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     

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     

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     

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)     

高介电复合材料及其介电性能的研究

研究了金属／铁电体／聚合物三元复合材料的介电常数和介电损耗。发现金属粒子的加入除了可以提高铁电体／聚合物复合材料的介电常数外,还可以非常明显地降低其介质损耗。金属／铁电体／聚合物三元复合材料是一种很有应用前景的高介电材料。     

复合电介质介电性能有限元仿真

以聚合物基体添加具有非线性填料非线性复合电介质为研究对象,利用编程实现填料颗粒在基料中随机分布和基于蒙特卡洛(MC)模拟的模型随机构建,并通过三维有限元数值分析软件求得不同电压激励下的响应电流.采用时域最小二乘法对仿真得到的总电流进行分解并获得材料的宏观介电参数与电场强度的关系.结果表明:填料在空间的随机分布导致复合材...     

The dielectric properties of meat

The permittivity and conductivity of beef and chicken samples were measured in the frequency range of 1 Hz to 1 MHz. Differences were observed in these dielectric spectra for commercially purchased, as compared to freshly slaughtered samples. In particular, fresh samples display a greater directional anisotropy in their electrical properties and a smaller, frequency-dependent conductivity. Changes in the dielectric properties are also produced by freezing and cooking procedures. These results indicate that measurement of the low-frequency dielectric properties of meat products could serve as a monitor of their storage and preparation history     

Computer-aided modeling of dielectric and ferroelectric properties

In this article the concept of charges fluctuating in double well potentials is used as a basis for a quantitative computer calculation of interactions between permanent dipoles. Numerical calculations are of advantage, because the dipole-dipole interaction energy can exceed the thermal energy. In this case nonlinearities can arise, which are difficult to treat analytically. Furthermore, a numerical recalculation of the Lorentz field resulting from induced dipoles has been carried out. Within the Lorentz calculation of the local field, two models are used in juxtaposed position: a discrete model, which takes account of dipoles inside a conceptual sphere, and a continuum model, which treats the dipoles outside this sphere as a continuum. Using both models the local field at the center dipole of the sphere is calculated. It is shown that several dielectric and ferroelectric properties can be calculated using very simple model assumptions     

电介质材料介电、铁电性能研究的计算机模拟新手段

通过构造双势垒模型以及蒙特卡洛方法的应用,成功地再现了材料的许多介电、铁电性能,这是目前国外研究电介质材料介电、铁电性能的一种有效的计算机模拟方法。将这种方法应用到具体的非晶相绝缘体中,以材料的实际结构来构造双势垒模型,得到的结果与实验相吻合。此外,该方法预期还能用以模拟界面、缺陷等等,并且极有可能发现某些目前通过试验还未被发现的现象,从而指导试验的方向。     

Effect of tacticity on the dielectric properties of polystyrene

Dielectric properties of polystyrene (PS) were investigated by measuring electrical conduction current and frequency spectra of complex permittivity at temperatures from 20 to 199 °C. To clarify the effects of tacticity, the properties were compared among two kinds of syndiotactic PS (SPS) with different crystallinity values and one atactic PS (APS). Experimental results indicate that the two SPS samples show a high melting point of about 250 °C. The conductivity is lowest in SPS with the low crystallinity in the whole temperature range from 20 to 199 °C, while APS had a breakdown at 140 °C. Moreover, the low‐crystallinity SPS shows the smallest permittivity values and the smallest increase in dielectric loss factor toward low frequencies among the three samples. The high‐crystallinity SPS has α crystals. Since the density of α crystals is lower than the amorphous region, the charge transport and polarization are easier in the high‐crystallinity SPS than in the low‐crystallinity SPS. © 2011 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

Cu取代Zn对NiCuZn铁氧体磁性能和介电性能的影响

用传统的陶瓷工艺合成Ni0.15Cu0.2+0.02xZn0.65-0.02xFe2O4(x=-2,0,2,4)铁氧体.发现Cu取代Zn对样品的微观结构、居里温度、磁性能和介电性能都有很大的影响.磁导率随x的增大先增大后减小,在x=2时取得最大值.但品质因数始终随x的增大而增大.与此同时,居里温度随x的增大而增高.随着x的增大,介电常数增大;而介电损耗先减小后增大,当x=2时取得最小值.实验结果表明,在x=2时,能制备出高性能的NiCuZn铁氧体材料.     

