Pressboard

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

Terahertz Detection of Wavelength-Size Metal Particles in Pressboard Samples

Abstract: Results of a theoretical and experimental investigation of THz detection of randomly-oriented metal particles smaller than 1 mm embedded in pressboard are reported and critically compared with X-ray scanner results. A theoretical description based on Gaussian beam theory and a transfer function approach enabled simulation of signals transmitted around and reflected from real particles and was able to predict signal detectability. Simulated signals and detection limits were compared with experimental transmission and reflection time domain spectroscopy (TDS) raster scanning data. Simulated and measured pulse amplitude and shape were in agreement. Reflection mode was superior to transmission mode in terms of both particle visibility and hit ratio. Imaging of particles was also possible in “reflection in transmission” mode, which can be used to complement classical transmission mode. X-ray images did not detect the smallest particles sufficiently and, therefore, could not be used as reference data for comparison with THz data. The results demonstrate that TDS reflection scanning is able to determine the position of small metal particles and the technique could be possibly used for quality control of pressboard insulation.

Modern insulation condition assessment for instrument transformers

Abstract: Instrument transformers in service are exposed to the harming effects of water and ageing. The increasing age is leading to a higher risk of explosions, which can damage surrounding parts and cause high follow-up costs. This paper introduces a new approach to use the dielectric response analysis for condition assessment of instrument transformers. The measurement of the dielectric response in a wide frequency range provides information about the insulation condition and especially for oil-paper/pressboard insulations about the water content in the solid insulation. The measured curve is formed by the superposition of the dielectric response of the cellulosic material and the oil. The curve can be used for the assessment of the insulation condition in various ways. Qualitative comparisons, e.g. between instrument transformers of the same type and age, might give general information which of these is in better condition. The dissipation factor and the capacitance trend can also deliver valuable data. Furthermore the water content in the solid insulation can be assessed using an automatic analysis algorithm. To confirm the validity of this assessment, measurements on several instrument transformers in service were performed. Dielectric response curves and the trend of the capacitances for new and aged instrument transformers with different water contents are discussed. Selected examples presented in this paper show, that the dielectric response is well modeled, the water content can be derived and ageing effects can be observed.

Moisture dynamic measurements of transformer board using a three-wavelength dielectrometry sensor

Abstract: The spatial distribution of dielectric permittivity and conductivity of an insulating medium affects the quasistatic distribution of the electric field. Multiple wavelength interdigital sensors using the imposed frequency-wavenumber (/spl omega/-k) dielectrometry technique can measure complex permittivity distributions in dielectrics. Measurements of oil-free and oil-impregnated pressboard transformer insulation using a three-wavelength sensor with changes in ambient moisture concentration are presented. With a calibrated mapping relating conductivity and permittivity to moisture concentration in oil-impregnated pressboard, the spatial distribution of moisture can be measured.

Surface discharge characteristics of impregnated pressboard under AC voltages

Abstract: Three typical electrode systems immersed in transformer oil, i.e., needle-plate, cylinder-plate, and sphere-plate electrode systems, have been used to study the characteristics of impregnated pressboard under AC voltages. According to careful observations, the six stages of the discharges which occur when the applied voltages are increased can be distinguished. The inception electric field strengths of the surface discharge in the three electrode systems were computed. The results of experiments and calculations may be useful for analyzing the surface discharge failures of pressboard barriers in power transformers which have occurred in recent years in China. >

Major factors influencing static electrification in an aged transformer

Abstract: Increase in static electrification was experienced during the service operation of aged power transformers The increase was noted a few years after on-site replace of the bushings and conservator Analysis of the dissolved gas in the transformer oil suggested that slow intrusion of air, which could have led to the increase in static electrification, took place after the on-site work However, the electrical characteristics of the oil did not demonstrate increase in static electrification The investigation on the aged oil by ECT (electrostatic charging tendency) measurement suggested the possibility that some deteriorated compound in oil was adsorbed to the pressboard and increased the static electrification However, the ECT measurement with the aged pressboard did not demonstrate enough increase, which suggested the necessity of the evaluation of the accumulated charge on the pressboard for assessing static electrification in transformers At the static electrification tests with the model transformer using the aged pressboard and oil, strong acceleration effect of oxygen on the increase of static electrification was demonstrated The rapid increase of the static electrification was succeeded by gradual decrease later This suggested the possibility that yet unknown transient products by oxygen injection played strong role on the static electrification