发电机中性点接地方式及消弧线圈的应用

本文介绍了消弧线圈的原理、使用抽头整定原则以及发电机单接地电容电流实测方法.     

某项目发电机中性点接地方式及接地装置选型

通过对非洲某国电站发电机的中性点接地方式进行分析,对发电机中性点接地变压器的选型进行了工程计算,指出发电机中性点接地变压器的参数选择须与发电机定子接地保护相配合。在发电机定子绕组绝缘有较高安全系数的情况下,接地电阻的选取应主要满足限制接地故障电流及与定子接地保护配合的需要。     

发电厂高压厂用电系统中性点新型接地方式

针对发电厂高压厂用电系统的特点,分析了发电厂高压厂用电系统中性点接地方式选择的基本要点,介绍了一种先进的新型接地方式--快速消弧加快速选线,并结合广东某电厂9^#机组的运用,阐述这种接地方式的可行性.     

配电网中性点经消弧线圈加并联选线电阻接地方式的运行安全可靠性探讨

分析了中性点不接地方式、中性点经消弧线圈接地方式、中性点经小电阻接地方式和中性点经消弧线圈加并联选线电阻接地方式的特点、适用范围和对配电网系统运行可靠性的影响。结果表明,中性点经消弧线圈加并联选线电阻接地方式适用范围最广,故障选线性能优越,且成本增加不多,可以进一步提高配电网运行的安全性和可靠性,具有良好的应用前景。     

10kV改进中性点接地方式的探讨

结合近几年国内中性点接地方式的现状,针对电网规模的不断扩大以及电缆线路的增多,造成新投运的消弧线圈补偿装置运行一段时间后容量不足的问题,以及现在传统中性点接地方式造成的单相接地故障诊断准确率低和10kV系统供电可靠性不高的问题。本文分析了中心点新的接地方式及运行方式的原理及其在10kV系统应用可行性分析,总结中心点新的接地方式及运行方式应用于10kV系统中的优势,其可重新发挥消弧线圈的优势和中性点电阻释放线路残余电荷的优点,可以有效限制暂态过电压,实现单相接地故障处置的功能,对10kV电力电缆线路自动化运行具有重大指导意义。     

10kV配电网中性点接地方式分析

中性点经消弧线圈接地方式难以满足以电缆为主的10kV配电网的发展需求。对中性点经消弧线圈接地和经小电阻接地两种方式进行了比较,结合上海市南供电公司的实际情况,运用Matlab软件建立以电缆出线为主的10kV配电网系统,仿真模拟了单相接地故障情况时两种接地方式下的弧光接地过电压、中性点电压,仿真结果表明中性点经小电阻接地可以将单相接地故障时的弧光接地过电压抑制在较低水平,可以提高10kV配电网系统运行的可靠性。     

风电场35kV系统中性点接地设计方案分析

大型风电场汇集线在发生单相接地故障时,因电弧不能自熄而产生间歇性电弧或谐振引起的过电压,造成电缆绝缘击穿、避雷器爆炸等故障,给汇集线的安全、可靠运行带来严重后果。介绍了35kV风电场汇集线中性点经消弧线圈接地及小电阻接地方式的设计方案和计算方法。通过应用案例分析,交流了运行经验和注意事项,可供优化设计提供参考。     

主变压器35 kV和6 kV中性点接地方式设计

主变压器6~35 kV采用中性点不接地或经消弧线圈或电阻器接地方式,当发生单相接地故障,电容电流过大,超过允许值时,接地电弧不易自熄,会在故障相产生间歇性弧光,对健全相产生很高的过电压,即弧光过电压,如何限制弧光过电压,对几种方法进行了比较,分析了各自的优缺点,并结合兰州石化公司的实际情况,确定主变压器35 kV和6 kV中性点接地方式采用配置自动跟踪补偿装置的消弧线圈成套设备。     

重庆城市配电网中性点接地方式的改进

根据重庆市主城区10kV配电网中性点经消弧线圈接地的统计数据及运行经验，分析了单相非永久性接地、金属性接地、相间短路、两点接地、两点异地接地等故障。参考国内的研究成果和运行经验，提出了对城市配电网中性点接地方式在不同情况下采取不同的接地方式。     

Impact study of short-circuit calculation methods on the design of a wind farm's grounding system

Safe operation of a wind farm (W/F), under fault conditions, requires a grounding study to ensure protection against developed voltages (step and touch). A key stage in the design of a wind farm's grounding system is to determine the maximum ground fault current. The aim of this work is to examine how different short-circuit calculation (SCC) procedures affect the calculation of developed voltages (step and touch) at a wind farm and therefore the provided level of safety. For this purpose, the response of the interconnected grounding system of an actual wind farm is calculated, under fault conditions, using three alternative SCC methods and the results obtained concerning violation or not of safety criteria are presented.     

