电导率对大型电力变压器油流带电影响的研究

分析了油流带电的产生及危害，利用循环管道模型研究了变压器电导率对大型电力变压器油流带电的影响。其结论为解决大型电力变压器油流带电问题提供了必要的参考依据。     

油流带电所形成的泄漏电流

利用油流带电模拟系统测量了不同油流速度、油温和外施电压下的泄漏电流,并对实验结果进行了理论分析。     

大型变压器中油流带电特性的研究

在了解和掌握国内外有关油流带电研究现状的基础上,研制出圆筒式油流带电模型,用于模拟大型变压器中的油流带电过程。用该装置对油流带电的转速特性,温度特性,油流带电的表征参数——泄漏电流与油的电气性能参数之间的关系进行了研究。     

循环管道式油流带电模型的研制及应用

在对国内外油流带电模型进行研究比较的基础上，研制了一种循环管道式油流带电模型用于模拟大型强迫油循环电力变压器油道中的电荷分离情况，并进行了常温及加温条件下的流速特性试验，探讨了表征油流带电大小的泄漏电流同油流速及温度的关系，对变压器油流设计及油流带电问题的解决有一定参考价值。     

变压器油流带电数学模型的研究及其应用第二部分数学模型的应用

针对变压器绝缘油道的结构特点,本文提取出均匀扁矩形截面的模型油道,进而利用作者提出的变压器油流带电数学模型［１］和本文给出的计算方法研究了这种模型油道中油流带电的流速特性、外电场特性、温度特性和电导率特性,还分析了该系统中因油流带电引起的电场的分布规律。用文献［５］给出的实验油道作为验证模型,对比结果表明,计算值与文献中的实验值基本吻合。     

Relationship between static electrification of transformer oils with turbidity and spectrophotometry measurements

The paper presents the research results on electrostatic charging tendency (ECT) of transformer oil in a spinning disk system. The measurements were performed at different aging severity. Changes in static electrification were related to some classical aging indexes (conductivity, dissipation factor, water content, resistivity, etc.). Fast, inexpensive and reliable laboratory testing procedures developed by ASTM (D 6802 and D 6181) were also used to monitor the decay products as trace impurities. The obtained results show that static electrification currents increase with temperature, oil flow velocity, coating disk material properties and oil’s aging byproducts. The polarity, the amplitude and the time constant of the streaming electrification currents are also affected. This contribution is not only intended to provide a fresh review in this domain of research, but also contains a substantial amount of new material with a view of closing some gaps in the present state of knowledge of transformer oil streaming electrification phenomenon.     

超高压变压器油流静电带电问题的研究现状

简要阐述了超高压变压器油流静电带电问题的重要性及研究现状，着重评述了有关油流带电机理的若干观点、研究手段及方法，详细介绍了已取得的研究成果及预防油流带电事故的对策。最后，本文还展望了变压器油流带电领域今后的研究方向和趋势。     

变压器油流带电数学模型的研究及其应用 第一部分：数学模型的推导

由油流带电引发的变压器事故或故障引起了各国电力部门的广泛关注，许多国家纷纷开展变压器油流带电的研究，大量的油流带电的机理模型也就应运而生。本文在国外学者提出的流动作用机理和电动作用机理两种机理模型的基础上，推导出变压器油流带电的数学模型，与目前存在的几种典型的油流带电计算模型相比，本模型的特点在于它可综合反映起电的流动作用和电动作用，并可基本反映油流流速、油品电导率、外加交流电场强度和系统温度等因素对油流带电的影响。关于本模型的应用实例及与实验的比较见第二部分。     

Static electrification of pressboard/oil interface and transientphenomena

The static electrification phenomenon of insulating materials used in power transformers is investigated through two devices. The first is a cell with a rotating disk covered on both sides with a given pressboard and immersed in a metallic tank containing ~41 of oil; and second device enables us to measure the electrostatic charge tendency of oils. The electrostatic charge tendency (ECT) of insulating oils and the leakage current generated by the charge concentration gradient at the oil/pressboard interface are analyzed as function of temperature, water content and aging of oils, the nature of the pressboard, and the rotating speed of the disk. The influence of the surface roughness of the pressboard and antistatic additives on the aging and ECT also are considered. A correlation between ECT and the physico-chemical and electrical characteristics of the oil is established. It is shown that the temperature gradients and the water migration phenomena at the oil/pressboard interface play an important role in the charge separation. Transient currents are strongly affected by the presence of air in the pressboard and the aging of the oil     

