Pressboard

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

Breakdown Characteristics and Its Mathematical Model of Oil-pressboard Insulation Under Compound Electric Field

Abstract: In order to study the breakdown characteristics of oil-pressboard insulation under compound electric field, the typical oil-pressboard insulating structure was taken as the study object. The breakdown characteristic of typical oil-pressboard insulation was obtained under compound electric field via breakdown tests at first. Then the electric fields in oil and oil-impregnated pressboard were simulated according to the equivalent circuit. The breakdown characteristic tests of oil and oil-impregnated pressboard were carried out separately under compound electric field. On the basis of the electric field mathematical expressions of the oil and oil-impregnated pressboard, the relationship between the electric field E and AC content was got, and the electric field distribution in oil and oil-impregnated pressboard was compared with their breakdown strengths. And then the breakdown voltage mathematical expressions with AC content were concluded. The results showed that the main reason why the breakdown voltage of oil-pressboard insulating structure rises before and falls later is that the electric fields in the two materials vary with the AC content and there is difference in breakdown characteristics between two materials.

Investigations on creeping discharges propagating over pressboard immersed in mineral and vegetable oils submitted to impulse voltage

Abstract: This paper deals with the experimental characterisation of discharges propagating over pressboard of different thicknesses immersed in mineral and vegetable oils, under impulse voltages, using a point-plane electrode arrangement. It's shown that the thickness of solid insulator and the kind of oil significantly influence the characteristics of creeping discharge and especially the stopping length Lf. For a given thickness, Lf increases quasi-linearly with the voltage; it decreases when the thickness increases. Lf is longer when the point is positive than with a negative point. For given voltage and thickness of pressboard, Lf is greater in vegetable oil than in mineral oil; Lf is generally greater of 60% in vegetable oil than in mineral oil when the point is positive and it's of 40% greater when it's negative. The values of Lf merge into one another in vegetable oils. The smaller the thickness of pressboard, the more branched are the discharge structures. This indicates the important role of the capacitive effect in the propagation mechanism.

Nonlinear phenomena in the constant electric field in insulation pressboard

Abstract: The paper presents the results of DC conductivity dependence of a transformer oil impregnated pressboard, with moisture content of 2.9% by weight, measured for temperature from 20 °C to 80 °C and a field strength from 10 kV/m to 1000 kV/m. It was found that the non-linear phenomena, which presence cannot be explained by the theory of ion conduction of oil-paper insulation, is intensifying with increase of the electric field strength.

Effects of Thermally Induced Bubbles on the Discharge Characteristics of Oil-Impregnated Pressboard

Abstract: Under temperature and moisture combined, bubbles will be formed in oil-impregnated paper/pressboard (OIP/OIPB). Although many studies have been done to understand the thermo-induced bubble phenomenon in OIPB, the formation mechanism is not, let alone its effect on discharge characteristics and insulation performance of OIPB. In this article, the phenomena and mechanisms of thermally induced bubbles, their effects and mechanisms on the partial discharge (PD), and breakdown characteristics of OIPB are investigated. The results show that the bubble inception temperature (BIT) decreases significantly with the increase of the moisture of OIPB. There is a growth process of bubbles from small to large, and the heating temperature and moisture content of OIPB affect the gas component inside the bubble. Thermal bubbles significantly reduce the PD inception voltage (PDIV) and breakdown voltage (BV), and the PD evolution and dissolved gas components in the oil show significant differences in the presence/absence of bubbles. Interestingly, PDIV and BV start to decrease in a temperature interval before BIT, and we infer that many microbubbles and gaseous channels exist inside OIPB before observable bubbles are formed on the surface. Considering the fibrous porous structure of OIPB and combining it with the bubble nucleation theory, we propose a new model for interpreting bubble formation and insulation degradation. The model suggests that bubbles (vapors) form first in microcavities and holes inside the OIPB and then spill over to the surface to form observable bubbles. The microcavities and pores in the OIPB are filled with gas (vapor) as the main cause of PD inception and insulation degradation. This study contributes to understanding the mechanisms of bubble formation in oil–paper insulation as well as provides a reference for risk assessment during overload operation and diagnosis of bubble-induced related faults of transformers.

Aging performance of Natural Ester Impregnated Nomex Paper Insulation

Abstract: In the power transformer, the oil-impregnated paper is used for providing insulation between live conducting parts, which comprises of transformer oil and insulating paper (either Kraft paper/Pressboard). These insulating papers are made up of cellulose fibers and it gets easily degraded at higher hot-spot temperature with increase in aging periods. So this affects the lifetime of solid insulation and further transformer life. In this research work, the latest advanced solid insulation named “Nomex paper” made up of aramid polymers is considered as a solid insulating paper material for analyzing the aging behavior. Furthermore, the electrical properties such as breakdown voltage of both oil and paper, flash point and fire point, viscosity have been measured to study the change in characteristics during aging. Also, the level of degradation of solid insulation has been identified by measuring Breakdown voltage of paper under all aging times. On looking standard IEEE C57.91, all these samples were analyzed at the maximum hot-spot temperature of about $130^{\mathbf {\circ }}$C. The results clearly show that the solid insulation gets affected due to deterioration and decomposition.