Pressboard

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

Space charge behaviour in oil and impregnated pressboard combined insulation system

Abstract: Dielectric performance of oil-pressboard insulation system used in high voltage direct current (HVDC) convertor transformers can be affected by the presence of space charge. In this paper, the space charge behaviors in a 0.5mm thick oil film combined with a 1mm thick impregnated pressboard have been investigated by the pulsed electroacoustic (PEA) technique under 12kV/mm and 20kV/mm at room temperature. Two types of oil with different aging status were used for comparison. The results show that a charge peak is quickly formed at the interface between oil and pressboard with the same polarity as the electrode at the oil film side. However, the dynamics of the interfacial charges are very different for fresh oil and aged oil samples. The maximum electric field occurs in the middle of the pressboard, which is significantly enhanced in the aged oil samples. Difference in the electric field between those obtained from measurement results and those calculated from Maxwell-Wagner theory has been discussed

Discharge mechanism at hvdc polarity reversal in oil / pressboard composite insulation system

Abstract: At the instant of polarity reversal of HVDC, very high electric field was generated in oil because the applied electric field was superimposed by the electric field of accumulated charges on pressboard (PB). When the total electric field exceeded the breakdown electric field strength, breakdown discharge in oil gap and surface discharge on the PB occurred. In this paper, by electric field measurement using Kerr electro-optic technique and optical observation, breakdown discharge characteristics and mechanisms in oil / PB composite insulation system were investigated at polarity reversal voltage. We revealed that the surface discharge neutralizes the accumulated charges on PB. The above experiments were carried out for different PB arrangements and discussed the discharge characteristics under HVDC polarity reversal conditions were discussed.

Measuring the Pressboard Water Content of Transformers Using Cellulose Isotherms and the Frequency Components of Water Migration

Abstract: The measurement of water within power transformer insulation is necessary for the unit's reliable operation. Probes can be inserted into the oil of a transformer to measure water activity, and then this water activity is used to determine the water content of transformer cellulosic insulation. The migration of water between the insulation media is driven by differences in water vapor pressure around the insulation system. Over time, this water reaches an equilibrium partition when cellulosic adsorption isotherms are used to calculate the concentration of water absorbed by the cellulose. However, the insulation of a normally operating transformer is highly unlikely to reach this state, as the migration of water between the insulation media is much slower than the rate of change of temperature caused by the varying load of the transformer. This leads to inaccuracies in analyzing water vapor pressure, which is a function of both oil water content and temperature. The frequency spectrum of the oil's water activity data was used to determine whether very slow changes in dissolved water, attributed to long diffusion time constants, could be separated by a filter from fast changes caused by temperature, leading to a better measurement technique. This filter was then used on data from three operating power transformers, which had their insulation water content measured using dielectric response. The results are discussed in this paper.

A three-wavelength flexible sensor for monitoring the moisture content of transformer pressboard

Abstract: A three-wavelength interdigitated flexible sensor has been developed for measuring the heterogeneous properties of transformer pressboard. The imposed spatial wavelengths are 1 mm, 2.5 mm, and 5 mm, and the temporal frequency ranges from 0.005 Hz to 10000 Hz. Because the penetration depth of the electric field is approximately 1/5 of the wavelength, the sensor can be used to observe spatial as well as temporal changes in the dielectric loss of transformer pressboard. Experimental results indicate that the measured response is sensitive to changes in the moisture content of the pressboard. In addition, the sensor can be used to monitor the absorption of moisture into pressboard as a function of time. This measurement provides an estimate of the diffusion coefficient of moisture in oil-free transformer pressboard at room temperature of 3.5*10/sup -11/ m/sup 2//s. >

Does the degree of cellulose polymerization affect the dielectric response

Abstract: The purpose of this work is to evaluate the influence of the cellulose polymerization degree (DP) on the dielectric response. The research objects were new and aged pressboard samples of the polymerization degree 1435 and 406, respectively. The authors investigated the dielectric response in the time and frequency domains. The research showed that dielectric response characteristics of new and aged samples, of different DP and an identical water content are very close. Their differences are within the limits of statistical dispersion.