Mechanical aspects of electrical treeing in solid insulation

Mechanical effects dominate the new theory, with the build-up of strain, fatigue failures and fracture due to shock waves being involved     

干热沙漠机电设备信息数据库建立初探

本文系统介绍了依托国家科技基础条件平台面上《干热沙漠机电环境技术标准及检测方法研究》项目建立的干 热沙漠机电设备信息数据库的建库思路、数据构成、查询功能以及发展设想。可供在沙漠、干热沙漠环境中使用机电设备 的环境适应性研究、产品设计、制造、使用和维护作为参考。     

Cycling induced by electrical stimulation improves muscle activation and symmetry during pedaling in hemiparetic patients

A randomized controlled trial, involving 35 post-acute hemiparetic patients, demonstrated that a four-week treatment of cycling induced by functional electrical stimulation (FES-cycling) promotes motor recovery. Analyzing additional data acquired during that study, the present work investigated whether these improvements were associated to changes in muscle strength and motor coordination. Participants were randomized to receive FES-cycling or placebo FES-cycling. Clinical outcome measures were: the Motricity Index (MI), the gait speed, the electromyography activation of the rectus femoris and biceps femoris, and the mechanical work produced by each leg during voluntary pedaling. To provide a comparison with normal values, healthy adults also carried out the pedaling test. Patients were evaluated before, after training, and at follow-up visits. A significant treatment effect in favor of FES-treated patients was found in terms of MI scores and unbalance in mechanical works, while differences in gait speed were not significant (ANCOVA). Significant improvements in the activation of the paretic muscles were highlighted in the FES group, while no significant change was found in the placebo group (Friedman test). Our findings suggested that improvements in motor functions induced by FES-cycling training were associated with a more symmetrical involvement of the two legs and an improved motor coordination.     

The improvement of the electrical insulation of high voltage electrical machines

Comparative parameters are presented for the electrical insulation systems of high voltage electric machines. Composite insulation materials produced by different manufacturers are studied. The influence of the structure and composition of electrical insulation materials on the main operation parameters (electric strength, dielectric losses, the mechanical characteristics, and resistance to thermal cycling) of the insulation systems of electric machines is shown.     

基于图形化主接线图的电气连通性分析和研究

电气元件的连通性判别是图形化分析的基础,从主接线图中各电气元件之间的连接性及其属性之间的匹配性入手,综合分析了元件连通性的判别方法.通过把母线/开关和接地点/变压器描述的物理模型转化为节点/支路描述的网络模型,提出了分序网图分别进行电气连通性分析的新思路,这种方法对序分量及序网分析有重要指导意义.同时,结合图论方法和网络模型,通过比较已有的分析方法,改进了节点矩阵法的计算流程,使它在运算次数上大大减少,计算速度也明显提高.     

PCCP受载响应分析中三种预应力施加方法的比较研究

本文重点开展PCCP受载响应分析中三种预应力模拟施加方法的比较研究。将等效荷载法、等效降温法和缠丝模型这三种PCCP的预应力模拟施加方法应用于南水北调中线4m内径的埋置式PCCP,模拟施加其预应力场,并对其进行受载响应的数值模拟分析,还对该PCCP进行了原型压力试验,并将试验结果与计算结果进行综合对比分析。结果表明,计算结果与试验吻合较好,均能反映PCCP的受载响应规律;但等效荷载法不能考虑钢丝的刚度贡献和承载作用,给出的PCCP的起裂荷载和爆管荷载偏低;等效降温法不能反映钢丝的实际应力应变状态;缠丝模型不仅能考虑钢丝刚度贡献和承载作用,反映钢丝的实际应力应变状态,还能描述钢丝与其余部件的相互作用,具有更好的适用性。说明今后更适合以缠丝模型作为PCCP数值模拟分析的基础,进一步对PCCP的断丝响应以及结构安全性进行深入研究。     

Envisaging links between fundamental research in electrical insulation and electrical asset management

The trend of industrial and even institutional funding for research in the electrical energy world is going clearly in the direction of short-term, applied projects. On the one hand, this may be unavoidable with globalization and the fast increase in the energy needs of developing countries, while on the other hand it may affect in the long term the capability of developing base research in a sector that requires, more than many others, innovation and interdisciplinarity. Research financial institutions, such as the EC, EPRI, CRIEPI, etc., are going in the direction of promoting applied work. This can be seen with favor as long as it can correct distortions of the past, when fundamental research had been seen sometimes as a permanent exercise of speculations without oversight for an applied end; but the risk is to lose the fundamentals of knowledge which is the only way to promote real and stable innovation.     

