Dalziel revisited

More than 37 years have passed since Charles F. Dalziel published his last of four seminal papers on ventricular fibrillation (v-f ). His empirical formula for the current necessary to produce v-f in man has been recognized by scientists and engineers as forming the basis for an analytical understanding of this major cause of death from electrical shock. In this article, the additional electrical parameters of energy, voltage, and resistance are related analytically to Dalziel's work. The fundamental equations for v-f have been used in this article to derive two additional relationships for the electrical parameters of interest in the shock process that can produce v-f in humans.It has been shown that the source energy necessary to produce v-f is a function only of the subject weight and the critical path resistance of the current path from made contact through the human body.     

Ground-differential protection revisited

The use of ground differential for the protection of impedance-grounded transformers and generators has been increasing. Because of its inherent selectivity and speed of operation, ground differential provides excellent protection against ground faults within the grounded winding of the equipment. However, several factors should be considered when applying ground-differential protection to a power system. These factors include the type and ratings of the equipment being protected, whether it is a new installation or a retrofit project, and the type of relay being used. Both static or electromechanical relays may be applied for ground-differential-protection schemes on impedance-grounded transformers and generators. Each application should be evaluated regarding current transformer burden and saturation to ensure proper operation. The protection engineer should carefully consider the application factors to ensure that the desired level of protection is provided     

RCD snubber revisited

The use of the polarized RCD turn-off snubber configuration across switching devices is popular because of its simplicity and use of only passive components. This configuration is limited by the fact that all capacitor-stored energy is dissipated in the discharge resistor. In this paper, it is shown that with the addition of a ferrite transformer to the standard RCD arrangement, in excess of 70% of the energy stored on the snubber capacitor may be passively recovered into the DC supply. Performance of this passive recovery snubber is supported by theoretical, simulated and practical results     

Third zone revisited

Zone 3 of a step-distance protection scheme has been identified as one of the contributing causes of cascading failures in power systems. The National Electric Reliability Council (NERC) has issued rules, and the IEEE Power System Relaying Committee (PSRC) has discussed recommendations to reduce the undesirable operation of this component of the protection chain. It is the purpose of this paper to reexamine the application of zone 3, to describe situations where it can be properly utilized, where it can be removed without reducing the reliability of the system protection and, if used, how it can be modified or set. A table is presented for a variety of station designs and protection schemes including two common local backup relay systems and the associated application of a remote third zone. Finally, the concept of critical locations is introduced which can assist the relay engineer in determining if potential zone 3 undesirable operations are a serious threat to the system and help determine if the expense and difficulty of removing zone 3 or modifying the relay or its associated station is justified.     

二次回路中寄生回路的消除

阐述二次回路在电力系统生产过程中的作用，并针对在安装调试中遇到的寄生回路造成误发信号问题，提出解决寄生回路的措施，确保电网安全运行。     

断路器新型限流电路的探讨

介绍在断路器中使用的新型限流电路 ,其满足了电力系统中限流技术的要求 ,大大提高了断路器的可靠性和分断能力 ,是很有前途的限流方案     

断路器新型限流电路的探讨

介绍在断路器中使用的新型限流电路,其满足了电力系统中限流技术的要求,大大提高了断路器的可靠性和分断能力,是很有前途的限流方案.     

IPM短路测试与短路能力分析

本文说明了IPM产品短路测试的基本方法,针对目前市场上常用的IPM产品进行短路测试并取得短路电流波形,分析了影响IPM产品短路能力的几个因素,结果发现,温度越高IPM产品的短路能力越差;驱动电源电压越大,短路耐量越差;IGBT的MOS沟道宽度越宽,IPM的短路能力越差。     

搭建断路器跳闸回路的全回路监视

鉴于目前电力设备保护回路中存在的缺陷,提出了一种搭建断路器跳闸回路的全回路监视的设想,以期进一步提高继电保护运行的可靠性.     

断路器操作回路的智能化监测系统设计

为了监测断路器操作回路中跳/合闸回路、压板和保护出口接点的状态,并对其薄弱环节故障进行预警以避免断路器误动或拒动,设计了断路器操作回路的智能化监测系统。该系统改进了现有跳/合闸回路,并给出了系统中元件的选型与参数整定依据,能够实现跳/合闸回路的全工况监视和保护。为了实时监测断路器操作回路压板和保护出口接点的状态,实现压板误操作和保护出口接点故障报警,该系统采取了配合使用电感式接近开关和霍尔电压传感器的方法,并给出了传感器的具体安装位置。该系统采用单片机处理并上传传感器采集的现场信息,利用LabVIEW编写后台软件界面,能够实现实时状态显示、人机交互、历史数据存储和故障报警等功能。     

