Showing papers on "Pressboard published in 2003"

Electrical properties of vegetable oil-impregnated paper insulation

Abstract: This contribution presents results from testing electrical properties of transformer paper-insulation with vegetable oil as paper impregnant. Investigations have been made with two kinds of typically used pressboard materials in power transformers. More precise, pressboards of type T I and T IV manufactured by Weidmann Transformerboard Systems AG were impregnated with an oxidation resistant biodegradable rape-seed oil. Tests included determination of power-frequency voltage strength according to IEC 641 and dielectric dissipation factor according to IEC 250 of the impregnated pressboards. Moreover, in order to shed light on the effect of ageing on electrical properties investigations with thermally stressed boards have been carried out. Therefore, 4 weeks oxidation period at 120/spl deg/C temperature of specimen was used. Obtained results are compared to additional tests of pressboard impregnated with conventional transformer oil Shell Diala D. The investigations establish possibilities of using environmental friendly rape-seed oil for transformer applications.

Flow electrification in high power transformers: BTA effect on pressboard degraded by electrical discharges

Abstract: The flow electrification process occurring at the oil-pressboard interface in high power transformers seems to cause electrical discharge incidents and may cause failures. The goal of this experimental study is to measure and to compare the streaming current obtained from unused pressboard, pressboard artificially degraded by electrical discharges, and pressboard obtained from a damaged power transformer. The influence of additive 1,2,3 Benzotriazole (BTA) in oil is also analyzed. The results show that flow electrification is greatly increased by the degraded pressboards compared with the new one. On the other hand, adding of BTA significantly reduces flow electrification.

Comprehensive diagnostic and aging assessment method of solid insulation in transformer

Abstract: Up to now, the diagnostic methods and criteria for operating oil-immersed power transformers are still under research. Besides the investigation of diagnostic methods for solid insulation in transformer, quite a lot of data collected from the in-service transformers under different condition included the data of failed or defected transformers have been analyzed systematically in this paper, such as its furfural concentrations, dissolved gases in oil, the degree of polymerization of insulating paper and pressboard, etc. Statistic analyses or the membership functions had been carried out to reveal the relationship between the contents of furfural or gases in oil and the aging of solid insulation. And the life expectancy of power transformer is studied. Finally a comprehensive diagnostic method is put forward for the aging assessment of solid insulation. The examples of application show the method is effective and easy to apply for the operating transformers.

Charge behavior in flowing oil in oil/ pressboard insulation system by electro-optic field measurement

Abstract: The electrical insulation structure of most power transformers is a combination of insulating oil and solid materials. One of the crucial problems we face in transformer operation is flow electrification, which occurs at a flowing oil/solid material interface. Thus, for the transformer insulation design, we need to clarify the now electrification phenomena. In this paper, we measured the electric field strength in an oil/pressboard composite insulation system using an electro-optic method of the Kerr effect. We obtained the time variation of electric field distribution in both flowing uncharged and charged oil. It is notable that we could quantitatively clarify the electric field distortion in flowing charged oil by flow electrification. Furthermore, we measured the leakage current from divided electrodes and derived a charge density distribution along the flow direction. Finally, we quantitatively discussed the electric field distribution and the charge behavior from the measurement results.

DC field measurement in Oil/Pressboard composite insulation system by electro-optic Kerr effect

Abstract: An insulating oil/pressboard (PB) composite insulation is generally utilized in oil-immersed power transformers. In such a transformer, charges accumulate at oil/PB interface which changes the electric field distribution depending on time and oil condition. In this paper, we report on directly measured dc electric field in oil/PB composite insulation system using the Kerr electro-optic field measurement technique. From measurement results, we propose a physical model for the charge behavior. We have calculated an electric field distribution using finite element method (FEM) based on the charge movement. We compared the results of measurements and calculations and confirmed that the proposed charge behavior model explains well the experimental results in the case of the polarity reversals as well. As a result, a significant validity of the charge behavior model was confirmed.

Charge accumulation mechanism in oil/pressboard composite insulation system based on optical measurement of electric field

Abstract: It is important to investigate electrostatic charging phenomena in insulating oil pressboard (PB) composite system in electrical insulation design of oil-immersed power transformers. Our research aim was to clarify the charge accumulation mechanism at the oil/PB interface under static and flowing oil. In this paper, we directly measured the time variation of the electric field in the insulation system using a Kerr electro-optic technique. Results show the time decaying characteristics of an electric field in oil by charge accumulation. The results are influenced by oil flow conditions. Based on the measurement results, we propose a theoretical model for charge accumulation to clarify the process quantitatively. In the model we took the oil volume contributing to the charge accumulation into account, and analyzed the charge behavior. Finally, we clarified the charge accumulation mechanism at the oil/PB interface under oil flow conditions both with and without charging.

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.

Charge behavior in flowing charged oil/pressboard composite insulation system based on electric field measurement

Abstract: Electrostatic charging may occur in oil immersed power transformers because of a flow electrification phenomenon. In this paper, we directly measured the time variation of electric field strength in the flowing charged oil using an electro-optic Kerr effect to clarify the charge behavior in the flowing oil/pressboard (PB) composite system. We discussed the measurement results from the viewpoint of charge behavior. Finally we found that the charging process is dependent on the three different electric fields, i.e. applied field, space charge field and counter field by accumulated charges, and is finalized by the balance of these fields.

