Track it or crack it

The article demonstrates that the first-order thermal model is superior in protecting motors with cyclic loads. The first-order thermal model faithfully tracks cyclic load without a premature process interruption due to motor trip, even though the maximum current exceeds the service factor (SF) rating, as long as the motor per unit (p.u.) temperature stays below the design limit of SF. As the period of the cyclic current approaches the motor RTC and the maximum current exceeds the SF rating, the motor temperature will approach the motor design limit p.u. temperature and will result in a motor trip and process interruption. It is imperative when applying a motor to a cyclic-load application that the thermal and electrical characteristics of the motor be scrutinized and compared with the mechanical process characteristics to ensure compatibility.     

基于单相背靠背H桥级联结构的仿真研究

级联型多电平变换器输出电压谐波含量小,易于实现模块化,适用于高压大功率场合。提出单相背靠背H桥级联结构,通过直流侧电压级联整流控制和载波移相PWM逆变控制,实现了高压大功率输出目的。通过Matlab/Simulink仿真,验证了该拓扑结构及控制方式的可靠性和正确性。     

Back to EDA

It is almost 12 years since Joe Costello left his job as president and CEO of Cadence Design Systems. In roughly a decade at the company?s helm, he helped turn it into the largest supplier of semiconductor design tools and one of the world?s most profitable commercial software vendors.     

构建特高压电网诱人的蛋糕属于谁

全国联网的格局初步形成,国家电网公司又提出构建特高压电网的设想。这是2月28日,中国电力企业联合会2005年经济形势与企业改革预测会上透露的消息。这将为输变电设备制造业提供了新的发展机遇,也将拉动输变电设备制造产业技术的提升。     

抽水蓄能电动发电机组背靠背起动过程仿真研究

本文对抽水蓄能电动发电机组背靠背起动(BTB)进行了研究,从工程实际出发,考虑水轮机输入转矩、水泵阻转矩及线路、变压器等参数的影响,进行起动过程的计算机仿真分析.仿真计算与响洪甸抽水蓄能机组的测试结果吻合较好,可用于抽水蓄能电站的计算.     

背靠背换流器控制策略的比较与分析

结合直流工程的实际设计和运行经验,对背靠背换流站工程中逆变器的3种控制策略进行了分析研究。背靠背换流站工程中逆变器的控制策略有3种:第1种为定阀侧空载直流电压控制,即阀侧空载直流电压恒定,通过调换流变压器分接开关,由熄弧角控制直流电压;第2种为定熄弧角控制,即熄弧角恒定,通过调阀侧空载直流电压控制直流电压;第3种为熄弧角带宽控制,即使熄弧角在17°～19.5°范围内变化,直流电压恒定,当熄弧角超出该范围时,通过调节换流变压器分接开关改变阀侧空载直流电压,使熄弧角回到17°～19.5°范围内。从换流变压器阀侧空载直流电压、换流变压器参数、换流站无功功率损耗以及系统运行参数4个方面进行比较,指出定阀侧空载直流电压控制在减少换流变压器分接开关档位、降低分接开关动作次数和提升紧急功率方面具有一定的优势,这一结果对选择背靠背直流系统控制策略具有借鉴意义。     

回眸2001 Look Back

财政收支超额完成预算 根据初步汇总,2001年全国财政预算执行总体情况较好,2001年财政收入可完成16371亿元,支出完成18844亿元,财政收支均超额完成预算。 财政部部长项怀诚日前向在京全国人大代表汇报了2001年财政预算执行情况。项怀诚说,2001年全国财政预算执行情况呈现出四个特点:     

Three-Phase Back PWM-PFC Rectifier

1 IntroductionTo mitigate the harmonic pollution in power systemscaused by power rectifiers,the Boost-mode (or voltage-source-type:VST) PWM-PFC rectifier has been applied to many appli-cations.Although the buck (or Current-Source-Type:CST)PWMrectifier can…     

抽水蓄能电站背靠背启动过程的数字仿真

详细推导出了抽水蓄能电站背靠背启动过程的数字模型,利用解耦的方法使得发电机与电动机的状态方程可以分别进行数值计算。模型中考虑了发电机和电动机两机的容量比、励磁电流比、初始相位角和水轮机导叶开度及导叶开启速度对背靠前启动的影响,编制了其通用计算机仿真软件,给出了数字仿真的计算结果。     

