Thermally and electrically induced bubbles in liquid argon andnitrogen

An experimental study of high field conduction phenomena in liquid argon and liquid nitrogen in a point-plane electrode geometry is reported. These liquids behave qualitatively like saturated hydrocarbons except when they are studied close to their normal boiling point. The generation and dynamics of microscopic bubbles (thermally and electrically induced) as a function of various parameters (nature of the liquid, injected energy, hydrostatic pressure) are presented and discussed. Possible influences of these phenomena on the electrical insulation at cryogenic temperatures is also discussed     

The behavior of different transformer oils relating to the generation of fault gases after electrical flashovers

Dissolved gas analysis is a common technique in the supervision and maintenance of transformers. It can give hints on defects and faults in oil-immersed transformers by determination and quantification of gases arising in consequence of thermal or electrical stress. Different algorithms for the assessment of transformers, which employ data obtained from dissolved gas analysis, have been published so far. However, only few investigations, dealing with the influence of the oil’s composition towards the oil’s tendency of releasing gases, exist. This research study presents a comparison of three commercially available transformer oils of different composition regarding that aspect. The results indicate that an oil with high percentages of paraffinic hydrocarbons forms gases to a lesser extent than naphthenic oils when it is exposed to electrical stress. This phenomenon can be explained either by a variable solubility of gases in the medium oil, or by the presumption that cyclic hydrocarbons are the main producers of gases.     

Analysis of water in oil-impregnated kraft paper and its effect onconductivity

Oil impregnated paper or polymer film is the main insulating system for many kinds of power apparatus. The oil impregnated materials, especially oil impregnated kraft paper, include a significant amount of water, and this water disturbs the insulating performance of the devices. The amount of water in the materials usually is represented by the difference in weight between the normal material and the same material after drying. However it is difficult to measure the absolute value of the water content and to determine the state in which the water exists in the materials. In this study, we examined the IR spectra of water in oil impregnated kraft paper, because the IR spectrum of the water indicates not only the amount of water but also its state. It was found that most of the water behaves as liquid water, and some as hydrogen bonded water, interacting with the paper fiber. The dc conductivity of the kraft paper depends only on the amount and state of the water associated with it whether or not the paper is impregnated with the oil     

微氧作用下天然酯变压器油热老化特性研究

天然酯变压器油因不饱和脂肪酸含量较高而易氧化,而变压器因储油罐与空气作用或密封设备产生泄漏等原因,会导致油中溶解微量的氧气.基于此,文章研究了微氧作用下天然酯变压器油的热老化特性,并分析了不同老化时间下油样的电气性能、油色谱特性以及两者之间的皮尔逊相关系数.结果 表明:适时微氧作用能在一定程度上延缓天然酯变压器油电气性能的降低;天然酯变压器油纸绝缘热老化的特征气体为CO2和C2 H6;天然酯变压器油的电气性能与油色谱中CO2-C2H6(油样中溶解的CO2与C2H6的百分比之差)之间存在强相关性.     

Dielectric behavior of insulating liquids at very low frequency

Dielectric spectroscopy in the wide frequency range of 1 mHz to 1 kHz has been used to study the polarization and conduction phenomena in insulating liquids. The dielectric spectroscopy of mineral oil and ester oil at different conditions, i.e. temperatures and electric fields, has been measured. It came out that at low frequencies, space charge polarization changes the permittivity of insulating liquid and at very low frequencies, the consideration of a RC parallel model for the dielectric behavior of insulating liquids is not adequate. The results indicate that the permittivity of insulating liquid increases with aging duration and therefore it can be used as a diagnosis parameter for insulating liquids. The calculation of the activation energy of the conduction process shows that consideration of single activation energy for compensation of temperature effect on dielectric loss for dielectric spectroscopy in the wide frequency range is not perfect.     

Water in oil-filled high-voltage equipment part II: water content as physicochemical tools for insulation condition diagnostic

In the first part of this investigations, we examined the current state of knowledge of the effect of water on paper and liquid-insulating materials. Demonstrated that the scientific representation of the states of water in insulating liquids has a direct practical application as a diagnostic tool for electrical equipment, at least for the dielectric properties of the insulation. The work presented in this second part of these investigations is divided into four sections. The first section deals with the influence of water on the electrical characteristics of the oil/paper insulating materials, followed by a critical review of up-to-date water quantification methods. Based on the physicochemical criteria of the limiting state discussed in the third section, this article proposes some analytical expressions that can help electrical engineers monitor and/or diagnose oil-filled, high-voltage equipment. Our investigations show the advantage of diverse methods for measuring humidity in insulating liquids, and a variety of analytical expressions for calculating the condition of liquid/ solid insulation systems.     

