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Showing papers on "Pressboard published in 2005"


Journal ArticleDOI
A.J. Kachler1, I. Hohlein1
TL;DR: In this article, the influence of air and oil type on the aging of a power transformer was investigated under a considerable amount of moisture, and the rate of the degree of polymerization, the development of furanic compounds, as well as the gas-in-oil analysis in comparison with the pure oil under the same conditions have been investigated.
Abstract: A power transformer is expected to operate up to 40 years. With current cost-benefit calculations, the user is forced to perform maintenance that will bring a further extension of transformer life. The maintenance can only be based on on-site and off-site monitoring with extended analytical and electrical tests, which can define the service condition of the transformer and predict its further life expectancy. The life of a transformer is mainly dependent on the life of its solid insulation, and the life-limit is determined by the thermal degradation of the winding paper. The Kraft paper decreases in tensile strength with the progress of aging and, at some point, can no longer withstand the short circuit stresses. The monitoring of the complex permittivity of transformer oils, as a function of frequency and temperature, may provide information concerning the state of the insulation. In this article, we show the influence of air and oil type on the aging of pressboard under the influence of a considerable amount of moisture. The rate of the degree of polymerization, the development of furanic compounds, as well as the gas-in-oil analysis in comparison with the aging of the pure oil under the same conditions have been investigated.

120 citations


Proceedings ArticleDOI
01 Aug 2005
TL;DR: In this paper, the authors investigated the breakdown process in transformer oil/cellulose insulation under a LI (lightning impulse) voltage and showed that a streamer propagates from the needle-axis direction to that along the surface of the solid insulation and carries electrical charges onto the solid surface and thus redistributed the electric field in the insulation.
Abstract: The work contributes to the understanding of breakdown processes in transformer oil/cellulose insulation under a LI (lightning impulse) voltage. The breakdown mechanism associated with streamer propagation, space charge distribution, material properties and insulation geometry is studied. The observed phenomena lead to a qualitative model which adds insight into the breakdown process in composite transformer insulation. Oil-impregnated pressboard, paper or polymeric material was inserted into a needle/plane electrode geometry in which oil gap distances exist between the solid insulation and the electrodes. Breakdown processes related to streamers were observed both in the oil gap and on the surface of the solid. Experiments showed that two important phenomena occurred when a streamer was initiated in oil and propagated to the surface of a solid insulation: the streamer changed its propagation from the needle-axis direction to that along the surface of the solid insulation; the streamer carried electrical charges onto the solid surface and thus redistributed the electric field in the insulation. The breakdown data were compared with those from a turn-to-turn model of transformer windings. It is found that it is the "average field" in the solid insulation after streamer development that governs puncture of the solid. A streamer can also puncture the solid insulation with no discharge pattern being observed on its surface, which happened when a large ratio exists between length of the oil gap and thickness of the solid insulation. The breakdown process is related to material type of the solid insulation.

23 citations


Proceedings ArticleDOI
01 Aug 2005
TL;DR: In this paper, the impact of moisture of cellulose pressboard on the dielectric characteristics of surrounding transformer oil was investigated as a function of the water content of the samples, in particular the interface oil/cellulose revealed pronounced effects.
Abstract: This paper reports and discusses test results from extensive laboratory work, investigating the impact of moisture of cellulose pressboard on the dielectric characteristics of surrounding transformer oil. The dielectric behavior at AC-voltage stress was investigated as a function of the water content of the samples. In particular, the interface oil/cellulose revealed pronounced effects. The partial discharge inception and the breakdown voltage are reported, and the statistical occurrence of the flashover paths is evaluated and discussed.

19 citations


Proceedings ArticleDOI
01 Aug 2005
TL;DR: In this paper, the authors used frequency domain spectroscopy up to 1 kHz to evaluate the effect of moisture and low-molecular carboxylic acids on the permittivity vs. frequency curves.
Abstract: Pressboard and Kraft paper with and without moisture, with and without added acids have been tested with frequency domain spectroscopy up to 1 kHz. Kraft paper with three moisture levels has also been tested at various ageing levels. Moisture and low-molecular carboxylic acids cause shifts in the permittivity vs. frequency curves. In addition, in paper but not pressboard, moisture is associated with an extra relaxation in the low-frequency part. High-molecular carboxylic acids have little effect on the permittivity. The same is the case for reduction in chain length of the cellulose polymer. The method should be useful as a non-invasive field test method for destructive agents in transformers, but not for the ageing (chain scission) itself. The measurements up to 3 MHz are so far inconclusive, but have yielded a few results that blend in well with the measurements below 1 kHz.

