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Showing papers on "Pressboard published in 2006"


Journal ArticleDOI
T.A. Prevost, T.V. Oommen1
TL;DR: A brief discussion on the development of electrical grade paper/pressboard for transformer use from the raw materials, improvements made, and particularly the use of thermal upgrading agents to extend the useful life of transformers is presented in this article.
Abstract: This paper presents a brief discussion on the development of electrical grade paper/pressboard for transformer use from the raw materials, improvements made, and particularly the use of thermal upgrading agents to extend the useful life of transformers

232 citations


Journal ArticleDOI
TL;DR: In this article, the authors provide an open access to the frequency domain spectra of oil impregnated paper and pressboard samples, which can then be used in modeling of the results of diagnostic measurements in power transformers.
Abstract: Knowledge about moisture content in oil impregnated paper insulation is essential when estimating remaining lifetime of power transformers. Direct evaluation of moisture content is rarely possible due to inaccessibility of the internal insulation system in transformers. Therefore, various indirect estimation techniques are utilized. Frequency domain spectroscopy (FDS) measurements of transformer insulation belong to this group. To perform high quality interpretation of results of FDS measurements a good knowledge on dielectric responses in oil impregnated pressboard and paper is required, especially as it refers to their variation with water content and temperature. The aim of this paper is to provide an open access to the frequency domain spectra of oil impregnated paper and pressboard samples, which can then be used in modeling of the results of diagnostic measurements in power transformers.

228 citations


Proceedings ArticleDOI
21 May 2006
TL;DR: In this article, the permittivity of natural ester fluid and various Kraft insulation materials including diamond pattern paper (DPP), low-density pressboard and high density pressboard impregnated with natural esters is presented.
Abstract: There is considerable knowledge of transformer insulation system design based on the use of cellulose insulation used in conjunction with mineral oil. This knowledge is based on over 100 years of transformer design and manufacture. Insulation design is based on the stress distribution between the solid insulation, in this case Kraft, and the fluid. In power and distribution transformers the stress is distributed in accordance with the permittivity of the various insulation components. The insulation designer must determine the stress in the fluid, in the solid insulation and along the interface. Design curves have been established for mineral oil, which give limits to the allowable stress at each of these critical areas. Considerable work has been done and is in progress to establish these criteria for Kraft insulation in natural ester fluids. The permittivity of natural ester fluid and various Kraft insulation materials including diamond pattern paper (DPP), low density pressboard and high density pressboard impregnated with natural ester is presented. A test program to determine the design criteria for interfacial stress (creep stress) is presented

45 citations


Dissertation
01 Jan 2006
TL;DR: In this paper, the authors presented application of dielectric response measurements for identifying condition of high voltage insulation in power transformers, where they used frequency domain spectroscopy (FDS) measurements (1E-4 Hz − 1E6 Hz) were performed on well-controlled oil-impregnated pressboard/paper samples.
Abstract: This thesis presents application of dielectric response measurements for identifying condition of high voltage insulation in power transformers. Results of such measurements, incorporated with different modelling techniques, allow to estimate moisture content in solid part of transformer insulation. For this to be accurate, a good understanding of the electrical behaviour of oil-impregnated pressboard/paper insulation is necessary. Calibrating measurements for correlating the dielectric response data and the moisture content in insulation were carried out. Furthermore, numerous field investigations were also performed for studying the feasibility on application of response measurements under different field conditions. The work presented in this thesis was mainly focused on frequency domain spectroscopy (FDS). FDS measurements (1E-4 Hz – 1E6 Hz) were performed on well-controlled oil-impregnated pressboard/paper samples. Results of these were used to form master curves of the dielectric responses in a broad frequency range (e.g. 1E-7 Hz – 1E6 Hz). It had been observed that the presence of moisture influenced the permittivity of impregnated pressboard and paper at very low frequencies (<1E-1 Hz), whereas its influence on the loss was more pronounced and visible in the whole frequency range below 1E3 Hz. All the measured responses were modelled with terms representing dc conductivity, low frequency dispersion and Cole-Cole polarisation mechanisms with two distinct relaxation time constants. Influences of temperature and moisture content were described by analysing variations in the model parameters. The FDS responses formed a database, which later was used to develop a computer program for interpreting the results of diagnostic measurements in terms of moisture content in the solid part of power transformer insulation. During the field experiments the influences of different conditions that could disturb the measurement were carefully studied and it was shown that guarded measurements between low voltage and high voltage windings (CHL) provide the most reliable data for further analyses. The estimated moisture content and the calculated oil conductivities from the results of FDS measurements were compared with the results obtained from Karl Fischer titration (KFT) and by direct measurements of conductivity of oils sampled from the investigated units. It had been shown that similar values could be attained by both methods when correct temperature values were used i.e. for analyses of FDS data the temperature value during the measurements was applied, whereas for KFT analyses the temperature of the unit during its normal service had to be considered.