Challenge of mixed insulating liquids for use in high-voltagetransformers.1. Investigation of mixed liquids

The aim of this work is to present results of investigations into mixtures of two insulating liquids, recently proposed as alternatives to mineral oil. The mixtures are a combination of the widely available mineral oil and a specific amount of ester liquid, which has similar electrical properties combined with fewer environmental risks but high hygroscopicity. The water saturation limit of esters is more than 40 times larger than that of mineral oils. Esters absorb water vapor from the air in larger quantities than mineral oil, and this hygroscopicity reduces the moisture content in solid insulation due to diffusion from the solid into the liquid, while the dielectric properties of ester liquids are only slightly changed . Although the life of an oil in service depends primarily on its initial quality, service conditions need to be considered also. The investigations have therefore been carried out on unaged mixed liquids as well as on specimens under severe ageing conditions. Pure liquids have also been investigated to provide baseline data for comparison purposes. The first part of the investigation compares the properties of the mixed liquids with those of pure liquids. The second part of the investigation, will evaluate the compatibility of the mixed liquids with insulating papers used in high-voltage transformers     

Hydrogen peroxide and ozone formation in hybrid gas-liquid electrical discharge Reactors

Ozone in the gas phase and hydrogen peroxide in the liquid phase were simultaneously formed in hybrid electrical discharge reactors, known as the hybrid-series and hybrid-parallel reactors, which utilize both gas phase nonthermal plasma formed above the water surface and direct liquid phase corona-like discharge in the water. In the series configuration the high voltage needle-point electrode is submerged and the ground electrode is placed in the gas phase above the water surface. The parallel configuration employs a high voltage electrode in the gas phase and a high voltage needle-point electrode in the liquid phase with the ground electrode placed at the gas-liquid interface. In both hybrid reactors the gas phase concentration of ozone reached a power-dependent steady state, whereas the hybrid-parallel reactor produced a substantially larger amount of ozone than the hybrid series. Hydrogen peroxide was produced in both hybrid reactors at a similar rate to that of a single-phase liquid electrical discharge reactor. The resulting concentration of H/sub 2/O/sub 2/ in the hybrid reactors, however, depended on the pH of the solution and the gas phase ozone concentration since H/sub 2/O/sub 2/ was decomposed by dissolved ozone at high pH.     

Application of synthetic fire-resistant oils in oil systems of turbine equipment for NPPs

Results of the investigation of the synthetic fire-resistant turbine oil Fyrquel-L state in oil systems of turbosets under their operation in the equipment and oil supply facilities of nuclear power plants (NPPs) are presented. On the basis of the analysis of the operating experience, it is established that, for reliable and safe operation of the turbine equipment, at which oil systems synthetic fire-resistant oils on the phosphoric acid esters basis are used, special attention should be paid to two main factors, namely, both the guarantee of the normalized oil water content under the operation and storage and temperature regime of the operation. Methods of the acid number maintenance and reduction are shown. Results of the analysis and investigation of influence of temperature and of the variation of the qualitative state of the synthetic fair-resistant oil on its water content are reported. It is shown that the fire-resistant turbine oils are characterized by high hydrophilicity, and, in distinction to the mineral turbine oils, are capable to contain a significant amount of dissolved water, which is not extracted under the use of separation technologies. It is shown that the more degradation products are contained in oil and higher acid number, the more amount of dissolved water it is capable to retain. It is demonstrated that the organization of chemical control of the total water content of fireresistant oils with the use of the coulometric method is an important element to support the reliable operation of oil systems. It is recommended to use automatic controls of water content for organization of daily monitoring of oil state in the oil system. Recommendations and measures for improvement of oil operation on the NPP, the water content control, the use of oil cleaning plants, and the oil transfer for storage during repair works are developed.     

