浅谈0-1背包问题的常用算法

0-1背包问题是典型的NP～完全问题,无论从理论上还是实践上都有一定的研究意义。本文综述了几种0-1背包问题的常用算法,分析算法的优劣,预测0-1背包问题的发展方向。     

2000年新发布IEC标准目录选登

标准编号名称版本起草 /工作组备注ＩＥＣ 6 0 0 2 7- 3电工技术用字母符号第 3部分　对数的量和单位第 1号修订单　 (2 0 0 0 - 3 -10 ) ＴＣ 2 5ＩＥＣ 6 0 0 76 - 1电力变压器　第 1部分　总则 第 2 .1版　 (2 0 0 0 - 0 4)ＴＣ 14本标准适用于三相和单相变压器包括自耦变压器。规定了其额定值和连接符号 ,给出了有一个抽头绕组的变压器的几种规格 ,还确定了取代依据ＩＥＣ 6 0 0 76 - 1(1976 )和ＩＥＣ 6 0 0 76 - 4(1976 )所进行试验的有关信息。ＩＥＣ 6 0 0 76 - 3电力变压器　第 3部分　绝缘等级、电介质试验和外部气隙第 2版　 (2 …     

新乡火电厂4号机组DEH系统改造

对新乡火电厂于 2 0 0 0 - 0 9- 2 0至 2 0 0 0 - 11- 0 3利用 4号机组大修期间进行的电调改造进行了论述 ,主要针对液压和控制部分进行了改造。经调试、运行后 ,汽轮机的控制水平和安全可靠运行水平都有了很大提高 ,对整台机组经济、安全运行提供了可靠的保障。     

LGJ-400/50与LGJ-400/35导线的比较

从机械强度、工程造价等方面 ,对两种钢芯截面的LGJ-4 0 0、LGJ -30 0导线进行比较分析 ,以供导线选型参考。     

电厂冷却水系统杀藻剂除藻试验研究

在对国内外除藻剂进行大量分析和筛选的基础上 ,提出 3种较为有效的杀藻剂 ,并进行了单、复配除藻对比试验 .结果表明 :DDAB有效浓度及最佳杀生浓度最低 ,CTAB次之 ,H2 O2 最差 ;DDAB及CTAB的最佳单用浓度分别为 1× 1 0 - 6 mg/ml、(5～ 1 0 )× 1 0 - 6 mg/ml;复配以 0 .2× 1 0 - 6 mg/ml+1 .4× 1 0 - 6 mg/mlCTAB复配除藻效果最好 ;对浮游藻类和丝状藻类效果相似     

EP200W-Ⅱ型空压机常见故障及处理

本文通过实例介绍了EP2 0 0W -Ⅱ型空压机在使用过程中遇到的几种故障 ,结合一些主要部件的作用及工作原理判断分析了故障产生的原因 ,并据此提出相应的解决方法。     

配电网电力线扩频数传终端设计方案的探讨

介绍了STANFORD和ZILOG公司联合研制的直接序列调制扩频芯片STEL - 2 0 0 0A(Z2 0 0 0 ) ,并提出了一种新型的基于该芯片并采用智能外围通信控制器Z80 182构成的电力线扩频数传终端方案 ,最后描述了其硬件结构和软件设计原理     

冷轧无取向硅钢带中杂质的分析

据（J.of3M）83（1990）381－383报导,匈牙利的IstvanBoc等人研究了杂质结构对无取向硅钢铁报特性的影响。结果表明,当析出相尺寸很大（大于0．5μm）或很小（小于0．05μm）时,它们对磁性的危害较尺寸在0．05～0．5μm时要大。该研究详细摘要如下：用工业冷轧电工钢试样（1．0～2．1％Si,0～0．55％Al）进行实验。试样由以下两种工艺进行试制。（1）热轧-酸洗-冷轧至最终厚度（0．5mm）－800℃连续退火。（2）热轧-酸洗-冷轧至中间厚度（0．58mm）-连续追火-冷轧至0．5mm-连续退火。试样的化学成份见表1。用一台Werner带测试仪测量…     