37 citations


Journal ArticleDOI
TL;DR: In this paper, the effect of the additives on the charge generation, accumulation and leakage currents in high power transformers was investigated using three experimental devices (conductivity cell, flow loop and electrostatic charging tendency tester).
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 flow electrification depends in a large part on the chemical functional groups of the pressboard surface, and especially carboxyl groups. In this study, the action of several additives has been tested. Three experimental devices (conductivity cell, flow loop and electrostatic charging tendency tester) 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 ionisable groups in paper. Some additives were found to reduce the electrification phenomenon. A comparison between these results and some aspects of ionic chromatography could be done, and the related theory can be attempted to explain the chemical process which takes place between the oil and the pressboard

27 citations


Journal ArticleDOI
TL;DR: In this article, the accuracy of different transformation methods for time domain dielectric response data to frequency domain and their limits are studied, including an approximated analytic function, an extended Debye model for the dielectrics behavior of impregnated pressboard and Fast Fourier Transform.
Abstract: The accuracy of different transformation methods for time domain dielectric response data to frequency domain and their limits are studied. First an approximated analytic function is considered, second an extended Debye model for the dielectric behavior of impregnated pressboard. The last method is a numerical integral form and Fast Fourier Transform. Hamon approximation relates time domain data at t to frequency domain data at f=0.1/t and gives the results by sole measurement of polarization current. Dielectric diagnosis of high voltage apparatus can be done by using Hamon approximation in minimum duration. All transformation methods show similar results and they are analyzed in order to demonstrate the limits of the methods.

23 citations


Proceedings ArticleDOI
01 Nov 2006
TL;DR: In this article, the authors introduced the time-frequency representation in analyzing the acoustic emission signals emitted by partial discharge sources and used seven descriptors to extract the features from each of the spectrogram.
Abstract: The subject matter of this paper is to introduce the time-frequency representation in analyzing the acoustic emission signals emitted by partial discharge sources. Three different types of partial discharge sources used to generate the acoustic emission signals during the partial discharge (PD) occurrences are created in an experimental tank filled with transformer oil. These partial discharge sources are the plain pressboard, the floating metal in the pressboard and the bubble in the pressboard. The acoustic emission (AE) signals are detected and stored as time-frequency representation, in the form of spectrogram, by utilizing the short-time Fourier transform (STFT). Finally, seven descriptors are introduced in order to extract the features from each of the spectrogram. The obtained results also confirmed the ability of the proposed technique to discriminate between different types of PD sources.

21 citations


Proceedings ArticleDOI
01 Oct 2006
TL;DR: In this paper, the electric fields under dc stress in a composite insulation consisting of transformer oil and oil-impregnated pressboard, typical for HVDC converter transformers are investigated.
Abstract: In this paper we report on basic studies of the electric fields under dc stress in a composite insulation consisting of transformer oil and oil-impregnated pressboard, typical for HVDC converter transformers. The time dependent electrical fields in our model geometry are measured using electro-optic Kerr method, and theoretically studied with an ion drift-diffusion conduction model. The measured and calculated electrical fields are compared and analyzed.

