Characterization of static electrification in power transformers

Static electrification due to oil now causes many field failures of large forced-oil cooled power transformers. Also, in practice under normal operating conditions, the oil volume in these power transformers is reduced due to the internal heat generated (from the energized windings) which accelerates the chemical processes occurring inside. To complete filling of the oil tanks of such transformers, either new oil of the same or different type is used. Laboratory analogs of these transformers; namely a closed and an open cycle, have been used for investigating this phenomenon. Such tests have been performed upon different types of fresh and aged oils and oil mixtures to measure the electrification current. Investigations of the effect of oil temperature, oil velocity, frequency and type of the applied voltage, type of the solid-phase material, and the length of the oil gap are introduced. Also, a 200 kVA, 3.3 kV/380 V distribution power transformer is used where the oil is forced and heated externally to examine and demonstrate this phenomenon for unenergized and energized cases and for both fresh and aged oils     

浅析大型变压器油流带电现象

从油流带电产生的机理、影响油流带电的主要因素、油流带电的测试方法和广东省大型变压器油流带电的测试实例等方面探讨了油流带电现象,提出如何抑制油流带电现象的产生是当前急需解决的问题。     

静态爆破技术在高压带电环境中的可行性分析

利用岩石的抗压强度高,抗拉强度低的特点,引进博亚牌液压分裂机应用于输变电工程中对岩石进行液压分裂,有效解决了高压带电环境中爆破安全维护难、成本高的难题。     

Influence of pressboard physico-chemical composition on static electrification in power transformers

As part of a research program in the field of flow electrification in power transformers, some fundamental studies have been undertaken on the physical chemistry of this phenomenon. The two main constituents involved in the process of charge generations are oil and pressboard. As oil composition is difficult to deal with, the choice has been made to understand the overall chemistry through the role played by the pressboard, whose composition is better mastered. In order to identify the chemical species in the pressboard responsible for the charge generation, in view of perfecting additives to neutralize the phenomenon, the French Institute of Pulp and Paper carried out modifications on commercial pressboards, and manufactured some others. Charge accumulation, measured from capacitive currents on insulated electrodes facing the pressboard ducts, has been observed for modified and manufactured pressboards with regard to oil flow rate and temperature. All the experiments have led to various behaviors in terms of kinetics and magnitude of the charge accumulation. The obtained results tend to prove that chemical composition of pressboards, with regard to their content in chemical functional groups (hydroxyl or carboxyl groups) or radical nature (lignin), as well as board manufacturing parameters (pulp refining, layer composition) and surface properties seem to be at the origin of the electrification phenomenon.     

Experimental study of static and dynamic losses in magnetic conductors

The order of studying static and dynamic power losses in magnetic conductors of different designations is expounded, and specified mathematical expressions are given for their calculation to ensure practical use of these conductors in design and construction of electrical-engineering equipment and devices.     

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     

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.     

堆石料蠕变特性试验研究

通过三轴蠕变试验,考虑坝体填筑的应力路径,对两河口水电站堆石料蠕变特性进行了探讨,分析了其蠕变机理、蠕变模型及参数确定方法。堆石料的轴向和体积蠕变可采用幂函数ε=a(t/t0)b拟合。a为试样初始蠕变,b表征了试样的蠕变速率,与应力状态有关。堆石料轴向和体积初始蠕变均随主应力差的增大而增大,轴向和体积蠕变指数均随围压增大而减小,体积蠕变指数还随主应力比增大而减小。拟合得到的蠕变模型具有良好的效果。     

New safety dielectric coolants for distribution and powertransformers

This article offers a summary of the development of dielectric fluids based on edible natural seed oils. We also include a discussion of the history of liquid dielectric coolants for distribution transformers. Additionally, we examine ester-based fluids; a key-properties comparison between new, natural ester-based fluids and other major dielectric coolant types; and details of field trials with transformers designed to use the new fluids     

A survey of new techniques in insulation monitoring of powertransformers

This paper presents a survey of new monitoring and diagnostic technologies and applications, including laboratory experimental work, in power transformer insulation monitoring for the purpose of condition assessment     

Relative properties of the new combustion-resistvegetable-oil-based dielectric coolants for distribution and powertransformers

Electrical distribution transformer insulation systems are being reevaluated based on their total life-cycle cost from economical, safety, and environmental perspectives. Due to the inherently higher efficiency design offered by liquid-cooled transformers, development has focused on fluids having improved environmental and health properties while maintaining the fire-resistant properties of “less-flammable” fluids. This paper reports our findings from several years of research and development on alternative dielectric systems using both natural and synthetic esters. Because esters have lower inherent resistance to oxidation than conventional mineral oil, a novel insulation system was developed to overcome this potential handicap. Single- and three-phase prototype field installations using these new dielectric coolants are discussed     