电触头材料文摘及专利摘录

1) Cu- Cr系统液态互溶区参数的阐述 [俄 ]/Kirievskii,B.A...//Metallofiz.Noveishie Tekhnol.-2 0 0 0 ,2 2 ( 5 ) .- 7～ 1 5根据液态下 Cu在 Cr及 Cr在 Cu里的溶解度的实验数据热扩散分析 ,绘制出了一条计算 Cu- Cr系统的液相线。指明了该系统中表示互溶区特性的偏晶线长度等于零 (偏晶温度下互溶区缩小为一个点 )。2 )制备 Ag- Sn O2 电触头材料的方法 :CN 1 2 345 91 [专 ,中 ].- 1 999.1 1 .1 0 .- 6页 .- Int Cl H0 1 H1 /0 2将 5 wt%～ 32 wt%的 Sn SO4 ,≤ 0 .0 4 wt%的 Mn、W或 Cu,一或两种≤ 0 .0 6wt%的 Ni、Bi、…     

关于照明电器谐波检测问题的探讨

随着社会的进步 ,人类对生存环境日益关注。为了限制各种污染的排放 ,国家出台了一系列环保方面的法规和标准。供电系统也是一种环境——电磁环境 ,同样存在污染和对污染源的治理问题。如 :照明电器、家用电器、计算机等大量小型谐波源接入供电系统 ,就是对电力系统电磁环境的一种严重污染。为此 ,国际电工委员会专门制定 IEC555- 2 -1998版《家用电器及类似电器设备在供电系统产生的干扰》;此后 ,1995年 3月颁布了 IEC610 0 0 - 3- 2《电磁兼容 EMC限值 -谐波电流发射限值 (设备每相输入电流≤ 16A)》标准 ,用以取代 IEC555- 2标准 ,…     

一种新型软开关BUCK变换器

针对影视照明用大功率电子镇流器的特殊要求，提出了一种新型软开关BUCK变换器。新型电路具有大功率、低损耗等优点。给出了控制策略，阐述了新电路的工作原理。给出了主电路的参数设计方法。对新电路进行了仿真研究。理论和仿真结果表明，新电路中的所有功率开关全是软开关，大大降低了开关损耗。制作了一台输出功率为6kW的实验样机。实验结果与理论和仿真结果吻合。实验结果表明，用新电路代替原来的硬开关电路，整机效率提高了8%，新系统的效率为93%。     

电厂典型管壳式换热器换热管选择探讨

电厂内各类管壳式换热器的使用环境相对简单,但工况复杂,对换热器的可靠性要求较高.结合传统方式的换热管选材准则,提出将换热器的整体经济性作为管材的选择原则,并进行了分类讨论.为了精选合适的管材,尝试对管材进行寿命试验,并将分析结果应用于管材的选择中,为突破设计方法开展了可行性基础研究.     

Integrated modeling of microgrid for steady-state analysis using modified concept of multi-carrier energy hub

The paper deals with a novel approach to modeling the energy hub for microgrid representation in steady-state analysis. The presented model enables to avoid some limitations identified for the conventional (original) energy hub model. First a mathematical model has been formulated with the use of graph and network theory. Then a proposed model has been verified by steady-state calculations for selected microgrid operation scenario and exemplary energy hub structure. Finally a possible application of the presented model has been identified and future works have been widely discussed.     