背靠背功率模块中IGBT的关断过电压抑制

IGBT的关断过电压一直是变流器设计中备受关注的重要课题.本文对IGBT关断过电压的产生原因及吸收电路抑制方法进行了分析,在背靠背变流器系统开发中采用了一些有效抑制IGBT关断过电压的措施,并通过双脉冲试验进行了测试验证.结果表明,本系统中通过加吸收电容有效抑制了IGBT的关断过电压,能够满足应用于该背靠背变流器安全运行的需求.     

Back to basics in business

In his foreword to Alison Branagan?s new book 'Making Sense of Business', Sir James Dyson says that as a designer and inventor he had "no choice" but to learn how to cope and flourish in the world of commerce. He modifies Shakespeare?s famous line to rather grandly explain that while "some are born business people, others have business thrust upon them". We can all agree that, despite the assumption that "designers are hopeless at business" Dyson has been a roaring success.     

Back Corona and Relaxation Time

Where the resistivity of a precipitated layer of dust exceeds a value in the neighborhood of 108 ?m, the phenomenon of back corona generally occurs. The fact that this is not always the case, however, shows that the phenomenon is not perfectly understood. In 1965, the author introduced to the theory the additional factor of the dielectric constant. This had the effect of making relaxation time the fundamental parameter of back corona, rather than resistivity alone. As a result, it is shown that back corona probably depends on conditions in the gas as well as in the dust.     

Flatten it out

Measuring the flatness of a cold-rolled steel strip or aluminum foil is a vital aspect of production quality control. Cold lamination control based on the results of this measurement crucially affects production efficiency, but further processes can modify flatness, which can be lost when the strip becomes cold. We describe a low-cost flatness measurement system to monitor this property at several production line points. The system is composed of a capacitive sensor array, some microcontrollers, and a PC for computing and visualization. Measurements on a production line are provided and analyzed.     

Shake it up

Since its launch in 2001, the DTI-funded Process Industries Centre for Manufacturing Excellence (PICME) has served manufacturing clients from all walks of the process sector - chemicals, polymers, pharmaceuticals, fine chemicals and agrochemicals. All UK-based process manufacturers qualify and can apply to benefit from the redcar-based industry forum's diagnostic and performance measuring/benchmarking activities that aim to save manufacturers money in areas such as stock management, machine utilisation, lead-times, process variability and supply chain efficiencies. According to an expert, waste minimisation or elimination should be the driving philosophy behind most manufacturing and operations improvement; not only in terms of wasted end-product, but also in terms of other wasted inputs to the operation. PICME uses tried and tested systems to analyse for all types of waste including the traditional seven as well as a few other categories in which experience suggest needs special focus in this sector including the waste of good ideas which are essential to innovation. This paper discusses how PICME helped process industries strive for process excellence.     

放下

在一个著名的道观里，住着一位非常有道行的静修道长。他每天都要在傍晚6时去喂他的狗。他的狗的名字很奇怪，叫做“放下”。每到日落时分，静修道长就为“放下”送饭了，嘴里还一边呼唤着：“放下！放下！”。     

灵宝背靠背直流工程换流站和系统调试总结

灵宝背靠背直流工程作为我国第一个联网背靠背直流输电工程,也是直流设备国产化的试验示范工程,工程的调试完全由国内技术力量完成,工程的建设和顺利投入运行,对直流工程国产化的发展具有指导意义。介绍了换流站和系统调试情况,包括换流站系统调试情况及结论、系统调试情况及结论、系统调试技术创新点、背靠背直流工程站系统和系统调试的经验总结和系统调试方案的优化。     

Student support ubiquitous when you know where to look

This article sheds some light on where IEEE Student Members look for support opportunities. Some of the major types of awards available are: regional student awards, graduate student fellowship, student paper contest, undergraduate student competitions, and travel grants. In addition to these awards SAC (Student Activities Committee) has initiated two new awards: IEEE Darrel Chong Student Activity Award and the IEEE XTreme 24-Hour Programming Challenges. Thus, this type of awards provides knowledge sharing among students