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Showing papers on "Pressboard published in 2010"


Journal ArticleDOI
TL;DR: In this paper, the authors used point-to-plate electrode configurations under AC voltages for both single flashover breakdown and partial discharge induced failure modes, and found that increased moisture content in pressboard reduces partial discharge inception voltage (PDIV) significantly, i.e. ~30% PDIV reduction for pressboard of up to 3% moisture.
Abstract: This paper presents experimental research of creepage discharge on insulation barriers in power transformers. Using point-to-plate electrode configurations under AC voltages creepage discharge is studied for both single flashover breakdown and partial discharge induced failure modes. It is confirmed that the dielectric strength of oil gap will not be reduced with introducing dry new pressboard surface into the oil gap, indeed the flashover breakdown voltage is hardly compromised by introducing aged pressboard with up to 3% moisture. However, increased moisture content in pressboard reduces partial discharge inception voltage (PDIV) significantly, i.e. ~30% PDIV reduction for pressboard of ~3% moisture as compared with dry pressboard. More importantly, high moisture contents in pressboard increase PD activities in oil pores which allow gasses to be trapped inside to develop gaseous channels which eventually lead creepage discharge to breakdown.

96 citations


Journal ArticleDOI
TL;DR: In this paper, a series of experiments are designed and carried out in a well-controlled laboratory, where accelerated thermal aging is performed on oil-immersed pressboard samples with different time intervals (0, 120, 250 and 400 h).
Abstract: Dielectric response measurements are non-invasive and promising diagnostic methods that are being gradually used for assessing the insulation and aging condition of transformer oil-paper insulation system. It is known that moisture content in oil-impregnated insulation has significant effect on its dielectric response phenomena, and whereas at present there is few research about the characteristics of aged cellulose without the impact of water. In this work, a series of experiments are designed and carried out in well-controlled laboratory. Accelerated thermal aging is performed on oil-immersed pressboard samples with different time intervals (0, 120, 250 and 400 h). Then these pressboard samples with different aging states are put into petroleum ether to remove the residual oil inside, and dried in a vacuum oven to remove the petroleum ether and moisture. The degree of polymerization (DP) and scanning electron microscope (SEM) are implemented to characterize the aging status of pressboard samples. Two kinds of dielectric response tests, i.e., the polarization and depolarization currents (PDC) and frequency domain spectroscopy (FDS), are performed on each oil/water-removed pressboard sample in vacuum and new-oil-impregnated ambient, respectively. Samples with different aging states show quite different dielectric response characteristics in both ambients. With the aging status more serious, the pressboard sample exhibits higher values of polarization/depolarization currents and complex capacitances. It is confirmed that, besides the influence of water induced by aging, the deterioration of cellulose itself also causes the increasing of pressboard conductivity, and hence greatly affects the PDC and FDS test results. Dielectric response diagnostic techniques have a potential to reflect the aging information of solid insulation.

78 citations


Journal ArticleDOI
TL;DR: In this paper, a study on field transformers gave results obtained through comparison of different samples in relation to the number of years in which they were in the field, and the patterns of changes in characteristics were studied.
Abstract: To ensure soundness of highly aged transformers in their operations, it is important to identify how aging influences insulating oil in these transformers. The characteristics of insulating oil are roughly classified into electrical, physical, and chemical characteristics. In the past research on insulating oil in transformers, some of the characteristics showed a downward trend with increasing age. Among the electrical characteristics, the volume resistivity and the dielectric loss tangent showed a downward trend with increasing age, which is likely to reflect degradation that accompanies aging. The analysis of insulating oil components found some components that increased with age, which may contribute to degrading electrical characteristics of insulating oil. This study on field transformers gave results obtained through comparison of different samples in relation to the number of years in which they were in the field. Detailed evaluation of aging requires study on aging patterns using the same samples. In this paper, heat-accelerated degradation test was conducted on the same samples, and the patterns of changes in characteristics were studied. In addition, the influences of interactions between characteristics and water and between characteristics and pressboard were examined. The study using accelerated degradation test was conducted on one brand of mineral oil (α1). The obtained characteristics were the breakdown voltage, volume resistivity, interfacial tension, total acid value, and water content, i.e., electrical characteristics and characteristics considered to be correlated with electrical characteristics were extracted. As a result of examination, characteristic deterioration was evident for the water content, breakdown voltage, volume resistivity, total acid value, and interfacial tension in descending order of deterioration. The characteristics showed evident deterioration in the initial stage of accelerated degradation test and, thereafter, showed a saturation tendency with increasing age.