19 citations


Journal ArticleDOI
TL;DR: In this paper, the surface breakdown characteristics of silicone oil have been investigated with a triple junction configuration where a solid insulator is in contact with the electrode and the test configuration consists of solid material (Nomexreg or pressboard) and liquid insulation oil (silicone or mineral oil).
Abstract: This paper describes the surface breakdown characteristics of silicone oil which has the possibility of application to innovative switchgears and transformers as an insulating medium. At the first step, we have experimentally studied the impulse breakdown characteristics of the configuration with a triple-junction where a solid insulator is in contact with the electrode. The test configuration consists of solid material (Nomexreg or pressboard) and liquid insulation oil (silicone or mineral oil). We have discussed the experimental results based on the maximal electric field at the triple-junction. As the second step, we have studied the configuration which may improve the surface breakdown characteristics by lowering the electric field on the insulator surface

19 citations


Journal ArticleDOI
K. Nakamura1, Katsumi Kato1, H. Koide, Y. Hatta, Hitoshi Okubo 
TL;DR: In this paper, the authors measured the electric field in the rapeseed ester oil with parallelplane electrode and the oil/solid dielectrics composite insulation system under DC voltage application using the Kerr electro-optic technique.
Abstract: In the future, environmentally friendly insulating oil such as rapeseed ester oil is expected to be utilized as a substitute for mineral oil for power transformers. In addition, electrical insulation design for transformers becomes more important regarding size reduction and enhancement of electric field stress. The fundamental property of the electric field distribution in the rapeseed ester oil and in the oil/solid dielectrics composite insulation system should be clarified. In this paper, we have directly measured the electric field in the rapeseed ester oil with parallel-plane electrode and the rapeseed ester oil/pressboard (PB) composite insulation systems under DC voltage application using the Kerr electro-optic technique. From the results, we compared measurements of electric field and charge behavior for the rapeseed ester oil and the mineral oil and confirmed the applicability of the rapeseed ester oil for use in transformers

19 citations


01 Jan 2006
TL;DR: In this paper, the results of frequency domain spectroscopy (FDS) measurements on oil-impregnated pressboard insulation were used for modeling high frequency response (FRA) of transformers.
Abstract: This paper presents results of frequency domain spectroscopy (FDS) measurements on oilimpregnated pressboard insulation, their analyses and use of the data for modeling high frequency response (FRA) of transformers. The dielectric responses were measured in a broad frequency range, i.e. from 0.1 mHz to 1 MHz, on model samples containing different amount of moisture. The responses were parameterized with terms representing dc conductivity, low frequency dispersion and Cole-Cole polarization mechanisms and they were thereafter used to model the FRA response of a three-phase transformer.

Proceedings ArticleDOI
01 Oct 2006
TL;DR: In this article, the authors present the lightning impulse voltage test results of service-aged pressboards taken from a failed power transformer after 29 years' service and reveal that there is a significant reduction of breakdown voltages, most probably due to the degradation of mechanical strength.
Abstract: This paper presents the lightning impulse voltage test results of service-aged pressboards taken from a failed power transformer after 29 years' service. Impulse voltage tests have revealed that there is a significant reduction of breakdown voltages, most probably due to the degradation of mechanical strength. The minimum impulse electric strength may reduce approximately by 30% after 29 years' service. Test results on the service-aged pressboard also indicate that when the moisture content in pressboard is less than 4%, there is no significant correlation between the reductions of the impulse electric strength with increasing moisture content.

Proceedings ArticleDOI
11 Jun 2006
TL;DR: In this paper, the first results from experimental investigations which have been carried out to study the partial discharge phenomena in power transformer insulation are described, using different types of modeled insulation defects and ageing tests.
Abstract: This paper describes the first results from experimental investigations which have been carried out to study the partial discharge phenomena in power transformer insulation. Using different types of modeled insulation defects and ageing tests it is aimed to organize a database of known defects, which will be used for recognition of discharges of unknown sources of defects. Moreover, the first results of the investigation of degradation processes of pressboard during ageing are described. The experiments were carried out using the classical IEC 60270 method and the UHF method. Phase resolved patterns of the defects were collected for statistical analysis. Different defects were discriminated using cluster analysis.