The effect of high voltage fields on epoxy laminates

Abstract: This thesis describes the characterisation of epoxy/glass fibre composite material before and progressively through electrical and thermal ageing. Glass fibre reinforced epoxy (GFRE) material is used in pressboard transformers for optical telecommunication systems, typically at voltages between 1 and 2kV. The material was characterised by means of space charge measurements using the Pulsed Electroacoustic (PEA) technique, Dielectric response, Dynamic Mechanical Analysis (DMA), Differential Scanning Calorimetry (DSC), and Scanning Electronic Microscopy (SEM). An ageing programme was set up to follow the thermal and electrical ageing (at DC fields) of the GFRE by the same means. The results show a q-dc transport process with an activation energy of 1.1eV. The qdc process is associated with a charge transport process on the surface of the fibres. The results for the aged samples show delamination and debonding between the epoxy and the glass fibre at the glass epoxy interface. The delamination creates free volumes and voids which lead to partial discharge and hence failure. Electrical ageing can be characterised in term of dielectric, PEA, and DSC responses. Thermal ageing does not produce the same effect as electrical ageing. The samples that were only thermally aged behave in the same way as un-aged samples.

Method for cutting groove on surface of pressboard

Abstract: PROBLEM TO BE SOLVED: To provide first a method for cutting grooves on the surface of a pressboard, by which the cutting of the grooves for multi-use pressboards can be quickly and economically carried out, and to provide secondly a method for cutting grooves on the surface of the pressboard, by which the cutting of the grooves also for a plurality of pressboard cards used as functional members, such as insulating materials, can be quickly and economically carried out. SOLUTION: The method for cutting the grooves on the surface of the pressboard comprises steps of feeding the pressboard into a groove cutting apparatus in which a cutting blade and a grooving blade are alternately arranged, forming cut lines on the surface of the pressboard by feeding the pressboard to a position facing the cutting blade, and carrying out a grooving operation by means of the grooving blade along the cut lines on the surface of the pressboard.

Recovery Voltage Measurement on Kraft Paper Pressboard

Abstract: The recovery voltage of oil-free pressboard is measured as part of efforts to understand the recovery voltage in oil-paper system. The results hinted non-Debye polarisation within the paper and important role played by migration of surface charge in the formation of recovery voltage. A model that describes the recovery voltage in time domain is developed based on charge diffusion and stretched exponential relaxation function.

The effects of insulator structure and insulating oil to charge accumulation in oil-immersed transformers

Abstract: We directly measured the electric field in transformer oil/pressboard (PB) system under dc voltage using an electro-optic method by Kerr effect. We measured time variations and spatial distributions of electric field in the insulating oil. We measured them in both fresh oil/PB and degraded oil/PB composite systems to clarify the effect of material characteristics. Additionally, we changed the PB arrangement to investigate the effect of the PB insulator structure. We obtained the time decaying characteristics in the electric field distribution. From the results, we discussed physical mechanism of the charge accumulation.

Non-power supply thermal compressor

Abstract: The utility model relates to a device which presses, levels or adhibits a working face by use of heat quantity from fuel combustion in a combustion chamber (3) of hot-pressing device via a heat-conducting hot pressboard (2) of heat-conducting board in case of no power supply. The device is composed of a hot pressboard (2) which is connected with a combustion chamber (3), a top cover (4), a switch (5), a support (6) and a handle. The utility model can be operated without power and is carried conveniently.

Electricity conducting sheet of cellulose fibers and composite material produced from them

Abstract: FIELD: cellulose layers for shielding electric and high-frequency fields. SUBSTANCE: thin electricity conducting cellulose layer capable of shielding electric and high-frequency fields is 30 to 80 mcm thick, it weighs 20 to 60 g/sq. m, and incorporates 95-100% of carbon and cellulose fibers in terms of absolutely dry weight, proportion of carbon fibers, 1 to 15 mcm in diameter and 1 to 29 mm in length, being 4 to 20 mass percent in terms of absolutely dry weight and proportion of cellulose fibers, 75 to 96 mass percent in terms of absolutely dry weight. Layer is noted for high electric conductivity and ability of shielding electromagnetic fields with added advantage of excellent permeability for steam. Layer can be easily included in pressboard composition. Layer and pressboard sheet are suited to use for standard materials of floors, walls, and ceilings, gypsum and concrete slabs. EFFECT: enhanced ability of shielding electric and electromagnetic fields, facilitated handling, reduced cost. 6 cl, 5 tbl, 3 ex

Chemical Composition and Toxicity of Wastewater from Production of Chemicothermomechanical Mass

Abstract: The article reports on the impurity composition and toxicological hazard of the wastewater from production of chemicothermomechanical mass for manufacturing pressboard and different types of paper

Dielectric Breakdown Characteristics of Oil-pressboard Insulation System against AC/DC Superposed Voltage

Abstract: This paper describes breakdown characteristics of an oil-pressboard insulation system to a superposition voltage of AC and DC voltages. Although AC electric field is decided by the ratio of the relative permittivity of a pressboard and insulating oil, DC electric field is decided by ratio α of volume resistivities. From the measurement in this study, 13—78 and 1.8—5.7 are obtained as the volume resistivity ratios α at temperature of 30°C and 80°C, respectively. The breakdown voltages against AC, DC, and those superposition voltages are surveyed to insulation models. In normal temperature, the breakdown voltage to the superposition voltage of AC and DC is determined by AC electric field applied to the oil duct. Since the α becomes as low as 2-3 at temperature of 80°C, AC and DC voltages almost equally contribute to the electric field of the oil duct as a result. That is, it became clear that superposed DC voltage boosts the electric field across oil ducts at operating high temperature.