Showing papers on "Pressboard published in 2001"

Evaluation of diffusion-driven material property profiles using three-wavelength interdigital sensor

Abstract: The response of a three-wavelength interdigital dielectrometry sensor to the moisture diffusion process in oil-impregnated transformer pressboard has been simulated using an empirical relationship between the moisture concentration and the dielectric properties of the pressboard. A benchmark test of the moisture diffusion process has been developed with the purpose of comparing alternative parameter estimation algorithms used in /spl omega/-/spl kappa/ (frequency wavenumber) dielectrometry. The results of simulations highlight characteristic features of the multi-wavelength sensor response, such as the sensor response delay from the start of the transient moisture diffusion process as a function of sensor wavelength, the influence of moisture boundary conditions, and the relation between the signal magnitude and variations of dielectric properties. One of the parameter estimation algorithms, linear calibrated admittance-based estimation (LCABE), has been applied to both simulated and measured data. Adequate performance of the LCABE approach in the absence of strong discontinuities of dielectric properties in the electric field penetration region is demonstrated and contrasted to an electrically shielded region case, in which the signal response becomes nonlinear. The proposed approach offers significant potential for the measurement of diffusion processes in various dielectrics, especially for cases with highly irregular geometry or material structure. Measurement results from moisture diffusion process monitoring are included. Parameter estimation of measurement results with LCABE confirm its applicability to the monitoring of moisture dynamics in transformer pressboard.

Influence of pressboard physico-chemical composition on static electrification in power transformers

Abstract: As part of a research program in the field of flow electrification in power transformers, some fundamental studies have been undertaken on the physical chemistry of this phenomenon. The two main constituents involved in the process of charge generations are oil and pressboard. As oil composition is difficult to deal with, the choice has been made to understand the overall chemistry through the role played by the pressboard, whose composition is better mastered. In order to identify the chemical species in the pressboard responsible for the charge generation, in view of perfecting additives to neutralize the phenomenon, the French Institute of Pulp and Paper carried out modifications on commercial pressboards, and manufactured some others. Charge accumulation, measured from capacitive currents on insulated electrodes facing the pressboard ducts, has been observed for modified and manufactured pressboards with regard to oil flow rate and temperature. All the experiments have led to various behaviors in terms of kinetics and magnitude of the charge accumulation. The obtained results tend to prove that chemical composition of pressboards, with regard to their content in chemical functional groups (hydroxyl or carboxyl groups) or radical nature (lignin), as well as board manufacturing parameters (pulp refining, layer composition) and surface properties seem to be at the origin of the electrification phenomenon.

Mechanism of charge accumulation at flowing oil/pressboard interface based on optical measurement of electric field

Abstract: Electrostatic charging may occur in oil immersed power transformers because of a flow electrification phenomenon. In this paper, we directly measured time dependence of electric field strength in the flowing oil using an electro-optic method based on the Kerr effect, to clarify the mechanism of charge accumulation at the flowing oil/pressboard (PB) interface. We quantitatively discussed measurement results from the viewpoint of charge behavior. Finally, we found the contribution volume of charge movement and quantified the charge density.

Surface flashover studies on precompressed pressboard insulation under superimposed AC/DC voltages

Abstract: The scale down models of pre-compressed mineral oil insulation system have been studied under surface flashover of the surface of insulation. The experimental investigations have been dealt with for conventional AC, DC and superimposed voltages of AC/DC at different electrode gap distances. Two types of models using cylindrical embedded electrodes and stuck electrodes on the surface are employed. The studies relating to different conditions of the insulation system namely dry pressboard, impregnated pressboard in air medium, impregnated pressboard in oil medium are detailed. The surface flashover voltages under AC, DC and superimposed voltages have predominant effect on small electrode gaps causing sufficient damage to the surface of insulation. The time to failure of insulation due to discharges are presented. The discharges are more severe on dry pressboard as compared to oil impregnated pressboard.

Behavior of multiple barrier insulation systems under impulse conditions

Abstract: Deals with prebreakdown and breakdown behavior of composite liquid-solid-insulation with multiple solid-barriers in liquid gaps submitted to impulse voltages. Experiments have been carried out in strong and weakly inhomogeneous fields with gap distances from 8 to 34 mm, respectively, using impulse voltages up to 700 kV. Configuration was close to transformer insulation with up to three pressboard layers of 2 mm thickness each in the liquid gap. Comparisons between streamer behavior in single and multiple barrier insulation are presented. Streamer inception and propagation was visualized via highspeed shadowgraph photography. Compared to pure liquid insulation an increase of the insulation ability of 470% of the pure liquid gap was observed, most likely due to field homogenisation through solid barriers. Streamer inception field strengths differ little from phenomena in pure oil gaps. Microdischarges appear at board surfaces closest to electrodes, leading to Lichtenberg-type figures on the board surface which cause degradations of the board. Investigations were made with pre-stressed and new pressboard.

Calculation method for power transformer clamping rings made from laminated insulating materials

Abstract: In core-form oil-filled power transformers, clamping rings are used to hold a clamping force on the windings. In this paper, data is presented from mechanical tests conducted on complete rings, using a custom-built test fixture, specifically designed to simulate the forces and conditions seen on clamping rings in power transformers. The tests were conducted on laminated wood and laminated pressboard rings, in sizes typically seen in medium power transformers. Mechanical equations that most closely apply to a ring under these loading conditions were determined, and flexural strength, modulus of elasticity and shear strength calculations were performed. A new method for calculating clamping ring thickness was determined, based on the test data. For laminated pressboard, the new calculation method was compared to a previous calculation method. A statistical interpretation of the values obtained using the new calculation method vs. the test results is presented.