Journal ArticleDOI
01 Dec 2006
TL;DR: In this paper, the results of frequency domain spectroscopy (FDS) measurements on oil-impregnated pressboard insulation, their analyses and use of the data for modelling high frequency response (FRA) of transformers are presented.
Abstract: This paper presents results of frequency domain spectroscopy (FDS) measurements on oil-impregnated pressboard insulation, their analyses and use of the data for modelling high frequency response (FRA) of transformers. The dielectric responses were measured in a broad frequency range, i.e. from 0.1 mHz to 1 MHz, on model samples containing different amount of moisture. The responses were parameterised with terms representing dc conductivity, low frequency dispersion and Cole-Cole polarisation mechanisms and they were thereafter used to model the FRA response of a three-phase transformer.

Proceedings ArticleDOI
26 Jun 2006
TL;DR: In this paper, the authors used the Atomic Force Microscope (AFM) to analyze the aging mechanism of power transformer insulation paper and found that the molecular arrangement of the initial cellulose paper is close and ordered, some of the hexagonal mesh structures of the Dglucopyranose units were broken down after a few weeks accelerated thermal aging.
Abstract: The life span of the transformer is mainly decided by its solid insulation, especially insulation paper (pressboard). In order to analyze the ageing mechanism of power transformer insulation paper, we use the Atomic Force Microscope (AFM), which is one of the important instruments in nanometer area to observe the surface of thermal aging insulation paper. Through the comparison of some specimens' AFM figures, we discovered that the molecular arrangement of the initial cellulose paper is close and ordered, some of the hexagonal mesh structures of the D-glucopyranose units were broken down after a few weeks accelerated thermal aging. Then we analyzed the micro mechanism of the aging process and the influence to the insulation paper caused by thermal aging. Some methods to improve the dielectric properties of insulation paper are also included.

Proceedings ArticleDOI
11 Jun 2006
TL;DR: In this paper, the authors used the recovery voltage measurement (RVM) technique to quantify the bulk insulation behavior of a high voltage transformer in virgin oil, using a test cell holding 370 litres of oil.
Abstract: Many experiments have been undertaken and results published on ageing of high voltage transformer insulation. The objective of these experiments has been to quantify how insulation is affected by moisture and temperature. However, the experiments have invariably been performed on small scale bench top equipment. The validity of scaled up results is always questionable and is exacerbated by the lack of published field data for comparison. A new apparatus has been developed to explore the effect of scale. The goal is to perform experiments representative of conditions inside a high voltage transformer. Electric stress of up to 10 kV can be applied to a pressboard insulated electrode immersed in the bulk oil. A series of experiments are performed to quantify the bulk insulation behaviour of pressboard in virgin oil. The apparatus has a test cell holding 370 litres of oil. The temperature of the test cell can be controlled up to 80 /spl deg/C and the condition of the oil/paper system evaluated using the usual techniques of moisture analysts, voltage breakdown, tan/spl delta/ etc. The paper contains a technical description of the apparatus and initial results taken from pressboard samples using the recovery voltage measurement (RVM) technique.

