城市配电电网故障以及改善分析

文章主要分析了近些年来我国城市配电电网发生的常见故障,并探析了导致这些故障的基本原因,并结合现代城市配电管理理论进行相应的改善,从而为城市配电电网工作提供参考。     

Long-term monitoring of tropical bats for anthropogenic impact assessment: Gauging the statistical power to detect population change

Bats are ecologically important mammals in tropical ecosystems; however, their populations face numerous environmental threats related to climate change, habitat loss, fragmentation, hunting, and emerging diseases. Thus, there is a pressing need to develop and implement large-scale networks to monitor trends in bat populations over extended time periods. Using data from a range of Neotropical and Paleotropical bat assemblages, we assessed the ability for long-term monitoring programs to reliably detect temporal trends in species abundance. We explored the magnitude of within-site temporal variation in abundance and evaluated the statistical power of a suite of different sampling designs for several different bat species and ensembles. Despite pronounced temporal variation in abundance of most tropical bat species, power simulations suggest that long-term monitoring programs (?20 years) can detect population trends of 5% per year or more with adequate statistical power (?0.9). However, shorter monitoring programs (?10 years) have insufficient power for trend detection. Overall, our analyses demonstrate that a monitoring program extending over 20 years with four surveys conducted biennially on five plots per monitoring site would have the potential for detecting a 5% annual change in abundance for a suite of bat species from different ensembles. The likelihood of reaching adequate statistical power was sensitive to initial species abundance and the magnitude of count variation, stressing that only the most abundant species in an assemblage and those with generally low variation in abundance should be considered for detailed population monitoring.     

增压柴油机无负荷测功系统的开发

推导了增压柴油机无负荷测功所用的理论公式,并根据该公式设计了无负荷测功系统,采用可视化编程语言设计了无负荷测功试验数据处理系统,用来对试验过程中的大量试验数据进行处理。利用该系统对柴油机进行了不同工况下的无负荷测功试验,试验结果与台架试验的结果之间的差值均不超过5%。     

DXB_2-12型电镜透镜电源原理分析与故障维修

本文概述了ＤＸＢ２—１２型电镜的透镜电源原理及几例特殊故障的分析要点和检修方法。     

BJW系列无功就地补偿器节电技术

在用电单位的感性电气设备上并联补偿器同时投切，BJW系列无功就地补偿器对提高用是设备和线路的功率因数，降低线路电流损耗，提高电源变压器负载率等效果十分显著。功率因数提高到95％以上，平均节约线损电20％－30％。     

Dynamic Lubrication of Micro Gas Bearings at an Ultra High Speed

Micro bearings of Power MEMS are usually designed to work at an ultra high speed more than 10~(6) r/min in order to improve their specific energy. So the dynamic lubrication of micro gas bearings at an ultra speed is researched. First the micro structural characteristics of micro gas-lubricated bearings are investigated, and a method to caculate the load-carrying performance of micro dynamic gas-lubricated bearings is put forword. Then the designs of two typical micro dynamic gas-lubricated bearings that are used in micro gas turbines are vertified. Moreover, the parameters affecting the load-carrying performance of micro dynamic gas-lubricated bearings are analysed.     

THE OVERLAPPING DECOMPOSITION DECENTRALIZED CONTRAL FOR GENERATOR''S EXCITER/GOVERNOR SYSTEMS

In this paper the generator's exciter/governor system are decomposed by using the overlapping decomposition method, and an overlapping decomposition decentralized control (ODDC) system is designed for the exciter /governor systems. In or.dar to enhance the dynamic qualities of the decentralized control system, the concept of the second feedback system is introduced to modify the first feedback gain matrix on the condition of the structure of the original decentralized control system maintaining unchanged. The practical decentralized control system design and its; simulation results show that this method greatly improves the control effect of the ODDC system and also holds all the advantages of the ODDC system. Besides, this paper indicates that it is a simple and effective method to control excitor/governor system by overlapping decomposition decentralized control strategy.     

A NEW METHOD FOR DESIGN OF PSS PARAMETERS

The eigenvalue sensitivity methods is very useful not only in analysis of electric power system stability but also in design of the controllers. In this paper a new optimal method is proposed to design the parameters of PSS. Using this method the PSS is designed for a single machine-infinite bus system, and the results of digital simulation show that this method is very effective and useful.     

Optimal Standby Capacity and Its Valuation in Power Pool

The problem of optimal standby capacity and its valuation in Power Pool is very important and complicated. On the basis of researching literatures concerned, this paper constructs an optimal standby capacity model and researches the problem of pricing optimal standby capacity and determining power price on the user-side. The result shows that the optimal standby capacity at some period t is completely determined by the probability distribution density function of power load demand at this period and surplus power loss and insufficient power loss, and the price of optimal standby capacity is determined by real power price of entering power grid and the power price of forecasting load demand, and the expected power price on the user-side consists of the settlement price with grid loss on generation-side and reasonable gains and expected additional loss.     

内燃机磨合及其规范研究

通过内燃机磨合台架试验，分析了摩擦副表面粗糙度、内燃机工作负荷及转速、润滑油粘度等因素对内燃机磨合过程的影响，探讨了内燃机磨合机理及其规范。