Traditionally, water mobility inside the cellulosic insulation, as those used in power transformers, has been modeled using the so-called Fick's diffusion theory, considering that the water movement in this porous material only depends on local conditions, such as temperature and moisture concentration. However, recent experimental works have demonstrated that the moisture movement inside the cellulose insulation could be also influenced by a global condition, that is, the insulation's thickness. In this paper, the influence of the insulation thickness in the mobility of moisture inside the cellulosic materials, such as Kraft paper and pressboard, is analyzed. In addition, the improvement in moisture dynamics estimation obtained when this variable is included into the diffusion models has been proved.