High field conduction and prebreakdown phenomena in dielectric liquids

The present paper is mainly devoted to phenomena occurring in point-plane electrode geometry, where breakdown is the result of the initiation and propagation of prebreakdown phenomena called "streamers". In this configuration, an investigative study of the streamer initiation processes, requiring very high electric field strengths (/spl sim/ MV/cm), and of propagation (requiring low electric field, /spl sim/ kV/cm) can easily be carried out for negative streamer development as well as for the positive case. From analysis of experimental results in pure liquids the physical processes connected with streamer initiation and propagation, particularly the electronic ones, are presented and discussed. Estimations of the main parameters of slower subsonic streamers and of the faster filamentary ones (such as field strength at the streamer tip, field inside the channel, charge density, etc.) have been obtained from qualitative considerations and compared to experimental data.     

微秒级高功率断路开关

介绍了几种用于脉冲功率电感储能技术的微秒级传导时间断路开关的原理和应用,并就它们的各处在的特点进行了评述。     

High voltage studies of dielectric materials for HTS power equipment

The discovery of high temperature superconductors (HTS) has triggered renewed interest in the study of dielectric materials at cryogenic temperatures. While considerable work was done in the 1970s and 1980s on dielectrics immersed in liquid helium for low temperature superconducting applications, there remains a need for dielectric research at liquid nitrogen temperature for HTS applications, requiring experimental data oriented toward practical situations. We report on AC breakdown (puncture and/or flashover), and impulse breakdown of solid materials in either vacuum or in liquid nitrogen. Solid materials which we examined, include fiberglass reinforced plastics, epoxies with and without filler, and polymeric tape. Combinations of some of these materials have also been studied at low temperatures. Additionally we have measured permittivity and dissipation factor for materials for which these parameters are not available at 77 K. Finally, we also discuss specific applications for HTS cables including breakdown and aging studies on model cables, with lapped tape electrical insulation, immersed in liquid nitrogen.     

DC-DC开关电源模块并联供电系统

为设计一种DC-DC开关电源并联供电系统,采用DC-DC主从模式实现两个开关电源的并联供电,并按比例自动分配电流.设计采用STC12C5A60S2单片机完成ND采集主从模块及其总电流,再通过D/A控制从模块的电流,以实现主从模块按比例输出电流供给负载.DC-DC主从模块是由开关电源控制芯片SG3525为核心完成PWM产生,BUCK拓扑结构和反馈电路组成.这个系统实现可手动或自动调节电源比例的并联稳压供电,最大输出可达到4A-8V直流,效率高达83％.介绍了系统结构、DC-DC主从模块、测量电路、系统供电以及主控机原理,详细介绍系统结构、DC-DC主模块和主控电路.     

Power factor correction using magnetic energy recovery current switches

In this paper, we propose a Magnetic Energy Recovery Switch (MERS). The switch consists of four MOSFET elements and one capacitor. A power factor improvement is automatically possible regardless of the impedance and power frequency of the load by synchronized switching of MERS with a power supply. MERS itself generates voltage and compensates for the inductance voltage unlike a conventional series capacitor, so that another DC power supply is not needed. An experiment was carried out to demonstrate the automatic correction of the power factor. We can also expect energy saving of electromachines such as an electric motor by the power factor correction with MERS. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 160(3): 56–62, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20321     

开关电源保护电路的研究

开关电源保护电路关系到电源的安全性和可靠性。本文较系统地研究了开关电源的防浪涌电流的软启动,防过压、欠压、过热、过流、短路、缺相等保护电路。并研究各种保护电路的综合应用及其注意事项。为开关电源的设计和保障开关电源安全可靠工作提供了经验。     

Nanosecond, electrical triggering of water switches

Spark gaps, which use water as a switching medium, allow fast closing and high repetition rate operation for high power and high voltage switching. They are usually operated in the pulse-charging mode and have a large jitter. To reduce the jitter, a trigger electrode with positive polarity is used to initiate breakdown between a negative high voltage electrode and a ground electrode. The trigger electrode consists of a tungsten wire with a diameter of 50 μm, enclosed in glass tubing. At the triple point where the three dielectrics (glass, water and metal) meet, the electric field is greatly enhanced. From the triple point, a trigger voltage of +16 kV at a pulse duration of 100 ns produces two streamer branches traveling towards the high voltage and ground electrodes. These two streamer branches bridge the main gap and serve as preionized channels for the initiation of the breakdown between the main electrodes. Arc transition develops along the two channels and completes the switching. It allows for the gap to be fired at various voltages independent of the gap?s self-breakdown voltage. The delay between application of the trigger pulse and the electrical breakdown is on the order of hundred nanoseconds. The jitter in breakdown is on the order of ten nanoseconds. It is less by more than an order of magnitude than that obtained with pulse charging.     