Partnerships for electrical safety

The authors present a case study of the successful development of an educational partnership between industrial collaborators and university researchers to promote electrical safety. For industrial and academic organisations considering a similar approach, we identify a development methodology to align people and resources to implement electrical safety education. Educational partnerships offer a bridge to speed the movement of technologies and concepts between different communities like those represented by a plant and a local hospital. This case study reviews the development of a direct R&D technology transfer educational project targeting electrical safety. Motives to partner were: to become more creative; to identify the best process and best practice; to facilitate the availability of the best care/treatment for those injured on the job through rapid technology transfer; and to specifically move electrical safety principles to a higher level of awareness for individuals, their workplaces, and their communities     

Response to electrical stimuli

Electrical safety is important in industrial work. This article provides considerable detail on how current can pass through different parts of the body and each parameter that can impede or limit the flow of current. Electric currents flowing through a human body can have varying effects, ranging from little or no perceptible effect, to shocking sensation, to possibility of electrocution, depending primarily on the magnitude and the duration of the current flow. The effect of current flow is a function of the applied voltage level, the duration of the exposure, and the resistances or impedances of the body and the other available current paths. A key consideration with energized objects is that, in order for the electric current to flow through the body, one body part must make contact with an energized object or conductor and another body part must make contact with the earth or an object or conductor that provides a path for the current to return to its source. This article supplies considerable detail on how currents can pass though different parts of the body and each parameter that can impede or limit that flow of current. The information presented indicates that the most likely scenarios for a dangerous condition would be that when a person comes in contact with an energized metallic object energized at 120 V and the person is barefoot and the ground is moist or wet as are the persons' hands or feet. Nearly, any other condition such as dry ground, rubber, or leather soled shoes; dry hands and so on have a lower probability of creating current flows that would be considered damaging or disruptive.     

Polyethylene under electrical stress

Fifty years ago, the concept of an intrinsic electric strength for insulating solids was fashionable. It was supported by the sophisticated theoretical models of von Hippel, Frohlich and others for the interaction of electrons with crystal lattices in an electric field. The models came to be applied, rather implausibly perhaps, to polymers such as semi-crystalline polyethylene (PE). In that climate, the work of van Roggen on the high-field conductivity of single lamellar crystals of PE was notable. Since then, the picture of the insulating properties of PE has had to be painted with an increasingly complex palette in which the electrical elements have had to be supplemented by mechanical, chemical, and optical ones. The present review of the conducting properties of the polymer considers these other features, but concludes that the fundamental characteristics of the lamellar PE crystal are still the determining factors.     

基于电能管理平台的电力营销变革与挑战

简介了电能管理平台的设计理念与体系架构,分析了其带来的营销变革与成效,指出了电力营销所面临的挑战.     

Thermodynamic model for electrical tree propagation kinetics in combined electrical and mechanical stresses

In this paper we develop a kinetic model for the growth of electrical tree structures in solid polymeric insulation that allows for combined electrical and mechanical stresses. We present an energy balance analysis during the tree growth process and show the total tree extension driving force is not a material constant due to the existence of a damage process zone around the tree tip and the dissipated heat and the trapped energy remaining in the damage process zone. We derive both the tree growth rate equation and life formula of tree propagation to breakdown, based on the specific tree growth mechanism and the fractal nature of tree structures. We perform electrical tree growth tests in epoxy resin samples with and without mechanical residual stresses, and present results which show that the proposed model can give predicted tree propagation times to failure in good agreement with the experimental data of the tree growth subjected to a combined electrical and mechanical stress     