High-field dielectric properties of polyethylene in the high-temperature region

Nonpolar polymers such as polyethylene or polypropylene are widely used as insulation materials, often under conditions involving strong electric fields and high temperatures. Under these conditions, the conduction loss due to DC-like carrier transport may give rise to a high-field AC dissipation factor (tan δ). This paper describes the high-field dielectric properties of polyethylene films at frequencies from 50 to 400 Hz and temperatures from room temperature to 100°C, as measured with a new type electrode design developed by the authors. In the high-temperature region, the AC dissipation current waveform at 50 Hz was also measured. At room temperature, the electric-field dependence of tan δ is almost unaffected by the frequency of the applied field. But at high temperatures and strong electric fields, tan δ tends to have a large field dependence and to be almost inversely proportional to the frequency. Thus the AC conductivity becomes independent of the frequency of the applied field in the region of strong fields and high temperatures. A theoretical analysis shows that the high-field dielectric loss is governed by two processes, namely, the dielectric relaxation loss inherent to the AC field and the DC-like carrier transport loss that becomes prominent in the high-temperature region, where AC dissipation current waveform becomes significantly nonsinusoidal.     

Positive streamer discharges along liquid dielectric surfaces: effect of dielectric constant and surface properties

This paper presents investigations on positive streamer discharges propagating in air along the surface of two nonmixing dielectric liquids. By measuring the currents associated with the streamer discharge propagating along the surface of the two nonmixing liquids for varying ratio of their volume, we analyzed the effect of the dielectric constant (the capacitive effect) and the surface properties. Especially, we separated and quantified the magnitude of each contribution. Two different combinations were studied: silicone oil together with glycerol and transformer oil together with glycerol. For these material combinations, we found that the influence of the dielectric constant is about 3 times larger than the effect of the surface properties. Further, by using a simple model of the streamer discharge, we determined with a 3D field calculation program the capacitive behavior of the two nonmixing dielectric materials for varying ratio of their volume. We found that, in order to obtain the observed capacitive dependence, the streamer must propagate literally on the insulator surface.     

Thermal and mechanical properties of lead-free transparent dielectric materials for plasma display panels

The transparent dielectric materials for front panel in PDPs require good thermal expansion matching to glass substrate. Lead oxide (PbO) has been broadly utilized in transparent dielectric layers for low-temperature firing process. According to environmental and human health problem, however, Pb-based glass ceramics are no longer suitable for transparent dielectric layers. Glass with the Bi-based system was examined as a potential replacement for Pb-based glass. Softening point and coefficient of thermal expansion of the glass were at 520^°C and 8.5 × 10^{? 6}/ ^°C, respectively. Optimum sintering temperature for the highest densification was at 560^°C, which indicated the highest flexural strength value derived from the lowest pore volume fraction. In addition, transmittance of specimen sintered at 560^°C was about 90% in a visible light region. These results suggested that Bi-based glass would be suitable as an alternative to Pb-based dielectric layer in PDPs.     

Test facility for investigation of heat transfer of promising coolants for the nuclear power industry

The results are presented of experimental investigations into liquid metal heat transfer performed by the joint research group consisting of specialist in heat transfer and hydrodynamics from NIU MPEI and JIHT RAS. The program of experiments has been prepared considering the concept of development of the nuclear power industry in Russia. This concept calls for, in addition to extensive application of water-cooled, water-moderated (VVER-type) power reactors and BN-type sodium cooled fast reactors, development of the new generation of BREST-type reactors, fusion power reactors, and thermonuclear neutron sources. The basic coolants for these nuclear power installations will be heavy liquid metals, such as lead and lithium-lead alloy. The team of specialists from NRU MPEI and JIHT RAS commissioned a new RK-3 mercury MHD-test facility. The major components of this test facility are a unique electrical magnet constructed at Budker Nuclear Physics Institute and a pressurized liquid metal circuit. The test facility is designed for investigating upward and downward liquid metal flows in channels of various cross-sections in a transverse magnetic field. A probe procedure will be used for experimental investigation into heat transfer and hydrodynamics as well as for measuring temperature, velocity, and flow parameter fluctuations. It is generally adopted that liquid metals are the best coolants for the Tokamak reactors. However, alternative coolants should be sought for. As an alternative to liquid metal coolants, molten salts, such as fluorides of lithium and beryllium (so-called FLiBes) or fluorides of alkali metals (so-called FLiNaK) doped with uranium fluoride, can be used. That is why the team of specialists from NRU MPEI and JIHT RAS, in parallel with development of a mercury MHD test facility, is designing a test facility for simulating molten salt heat transfer and hydrodynamics. Since development of this test facility requires numerical predictions and verification of numerical codes, all examined configurations of the MHD flow are also investigated numerically.     

Preparation and dielectric properties of La doped NBCCTO ceramics

Journal of Electroceramics - CaCu3Ti4O12 ceramics have great dielectric constant, excellent temperature stability and good frequency stability. However, due to high dielectric loss, its practical...