67 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed to use water saturation in oil and in cellulose to describe water in power transformers, which can be used for assessing moisture in oil-paper-insulated transformers.
Abstract: This paper aims at providing reliable methods of assessing moisture in oil-paper-insulated power transformers. The traditional method of moisture evaluation, oil sampling with the subsequent application of an equilibrium diagram, suffers from severe errors resulting in an overestimation of water concentration. To improve this, moisture sorption in cellulose (paper, pressboard) and moisture solubility in insulation oils were theoretically described and represented as sorption isotherms and equilibrium diagrams under the special consideration of aging. Several steps lead to the key recommendation of this paper, which is to use water saturation in oil and in cellulose to describe water in power transformers. The practical application and the use of vegetable oils are considered as well.

59 citations


Journal ArticleDOI
TL;DR: In this paper, the authors discussed the conduction and polarization mechanisms in the oil and paper of a power transformer and suggested reasonable upper limits have been suggested for new and in-service oil.
Abstract: Conduction and polarization mechanisms in the oil and paper of a power transformer are discussed in this article. Some of the electrical characteristics of an insulating oil sample can be determined accurately at room temperature using the IEC 61620 test procedure. High voltage stress and high temperature may modify these characteristics. Deterioration products, both acid and non-acid types, influence the measured conductivity, but moisture or contaminants do not do so. Reasonable upper limits have been suggested for new and in-service oil. Pressboard moisture content and conductivity of the oil in the main ducts of a transformer may be measured using dielectric response techniques, which also give information on the state of the insulation at interfaces. Measurement of polarization and depolarization currents in a transformer without oil allows conduction and polarization phenomena occurring in the insulating paper to be identified. The depolarization current characterizes the type of aging in the paper, provided the applied voltage stress is very low.

25 citations


Proceedings ArticleDOI
06 Jun 2010
TL;DR: In this paper, the partial discharge behavior of synthetic and natural esters compared to commonly used mineral oil is compared. But, there is little experience with those fluids in large power transformers.
Abstract: In times when personal safety and the security of electrical power supply become more and more important, the usage of alternative insulation fluids is demanded in large power transformers. The minimizing of fire loads is another significant reason for new liquids. Different companies are offering such alternative insulation liquids which are already used in distribution transformers. On the other hand there is little experience with those fluids in large power transformers. For the confirmation of the usability of new insulating liquids comparison methods must be tested to find the differences between the alternative insulating fluids and commonly used mineral oil. There are different methods for characterising insulating materials, like AC-Breakdown tests, partial discharge tests, lightning and switching impulse voltage tests, etcetera. Partial discharge behaviour is a distinguishing characteristic of an insulating medium. This paper shows the partial discharge behaviour of alternative insulation liquids such as synthetic and natural esters, compared to commonly used mineral oil. To generate the PD patterns, voltages up to 30kV and inhomogeneous test arrangements were used. A model of an oil/board insulation system was created by using sheets of pressboard.

20 citations


Patent
07 Jun 2010
TL;DR: In this article, the authors describe a system for molding cheese having a pressboard for compressing cheese in a cheese mold, which includes spring alignment features to align a set of leaf springs that help ensure even compression of the cheese.
Abstract: Embodiments described herein provide a system for molding cheese having a pressboard for compressing cheese in a cheese mold. The pressboard includes spring alignment features to align a set of leaf springs that help ensure even compression of the cheese.

16 citations


Journal ArticleDOI
TL;DR: In this article, the authors investigated the charge behavior under dc voltage application by direct measurement of the electric field using Kerr electro-optic method, and the time dependence of electric field strength in silicone liquid / pressboard (PB) composite systems was measured.
Abstract: From the viewpoints of less flammability and environment protection, a new type of electrical insulating liquid for power transformers is strongly required. Low viscosity silicone liquid (20 cSt) is suitable for the requirements owing to the following excellent features; high flash point, low environmental impact concerning pollution and high chemical stability. In this paper, we investigated the charge behavior under dc voltage application by direct measurement of the electric field using Kerr electro-optic method. At first, Kerr constant of 20 cSt silicone liquid was investigated. Then, the time dependence of electric field strength in silicone liquid / pressboard (PB) composite systems was measured. The time constant of the decay was much larger in silicone liquid than in mineral oil. We discussed the charge behavior based on the physical properties of silicone liquid and we suggested that the influence of negative charge injection from a negative electrode?s surface in silicone liquid played a significant role because of the high volume resistivity.

