Showing papers on "Pressboard published in 2004"

PDC measurement evaluation on oil-pressboard samples

Abstract: In this paper the measuring results of polarization and depolarization currents (PDC) on oil-pressboard samples will be presented. The measurements were carried out under different condition and the results compared. For repeatability purpose the samples were provided at specific condition. Moisture of samples was measured by Karl Fischer titration method. To obtain a quantitative parameter from PDC for the evaluation of the moisture content of the solid insulation, the depolarization current curves are decomposed to basic exponential functions. Obtained results show a relation between magnitude of mid decade (100 s - 1000 s) approximate exponential function and moisture content of solid insulation.

Flow Electrification in Transformers: Sensor Prototype for Electrostatic Hazard

Abstract: As far as Static Electrification diagnosis in transformers is concerned, previous works have shown that the commonly applied measurements (leakage currents, Electrostatic Charging Tendency or ageing test for tan˜) were not completely reliable. As part of the research program of Electricite de France, a prototype of a new sensor dedicated to characterization of the phenomenon, when pressboard-oil insulation is present, has been developed with the University of Poitiers. To simulate the pressboard-made channels inside transformer, this device consists in a small pressboard with facilities for measuring reliable parameters related to the generation (accumulated charge) and leakage (leakage current) phases of the phenomenon. As it was likely to be installed on a real transformer, the sensor has been inserted, for its development, in a loop representing at a small- scale the oil path in a transformer with "on line" conductivity and moisture content monitoring. This complete setup has made it possible to investigate the parameters behaviour with regard to oil temperature and velocity during transient and steady states with and without flow. A first electrical model for the electro-kinetics of the sensor has been deduced from the analysis of the results. This device seems a promising tool to predict electrostatic hazards and to derive criteria for Static Electrification diagnosis in transformers.

Detection of oil-pressboard insulation aging with dielectric spectroscopy in time and frequency domain measurements

Abstract: The insulation system of power transformers consists of oil and cellulose, whose dielectric properties are strongly influenced by moisture, temperature and aging. Their condition can therefore, be evaluated using dielectric response measurements. This contribution describes the return voltage measurement (RVM) diagnostic method based on scanning the polarization spectra of the oil-paper insulation in the time range of 1 s to 1200 s at an excitation voltage of 500 V (DC). The variation of the dissipation factor (tan /spl delta/) and power factor (cos /spl theta/) in the frequency range of 0.0001 to 1000 Hz were measured and the effects of moisture and aging were analyzed. Furthermore accelerated aging processes of oil-paper samples were investigated under air environment up to a temperature of 388 K (115/spl deg/C). Typical transformer proportions of copper, aluminum, zinc and iron were added to oil-paper insulation during the aging process in order to simulate the possible oxidation processes. For the investigation of the long time behavior, the oilpaper insulation samples were aged at different aging times at 250, 500, 1000 and 2000 hours which simulate long time service condition due to the used severe aging conditions.

An attempt to correlate time & frequency domain polarisation measurements for the insulation diagnosis of power transformer

Abstract: The insulation system of power transformers (oil and paper/pressboard) generally change their dielectric properties during the life of the transformer and dielectric measurements have therefore been applied to assess the quality or state of ageing of the system. Both time domain and frequency domain dielectric diagnosis techniques have recently gained popularity in providing information on the condition of transformer oil-paper insulation. The present paper aims at deriving a correlation between these two methods of diagnosis. Simulation results along with actual field test results have demonstrated a direct correlation between the time and frequency domain tools for insulation diagnosis.