The vector potential revisited

The vector potential in electrodynamics is investigated through the decomposition of its form to the following two parts: 1) the so-called transverse part represented by a divergenceless vector; and 2) the longitudinal part represented by an irrotational vector. The decomposition can be done by the Helmholtz theorem in the vector analysis because the conditions which should be required when the Helmholtz theorem is used are satisfied for the almost vector potentials of physically interesting problems. As an example of such interesting problems, the Aharonov-Bohm effect is chosen here. As for the Aharonov-Bohm effect, the vector potential given in the original paper of Aharonov and Bohm has the singularities along the z-axis. It is shown that even for such a singular potential the Helmholtz theorem is held provided that the concept of the distribution is introduced in it. Generally, the transverse part of the vector potential obtained through such a decomposition is determined uniquely by the magnetic field and does not alter by a gauge transformation. On the other hand, the longitudinal part depends on the choice of special gauge. It is shown that the Aharonov-Bohm effect is due to the contribution of the transverse part of the vector potential and therefore should not be influenced by any gauge transformations.     

Active RC impedances revisited

The aim of this paper is to review the synthesis, analysis and design of active RC impedances. First of all, major gaps in this classical research topic are identified. Second, a synthesis procedure is outlined to generate op-amp-based circuits which can simulate several classes of impedances of practical interest. From the resulting classification, all circuits are analysed from a perspective wider than those normally used in previous works, yielding some new interesting design conditions. A method is suggested to convert ladder passive prototypes containing either grounded inductors or FDNRs into MOSFET-C equivalent circuits using some of the new structures obtained. Finally, the use of current feedback amplifiers instead of op amps is considered. Experimental results corroborating all our theoretical predictions are incorporated in the work. © 1997 John Wiley & Sons, Ltd.     

Coupled transmission lines revisited

The author presents a very satisfying and disarmingly simple way of introducing students to the parallel line coupler, which derives its S matrix directly from a knowledge of its eigenvectors and eigenvalues. For a pair of symmetrical coupled lines, the eigenvectors can be found by inspection, and the eigenvalues determined easily by means of flow graphs. The elements of the S matrix are then known, being linear combinations of the eigenvalues     

Complementary root locus revisited

In this paper, a new finding related to the well-known root locus method that is covered in the introductory control systems books is presented, It is shown that some of the complementary root locus rules and properties are not valid for systems with loop transfer functions that are not strictly proper. New definitions for root locus branches have been presented which divide them into branches passing through infinity and branches ending at or starting from infinity. New formulations for calculating the number of branches passing through the infinity point of intersection of the asymptotes on the real axis, and angles of these asymptotes with the real axis have been introduced. It has been shown this type of system with the order of n will have at least one and at most n branches which will pass through infinity. The realization and stability of these systems have been investigated, and their gain plots have been presented. The new finding can be used by educators to complement their lecture materials of the root locus method. By using problems similar to examples presented in the paper, analytical understanding of the students in a classical control systems course can be tested     

断路器操动机构与继电保护控制回路的协调与配合

在分析断路器操动机构压力闭锁的设置和使用方式的基础上,针对存在的问题,提出了线路间隔断路器操动压力低闭锁重合闸回路的解决方案;明确了断路器操动机构压力和SF6气体压力低闭锁功能的实现方式.通过对操作箱和机构箱内防跳功能的分析比较,给出了防跳功能的推荐方案;还对线路保护带断路器传动试验中的时序配合问题进行了分析.     

Service-life evaluations of low-voltage power circuit breakers andmolded-case circuit breakers

This paper summarizes the methods that are typically used in industry to evaluate the service life of low-voltage power circuit breakers and molded-case circuit breakers. It reviews the electrical ratings and endurance requirements set forth in manufacturing standards, the ways that these endurance requirements can be used to develop expectations of circuit breaker life, the methods of maintenance inspections, and the interpretations of these inspections     

断路器操动机构与继电保护控制回路的协调与配合

在分析断路器操动机构压力闭锁的设置和使用方式的基础上,针对存在的问题,提出了线路间隔断路器操动压力低闭锁重合闸回路的解决方案;明确了断路器操动机构压力和SF6气体压力低闭锁功能的实现方式。通过对操作箱和机构箱内防跳功能的分析比较,给出了防跳功能的推荐方案;还对线路保护带断路器传动试验中的时序配合问题进行了分析。     

一种新颖的过温保护电路

介绍了一种用于开关电源内部的过温保护电路，采用0.8μm的BICMOS 工艺并用HSPICE信真结果表明，该电路对因工艺参数，电源电压变化而引起的过温保护阈值漂移有很强的抑制能力，通过反馈方法带来20℃迟滞消除热振荡带来的危害。