16 citations


Proceedings ArticleDOI
01 Oct 2010
TL;DR: In this paper, the authors used a needle-plate electrode construction to form parallel electric field, and study the partial discharge phenomena under this situation, especially the development of the carbon trace on the surface of the pressboard and the pattern of the PD.
Abstract: In power transformers, the interface between the oil and the paper is always the weak point of the electrical insulation. Along on the surface of the paper and the pressboard, Partial discharges (PD) may often appear. They could destroy the paper and lead to electric fault. In this paper, the authors used a needle - plate electrode construction to form parallel electric field, and study the partial discharge phenomena under this situation. High voltage of 30kV or 35kV was applied on the oil impregnated pressboard specimens for 30 h to study the PD phenomena, especially the development of the carbon trace on the surface of the pressboard and the pattern of the PD. The white mark, gas bubbles, flashover, carbon trace, and PD phenomena will be described. Within high voltage experiments it was found that the carbon trace can reduce the strength of the electric field near the needle and the partial discharge activities will be rapidly reduced at the beginning of high voltage test. PD with small magnitude will not change the carbon trace in some ten hours and the pattern of the PD is not related to the carbon trace

14 citations


Journal ArticleDOI
TL;DR: In this article, the effect of isolated small alien substances on the creeping discharge progressing the surface of the pressboard immersed in PFAE oil has been investigated using 1.2/1000 μs impulse voltages with ± 90 kVpeak in maximum.
Abstract: The effect of isolated small alien substances on the creeping discharge progressing the surface of the pressboard immersed in PFAE oil has been investigated using 1.2/1000 μs impulse voltages with ± 90 kVpeak in maximum. PFAE oil is new vegetable-based insulating oil which was recently developed as a substitute of mineral oil for environmental requirements. In this paper, it is shown that the creeping streamer is largely extended by the presence of isolated small alien substances in the surface or inside of the pressboard. The effect of such alien substances also appears in the streamer shape, discharge current and streamer velocity. These are discussed qualitatively on the basis of the experimental results.

14 citations


Proceedings ArticleDOI
01 Oct 2010
TL;DR: By using Kerr electro-optic technique, electric field in oil/pressboard composite insulation system, which is the typical insulation system of a transformer, was investigated at polarity reversal of HVDC voltage as mentioned in this paper.
Abstract: By using Kerr electro-optic technique, electric field in oil/pressboard (PB) composite insulation system, which is the typical insulation system of a transformer, was investigated at polarity reversal of HVDC voltage. When the applied voltage polarity was sharply reversed, the applied electric field was superimposed by the electric field of accumulated charges on PB, and very strong field appeared right after the polarity reversal. This could cause the discharge in the oil gap and on the PB surface. The critical value of the discharge initiation at the polarity reversal was verified to be determined by the sum of the applied electric field and the electric field of accumulated charges on PB. The discharge was observed by a high-speed video camera. It was clarified that the surface discharge on PB did not overlap with each other, which was explained by that the surface discharge could neutralize the charges on PB.

01 Jan 2010
TL;DR: In this article, the impact of aging condition and temperature on the frequency domain spectroscopy (FDS) test results of oil-paper insulation, accelerated thermal aging experiments were performed on oil-impregnated pressboard sample in this work.
Abstract: To investigate the impact of aging condition and temperature on the frequency domain spectroscopy(FDS) test results of oil-paper insulation,accelerated thermal aging experiments were performed on oil-impregnated pressboard sample in this work.FDS tests ranging from 1 mHz to 1 kHz were carried out during the aging process,and for the same aging condition,FDS tests were repeated at different temperatures.The variations of dissipation factor(tanδ),real capacitance(C'),imaginary capacitance(C'') and moisture content caused by aging time and measurement temperature were analyzed.Experimental results show that both tanδ and C'' of oil-impregnated pressboard increase with the increasing measurement temperature and thermal aging time at lower frequencies,while have no obvious change at higher frequencies.When temperature and thermal aging time increase,the frequency point where C' changes rapidly shifts to higher frequencies.The moisture content of pressboard sample obtained from FDS test results increases with the increment of thermal aging time in the earlier stage and shows no obvious change in later stage.The estimated moisture content is also influenced by temperature.When the temperature of sample is higher,the value of estimated moisture content is obviously larger.