Impact of automatic switches on power distribution system reliability

In this paper quantitative impact of automatic switches on the reliability of power distribution systems is studied. Based on the characteristics of the studied system's topology, the reliability model is developed for the implementation of Monte Carlo simulation. Reliability indices on each load have been computed to obtain an overall reliability assessment of the system, and the sensitivity of the reliability indices to the location of automatic switches is also studied. Simulation results are used to illustrate the validity of the approach and are compared with the historical reliability records.     

基于谐振电抗器和磁能恢复开关的单相AC-DC变换器

将谐振电抗器和磁能恢复开关引入到单相AC-DC变换器中,设计了一种新颖的混合单相AC-DC变换器.在理论分析谐振电抗器和磁能恢复开关单独在单相功率因数校正器(PFC)应用中的优点和不足的基础上,提出了一种结合两者长处的功率因数校正方法,能够获得更高输入功率因数(PF)和更高输出直流电压.并利用仿真软件ORCAD 10.5建立了完整的单相AC-DC变换器-逆变器仿真电路,对上述3种情况进行了FFT和参数扫描等仿真分析.结果说明了所提出的方案是可行的和低成本的,能够支持较大的输出功率,可以作为变频家用电器等的前级单相AC-DC变换器.     

Transfer switches applied in systems with power circuit breakers

This paper is an overview of the industry standards for short-time current ratings of low-voltage transfer switches and power circuit breakers. It defines and compares the standard withstand and closing ratings of transfer switches and the short-time current rating of power circuit breakers. It reviews a typical distribution system using transfer switches and power circuit breakers to demonstrate the need to consider switches with extended short-time current ratings for such applications     

中压配电网的线路分段开关优化规划

介绍了确定中压配电网分段开关位置的实用计算方法。分段开关是为了提高供电可靠性而装设,所设开关应尽可能保护它所在位置的电源侧用户免受开关负荷侧故障的影响。通过采用以最小停电费用为目标函数,以供电可靠性为约束条件的枚举法来求解。此方法可使分段开关安装位置的选择更合理。     

开关电源的新技术与发展前景

开关电源处于电源技术的核心地位,它是在新型功率器件、新型电路拓扑不断出现的条件以及实际需要的推动下发展起来的,开关电源技术近十年来得到了突飞猛进的发展。     

High frequency properties of shielded power cable. Part 2: sources of error in measuring shield dielectric properties

This paper provides a theoretical context for the types of errors that are likely to occur during the measurement of high frequency cable shield properties. The paper considers a RC dielectric system as it relates to measuring the dielectric properties of cable shield materials.     

The choice of power electron switches for converters in electroenergetics

A comparison of different power electron switches for power electron converters is presented. The estimation method of steady and dynamic power loss in the switches is also described.     

Skin effect and dielectric loss models of power cables

In power electronics applications, power cables spread paths of conducted disturbances throughout the system. This paper proposes a high frequency modeling method for power cables that takes into account phenomena which appear when the switching frequency of the static converter increases, such as skin effects, proximity effects and dielectric losses. The proposed power cable models are obtained by the seriesassociation of n identical RLCG basic cells. The skin and proximity effects are represented as the impedance of an R-L ladder and the dielectric losses as the admittance of an R-C ladder. The proposed method was successfully applied to a threewire unshielded cable and extended to a four-wire shielded cable.     

Partial discharge. XXII. High frequency attenuation in shieldedsolid dielectric power cable and implications thereof for PD location

PD testing and location is an essential part of factory testing of shielded solid dielectric power cable. The accuracy with which a PD source can be located is limited by high frequency attenuation of PD pulses as they propagate through the cable     

High speed power

This paper presents the need for compatibility between European rail networks. This leads to the adoption of dual 25 kV as the power of choice for operators. Dual 25 kV literally doubles the power available to rail networks, helping rail operators to meet some of the demands they are facing. Not surprisingly, this fact, along with the EU directive on 'interoperability of the trans-European high speed rail system', which aims to ease the circulation of high-speed trains through the various train networks of the European Union, will lead it to become the future standard across Europe