Experimental study and modeling of static electrification in powertransformers

For the last 20 years, static electrification has been suspected to he responsible for failures in power transformers (electric “tree” paths, “worm holes,” etc.). The phenomenon consists in a preferential adsorption of negative ions from the oil (impurities) into the pressboard. This yields, on the one hand, a space charge in the oil which can relax in contact with grounded metallic walls and, on the other hand, a space charge in the pressboard which can accumulate depending on the leakage paths. As part of a research program by Electricite de France in the field of static electrification in transformers, an experiment has been carried out, at the Universite de Poitiers, Poitier, France, to study the most constrained parts in transformers with regard to this phenomenon: the insulated pressboards close to the oil inlet. For this, the experimental loop consists in impinging an immersed oil jet on a pressboard target in which annular insulated electrodes have been inserted to determine the charge in the pressboard. Considering the scale effect, the equipment involves taking oil from an operating transformer and making it possible to study the influence of the flow velocity and the length of the free jet. From a first modeling, compared to the authors' experimental results, it seems that the local wall current coming from the pressboard is proportional to the local wall shearing stress. Considering the magnitude of the process, it finally turned out that this new configuration increases greatly the charge generation process in comparison to a flow parallel to the pressboard     

Increase of static electrification in an aged oil‐immersed transformer

Increase of static electrification activity and discharge generation was experienced during the service operation of an aged power transformer. The transformer oil had high sulfide and sulfoxide contents and was liable to show high ECT value after aging. However, there was no apparent increase in standard ECT (electrostatic charging tendency) measurement of the insulating oil and, therefore, deterioration of pressboard was suspected as the cause of the increase. The ECT tests with aged oil and pressboard sampled from the aged transformer were insufficient to demonstrate the increase in static electrification for the aged transformer. On the other hand, the results suggested a possibility that increase in static electrification can be caused by adsorption of some deterioration compound in the aged oil to the pressboard. In order to make more effective evaluation to the transformer insulation, potential measurement on the pressboard in the oil duct was carried out. The experimental results demonstrated strong increase of the accumulated charge by the aged pressboard, which suggested effectiveness of potential measurement for the assessment of static electrification in transformers. The device of potential measurement for practical use was designed by reducing the necessary amount of oil sampling. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(3): 10–19, 2009; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20789     

Effect of streaming potential on heat transfer in transformer oil

The results of an experimental study of the effects of streaming electrification on the heat transfer of transformer oil (Voltesso 35) in Plexiglas and paper/pressboard pipe models are reported. The magnitude and the polarity of the charge in the oil entering the test section was varied by using two different filters (Millipore cellulose and Sartorius fiber glass) in the upstream of the oil flow. An enhancement in heat transfer was observed with both types of filters in the Plexiglas model and with cellulose filter in the paper/pressboard model; whereas a reduction in heat transfer was observed with fiber glass filter in paper/pressboard model under similar flow rates and temperatures. With uncharged oil, heat transfer was either inhibited or no enhancement was noticed in both models. The results have been discussed considering the temperature gradients, the flow conditions and the electrical forces due to static charge in the liquid     

Charge behavior in flowing oil in oil/ pressboard insulation system by electro-optic field measurement

The electrical insulation structure of most power transformers is a combination of insulating oil and solid materials. One of the crucial problems we face in transformer operation is flow electrification, which occurs at a flowing oil/solid material interface. Thus, for the transformer insulation design, we need to clarify the now electrification phenomena. In this paper, we measured the electric field strength in an oil/pressboard composite insulation system using an electro-optic method of the Kerr effect. We obtained the time variation of electric field distribution in both flowing uncharged and charged oil. It is notable that we could quantitatively clarify the electric field distortion in flowing charged oil by flow electrification. Furthermore, we measured the leakage current from divided electrodes and derived a charge density distribution along the flow direction. Finally, we quantitatively discussed the electric field distribution and the charge behavior from the measurement results.     