Testing of algorithms for a stand-alone digital relay for powertransformers

A stand-alone digital relay has been designed and implemented. The relay can be modified easily to accommodate the protection of different types of transformers by changing the software only. Presented in this paper are the real-time experimental results of five selected algorithms implemented using this digital relay. These algorithms are: discrete Fourier transform, Walsh function, rectangular transform, finite impulse response and least-square. Based on the experimental results, the discrete Fourier transform (DFT) algorithm is found to be the best algorithm in terms of accuracy and speed for digital implementation of the differential relay for power transformers     

Rural electrification in Nicaragua

The paper discusses the rural electrification (RE) project of the Cua-Bocay municipality, situated in Nicaragua's northern province of Jinotega. The electrification program has been led by a nongovernmental organization (NGO) called the Cua-Bocay Project. In general, NGOs have the potential to work as facilitators of the rural electrification infrastructure and to affect the normal set of rural electrification costs and benefits by emphasizing local training and participation. The paper considers the project history, changing goals, infrastructure and programs, project benefits and training emphasis     

Adaptive fuzzy diagnosis system for dissolved gas analysis of powertransformers

To enhance the fault diagnosis abilities for the dissolved gas analysis (DGA) of the power transformers, this paper proposes a novel adaptive fuzzy system for the incipient fault recognition through evolution enhanced design approach. Complying with the practical gas records and associated fault causes as much as possible, a fuzzy reasoning algorithm is presented to establish a preliminary fuzzy diagnosis system. In the system, an evolutionary optimization algorithm is further relied on to fine-tune the membership functions of the if-then inference rules. To make the diagnosis system intensively compact and the inference process more understandable, a pruning scheme is then developed to filter out the insignificant or redundant rules. The capabilities of the proposed diagnosis system for the transformer DGA decision support have been extensively verified through the practical test data collected from Taiwan Power Company (TPC)     

畸变磁通作用下变压器铁心模型损耗的实验研究与模拟分析

对畸变磁通条件下产品级变压器铁心模型的损耗进行了实验研究,考察了谐波相位差变化对铁心损耗的影响。给出了一种能够考虑畸变磁通条件下铁心损耗的工程计算方法,该方法可有效地考虑局部磁滞回环对铁心损耗的影响。结合MagNet电磁分析软件,计算了产品级变压器铁心模型的铁心损耗,通过对比实验结果证明了方法的有效性。     

中外电气化发展历程探讨

论述了电气化的涵义与分析指标,分析了美国、日本、韩国和中国的电气化水平变化历程,以及主要行业电气化水平差异,用因素分解法分析了各国电气化水平提升的原因,指出了未来中国电气化水平的发展趋势,提出了相关的措施建议.     

基于PCC的大系统与微电网静态建模仿真

针对微电网电源类型多样性及其在并网模式下运行状态易受大系统影响的特性,建立了基于大系统与微电网公共耦合点PCC端口的系统静态仿真模型.分布式直流电源(燃料电池等)通过逆变器转换为等值交流电源后,同分布式交流电源(风能发电机组)一起通过可调变压器接在微电网母线上,这时微电网可等值为包含燃料电池、光伏电池、储能装置及风能发电机组的戴维南电路并与大系统等值电路建立电气联系,通过Mat lab/Simulink仿真验证了大系统等值电路及各种分布式电源等值交流电路的有效性,所建模型为进一步研究微电网提供了良好的仿真平台.     

家庭电气化及示范小区建设

电能属二次能源,与传统煤气等能源相比,具有更安全、便捷、环保、经济等优点。面对日益严峻的环保形势,加快实施电能替代,增加电能在终端能源消费中的比例,既有经济性和可行性,又能在很大程度上减少污染,保护环境。国网三明供电公司联合电器厂商、小区物业公司及有关媒体,成立家用电器推广联盟,开展“家庭电气化,共建美好家园”专题活动,建设家庭电气化示范小区,促进家庭电气化。家庭电气化获得清新洁净的家居环境和真正绿色健康的生活,势必成为未来家居生活的主导者。     

Detailed modeling of an actual static VAr compensator forelectromagnetic transient studies

The authors present a detailed model of a static VAr compensator (SVC) for digital simulation of electromagnetic transients. It is also demonstrated that this model can adequately reproduce SVC transient behavior as verified in transient network analyzer studies carried out with a replica of the SVC control system. The SVC control system is described, with emphasis on some special blocking schemes needed to meet particular requirements of the power system transient performance. The complete system and SVC data are also included