大型热网加热器的改型设计

大型热网加热器主要用于城市集中供热,设备在制造完工后,运至电厂安装。文章介绍某电厂热网加热器失效现象并对原因进行了分析,确定现场改型设计方案．制定了改造工艺,最终,在现场将大型U型管式热网加热器成功改造为固定管板式热网加热器。     

Synthesis of optimal controller for synchronous power system

During the last decade research work has been in progress in the area of system optimisation by control system engineers. Power system engineers have been endeavouring to apply the optimisation technique to obtain an optimal controller to improve the transient response of a synchronous power system.In this paper an attempt has been made to select the best control quantities with a view to extending stability boundaries and improving transient response. The transient response corresponding to different combinations of control quantities was considered when selecting the most effective control law.The optimal control law obtained on the basis of the quadratic index of performance for one particular condition has been tested for operating conditions over a wide range, and the possibility of adopting the same controller for all other operating conditions has been investigated. The influence of local load on the optimal control law and transient response has also been examined, and that of governor and turbine dynamics on the transient response has been assessed.     

Dynamic analysis of a current transformer during faults

A mathematical model has been developed for a current transformer to predict the transient performance with a complex burden consisting of inductance and resistance, taking core saturation into account. A typical 1200/5 A current transformer has been simulated with various maximum offset fault currents and the secondary current response has been computed for different values of burden angles with various values of burden impedance. The current transformer error has been calculated for the above conditions.     

Novel modeling for the prediction of aged transformer oil characteristics

The effect of aging on transformer oil physical, chemical and electrical properties has been studied using the international testing methods for the evaluation of transformer oil quality. The study has been carried out on twelve transformers in the field and for monitoring periods up to 8 years. The properties which are strongly time dependent have been specified and those which have a great impact on the transformer oil breakdown voltage have been defined. Mathematical models for the breakdown voltage, total acidity and water content as a function of service periods have been given. The validity and applicability of these models for future prediction of these properties have been verified by the good agreement between the measured end predicted values. A multiple linear regression model for each transformer oil breakdown voltage as a function of its water content, total acidity and service period has been introduced and its adequacy has been illustrated by statistical analysis. Another multiple linear regression model has been developed by combining the results of a group of transformers into that of a single equivalent transformer. This model has been validated by predicting the properties of some other transformers and comparing them with the measured values. The comparison showed a good agreement for the results of transformers which have either been used or not in the derivation of the model.     

Dependence of the reactivity compensation degree of a synchronous compensator on its parameters

The problems of asynchronous self-excitation of a synchronous machine with two windings on the rotor and a series capacitance in the circuit have been considered. A formula for calculating free oscillations has been given. It has been shown that, for a system consisting of a symmetric synchronous machine and a series capacitance, there are two natural frequencies, each corresponding to a certain zone of self-excitation. The equation of the curve that describes the region of self-excitation has been obtained. The effects of different parameters of machine on the lower part of the self-excitation zone have been investigated. It has been shown that this part of the zone is determined by the ratio between the active resistances of the machine circuits, but not their absolute values. A method to determine parameters providing the required compensation of the machine reactance has been given.     

A dissociation-injection model for non-polar liquid conduction andwire-cylinder geometry

The conduction of a nonpolar liquid filling a cylindrical capacitor has been investigated with a model that includes both the dissociation of ionic pairs in the bulk of the liquid and charge injection at the inner electrode. Three different cases, of increasing complexity, have been analyzed. Firstly, injection has been neglected and the dissociation rate has been taken as constant. Then, the effect of the electric field on the dissociation rate has been considered. And, finally, a field dependent injection of charge has been also included in the model. The current voltage characteristics corresponding to these three models have been evaluated for different ratios of the electrodes radii. Approximate analytical expressions are provided for the charge density and electric field distributions over a wide range of parameters of physical interest     

含有PFC的LED驱动线路的改进设计

LED照明愈加得到世界各国的重视,针对LED特性文中描述了其驱动方式,分析和讨论了填谷式无源功率因数校正(Power Factor Correction,PFC)和反激拓扑的工作原理,提出了一种新的改进填谷式功率因数校正线路,并给出了仿真波形.针对高亮度LED照明的应用,文章进一步阐述了更加适合于LED照明特性的反激线...