13 citations


Proceedings ArticleDOI
19 Dec 2005
TL;DR: In this paper, an 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.
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

11 citations


Proceedings ArticleDOI
05 Jun 2005
TL;DR: In this article, the results of dielectric response measurements in frequency domain were obtained at different temperatures for oil-impregnated pressboard samples (new and aged) containing different amount of moisture.
Abstract: This paper presents results of dielectric response measurements in frequency domain. obtained at different temperatures for oil-impregnated pressboard samples (new and aged) containing different amount of moisture. Description of the sample preparation and the ageing procedure is also included. The dielectric responses were used for defining master curves and activation energies at the different humidity levels, to be later used in the modelling of diagnostic measurements on transformers. Spread of the results from samples containing similar amount of moisture are also presented.

11 citations


Proceedings ArticleDOI
K. Nakamura1, Katsumi Kato1, H. Koide, K. Fujii, H. Okubo 
01 Aug 2005
TL;DR: In this article, the authors measured the electric field in parallelplane electrodes and rapeseed ester oil/pressboard composite insulation system under dc voltage application using Kerr electro-optic technique.
Abstract: In oil-immersed power transformers, an insulating oil/pressboard (PB) composite insulation system is generally applied. In order to make power transformers more compact, it is necessary to optimize the insulation design with considering the charge behavior in liquid dielectrics. In addition, environment-friendly insulating oil for transformers is being interested. In this paper, we directly measured the electric field in parallel-plane electrodes and rapeseed ester oil/PB composite insulation system under dc voltage application using Kerr electro-optic technique. From the results, we compared the electric field in rapeseed ester oil with that in mineral oil and discussed the charge behavior in composite system. Finally, we confirmed the basic applicability of rapeseed ester oil for transformers.

10 citations


Proceedings ArticleDOI
01 Aug 2005
TL;DR: In this paper, the effect of carboxyl complexing agents on the charge generation, accumulation and leakage currents of high power transformers was investigated using three experimental devices available in Poitiers laboratory (conductivity cell, flow loop and ECT test devices).
Abstract: Understanding the exact nature of the phenomena at the origin of the electrical charging tendency of transformer pressboards submitted to oil circulation in high power transformers is still a challenging problem. Former studies demonstrated that the flow electrification phenomenon depends a lot on the functional groups of the pressboard surface, and especially carboxyl groups. In this study, the action of several additives has been tested. Three experimental devices available in Poitiers laboratory (conductivity cell, flow loop and ECT test devices) have been used to investigate the effect of the additives on the charge generation, accumulation and leakage currents. Moreover, experiments with demineralised pulps treated by carboxyl complexing agents such as methylene blue have confirmed the important role of ionizable groups in papers. It has appeared that some additives can reduce the electrification phenomenon. In addition, as these results remind of some ionic chromatography (IC) aspects, the related theory can be attempted to explain the chemical process, which takes place between the oil and the pressboard.

10 citations


Journal ArticleDOI
TL;DR: In this article, the accumulated charge in a pressboard duct can then be estimated by the integration of the measured capacitive current up to infinite time, by injecting a chemical salt into new and aged oil at different concentrations.

9 citations



Patent
24 Aug 2005
TL;DR: In this article, the utility model consisting of a nut, a drawing threaded rod device, a supporting board, a press nail and a press board device was designed for an iron-core reactor.
Abstract: The utility model belongs to the technical field of transformer, relating to a late-model iron-core compacting structure of reactor with magnetic core. The utility model comprising a nut, a drawing threaded rod device, a supporting board, a press nail and a press board device is suitable for an iron-core reactor, in particular suitable for a large iron-core reactor. The drawing threaded rod device is screwed tightly with the nut welded under a pad foot to pass through the center bore of the iron core cake and the center bore of the pressboard device, and the supporting board is provided on a clamp, while the pressboard is provided at the center of the supporting board, and with the hydraulic amplifier, the iron core cake is impacted via a plurality of press nails on the pressboard, then finally the nut is covered on the threaded rod to be locked, obtaining the purpose that the iron core cake is impacted.