Predicting liquid filled transformer loading capability

The IEEE Transformer Loading Guide equations use the top oil temperature rise over ambient to determine the winding hottest spot temperature during an overload. Recent investigations by the author and others have shown that during overloads there is a time lag between the top oil temperature rise and the oil temperature rise in the winding cooling ducts. This phenomena results in winding hottest spot temperatures greater than predicted by the current (1981) IEEE Loading Guide equations. Accurate predictions of the winding hottest spot temperature requires the use of the temperature of the oil entering and exiting the winding cooling ducts. Low flammability liquids such as silicone or high temperature hydrocarbons are not covered in the present Loading Guide. Resistance change with temperature and liquid viscosity are not considered in current Loading Guide equations. Loading Guide equations also assume a constant ambient air temperature during a load cycle. Improved loading equations based on analysis and testing are presented in this paper. The improved equations consider type of liquid, cooling mode, winding duct oil temperature rise, resistance and viscosity changes, and ambient temperature and load changes during a load cycle. A PC BASIC computer program to perform the calculations was developed and will be included in the next edition of the IEEE Loading Guide for Mineral Oil Immersed Transformers     

电机三维温度场新的有限元计算模型

提出了一种新的适合于电机温度场计算的圆柱坐标系下的有限元模型。通过数值计算结果与解析计算结果的实例对比,证明了本方法的正确性与有效性。最后应用本文提出的模型,对ＳＦ１２５－９６／１５６０型发电机的定子铁芯三维温度场进行了计算,并与实测结果作了比较,计算精度满足工程计算的要求。     

检测变压器油中溶解气体的碳nm管传感器研制

对变压器油中溶解气体进行检测分析是判断油浸式电力变压器早期潜伏性故障的重要手段。为克服常用油气分析方法的缺点,提出了一种基于碳nm管传感器检测油中气体的方法,并研制了一种用混酸修饰,以印刷电路板为基底,用于检测油中气体的多壁碳nm管传感器。分析了碳nm管膜的电学特性以及气敏响应机理,在实验室采用甲烷等标气对修饰前后的传感器的气敏性进行了测试,试验结果表明,用经混酸修饰后的样品缺陷多,并含有活性官能团,对油中气体表现出较强的吸附性,具有良好的灵敏度和快速响应特性。     

Electrical conduction in highly resistive polyolefin films modified by polar groups

Electrical conduction and space charge distribution in oxidized low-density polyethylene (samples A1–A6) and copolymers of ethylene and carbon monoxide (samples B1–B3) with different carbonyl contents have been studied. A V-shaped dependence of conduction current on carbonyl content was observed for samples A1–A6, while the current decreases monotonically with an increase in carbonyl content for samples B1–B3. The effect for polar groups on electrical conduction is discussed, focusing on their bonding forms in polymer molecules. © 1997 Scripta Technica, Inc. Electr Eng Jpn, 120(3): 9–16, 1997     

多相多边形无刷励磁机及旋转整流系统的运行状态分析

多相多边形无刷励磁机由于其固有的一些技术特点在一些大容量常规火电站和核电站中得到应用,对该励磁机整流系统运行状态的分析是研究其电气原理和特性的关键。基于多相多边形无刷励磁机电枢实际的空间分布与连接,得到了二极管的理想导通规律;进一步地,考虑换相过程中各阶段的二极管导通数量及等值电路,解析了各状态的电气量波形,获得了各导通状态所满足的临界条件;对一台十一相动模样机进行了实验研究,将实验结果与通过理论解析得到的二极管电流进行了对比,验证了理论分析的准确性。从而完整地揭示了多相多边形无刷励磁机及旋转整流系统的导通换相规律,为该系统的设计提供了理论依据。     

Basic electrical processes in dielectric liquids

The basic processes of electrical conduction in dielectric liquids are reviewed, attention being drawn to the similarities between conductive electrolytes and insulating liquids. The concepts of the electronic amorphous solid state are employed to provide a framework for the review. The conditions at metal electrodes can be incorporated naturally into the scheme, and it is known that the space charge layers occurring on them can control conduction. Although electrical breakdown itself is not considered, the underlying electronic processes which will develop when breakdown electrical fields exist in the liquid are considered     

