Pressboard

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

A Comparative Study of Moisture and Temperature Effect on the Frequency Dielectric Response Behaviour of Pressboard Immersed in Natural Ester and Mineral Oil

Abstract: It is important to investigate the dielectric behaviour of natural ester-paper insulation as the number of transformer choosing natural ester as its insulation oil is increasing. A comparative study of the influence of moisture and temperature on the frequency dielectric response of pressboard immersed in natural ester and mineral oil was provided. X-Y model simulation was used to indicate the difference between the frequency domain spectroscopy (FDS) characteristics of transformer main insulation system using natural ester-pressboard and mineral oil-pressboard, respectively. Compared to the mineral oil impregnated pressboard with lower moisture content, the natural ester impregnated pressboard with lower moisture content has higher E'r and tan? values in the lower frequency region at various temperatures. While there is no significant difference existing in the E'r and tan? curves of mineral oil impregnated pressboard and natural ester impregnated pressboard with higher moisture content in the lower frequency. X-Y model simulation results show that the dielectric loss difference between natural ester-paper insulation system and mineral oil-paper insulation system with the lower moisture content is more obvious at higher temperature.

Finite-Element Analysis for Surface Discharge Due to Interfacial Polarization at the Oil-Nanocomposite Interface

Abstract: The propagation of surface discharge due to interfacial polarization was numerically analyzed at the oil-nanocomposite interface using fully coupled finite-element analysis incorporating the relative permittivity from experiments. To improve the insulation ability, a new nanodielectric insulating material has been proposed in which a pressboard is coated with epoxy resin mixed with silica nanoparticles; this nanocomposite material can enhance the breakdown voltage in power systems with a certain level of silica nanoparticles. To specify the electric breakdown performance of this nanocomposite material, we measured the bulk relative permittivity of epoxy resin containing different percentages of silica nanoparticles on the pressboard. Surface discharge, or creepage discharge, tends to propagate along the solid–liquid interface and then leads to flashover. The mechanism of surface discharge, therefore, is a critical issue for understanding the dielectric breakdown strength in solid–liquid interface problems. To quantitatively analyze and explain the characteristics of surface discharge, here, the fully coupled finite-element analysis technique has been applied and tested with various relative permittivity values of nanocomposite materials. This phenomenon has been simulated using the fully coupled governing equations using Poisson’s equation for electric field and charge continuity equations, including surface charge accumulation for charge transport. After verification of our numerical setup in a conventional oil-pressboard system, a needle-bar electrode system was proposed and applied to the analysis of surface discharge propagation for the new nanocomposite materials with bulk dielectric permittivity. The propagation speed at the oil-nanocomposite interface was compared with different percentages of nanosilica. Finally, the physical mechanism of surface discharge due to the interfacial polarization was analyzed with the space, bounded, and surface charge densities at the oil-nanocomposite interface based on the numerical results.

Investigation of AC breakdown properties of paper insulators and enamel insulation impregnated with rice oil, corn oil and peanut oil for transformers

Abstract: The AC breakdown properties of Kraft paper, pressboard and the enamel insulation layer in rice oil, peanut oil and corn oil were investigated under both new and aged conditions. The ageing of paper insulators and the enamel insulation layer in oils with the open cup method was carried out at 130 oC for 500 h in an air circulation oven. The puncture breakdown strength was determined by varying the number of layers and thickness of Kraft paper, while various electrode gap distances were used to measure the surface breakdown strength. Experimental results show that the breakdown strength and the tensile strength of paper insulators impregnated with these vegetable oils are comparable to that in mineral oil, and the surface breakdown strength of paper insulators is slightly affected by types of impregnating oils. The ageing significantly reduces both the breakdown strength and the tensile strength of paper insulators in investigated oils. In addition, it was also found that the enamel layer in vegetable oils withstood higher puncture breakdown strength than in mineral oil, and the ageing process significantly reduced the puncture breakdown strength of the enamel layer. This enamel layer was observed to markedly enhance the surface breakdown strength of pressboard.

Partial discharge behaviour in oil-impregnated insulation

Abstract: The insulation within an oil-insulated power transformer consists of mainly organic materials including mineral oil, cellulose paper and pressboard layers. The presence of moisture, coupled with high operating temperature in the insulation reduces the dielectric strength of the cellulose paper, the pressboard and the transformer oil. This paper reports results of an experimental investigation of partial discharge behaviour in a laboratory model of transformer oil-impregnated insulation at high temperature and with different levels of moisture contamination of both the oil and paper. The experiments were performed in the laboratory with an environment and configuration similar to practical operating conditions in a transformer. The partial discharge patterns together with inception and extinction data were recorded and correlated with moisture and temperature effects and age of insulation. The thermal generation of gas bubbles and, moisture levels and their associated discharge characteristics were also recorded and analysed. The effect of aged and new transformer oil on partial discharge activity patterns was also investigated.

Fabrication of ZnO-Al2O3-PTFE Multilayer Nano-Structured Functional Film on Cellulose Insulation Polymer Surface and Its Effect on Moisture Inhibition and Dielectric Properties

Abstract: After a century of practice, cellulose insulating polymer (insulating paper/pressboard) has been shown to be one of the best and most widely used insulating materials in power transformers. However, with the increased voltage level of the transformer, research has focused on improving the insulation performance of the transformer's cellulose insulation polymer. Considering the complex environment of the transformer, it is not enough to improve the single performance of the insulating polymer. In this study, a nano-structured ZnO-Al2O3-PTFE (polytetrafluoroethylene) multifunctional film was deposited on the surface of insulating pressboard by radio frequency (RF) magnetron sputtering. The effect of the multilayered ZnO-Al2O3-PTFE functional film on the dielectric and water contact angle of the cellulose insulating polymer was investigated. The scanning electron microscopy/energy dispersive spectrometry (SEM/EDS) showed that the nano-structured ZnO-Al2O3-PTFE functional film was successfully deposited on the cellulose insulation pressboard surface. The functional film presented an obvious stratification phenomenon. By analyzing the result of the contact angle, it was found that the functional film shields the hydroxyl group of the inner cellulose and improves hydrophobicity. The AC breakdown field strength of the treated samples was obviously increased (by 12 to ~17%), which means that the modified samples had a better dielectric insulation performance. This study provides a surface modification method to comprehensively improve electrical properties and the ability to inhibit the moisture of the cellulose insulating polymer, used in a power transformer.