Proceedings ArticleDOI
11 Jun 2006
TL;DR: In this paper, the results from accelerated aging tests investigating the behavior of laminated pressboard and laminated wood in mineral oil were presented, and the results showed significantly more acids in the case of wood, which contains high quantities of lignin and natural resin compounds.
Abstract: Presspaper and pressboard products made from pure kraft pulp have been used successfully for decades for the solid insulation of power transformers. Many researchers have investigated the aging behavior of such cellulose products in the past. In the recent years, the transformer industry started to use significantly higher quantities of laminated wood (plywood) products. Yet, manufacturers and users have not thoroughly studied the long-term characteristics of these alternative products in comparison with kraft products. This paper reports and discusses results from accelerated aging tests investigating the behavior of laminated pressboard and laminated wood in mineral oil. The test conditions were chosen to simulate realistically the operation of open breathing transformers from commissioning to end of life, when the cellulose has decomposed to an extent that the apparatus has to be taken out of service. Two different types of laminated wood (low and high density) from two different suppliers were tested in parallel with laminated pressboard at temperatures from 105 to 135 /spl deg/C, and an aging time of up to 16 months. Regular testing of the condition of the liquid and solid insulation included flexural strength, water and acid contents, degree of polymerization, dissolved gas analysis and furan content. The results show significantly more acids in the case of laminated wood, which contains high quantities of lignin and natural resin compounds. Faster degradation of the mechanical strength associated with cracks and carbon deposits, corrosion and sludge formation was observed with laminated wood. Moreover, the combustible gases composition is different. In the case of laminated wood, hydrogen production and even gas bubble formation was observed.

Proceedings ArticleDOI
11 Jun 2006
TL;DR: In this article, the effect of water adsorption during the final clamping of the transformer active part, prior to the ultimate drying cycle was simulated, and the merit of oiling the insulation, a measure that slows down the water adsoration rate and the water diffusion significantly, was examined systematically.
Abstract: This paper reports and discusses results from small-scale laboratory tests investigating the moisture transients of different cellulosic insulation components subjected to selected conditions and drying procedures. The effect of water adsorption during the final clamping of the transformer active part, prior to the ultimate drying cycle, was simulated. The merit of oiling the insulation, a measure that slows down the water adsorption rate and the water diffusion significantly, was examined systematically. The macroscopic water gradients from the surface to the interior of pressboard and crepe paper insulation were determined, using the Karl Fischer titration method. It has been found that the water ingress to previously dried paper and pressboard insulation is strongly dependent on time, type of insulation and pressboard ply orientation relative to the air-exposed surface. The effectiveness of oiling the cellulosic transformer insulation is depending on the exposure time elapsing during the final assembly work, and varies with the type of insulation. The impact of the relevant parameters on the water extraction behavior during the subsequent, fine vacuum cycle is reported in detail.

01 Jan 2006
TL;DR: In this paper, the authors present the results of a parametric study made with an electrical analogy model, which represents the processes taking place when transformer oil flows through a rectangular pressboard duct.
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 charge convection) 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 remains unknown (production and displacement of charges, equilibrium, etc.). In this paper we present the results of a parametric study made with an electrical analogy model, which represents the processes taking place when transformer oil flows through a rectangular pressboard duct. The duct's geometry and the materials were selected to compare some of the numerical results to experimental ones. The facility used to obtain these experimental results was developed some years ago as a part of the research program of Electricite de France and the University of Poitiers.

Patent
30 May 2006
TL;DR: In this article, an inductive component in the form of a transformer or a choke, but in particular a medium-frequency transformer, with at least one winding, where between individual layers of the winding and / or another winding one or more thermal bridge intermediate insulation are arranged, wherein the thermal bridges -Intermediate insulation flexible insulating include foils, are incorporated in the heat-conductive fillers, and over conventional intermediate, winding or earth insulation, z.r.t.
Abstract: The invention relates to an inductive component in the form of a transformer or a choke, but in particular a medium-frequency transformer, with at least one winding, wherein between individual layers of the winding and / or another winding one or more thermal bridge intermediate insulation are arranged, wherein the thermal bridges -Intermediate insulation flexible insulating include foils, are incorporated in the heat-conductive fillers, and over conventional intermediate, winding or earth insulation, z. For example, mica, polyesters, polyamides, various insulating papers, pressboard, mixed insulation, and also various resins, casting and injection molding techniques, have a significantly higher thermal conductivity. The winding may be hermetically embedded in a Spulenumgus and having a core which is held in a corresponding Spulendurchdringung in the Spulenumgus. The thermal bridge insulation can also be designed as ceramic tiles or rigid overlapping elements and optionally be equipped with additional coolers and heat pipes, for the purpose of better heat dissipation from the windings or heat transfer of windings and cores into other rooms.