Proceedings ArticleDOI
01 Jan 2010
TL;DR: In this article, the impact of temperature and moisture on dielectric response under a controlled condition was investigated. And the authors compared the performance of time domain and frequency domain polarisation tests for transformer insulation diagnostics.
Abstract: Nowadays, time domain and frequency domain polarisation tests are popular in power utilities for transformer insulation diagnostics Therefore, it is quite essential to understand the impact of temperature and moisture on dielectric response under a controlled condition This paper presents the dielectric response of pressboard samples with different moisture and temperature conditions Both, time domain and frequency domain measurements were carried out in sequence and impact of temperature and moisture on dielectric response were studied in detail In addition, dc conductivity (σ 0 ) of pressboard insulation is calculated from both methods and comparison between FDS and PDC methods is made It has been observed by comparing dc conductivities that both methods are in agreements with each other and almost same level of accuracy in the result can be obtained with both methods

Proceedings ArticleDOI
04 Jul 2010
TL;DR: In this paper, the dielectric response of cellulose in the form of paper and pressboard was investigated and the results can be useful for moisture evaluation in various impregnated cellulose insulations e.g. transformers, bushings, capacitors.
Abstract: The dielectric response of cellulose in the form of paper and pressboard was investigated. Samples of pressboard were impregnated with different insulating liquids: new and aged transformer oil and synthetic ester. Samples of non-impregnated paper were investigated during drying process. The research was done for two groups of pressboard with about 5 % and 0.5 % moisture content. The moisture level was determined using Karl Fischer titration. Obtained data were analyzed using Havriliak-Negami relaxation function. The results can be useful for moisture evaluation in various impregnated cellulose insulations e.g. transformers, bushings, capacitors.

Journal Article
TL;DR: In this article, the authors used the Concept 80 broadband dielectric spectroscopy measurement system to investigate the influence of water content on the dielectrics of transformer oil-paper insulation.
Abstract: As a non-destructive electrical diagnostic technique,frequency domain spectroscopy is quite applicable to field diagnosis of the state of transformer insulation.Considering the great hazard of water content to transformer oilpaper insulation system,the influences of water content on dielectric properties of mineral oil and different kinds of oil-impregnated papers,as well as comparison of dielectric properties for plain paper,insulation pressboard,and thermal upgraded paper with the same water content,are studied with the help of the Concept 80 broadband dielectric spectroscopy measurement system.Results show that the dielectric properties of mineral oil-paper samples are remarkably affected by water content.The DC conductivity of mineral oil increases exponentially with water content;at the frequency range of 10-3~10-1 Hz,the real part of complex permittivity for oil-impregnated paper increases linearly with moisture content.Therefore,with the help of dissipation factor(DC conductivity)of insulation oil,as well as the real part of complex permittivity of insulation papers,water content of transformer oil and oil-impregnated paper can be diagnosed,respectively.

Patent
21 Jul 2010
TL;DR: In this paper, a drying process of a super thick insulated pressboard is described, where 0.5-0.7 percent pulp is prepared by insulation pulp through conventional treatment, enters a pulp stabilization box and is sent into a wet ground paper forming device through a pulp pump.
Abstract: The invention belongs to a drying process of a super thick insulated pressboard. In the process, 0.5-0.7 percent pulp is prepared by insulation pulp through conventional treatment, enters a pulp stabilization box and is sent into a wet ground paper forming device through a pulp pump, a prepared wet ground paper is sent into a die which is sleeved with an inner net and is sent into a pressurizer with the die together for water extrusion with the pressure of 0.7-0.9MPa, a vacuum pump assists with water suction and absorption, the wet ground paper is taken out when the moisture achieves 40-50 percent, is sent into a micorwave drying box to be dried through a conveyor belt and is pulled out and sent into a hot press to be dried with the temperature of 115-125 DEG C when being dried with the water content of 25-35 percent, the drying time is determined by the thickness, the wet ground paper is dried until the pressboard water content achieves 4-6 percent and enters a half finished chamber to be in balance treatment for 3-5 days after board disassembly, the paper is treated by edge trimming and finishing and is packaged to be put into a storage after passing the inspections.

