Pressboard

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

Charge accumulation phenomenon in oil immersed pressboard exposed in positively charged transformer oil

Abstract: It was dicovered that the pressboard immersed in positively charged oil were highly charged up. The experiments to evaluate the charge density and the charge distribution in the pressboard were carried out to investigate the mechanism of charge accumulation. In the experiment, positive charges generated by oil flow were supplied to the pressboard sample. Charge densities in oil and pressboard were evaluated from the potential measurement. Charge distribution in pressboard was estimated from the current-time characteristics at DC voltage application to the pressboard.

Tea machine is fried in steerable heating temperature's suppression

Abstract: The embodiment of the utility model discloses tea machine is fried in steerable heating temperature's suppression, it includes motor, arc pressboard, frying pan, is located heater, telescopic suppression support, the control panel who has heater heating temperature control button, axis of rotation and the axis of rotation support of frying pan below, the axis of rotation is connected with axis of rotation support axle housing, the axis of rotation with the one end fixed connection of telescopic suppression support, telescoping support's the other end and pressboard fixed connection, the pressboard with frying pan bottom of a boiler arc shape is approximate, control panel is connected with the heater electricity The utility model discloses simple structure, through ingenious design, the pressboard can carry out the effect of extrusion in order to reach the artifical system of frying of certain degree to tealeaves in frying process, and the heating temperature who freely sets for simultaneously also can satisfy the stir -fry system requirement of different cultivars tealeaves

Study of electrode for measuring dielectric properties of oil immersed material

Abstract: Dielectric properties including relative permittivity and dc resistivity has been used widely as a design parameter of insulation system. In measuring dielectric properties of oil immersed material (OIM), we have to make some adaptations from IEC 60093 and IEC 60250 i.e. the detail of live electrode curvature corner shape and the effect of electrode's weight. The effect of the electrode curvature shape on the electric field stress distribution should be reduced as small as possible when measuring the dielectric properties of the pressboard. Meanwhile the weight of electrode plays an important role to reduce the effect of non-flatness surface of the pressboard. This paper focused on electric field analysis distribution for three electrode configurations and pressure simulation of different electrode's weight. Then the simulation results were deepened with the laboratory experiment, permittivity, partial discharges inception voltage (PDIV) and partial discharge (PD) pattern respectively. In this experiment, the dielectric interface configurations consists of oil immersed pressboard operated under oil bath in a test vessel. For PDIV measurement, the pressboard samples were placed on a grounded plane under cylindrical live electrode with three types of corner shape. The live electrodes used were sharp-cornered electrode and rounded-cornered with radius 3 mm and 5 mm. Meanwhile for the permittivity measurements, a guard electrode was used to prevent edge capacitance. The solid dielectric were oil immersed transformer board type B 3.1A with 2 mm and 4 mm thickness operated under mineral oil, Nynas Nytro 4000x. The PD experiment was set up according to IEC 60270, the PDIV test procedure was performed in accordance with IEC 61294 and the permittivity and tan δ measurements performed in accordance with IEC 60250. We concluded that, eventhough round-cornered electrode yields more uniform electric field at the pressboard side, it also yields steep electric field enhancement at the oil side. This nature of rounded-corner electrode makes it easier to generate oil discharge in the wedge (small oil gap) when compared to sharp-cornered electrode. Meanwhile, the D/R (ratio of the sample thickness to corner radius of electrode) parameter does not seem to have any real important meaning. It was also found that electrode with pressure higher than 1.9 N/cm2 give enough pressure to prevent a thin oil layer that present on surface. These results showed the effect of electrode corner shape on electric field enhancement and pressure of electrode at the contact point of dielectric interface. Furthermore, the results could be used as a consideration on which electrode is suitable for measuring dielectric properties of pressboard immersed in oil in compliment with IEC 60093 and IEC 60250.

Investigation of Particle Initiated Partial Discharges in Transformer Oil with Pressboard Barrier Under Divergent Fields

Abstract: Particle initiated partial discharge (PD) in oil is one of the significant problem associated with transformer. Among particles, conductive particles play very detrimental role. The existence of conducting particles is very difficult to avoid completely during the manufacturing process and also it can be developed during service period of the transformer. These free conductive particles can adhere to paper or pressboard insulation barrier or freely move in the bulk oil. In transformers divergent (non-uniform) fields are often present due to the geometry of the internal parts and may be due to sharp points. Therefore to understand and characterize the effect of conducting particle in oil with pressboard barrier under divergent fields are very critical for the life assessment of transformer. Sphere-plane and needle-plane electrodes are used to generate different non-uniform fields. The discharge measurements are carried out using partial discharge measurement technique according to IEC 60270. Phase resolved partial discharge (PRPD) pattern, discharge characteristics such as average and peak discharge magnitude, number of discharges per cycle, discharge power, rise and duration time of PD pulse due to conducting particle in oil with pressboard barrier under divergent fields are analyzed. The observed PRPD pattern were relatively similar regardless of applied divergent fields. The observed PD inception is much earlier in quasi uniform field compare to non-uniform filed, the PD inception voltage (PDIV) in non-uniform field is three times higher than that occur at quasi-uniform field.