Transformer insulation condition monitoring using artificial neural network

Abstract: Partial Discharge (PD) is the most hazardous phenomena that deteriorates the insulation life of an electrical device in a covert way (and finally with an overt puncture or flashover) in an otherwise healthy insulation. Mostly the conventional EHV and UHV transformers used in the present times employ the oil impregnated paper/pressboard insulation. Recently, a radically new approach to the PD pulse-pattern analysis in oil impregnated pressboard insulation has been established in a relevant study, where an experimental setup was prepared to simulate the commonly encountered wedge shaped oil gaps between the edges of rounded conductors and pressboard spacers inside transformer. The observed PD pulse patterns at different stress levels are classified into five distinct categories with each one having some relevance to the deteriorating condition of insulation health. The interesting results revealed by this study are serving as the underlying principle to carry out an ANN based insulation condition monitoring system. A backpropagation learning model multi-layer perceptron (MLP) paradigm is characterised, which is used as a tool to further automate and achieve a fast classification of an unknown PD pulse pattern to a particular class (without visual or statistical interpretation), thus enabling addressing the insulation health condition or imminent breakdown probabilities. Diverse structures of MLP were implemented using single or double layers with different number of processing elements in each layer and different learning coefficients. The performance is studied and the intricacies involved are addressed in the light of achieving an optimal structural configuration.

Charge accumulation phenomenon in oil immersed pressboard exposed in positively charged transformer oil

Abstract: It was dicovered that the pressboard immersed in positively charged oil were highly charged up. The experiments to evaluate the charge density and the charge distribution in the pressboard were carried out to investigate the mechanism of charge accumulation. In the experiment, positive charges generated by oil flow were supplied to the pressboard sample. Charge densities in oil and pressboard were evaluated from the potential measurement. Charge distribution in pressboard was estimated from the current-time characteristics at DC voltage application to the pressboard.

Electronic-module data medium and its manufacturing process

Abstract: single-layer or multilayer data media with built-in electronic modules such as chip-cards. SUBSTANCE: dimensions of card body comply with ISO 7810 Standard; it is made of layers of paper and/or pressboard joined together by means of heat-activated or contact adhesives. Cards may be manufactured using strip reeled off coils when separate layer of card is produced from strip reeled off respective coil; layers are provided with ports required to receive module. For the final procedure, layers are joined together. Modules are placed in depressions formed in the process and separate cards are cut by sheet stamping method. EFFECT: reduced cost of chip manufacture. 32 cl, 25 dwg

Secondary low-gas-emission chemical power supply

Abstract: electrical engineering; secondary power supplies and electrochemical aqueous-electrolyte capacitors. SUBSTANCE: power supply (it may be nickel-cadmium, nickel-iron, nickel-metal-hydride, or lead storage cell) has its auxiliary electrode manufactured from material made of activated carbon fibers and placed between separator and negative electrode; it is mounted on negative-electrode surface; size of most pores of auxiliary electrode is greater than that of most separator pores. Auxiliary electrode may be made in the form of fabric or non- woven material, pressboard, or paper. It may be placed on one or both sides of negative-electrode plates. Total volume of electrolyte in pores of separator and electrodes is smaller than total volume of their pores. EFFECT: reduced gas-emission level in the course of charge; reduced electrolyte level check and replenishment intervals. 5 cl, 2 dwg

Comparison of measured PDs in oil-impregnated insulation using different sensor bandwidths

Abstract: This paper presents the statistical analysis of partial discharge distributions in oil-impregnated pressboard and paper configurations. The experiment reported here was aimed at an investigation of the characteristics of partial discharges in a cavity for both new and aged oil-impregnated pressboard-paper samples. Two different measurement systems, which provide four different measurement bandwidths were used to observe whether they would produce similar characteristics of discharges. The results indicated that, while there was some general similarity in the shape of PD patterns, a detailed statistical analysis of the PD data showed some significant differences in the results. These differences were significant in terms of the frequency response of the PD sensor systems. As a conclusion, the analysis of such PD data must be performed carefully with particular attention being given to the frequency response.

New insulation structure for shell-form transformer

Abstract: New insulation structure for shell-form transformers has been developed to optimize dielectric strength and cooling efficiency. Tapered joint of pressboard barriers in the oil/paper insulation structure enabled minimization of oil gap length and formation of uniform gap length between barriers, which greatly enhances dielectric strength of the barrier system. By use of nonwoven fiber elimination of leakage oil flow was realized in the insulation space. This not only improves cooling efficiency but also reduces static electrification by oil flow. Excellent improvement in dielectric strength as well as static electrification was confirmed by the test results of model transformers.

Study on relationship between the current of oil flow electrification and characteristics of solid materials

Abstract: In this paper, the relationship between the current of oil flow electrification in spinning disk system and characteristics of solid materials is investigated. It is found that current of oil flow electrification is related to characteristics of solid materials and surface roughness of pressboard paper.

Studies on compatibility of silicone oil with pressboard insulation

Abstract: The paper oil insulation system is an integral and essential part of large power transformers. The failure of power transformers under combined stresses and fast transients has made it necessary to look for an alternate liquid insulant. In this study, silicone oil was investigated for use as a liquid insulant. The samples of pressboard are subjected to dielectric tests like electric strength, surface electric strength under AC, DC and combined AC/DC voltages, dielectric dissipation factor and others. The variation of dielectric constant, dissipation factor of silicone oil has been studied over a range of frequency. The surface electric strengths of cellulosic insulation with silicone oil and with mineral oils have been compared. Some very interesting results on the performance of silicone oils have been observed and discussed.