Proceedings ArticleDOI
23 May 2010
TL;DR: In this paper, the partial discharge behavior of synthetic and natural esters compared to commonly used mineral oil is compared. But, there is little experience with those fluids in large power transformers.
Abstract: In times when personal safety and the security of electrical power supply become more and more important, the usage of alternative insulation fluids is demanded in large power transformers. The minimizing of fire loads is another significant reason for new liquids. Different companies are offering such alternative insulation liquids which are already used in distribution transformers. On the other hand there is little experience with those fluids in large power transformers. For the confirmation of the usability of new insulating liquids comparison methods must be tested to find the differences between the alternative insulating fluids and commonly used mineral oil. There are different methods for characterising insulating materials, like AC-Breakdown tests, partial discharge tests, lightning and switching impulse voltage tests, etcetera. Partial discharge behaviour is a distinguishing characteristic of an insulating medium. This paper shows the partial discharge behaviour of alternative insulation liquids such as synthetic and natural esters, compared to commonly used mineral oil. To generate the PD patterns, voltages up to 30kV and inhomogeneous test arrangements were used. A model of an oil/board insulation system was created by using sheets of pressboard.

Patent
29 Sep 2010
TL;DR: In this article, a continuous calendar press with a flexible hot pressboard is described, where a master press roll is arranged between the drive roll and the guide roll to form a primary pressurization mechanism of a plate blank.
Abstract: The invention discloses a continuous calendar press with a flexible hot pressboard. A drive roll, a tension roll and a guide roll are supported and distributed on a frame in triangle shape. A master press roll is arranged between the drive roll and the guide roll. The master press roll and the guide roll form a primary pressurization mechanism of a plate blank. An annular metal strip covers the master press roll, the drive roll, the tight roll and the guide roll sequentially to form a circular closed heat conduction transmission mechanism. The metal strip drives each roll to rotate and heat up and pressurize the plate blank. The flexible hot pressboard covers the outer side of the metal strip. A plurality of hydraulic cylinders are distributed at the outer side of the hot pressboard. Pressure and heat are transferred to the metal strip by a roller blanket. The temperature, pressure and displacement applied to the plate blank can be adjusted according to the requirement of the plate-making technology. The invention can adjust the density distribution of the plate blank along the direction of the thickness conveniently, increases a high-density layer on the surface, improves the surface quality, increases the heat input to the metal strip and ensures that the plate blank is heated evenly, and the invention also improves the density of a core layer and bonding strength.

Proceedings ArticleDOI
01 Dec 2010
TL;DR: In this paper, acoustic emission (AE) detection system is used to detect partial discharge in an experimental tank filled with transformer oil, three different types of PD sources to generate PD in the experimental tank are created from pressboards which are the plain pressboard, the floating metal in the pressboard and the bubble in pressboard.
Abstract: Partial Discharges are major source of insulation failure in power transformers. Therefore, partial discharge (PD) measurement has been commonly carried out to detect and monitor PD activity in insulation in order to avoid from any catastrophic failure. In this research work, acoustic emission (AE) detection system is used to detect PD in an experimental tank filled with transformer oil. Three different types of PD sources to generate PD in the experimental tank are created from pressboards which are the plain pressboard, the floating metal in the pressboard and the bubble in pressboard. The AE signals due to the occurrence of PD from these sources are captured and recorded. Due to the large number of AE signals to be recorded by the Data Acquisition System, some of these signals may not be stored correctly in the system. Some of these signals may also be affected by the reflection and refraction phenomena, interference and attenuation of the AE signals. Hence, the preprocessing and validation of the acquired AE signals from the experimental setup are also explored in this paper. Finally, the valid AE signals due to three different types of PD sources are identified for further analysis.

Proceedings ArticleDOI
01 Nov 2010
TL;DR: In this article, acoustic emission (AE) detection system is used to detect partial discharge (PD) in an experimental tank filled with transformer oil, three different types of PD sources to generate PD in the experimental tank are created from pressboards which are the plain pressboard, the floating metal in the pressboard and the bubble in pressboard.
Abstract: Partial discharge (PD) is one of the major contributors of the problem in high voltage electrical system. It can cause the insulation of a high voltage equipment to fail and lead to catastrophic incident. In a power transformer, detection of PD using acoustic emission technique has been gaining popularity due to its nonintrusive application and capability of locating PD sources. In this research work, acoustic emission (AE) detection system is used to detect PD in an experimental tank filled with transformer oil. Three different types of PD sources to generate PD in the experimental tank are created from pressboards which are the plain pressboard, the floating metal in the pressboard and the bubble in pressboard. Several samples of AE signals due to the occurrence of PD from the same discharge source are captured and recorded. In order to characterize the different types of PD sources, five features or descriptors were extracted from the Short-Time Fourier Transform spectrogram of the AE signals. Then, the preprocessing of the AE signals are carried out from the extracted features using Self-Organizing Map (SOM) Neural Network. Finally, the characteristics of the AE signals from the acquired samples can be obtained and the outlier samples can be determined.

