Pressboard

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

Experimental research on creepage discharge between oil-impregnated pressboard layers

Abstract: Partial discharges are considered to be an important role in the deterioration process of the oil-impregnated pressboard insulation system. It was found that the PDs are favor to produce tree like carbonized trace inside the oil-impregnated pressboard. High voltage experiments were carried out on the needle-plate configuration to research the change of the PDs, the formation and propagation of the carbonized trees. The oil-impregnated pressboards were parallel with the electric field, and the needle was inserted the pressboard so that the trees can propagate between the layers of the pressboards. The PDs and the tree phenomena were continuously record until the pressboard was breakdown under certain AC voltage. Then the characteristic parameters of the PDs and the length of the trees were contrast to find out their correlation. The white mark was the outside appearance of the carbonized trees inside the pressboard. The propagation of the carbonized trees appeared as the expending white mark, which can be observed and recorded easily. Two kinds of PDs were found, one type of PDs has high and increasing charge quantity and numbers, the other has low and decreasing charge quantity and numbers. Before and after the appearance of the white mark, the PRDP of the PDs has changed. The repetition rate of the PDs and their total charge quantity in one minute have linear relationship with the length of the white mark, except the accelerative stage near the breakdown. Thus, they can be used to indicate the propagation of the carbonized trees. But there is exception that the PDs are very small but the carbonized tree develops quickly.

Investigation of interfacial surface creep breakdown at oil-pressboard interfaces in natural ester liquid and mineral oil

Abstract: Natural ester liquids are increasingly established in power transformers, especially if the water protection and prevention of fire hazard in operation region of transformer are in focus. They show a comparable dielectric strength to mineral oil in homogeneous and slightly inhomogeneous fields. Nevertheless, differences exist between natural ester liquids and mineral oils in terms of electrical properties. The different ratios of liquid and solid insulation materials permittivities at interfaces cause a shift in electric field distribution within the insulation system of a transformer. Therefore, it is important to explore the effects of interfacial surface creep breakdown strength at high stressed oil-paper interfaces inside power transformers. This will be called simply creep breakdown. This study investigates the creep breakdown along an oil-paper interface at defined oil gap in natural ester liquid and mineral oil. A high-density pressboard sheet is impregnated and prepared giving a vertical electrode gap for AC creep breakdown test setup. Pressboard is fixed within one rounded electrode at the upper end and within one rounded electrode at the lower end. Special care is taken in the electrode design to avoid / minimize possible oil wedges in the setup. Tests are conducted with dry oil at a relative moisture content of less than 12 % of saturation. Breakdown mean values, 2 % withstand values and standard deviations are compared. The empirical breakdown results and the measured differences between the insulation liquids are used to interpret the effects of electric stress shift in natural ester liquids on transformer design rules.

Recovery Voltage Measurement on Kraft Paper Pressboard

Abstract: The recovery voltage of oil-free pressboard is measured as part of efforts to understand the recovery voltage in oil-paper system. The results hinted non-Debye polarisation within the paper and important role played by migration of surface charge in the formation of recovery voltage. A model that describes the recovery voltage in time domain is developed based on charge diffusion and stretched exponential relaxation function.

Effects of polymeric materials and contaminants on streaming electrification

Abstract: In order to study the effect of material characteristics on static electrification phenomena, the charging current characteristics of different polymeric materials, such as, PTFE, XLPE (cross-linked polyethylene), LDPE (low-density polyethylene) silicone rubber, EVA, EPR, pressboard, etc., in paraffinic-based transformer oil were investigated. Use was made of spinning disc system (SDS) over a temperature range of 27-60/spl deg/C and at a rotational speed varying from 250 to 2000 rpm. The charging current characteristics of the above materials were also investigated in the presence of conducting contaminants like cupric oxide and iron particles. The oil/silicone system had the lowest and the oil/LDPE system had the highest charging current characteristics. The oil/silicone, oil/EPR, and oil/PTFE systems exhibited peak current characteristics. The presence of contaminants particles like CuO and iron reduced the charging current characteristics of the oil/polymer systems significantly. >

Method for cutting groove on surface of pressboard

Abstract: PROBLEM TO BE SOLVED: To provide first a method for cutting grooves on the surface of a pressboard, by which the cutting of the grooves for multi-use pressboards can be quickly and economically carried out, and to provide secondly a method for cutting grooves on the surface of the pressboard, by which the cutting of the grooves also for a plurality of pressboard cards used as functional members, such as insulating materials, can be quickly and economically carried out. SOLUTION: The method for cutting the grooves on the surface of the pressboard comprises steps of feeding the pressboard into a groove cutting apparatus in which a cutting blade and a grooving blade are alternately arranged, forming cut lines on the surface of the pressboard by feeding the pressboard to a position facing the cutting blade, and carrying out a grooving operation by means of the grooving blade along the cut lines on the surface of the pressboard.