Pressboard

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

Partial discharge characteristics in UHF-band of composite insulation system including various artificial defects in transformer

Abstract: Experiments of partial discharge (PD) current pulse and phase resolved PD characteristics were performed using various artificial defects in oil/pressboard composite insulation system in oil-filled transformer. As artificial defects, we used barrier insulation model-in-oil, oil wedge model, air void model, floating electrode model, and oil gap model. As a result, it was found that the rise time, fall time, and pulse width of each PD current pulse differed depending on each model. Moreover, we confirmed the existence of PD-radiated electromagnetic wave with frequency UHF band for the defects. It was shown from these results that UHF method is applicable for detecting PD originating from the defects and identifying the defect types in oil-filled transformer.

Effect of temperature gradient on space charge in multilayers pressboard oil and pressboard system

Abstract: The presence of space charges within the oil and pressboard of converter transformers could distort the original Laplacian field. This could lead to the local electric field enhancement and accelerate the degradation of the insulation materials, which could ultimately result in electrical breakdown. Therefore, space charge measurement is the significant tool to evaluate the insulation properties of dielectric materials. Several factors could affect the space charge behaviour including temperature, moisture, ageing and electric field. Considering the joule heating and stray losses, this paper mainly focuses on the temperature gradient effect on space charge behaviour of multilayers pressboard/oil/pressboard. Space charge behaviour is measured using the modified pulsed electroacoustic (PEA) technique. The space charge recovery methodology is proposed in this paper for three layers pressboard/oil/pressboard. It has been found that the maximum electric field position is opposite depending on the temperature of the anode. The maximum electric field occurs at the pressboard near the anode under the ambient temperature while that is near the cathode under the temperature gradient.

Effect of carbonized patterns on oil-impregnated aramid pressboards surface on acoustic emission signals at inhomogeneous electric field

Abstract: The acoustic emission signals produced by discharges of a point-plane electrode on the surface (surface discharge) of different oil-impregnated aramid pressboards are detected by a 150 kHz acoustic emission sensor mounted on the outside of the experimental tank sample. Numbers, maximum amplitudes and average amplitudes of acoustic bursts are measured via a digital signal processor device and evaluated. The effect of transition mechanism from spark to pseudoglow discharge on acoustic emission signals at different voltages is examined. The tracking patterns on the surface of four different aramid pressboard insulations are compared together by using Matlab image processing program. By experimental results, tracking patterns on the surface of the bulk impregnated pressboard insulation have a significant effect on the acoustic emission signals. Acoustic emission signals amplitudes decrease dramatically on damaged pressboards and cause so called silent PDs.

Partial Discharge Simulation of Air Gap Defects in Oil-Paper Insulation Paperboard of Converter Transformer under Different Ratios of AC–DC Combined Voltage

Abstract: A converter transformer is important primary equipment in a DC transmission project. The voltage on the valve side winding is complex when the equipment is running, including DC, AC, and AC–DC combined voltage. The insulation structure of the valve side winding of a converter transformer is an oil-paper insulation structure, which may have a variety of defects in the manufacturing stage and daily use, resulting in partial discharge. Therefore, it is the key to studying the partial discharge characteristics and mechanism of oil-paper insulation under AC–DC combined voltage. In this paper, we build a two-dimensional air gap model of oil-paper-insulated pressboard considering the actual particles and actual reaction based on the fluid model. The characteristics and evolution mechanism of partial discharge (PD) in pressboard under different AC/DC combined voltages are studied by numerical simulation. The results show that when the DC component increases, the polarity effect of partial discharge is more obvious, while the potential and discharge intensity in the air gap decrease. Further analysis revealed that the DC component in the combined voltage accumulated a large number of surface charges on the surface of the air gap, and the space charge distribution was more uniform and dispersed, which generated an electric field with opposite polarity to the DC component in the air gap and, then, inhibited the development of local discharge in the paperboard. The results of the simulation are consistent with the previous experimental phenomena, and the mechanism analysis of the simulation results also verifies the previous analysis on the mechanism of experimental phenomena. This will lay a theoretical foundation for the further study of partial discharge phenomenon of oil-paper insulation structures in practical operation in the future.

Influence of moisture content on dielectric properties of pressboard impregnated in mineral insulating oil and natural ester

Abstract: Natural ester as a substitute for mineral insulating oil has been used more and more widely in distribution transformers and large power transformers. The reliable operation of the natural ester transformer is essential to the safety and stability of the power grid. And the safe operation of the natural ester transformer relays the good dielectric properties of oil-pressboard insulation. In recent, the effect of moisture content on the dielectric properties of natural ester has been studied, while the research on the influence of moisture content on dielectric properties of pressboard impregnated is not detailed. In this paper, the temperature characteristics of permittivity, dissipation factor and resistivity at power frequency of pressboard impregnated respectively both in mineral insulating oil and natural ester with the moisture content about from 0.2% to 6% were studied. And the authors also studied the AC breakdown characteristic of oil-impregnated pressboard. The results were important for the safe and reliable operation of natural ester transformers.