Proceedings ArticleDOI
01 Jan 2005
TL;DR: In this paper, the relationship of relaxation characteristics of pure oil, pure pressboard and composite insulation of oil-impregnated pressboard is studied with reference to equilibrium and geometry, and it is found that all the insulation characteristics vary with equilibrium time in a narrow band even when the samples were kept in sealed chamber.
Abstract: In this relaxation study, the relationship of relaxation characteristics of pure oil, pure pressboard and composite insulation of oil-impregnated pressboard is studied with reference to equilibrium and geometry. Low frequency response of dielectrics is very sensitive to moisture movement and temperature of operation due to variation of relaxation characteristics. In this the roles of components of composite insulation on the integrated insulation system and the geometry have to be explored with application point of view where the geometry of operating oil-filled transformer and the layout of the components vary from one design to another. A simple laboratory study with two components suggests that a simple model can be come up to predict the behavior of composite insulation. Also, it is found that all the insulation characteristics vary with equilibrium time in a narrow band even when the samples were kept in sealed chamber. The model is found to be valid irrespective of geometrical size

01 Jan 2005
TL;DR: In this article, the authors present results from a study of a 50/10 kV - 40 MVA power transformer, which was sent to a workshop for repair, thus allowing for collecting samples of the solid insulation.
Abstract: Methods, based on characterisation of dielectric response, for assessing moisture content in pressboard and paper are gaining ground. However, there is a need for calibrating obtained results with results from other techniques. This communication presents results from a study of a 50/10 kV - 40 MVA power transformer, which was sent to a workshop for repair, thus allowing for collecting samples of the solid insulation. Dielectric spectroscopy measurements in frequency domain were conducted at several occasions before and after the repair. Moisture estimation based on dielectric response measurements as well as on titration of oil samples yielded similar results to those obtained by direct titration of paper samples, as long as appropriate temperature values were used in all the analyses mentioned. The temperature value during measurements should be used for the analysis of the dielectric response, while in-service temperature of oil should be used for the evaluation based on Karl Fisher titration.

Journal Article
TL;DR: In this article, the on-line monitoring used in the process of drying of pressboard is discussed by dielectrometry and weight-loss method according to the moisture influence on dielectric characteristics of press board, comparing the signal of capacitance sensor detecting on the touching area with the results of sample weighing, an expression between the signal and the weight of the sample is obtained An exponential decay expression of the bulk moisture concentration of the pressboard during drying process is presented
Abstract: The on-line monitoring used in the process of drying of pressboard is discussed by dielectrometry and weight-loss method According to the moisture influence on dielectric characteristics of pressboard, comparing the signal of capacitance sensor detecting on the touching area with the results of sample weighing, an expression between the signal of capacitance measurement and the weight of the sample is obtained An exponential decay expression of the bulk moisture concentration of pressboard during drying process is presented The results of sample weighing show that drying rate is a process of wavy decay It is determined by the interaction between pressboard and vapour

Patent
02 Mar 2005
TL;DR: In this paper, an improved liquid level switch structure for electric water machine is described, where an elastic membrane, a pressboard and a bottom cap are arranged on the bottom of the level switch, and an inching switch is connected with the electronic circuit.
Abstract: Disclosed is an improved liquid level switch structure for electric water machine. The level switch is provided with a pipe connection which is connected with the hot bladder or the raw water tank via the water inlet pipe to make the water in the hot bladder or the raw water tank flow into the level switch. An elastic membrane, a pressboard and a bottom cap are arranged on the bottom of the level switch. The elastic membrane can drive the pressboard to move downward when the hydraulic pressure is big and drive the pressboard to spring back to home position when the hydraulic pressure is small. The pressboard is provided with a touch column in center, and an inching switch is arranged on the corresponding position of the center of the bottom cap. The inching switch is connected with the electronic circuit and then can automatically control the on-and-off of the signal light for supplementing water or not supplementing water and the movement of electric heating plate for heating or not heating with the change of the hydraulic pressure in the hot bladder or the raw water tank.

Proceedings ArticleDOI
19 Dec 2005
TL;DR: In this article, an electrical double layer was used to model flow electrification at the interface between pressboard and oil, and the authors used an electrical analogy to model these processes in the prototype.
Abstract: A charge zone named electrical double layer exists at a solid-liquid interface. The liquid flow induces a phenomenon called flow electrification: it generates a streaming current (caused by the convection of charges present in the liquid) and a potential rise in the solid (if this one is insulated from the ground). These potentials may reach values high enough to produce electrical discharges and provoke accidents. Although this phenomenon has been identified a long time ago, its physical description rests unknown (production and displacement of charges, equilibrium, etc.). As part of the research program of Electricite de France, a prototype sensor dedicated to flow electrification characterization at the interface between pressboard and oil has been developed with the University of Poitiers. In this paper we propose to use an electrical analogy to model these processes in the prototype. This electrical model is based on the analysis of experiences carried out with the sensor.