电力变压器中的静电起电

对变压器中绝缘油流动带电现象进行了研究，给出了一些大型变压器运行故障实例，分析了变压器静电起电的原因和条件，介绍了静电起电的监视技术。     

变压器油中局部放电下的油流带电分析

对变压器油漉带电现象进行了研究,分析了油流带电问参数的关系以及影响因素,阐述了油流带电现象产生的原因.     

dc field effects on streaming electrification in insulating oils

The results of an experimental investigation into the influence of impurities on electrification in insulating liquids in a tube model under an external dc field effect is described. Both conduction and streaming currents were measured as a function of temperature and flow rate using a paper-pressboard model with concentric cylindrical electrode geometry. Positive or negative dc voltage was applied to the inner electrode. The streaming current was measured from a shielded test chamber and the conduction current was measured from the ground electrode. Energization by positive dc voltage always enhanced the streaming electrification; however, when the applied voltage was negative, the polarity of streaming current was field strength dependent. At low fields (<0.52 kV/mm), the streaming current with negative dc field I_sn^c increased with increased field and with field strength >0.52 kV/mm, polarity reversal was observed. The field at which current crossed the zero value has been defined as the zero cross over point (ZCOP). Flow rate did not have any influence on the ZCOP; however, the additive concentration, moisture content and the temperature affected this ZCOP. In the presence of the corrosion inhibitor carbazole, the streaming current with negative dc field, I_sn attained zero at low fields. The conduction currents corresponding to fields where streaming currents were zero were also relatively low. It is therefore possible that by applying a moderate dc field of appropriate polarity the streaming current can be reduced to very low values by adjusting the carbazole concentration in the test liquid     

Development and calibration of a network-based streamingelectrification model for core-form transformer structures

Streaming electrification occurs in large power transformers when oil circulated for cooling purposes acts to separate charges from the Debye layer on the cellulose insulation surfaces. This phenomenon is believed to have caused several catastrophic transformer failures and remains to be satisfactorily understood in realistic geometries. A network-based streaming electrification model is presented which utilizes single winding ducts as the basic element to investigate a core-form structure. The network is first analyzed using hydraulic duct parameters to calculate the oil flow distributions within the structure. This data is then provided to the electrification solver which predicts the charge densities at each duct outlet. The charge density results are ultimately used to determine the streaming potentials at each node based on an a suitable matrix of leakage resistances. Development of the network model is presented along with empirically-based calibration data for a realistic section of core-form transformer geometry     

A parametric study of streaming electrification in a full-scalecore-form transformer winding using a network-based model

Streaming electrification remains a problem for large power transformers which require forced-oil cooling. Oil flowing against cellulose insulation surfaces results in the separation of charges from the electrical double layer at the interface. This process can generate hazardous static potentials and volume charge densities in the transformer dielectric system. While streaming electrification has been studied in great detail using small-scale laboratory models, extension of these results to full-scale transformers is rather difficult. This issue has been addressed through the development of a network-based analytical approach which is calibrated against empirical data at the elemental duct level. The model has been utilized to perform a parametric study of streaming electrification in the full-scale high-voltage winding of a core-form transformer. Volume charge densities exiting from each duct in the structure and the local surface potentials are predicted as a function of influent charge, oil volume flow rate, temperature and applied voltage     

变压器油的静电性能及变压器油流静电试验方法

本介绍了采用“过滤式”带电度测试装置对国产变压器油的带电度及有关静电带电性能进行试验研究的结果，分析了变压器油流带电过程及静电放电特点。此外，初步试验研究苯并三唑对油中静电的抑制作用及其影响，在此基础上，探讨了检测变压器中油流静电的试验方法。     

10kV电容器渗漏问题调查分析及处理

电容器在使用中发生渗漏是严重影响电容器正常运行和使用寿命的因素。通过对变电站10 kV并联电容器组,投运以来不断发生电容器渗漏油现象,进行现场调查分析。查找出电容器发生渗漏油、外壳膨胀及温升过高等故障的原因,提出电容器发生渗漏油故障处理方案、见解以及在处理电容器过程中的安全措施及今后工作中的注意事项。