Pressboard

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

Disequilibrium of moisture in oil-pressboard insulation under transient temperature condition

Abstract: Moisture has strong influence on insulation performance of oil-pressboard system in power transformer. Moisture in oil and pressboard can be obtained from Oommen paper oil equilibrium curves under constant temperature condition. Temperature of power transformer is related to its load and the atmospheric temperature. If atmospheric temperature or load changed, oil-pressboard insulation will work under transient temperature condition. In present, there are few attentions to the disequilibrium of moisture in oil-pressboard insulation under transient temperature condition. In this paper, a test system has been set up which consists of programmable oven, Karl Fischer moisture meter and oil-pressboard samples. Two kinds of transient temperature conditions have been simulated which were 80 °C to 20°C in 5 hours, 20 °C to 80°C in 5 hours. Moisture in oil and various thick pressboards from 0.5mm to 5mm have been measured in these two conditions. The results have been presented and analyzed.

Insulating pressboard for electrical transformers

Abstract: Insulating pressboards, made from low-yield softwood kraft pulp, are an important component of electrical transformers. Although current pressboards are satisfactory, dielectric strength, thermal conductivity, dimensional stability, and physical strength could be improved and manufacturing cost reduced. In this study, a limited number of experimental insulating pressboards were made from high-yield hardwood pressure-refined mechanical pulps. Pressboards were evaluated for strength properties, weight change, dimension change, and dielectric properties after oil impregnation. Experimental hardwood insulating pressboard properties were compared to those of softwood insulating pressboards. Results show that strength properties and dimensional stability of experimental hardwood pressboards improved slightly, dielectric constants stayed about the same, dissipation factors increased, and dielectric strength decreased. The authors conclude that substituting insulating pressboard made from high-yield hardwood mechanical pulp for insulating pressboard made from low-yield softwood kraft pulp in the manufacture of electrical transformers has no advantage.

Effect of thin solid layer coating on creepage discharge characteristics in oil/pressboard composite insulation system

Abstract: This paper deals with experimental characterization of creepage discharge to improve the electrical characteristics of oil/pressboard (PB) composite insulation system by thin solid layer coating such as epoxy resin and Teflon on PB surface under positive standard impulse voltage (1.2/50 µs) using a rod-plane electrode arrangement in mineral oil. To evaluate the creepage discharge properties according to surface condition, the number of discharge branches, discharge final length (ld) and partial discharge inception voltage (PDIV) are investigated versus the type of solid layer coating for different applied voltage using a digital camera. As a results, it is found that solid layer coating of PB surface significantly influences the PDIV and creepage discharge properties.

Investigation on creeping discharges propagating over pressboard immersed in mineral and vegetable oils submitted to AC and DC voltages

Abstract: This paper deals with the experimental characterization of discharges propagating over pressboard of different thicknesses immersed in mineral and vegetable oils, under AC and DC voltages using a point-plane electrode arrangement. It's shown that the thickness of pressboard and the type of oil significantly influence the characteristics of creeping discharge and especially the stopping length Lf and the density of branches □. For a given thickness, Lf increases with the voltage; it decreases when the thickness increases. For a given voltage and thickness of pressboard, Lf is longer under AC than under DC whatever the oil type. And under DC, Lf is longer with positive point than with a negative point. However, the characteristics Lf(U) in presence of vegetable oil and mineral oil are very close except for thin pressboard.

Space charge characteristics of oil gap and pressboard mixed insulation based on the pulsed electro-acoustic measurement

Abstract: There are many researches about the space charge behavior of solid insulation (oil immersed insulation paper/pressboard) in transformer based on the pulsed electro-acoustic (PEA) technique. However, no research on the space charge behavior of the oil-paper insulation system consisted by oil gap and oil immersed insulation pressboard was conducted. The space charge characteristics of the oil immersed insulation paper, the mixed insulation consisted of oil gap and pressboard were investigated using the PEA Measurement System. The space charge accumulation behaviors at the interface between oil gap and pressboard were analyzed. The distortion of the electrical field in the oil gap and pressboard was also analyzed. Results show that there are many charges injected into the oil and the pressboard. The charges accumulated at the interface between oil gap and pressboard increases with the electric filed applied. The electrical field distortion is obvious with the applied electric filed for the sample with 0.68% moisture content. While the charges accumulated in the mixed insulation system with 3.83% moisture content become less with the conductivity increased, as well as the electrical field distortion.