Proceedings ArticleDOI
01 Oct 2010
TL;DR: In this article, the authors used Fractal Features to extract fractal features from the time domain acoustic emission (AE) signals produced by partial discharge (PD) in oil pressboard insulation system.
Abstract: Oil pressboard insulation used in transformer deteriorates due to partial discharge (PD). This paper reports experimental results and analysis for classification of PDs using acoustic emission (AE) signal of laboratory simulated PDs in oil pressboard insulation system using three different electrode systems. AE signal produced by PD are detected by sensors mounted on the experimental tank surface, stored on an oscilloscope and fed to computer for further analysis. The measured AE signals are analyzed using Fractal Features. A variety of algorithms are available for computation of Fractal Dimension. In this paper, Box counting and Higuchi's algorithm for the determination of fractal dimension, Lacunarity and Approximate Entropy are used for the extraction of fractal features from the time domain PD AE signals. There are significant overlaps of few features for different types of PDs. But few features are distinct for different types of PDs. These features are used for the classification PDs.

Journal Article
TL;DR: In this paper, a discharge test assembly was established to simulate the surface discharges in transformers, which consisted of a surface discharge model, a test rig and a PD detect complex.
Abstract: In order to study the influence of temperature on the developing processes of surface discharges in oil-paper insulation,a discharge test assembly was established to simulate the surface discharges in transformers,which consisted of a surface discharge model,a test rig and a PD detect complex. Long-term laboratory tests under 60°C,90°C and 100°C were conducted to observe the entire evaluation process of surface partial discharges from its inception to the eventual occurrence of flashover,using boosting voltage application. PD was detected by conventional impulse current (CIC) signals. Phenomena and features of surface discharges at different developing stages were observed and captured by a camera. The experimental results show that,(a) as the oil temperature increases,the PD inception voltage and flashover voltage gradually descend; (b) the destruction to pressboard is much serious under high temperature. These features could be used as criteria to infer different evolutionary stages of surface discharges under different temperatures.

Journal Article
TL;DR: In this article, a new diagnostic technique based on frequency domain spectroscopy (FDS) is presented to diagnose transformer insulation and lifetime evaluation for oil-immersed transformers.
Abstract: The reliability of oil-immersed power transformers depends on the insulation system to a large extent,and the lifetime decrease with the deterioration of the insulation systemTherefore,insulation diagnosis and lifetime evaluation for oil-immersed transformers are necessaryIn this paper,diagnostics of transformer insulation are analyzed,and a new diagnostic technique based on frequency domain spectroscopy(FDS)is presentedThe 750 kV transformer operated in Lanzhou East Substation is measured on-site with the FDS methodThe experimental results show that the moisture content in transformer pressboard is eligible,and its insulation condition is wellAnd the experimental results are consistent with those of the conventional preventive testThe validity of FDS method is proved,and it is promising as a novel preventive test method

Proceedings ArticleDOI
26 Jun 2010
TL;DR: In this article, the reliability of the quantification of water content using dominant time constant in transformer pressboard was further investigated, and field tests performed on several transformers in different status have shown that the return voltage measurement method can estimate the moisture content in paper insulation of power transformers effectively.
Abstract: Moisture in power transformer strongly influences the dielectric properties of oil-paper insulation system. The insulation paper gradually degrades over time, therefore, it is imperative to assess integral condition of oil-paper insulation for assuring a normal operation of power transformers. As a non-destructive diagnostic technique, return voltage measurement is an effective assessment method of water content in transformer pressboard. The study presented in this paper aims of further investigating the reliability of the quantification of water content using dominant time constant in transformer pressboard. Field tests performed on several transformers in different status have shown that the return voltage measurement method can estimate the moisture content in paper insulation of power transformers effectively.