USB 机械特性

提供了电缆、连接器及连接不同USB设备的电缆部件机械和电气方面的规范,包括尺寸、材料、电气及可靠性等方面的要求。同时说明了外部USB设备互连的最低要求,只要符合这些最低要求,也可以使用别的材料。USB电缆由2条电导线和2条信号线组成。USB可以在2种数据速率下工作;全速为12Mbit/s,要求使用带2条电导线和双绞信号线的具有屏蔽层的电缆;低速为1．5Mbit/s,降低了对电缆的要求,不需要使用蔽层和双绞信号线,连接器设计为热插拨,在USB插头的图标上提供了标识以便于正确定向。     

Digital excitation enhances performance and improves diagnostics

The authors describe how new AC generator digital excitation systems are being introduced that provide many advantages over existing systems. Chief among these improvements are advances in performance and diagnostics. In addition to the classic excitation functions, new features provide additional protection. One innovation that has been added to some of the previous limiter functions modifies the pickup point based on external conditions. Additionally, entirely new limiter functions and monitoring capabilities have been added. These enhancements allow the generator to operate closer to its design limit and help keep the unit online during adverse conditions, increasing reliability and reducing down time     

Local heating of electrical pathways of power electrical equipment under emergency conditions and overcurrents

Based on the positions of classical and quantum electrodynamics, this paper shows that when a direct, alternating or pulsed current of high density (100 A/mm² or more) flows in emergency situations through metal electrical pathways of power electrical equipment, such electrical pathways in areas of their narrow “hot” longitudinal sections may experience intense local heating. It was found that Joule heating temperatures, which occur in this situation on the “hot” longitudinal sections of the electrical pathways due to periodic localization of electrons on them, are higher by up to 3.5 times than the corresponding temperatures on their adjacent “cold” sections and may lead to electrothermal destruction of these electrical pathways. Experiments confirmed the main results of calculations.     

Modern electrical insulating impregnating compounds

A comparative analysis and trends in the development of electrical insulating impregnating compounds manufactured in Russia and abroad are given. A tendency toward increasing the output of more heat-resistant compounds is revealed.     

Engineering your electrical engineering education

Electrical and computer engineering (ECE) courses are usually structured in such a way to provide the student with the basics to solve problems in the field and then challenge the student with increasingly more difficult problems to effectively stretch those basic problem-solving approaches into more advanced techniques. While most of this problem-solving focus is placed on the technical arena, this is only one part of the educational experience for an ECE student. There are many nontechnical facets to one problem-solving repertoire that require development to become a successful practicing engineer in industry or academia after graduation. This article serves to provide some of these facets in a career-direction informational guide to junior- and senior-level undergraduate students and graduate students early in their ECE career. It also serves as a guide to outline some useful strategies not found in an engineering text to maximize one's educational experience at the undergraduate and graduate levels as well as the transition between them.     

隔爆型电气设备的检查

简要介绍了隔爆型电气设备的基本检查要求、检查等级、类型、项目要求。     

The PCIC and electrical safety

The Petroleum and Chemical Industry Committee (PCIC) has evolved into a leadership role in the IAS and the IEEE for industrial electrical safety measures. PCIC has accelerated progress in standards, regulations, product designs, work practices, and perhaps, more importantly, how to eliminate electrical injuries. In developing this article, the authors conducted surveys, reviewed historical documents, and interviewed long-time PCIC members in an attempt to document the evolution and impact, the organization has had on electrical safety. One of the goal of this article is to provide comprehensive bibliography and appendices that may be useful in developing further improvements and contributions to electrical safety.     

Electric fields and electrical insulation

The adoption of a field-theoretical approach to problems arising in the framework of electrical insulation is discussed with reference to six main topics, which have been addressed over the last 30 years. These include uniform field electrodes, Green's differential equation, electrode surface roughness, induced charge, electrostatic probes, and partial discharge transients, together with several follow-on aspects. Each topic is introduced and thereafter the progress achieved through the use of a field-theoretical approach is reviewed. Because the topics cover a wide spectrum of conditions, it is amply demonstrated that such an approach can lead to significant progress in many areas of electrical insulation.