110kV及以上并联及滤波电容器装置桥差保护

介绍了电容器内部故障保护方式大多采用桥式差流保护公式的推导过程及求解方法,并通过计算实例分别求出元件故障击穿被隔离后,同一串联段完好元件的过电压倍数、故障电容器的过电压倍数及不平衡电流值,为产品运行提供参照。最后给出了求解的计算程序。     

直流单极运行时谐波对并联电容器的影响

电力系统中实际运行情况表明,谐波问题是并联电容器安全运行的主要威胁。特别在直流单极运行时,交流变压器因为直流偏磁而使各次谐波电流剧增,这些谐波电流进入运行中的并联电容器并被放大,会导致电容器谐波过载,损坏电容器。某500 kV变电站的35 kV无功补偿电容器组就因为三-广直流单极运行而曾发生多次电容器爆炸事故。文中阐述了直流单极运行时各次谐波电流是如何产生的,然后分析了谐波被放大的原理、谐波对电容器组的危害,并详细分析了该500 kV变电站的无功补偿电容器组在三-广直流单极运行时发生爆炸的原因,最后提出几点抑制谐波电流放大的措施。     

基于迭代学习控制的并联型有源电力滤波器研究

在并联型有源电力滤波器控制方法中,传统PI控制的滤波效果不够理想。针对稳定性负载电网谐波具有重复周期的特点,提出迭代学习控制算法,并嵌入反馈环节,以提高迭代学习收敛速度。该方法计算量小,稳态误差小,易于实现,仿真分析和实验结果表明了该控制方法的有效性。     

Modified static VAR compensator using a large value AC capacitor

To overcome some of the limitations of conventional static VAR compensators (SVCs) which are widely used for reactive power compensation, a modified SVC (MSVC) has been proposed. MSVC uses a large value AC capacitor. The large value AC capacitor is realized using unipolar DC capacitors and power semiconductor devices. Unlike the conventional SVCs, the proposed MSVC does not require additional shunt passive filters for harmonic filtering. MSVC has been verified through analysis and simulation. A practical implementation of MSVC has been realized and tested.     

10kV电力电容器烧坏原因分析及处理

运行中并联电容器装置事故时有发生,由于电容器事故不作为考核事故统计,忽略了对电容器装置事故的分析。而设计人员在设计中也从来没有认真对变电站的谐波进行过详细的计算,谐波超标或放大时便造成了电容器的损坏。     

Multilevel converters control for renewable energy integration to the power grid

The paper deals with the multilevel converters control strategy for renewable energy resources integration in distribution grids. The proposed control scheme ensures the injection of the generated power in the distribution grid with fast dynamic response, while providing an additional active power filtering capability providing the required harmonic and reactive currents to the considered non-linear loads. The proposed control scheme is applicable to a general multilevel converter and to any types of the renewable energy resources. The control scheme is validated by means of simulations with a three-level diode-clamped converter which interfaces a wind power generation system to a distribution grid supplying non-linear loads. From extensive simulation results, high performance of this control strategy in renewable energy application is demonstrated with reduced total harmonic distortion, increased power factor and compensated load’s reactive powers.     

ROOM FOR THE WAAL IN NIJMEGEN,THE NETHERLANDS

The Room for the River project around Nijmegen, The Netherlands is one of the most integrated and most complex cases in the national flood safety strategy. Along the Waal River in Nijmegen, a bypass channel and a new urban river park were created that not only reduce flood risks, but also offer recreational, ecological and aesthetic values.     

一种三相并联有源滤波器的仿真研究

分析了并联型有源电力滤波器的基本工作原理,采用基于瞬时无功功率理论的改进型ip—iq电流检测算法,建立了基于电流滞环控制策略的仿真模型,并进行了仿真研究,结果证实了所提方案的正确性和可行性。     

Bypass line assisted start-up of a loop heat pipe with a flat evaporator

Loop heat pipes often experience start-up problems especially under low thermal loads. A bypass line was installed between the evaporator and the liquid reservoir to alleviate the difficulties associated with start-up of a loop heat pipe with flat evaporator. The evaporator and condenser had dimensions of 40 mm (W) by 50 mm (L). The wall and tube materials were stainless steel and the working fluid was methanol. Axial grooves were provided in the flat evaporator to serve as vapor passages. The inner diameters of liquid and vapor transport lines were 2 mm and 4 mm, respectively, and the length of the two lines was 0.5 m each. The thermal load range was up to 130 W for horizontal alignment with the condenser temperature of 10°C. The experimental results showed that the minimum thermal load for start-up was lowered by 37% when the bypass line was employed. This paper was recommended for publication in revised form by Associate Editor Dae Hee Lee Joon Hong Boo received his B.S. degree in Mechanical Engineering from Seoul National University in 1978. He then received his M.S.M.E. and Ph.D. degrees from Georgia Institute of Technology in 1984 and 1989, respectively. Dr. Boo is currently a Professor in the School of Aerospace and Mechanical Engineering at Korea Aerospace University, where he joined in 1989. His research interests include heat transfer, heat pipes, and energy systems. He conducted joint research with Texas A&M University and Waseda University in 1994 and 2008, respectively, as Visiting Professor. Dr. Boo is an active member of the International Heat Pipe Conference Committee. Eui Guk Jung received his B.S. and M.S. degrees in Aerospace and Mechanical Engineering from Korea Aerospace University, in 2002 and 2004, respectively. He is currently a Ph.D. candidate in the Graduate School at Korea Aerospace University. His research interests include applications of heat pipes and loop heat pipes.     

The Global Architectural Influences on London

London today has become ‘a laboratory and testing ground’ for neoliberal capitalism, attracting investment from the Middle East, Russia, India, the Far East and Australasia as well as the US. Murray Fraser describes the urban impact of economic globalisation in the capital, while exploring ways that it might potentially be countered. Copyright © 2012 John Wiley & Sons, Ltd.