Pressboard

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

Heat conducting oil heating press

Abstract: The utility model discloses a heat-conducting oil hot press which comprises a stand (1); a hollow hot pressboard (2) is arranged in the stand (1); the hot pressboard (2) can moves up and down in the stand (1); an oil delivery pipe (3) is connected on one side of the hot pressboard (2); an oil return pipe (4) is arranged on the other side of the hot pressboard (2); and the oil delivery pipe (3) and the oil return pipe (4) are respectively connected with a heat-conducting oil temperature machine (5). The hot press uses the oil pipes to deliver heat-conducting oil to the hot pressboard and heat the hot heat-conducting oil, and the heat-conducting oil conducts thermal circulation in the heat-conducting oil temperature machine, so that traditional steam heating is replaced. And the hot press has the advantages of quick heating up, even temperature distribution, simple structure, easy operation and the like.

Angularly resolved field mapping in transformer oil

Abstract: The authors report angularly resolved measurements of the electric field in transformer oil around two overlapping pressboard barriers, a geometry relevant to HVDC transformer design. Measurements have been performed at room temperature and at 80 degrees C and the data are compared with the results of electrostatic calculations. It is concluded that the Kerr electro-optic field mapping technique has been developed into a versatile engineering tool for investigations concerning HVDC converter transformer insulation. The present study of oil/pressboard insulation shows that traditional electrostatic field mapping gives a reasonable picture of stress levels, provided the resistivity ratio between oil and pressboard is not chosen too high. >

Prebreakdown behavior of a composite liquid-solid insulation system under impulse conditions

Abstract: This paper deals with the prebreakdown and breakdown phenomena of composite liquid-solid insulation systems in strongly non-uniform (point-point geometry) and weakly non-uniform fields (rod-rod geometry) at impulse voltages up to 500 kV. The investigations were carried out in oil-pressboard-oil barrier configurations with electrode gaps up to 22 mm. Streamer inception and propagation were visualized via high-speed shadow-graph photography. Compared with purely liquid insulation systems, the predischarges show identical propagation behavior, i.e. they appear either as primary or secondary streamers depending on the field. However, the propagation ceases at the liquid-solid interface and a luminous micro discharge (MD) without subsequent breakdown occurs. The light intensity of this MD becomes stronger with increasing voltage levels. Further, the MDs lead to surface discharges on the pressboard and, beyond a critical voltage level, Lichtenberg-type figures can be observed on the pressboard surface.

Influence of additives and pressboard degradation on flow electrification in high power transformers

Abstract: The aim of this work is a better understanding of the flow electrification process occurring in high power transformers. In order to characterize the effect of the pressboard degradation and the additive benzotriazol, the experiments consist in measuring the streaming currents generated by an oil flow through a pressboard sample. Two main results have been obtained: the addition of several ppm of benzotriazol in oil permits to reduce significantly the flow electrification process whereas the degradation of the pressboard by electrical discharges induces a high increase of the phenomenon.

Static and quasi-static behavior of dry and oil-impregnated pressboard

Abstract: Pressboard has been used as insulation material in transformers due to its outstanding mechanical behavior. Spacers, collars, press rings and common spacer rings are subjected to a number of mechanical loads that include out-of-plane (through-thickness) compressive load. Once the assembly process is finalized and the oil filling is completed, the pressboard components in the windings are subjected to both a constant compressive load applied during manufacturing and to a superimposed pulsating compressive force during service. Pressboard, as most of the fiber-based materials, can be described as an open pore structure characterized by irregularly shaped voids. The internal structure of the material affects the overall mechanical behavior. The oil filling in the pores is said to contribute to the overall stiffness of pressboard when compressive (through-thickness) load is applied. However the size of the contribution to the overall through-thickness stiffness of pressboard is not clear. The present report investigates the difference between the mechanical behavior of dry and oil-impregnated pressboard. The experiments elucidate the contribution that oil impregnation gives to the overall stiffness of the pressboard system. Compressive tests on model systems have been carried out and precise measurements of the deformation of pressboard were performed.