Patent
15 Sep 2010
Abstract: The invention relates to a baking and printing machine of chopsticks, which comprises a stand, wherein a hot pressboard and a printed film conveying mechanism are arranged on the stand; a chopstick conveying belt is arranged below the hot pressboard; the hot pressboard is fixed at the lower end of a sliding bar which can move up and down; a sliding bar seat is arranged on the stand; and the sliding bar is installed in the sliding bar seat and in sliding fit with the sliding bar seat. The invention has compact and reasonable structure and high degree of automation, and changes the original baking and printing mode with an immovable hot pressboard into a mode of pressing the hot pressboard for baking and printing, thereby enabling the baked and printed patterns to be more clear and integral, and improving the production efficiency. A positioning mechanism is additionally arranged to improve the rate of finished products, and a photoinduction control switch is additionally arranged to greatly reduce the energy consumption of the machine, thereby saving the production cost, improving the production efficiency and being suitable for popularization and application in a large scale.

Journal Article
TL;DR: In this paper, the same winding under the same state at different times was used to test the same vibration frequency response analysis (VFRA) to detect the faults of windings' deformation.
Abstract: Vibration frequency response analysis(VFRA) was used to test the same winding under the same state at different times.The winding of phase C was artificially made faults of pressboard missing and winding radial deformation.The experimental data show that the VFRA can effectively detect the faults of windings' deformation and the results are repetitive.Compared with short-circuit reactance measurement,the VFRA is more sensitive.

Patent
03 Mar 2010
TL;DR: In this article, a cooling device for an industrial belt hot-press, which comprises a hot pressboard with cooling function, is presented, where a cooling medium can directly pass through the pore passage to realize the cooling.
Abstract: The invention relates to a cooling device for an industrial belt hot-press, which comprises a hot pressboard with cooling function. The hot pressboard is provided with pore passage which is manufactured in a heating plate; the pore passage is a structure which is parallel to the upper plane and the lower plane of the hot-press board and is manufactured along the vertical direction in a board bodyof the hot pressboard; and a cooling medium can directly pass through the pore passage to realize the cooling of the hot pressboard. The cooling device has high cooling efficiency with the effect improved by over 80 percent compared with the prior cooling device, has a small volume without assembly positioning problem, works stably without water leakage problem, and has no restriction on the length of the hot pressboard.

Patent
08 Dec 2010
TL;DR: In this paper, the utility model relates to a complete set of equipment for hot-pressing a large-format pressboard for a transformer, in order to overcome the disadvantages that the existing equipment has low loading efficiency, poor reliability, poor insulating performance of products and high proneness to generate metal abrasive dust in loading and unloading.
Abstract: The utility model relates to a complete set of equipment for hot-pressing a large-format pressboard for a transformer, in order to overcome the disadvantages that the existing equipment has low loading efficiency, poor reliability, poor insulating performance of products and high proneness to generate metal abrasive dust in loading and unloading. A pressboard pre-loading machine and a pressboard loading machine are connected into a whole by an upper beam and a lower beam to form a loading machine set; the loading machine set and a pressboard multi-layer hot press are fixed into a whole via one end of the upper beam and one end of the lower beam; the trolley on each layer of a non-backing-plate belt/trolley loading machine corresponds to the position of the hot-pressed board on the corresponding layer of the hot press; and a vacuum chuck type unloading machine is connected with the other end of the hot press via a rack IV. The utility model can greatly improve the efficiency and reliability of loading and prevent the metal abrasive dust from being generated in the loading process.

Journal ArticleDOI
TL;DR: In this paper, the Angle Ring and Cap which is called pressboard are settled at the primary and secondary coil winding of 154 kV transformer that can reduce effectively distance of insulation.
Abstract: The Angle Ring and Cap which is called pressboard are settled at the primary and secondary coil winding of 154 kV transformer that can reduce effectively distance of insulation. As it has not manufactured pressboard of Angle Ring and Cap for high voltage grade, insulation components industry especially high voltage transformer has not participate in a competition with worldwide yet. That`s why is difficult to make an specialized shape of insulation components of high voltage grade. Therefore it has finally completed to make an deformation manufacturing utility using an bellowed special analysis tools. This study that uses various analysis program determining optimum shape about insulation of Angle Ring and Cap which is related life of high voltage transformer. In addition to develop forming equipment with an specialized five steps pressing. That is also based on the mechanical strength evaluation and test, it is investigated optimized processing components.