Impulse creepage discharges in rapeseed ester oil [power apparatus insulating oil]

Abstract: Rapeseed ester oil is considered to be a substitute for the mineral oil that is used in electric power apparatus because of advantages of environmental adaptation and high dielectric strength. This work presents the results obtained on creepage discharges over the pressboard surface in rapeseed ester oil as well as mineral oil and silicone oil under standard lightning impulse voltage conditions. The basic discharge properties such as discharge shape, streamer length, discharge current and charge were measured for the creeping streamer propagating from a needle electrode. It is shown that rapeseed ester oil has a high insulating ability. The barrier effect on the propagation of creeping streamers in rapeseed ester oil was also examined using a high-speed image converter camera (ICC). The streamer propagation velocity appears to be significantly affected by the existence of the barrier.

Charge behavior in flowing charged oil in transformer oil duct

Abstract: The electric field in flowing charged oil in an oil/pressboard (PB) composite insulation system was directly measured by an electro-optic Kerr effect. We discussed the charging mechanism and proposed the charge behavior model based on the measurement results. We compared the results of measurements and calculations and confirmed the validity of charge behavior model.

Transformation of time domain spectroscopy data to frequency domain data for impregnated pressboard [power system insulation]

Abstract: If the insulation system is considered as a linear system, transformation of data from one domain to another domain is possible. In this paper, the transformation of data from time to frequency domain for impregnated pressboard is presented. Both frequency and time domain measurements are carried out on impregnated pressboard. The accuracy of different transformation methods and their limits are studied. Several methods for transformation of polarization depolarization current data are investigated in detail. The first method is considered as an approximated analytic function using the general relaxation response. The second method is based on an extended Debye model for the impregnated pressboard to obtain frequency domain spectroscopy data. The last method is a numerical integral form of transformation. All methods show similar results. However, non-linearity exists in the insulation system caused small errors in some case, which have to be analyzed in order to demonstrate the limits of the used methods.

Multifunctional waterpower control valve

Abstract: The utility model relates to a check valve installed on a pump exit in a transportation liquid pipe system of a water pump, which is used for eliminating a water hammer. The utility model is composed of a rubber sheet, a lower cover, a small valve board, a rubber seal board, a small pressboard, a big valve board, a valve base, a valve body, a lining sleeve, a big pressboard, a spring, a valve rod, a lower cover lining sleeve, a lower pressboard, an upper pressboard, etc., wherein the rubber seal board is embedded in the small valve board and is pressed by the small pressboard; the spring arranged on the valve rod is positioned between the lower cover and the small valve board; the rubber seal board is embedded in the big valve board and is pressed by the big pressboard. The utility model which also adopts a bi-current limiter integrates opening, slowly closing, checking and eliminating the water hammer, and can completely replace various combined devices on the pump exit without external dynamic force and manual operation. The utility model is convenient and practical, and can enhance the work efficiency and the reliability of the pipe system.

Chemical machinery grinding equipment

Abstract: The invented chemical mechanical polishing (CMP) device is suitable to present manufacturing technique. Slim grinding pressboard with size less than the size of wafer is utilized in the invented CMP device. Thus, the layout can be pressed and space can be used effectively so as to reach high yield and effective production management. The CMP device can select diversified grinding pad and/or grinding pulp, thus, flexible manufacturing procedure can be arranged by the CMP device.

Moulded hot press

Abstract: The utility model is a molding hot press, which comprises a doorframe, a delivery mechanism, a lower pressboard, an upper pressboard and an oil pressure elevating system, as well as a guide pole and a guide plate. The delivery mechanism is comprised of a guide way, a guide fixing frame and a moving platen; the guide pole is arranged between the homolateral doorframes; a side of the guide plate is positioned on the lower pressboard, while the other side slides in concert with the guide plate lateral wall. Meanwhile, the guide is positioned on the guide plate and the homolateral guides between two guide plates can be positioned on the guide pole. Moreover, because the guide fixing frame is adopted, the vibration when the moving platen feeds is reduced and the mechanical deformation of the lower pressboard subject to repeated pressing of a workpiece and the moving platen is eliminated. Furthermore, through the guide plate and the guide pole, the deviation can be reduced when the lower pressboard is working, so as to not only improve the product quality, but also greatly promote work efficiency and even relieve labor strength of operators.