变压器油中溶解微量糠醛的激光拉曼光谱检测方法

研究变压器油中溶解微量糠醛含量的检测方法及其应用,对运行变压器油纸绝缘老化评估具有重要意义。激光拉曼光谱(LRS)技术作为微量液体检测的有效手段,已经在很多领域得到了广泛应用。本文应用Gaussian 09W程序构建了糠醛分子仿真模型,分析其拉曼振动特性,进而证明了拉曼光谱检测糠醛分子的可行性;应用共聚焦拉曼技术搭建了激光拉曼光谱液体检测试验平台;结合萃取技术研究了糠醛分子的拉曼光谱检测特性,建立了基于特征频谱和最小二乘法对糠醛含量进行定量检测的方法。最后,应用激光拉曼光谱方法对不同糠醛含量的变压器油样进行检测,并与实验室高效液相色谱法(HPLC)的检测结果进行对比,对比结果表明:结合萃取技术的激光拉曼光谱能有效地对变压器油中溶解微量糠醛进行定量检测,为实现变压器油中糠醛含量的快速检测提供了一种方法。     

Bubble formation in synthetic insulating liquids in a pulseddivergent electric field

This is a study of high field conduction phenomena in two aromatic insulating liquids (monobenzyltoluene and dibenzyltoluene) in a point-plane electrode geometry. These liquids behave qualitatively like saturated hydrocarbons; current instability (electron avalanche) for high enough fields near the negative point giving rise to a current pulse regime, which causes the formation of bubbles by local heating. The generation and dynamics of these bubbles as a function of various parameters (injected energy, hydrostatic pressure and the nature of the liquid) are presented and discussed     

面向电力变压器状态评价的油中溶解气体监测数据补全方法

基于马尔可夫理论充分考虑相邻时间点系统在所有状态间的转移特性,提出了一种基于马尔可夫模型的变压器油中溶解气体数据补全方法,将油中溶解气体数据时间序列转化为在不同状态间转移的马尔可夫链,利用正、反向的状态转移矩阵计算得到油中溶解气体数据的补全值。从数据挖掘的角度建立了油中溶解气体数据质量的综合评估体系,从多个角度对数据补全的效果进行评估,并基于D-S证据融合理论融合各个角度的评估结果,得到综合评估结果。利用所提方法对某变压器100组油中溶解气体数据中25组随机缺失值进行补全,结果表明补全后的数据与实际值相似度可以达到99.999%。进一步地,验证其中15组极值点、跃变点处缺失数据补全效果,经过综合评估,补全后的数据与实际值相似度可以达到98.956%。经过验证表明所提方法能够在不改变数据特征的前提下对变压器油中溶解气体的缺失值进行准确的补全,有利于提高变压器状态评估方法的准确性。     

Emulsification and Demulsification Processes in Liquid–Liquid System by Electrostatic Atomization Technique

A new electrical emulsification and demulsification apparatus using an electrostatic atomization technique was developed, and the investigation of both processes in a liquid–liquid system was conducted. First, fine water droplets were generated in silicone oil using a nozzle electrode with ac high voltage, and then, a stable water-in-oil (W/O) emulsion was produced without surfactants. The mode of electrostatic atomization and the trajectory of the fine droplets' flow were observed. The diameter of fine droplets and their distributions were measured as a function of the applied voltage and its frequency. Experiments indicated that electrohydrodynamic (EHD) induced liquid flow with water droplets played an important role in the formation of the emulsion. Next, the demulsification of W/O emulsion was carried out by two injections of oppositely charged water droplets, using the method of electrostatic atomization. The test liquid, which was prepared by the electrostatic atomization technique, was maintained in a state of emulsion for a longer time if no electric field was applied. When the positive- and negative-charged droplets were injected into the test liquid, the emulsion, with a dull color, gradually became transparent as time elapsed. The aggregated droplets fell down due to gravity and the EHD flow effect, resulting in the separation of water and oil. It was found that two injections of oppositely charged water droplets were effective for resolving the emulsion.      

主变压器绝缘油在线监测系统的应用

变压器绝缘状况的优劣是电力系统安全运行的关键因素之一。常规的实验室油色谱分析法存在一些不足之处,提出了变压器油中溶解气体色谱分析的在线监测方法,该方法具有很强的时效性。阐述了色谱分析在线监测装置的必要性和该装置的作用,以及基本技术要求和评价方法,指出具有多功能的油中溶解气体在线监测及智能诊断装置最终将取代常规的离线油中气体色谱分析。