Electrodeposited behavior of lead on the negative electrode in the neutral lead-carbon hybrid capacitor: Influence and inhibition

Because negative electrode of the neutral lead-carbon hybrid capacitor is composed by the active carbon and graphite, it is general believe that only the absorption-desorption process occurs in the negative electrode. However, in this work, we find that there is a second reaction going on the negative electrode: During charging, lead ions diffused from the positive electrode can be reduced to lead crystals when the charging cut-off voltage of the negative electrode is negative to the reduction potential of lead ions. These electrodeposited lead crystals can be converted into lead sulfate crystals during discharging, and these lead sulfate crystals cannot be completely dissolved in the next charging process. When lead sulfate crystals are accumulated on the surface of the carbon material gradually, the performance of the negative electrode is inhibited. Current densities have a great influence on this phenomenon because the charging cut-off voltage of the negative electrode is negatively shifted with the decrease of current density. The anion exchange membrane can completely inhibit this phenomenon by preventing the free diffusion of lead ions. After cycling at 2 A g^?1 for 3400 times, the energy retention rate of the neutral lead-carbon hybrid capacitor increases from 34% to 81%.     

Effect of mode of operation on hydrogen production from glycerol at thermal neutral conditions: Thermodynamic analysis

Thermodynamic analysis of hydrogen production from glycerol under thermal neutral conditions is studied in this work. Heat requirement from the process can be achieved from the exothermic reaction of glycerol with oxygen in air fed to the system. Two modes of operation for air feeding are considered including (i) Single-feed mode in which air is fed in combination with water and glycerol to the reformer, and (ii) Split-feed mode in which air and part of glycerol is fed to a combustor in order to generate heat. The thermal neutral conditions are considered for two levels including Reformer and System levels. It was found that the H₂ yield from both modes is not significantly different at the Reformer level. In contrast, the difference becomes more pronounced at the System level. Single-feed and Split-feed modes offer high H₂ yield in low (600–900 K) and high (900–1200 K) temperature ranges, respectively. The maximum H₂ yields are 5.67 (water to glycerol ratio, WGR = 12, oxygen to glycerol ratio, OGR = 0.37, T = 900 K, Split-feed mode), and 3.28 (WGR = 3, OGR = 1.40, T = 900 K, Single-feed mode), for the Reformer and System levels, respectively. The difference between H₂ yields in both levels mainly arises from the huge heat demand for preheating feeds in the System level, and therefore, a higher amount of air is needed to achieve the thermal neutral condition. Split-feed mode is a favorable choice in term of H₂ purity because the gas product is not diluted with N₂ from the air. The use of pure O₂ and afterburner products (ABP) stream were also considered at the System level. The maximum H₂ yield becomes 3.75 (WGR = 5.21, OGR = 1.28, T = 900 K, Split-feed mode) at thermal neutral condition when utilizing heat from the ABP stream. Finally comparisons between the different modes and levels are addressed in terms of yield of by-products, and carbon formation.     

关于客货列车平稳操纵的探讨

重载货物列车和扩编旅客列车的提速,使列车所受冲击力加剧,断钩的可能性增加,列车平稳操纵的难度加大。因此探讨平稳操纵的经验,分析造成列车冲动、断钩的原因是具有现实意义的。     

The operation types and operation window for high-purity hydrogen production for the sorption enhanced steam methane reforming in a fixed-bed reactor

The operation types and operation window for high-purity H₂ production for the sorption enhanced steam methane reforming (SE-SMR) with Ni/Al₂O₃ catalyst and CaO sorbent in a fixed-bed reactor are investigated by an experimentally verified 2D numerical method. Four chemical reactions including steam reforming, water gas shift, global steam reforming, and CO₂ sorption are considered. The operation window is defined as the H₂ and CO molar fractions at outlet satisfying both y_H2,out ≥ 90% and y_CO,out ≤ y_CO,allow (= 1%, 2% or 3%) in dry base. Under the conditions of y_H2,out and y_CO,allow, there are six operation types, of which 2 types are within the operation window and 4 types are not within the operation window as the temperature, weight hourly space velocity (WHSV) and steam to methane (S/C) molar ratio vary. For a common case of S/C = 3, the operation windows for y_CO,allow = 3% at WHSV = 8.5 h^?1 and 42.5 h^?1 are located at 570–670 °C and 640–690 °C respectively, based on the parameters in this work. The operation window of temperature is wider with decreasing WHSV, and it becomes wider remarkably as the S/C ratio increases. The lowest temperature inside the operation window is 550 °C. The effects of the temperature, WHSV and S/C ratio on the operating types, y_H2,out and y_CO,out are also presented and discussed in details.     

生物质气化集中供气工程企业化运作模式的探讨

辽宁省丹东市政府在生物质气化集中供气工程企业化运作方面进行了大胆尝试,在政府主导、企业运作、信贷支持、市场化经营、物业化管理的工作思路指导下,解决了气化站在传统管理模式下存在的成本、维护和安全等问题,为生物质气化集中供气的发展探索了一种新的模式。     

秸秆气化集中供气项目运行经验及其问题探讨

以中国秸秆气化第一村--东潘村为研究案例,通过多层面调查分析,总结出了秸秆气化项目失败的原因：①村集体经济无法承受项目的长期无盈利运行;②秸秆气化的村级管理方式无法与项目所需的管理模式相匹配;③供气时间受限制;④部分农户负担不起等.采用Probit模型对农户选择秸秆气化装置的影响因素进行了综合评价,结果表明：农户了解使用化石能源的环境危害以及从事非农工作对采用气化装置具有促进作用;使用不方便、气化燃气价格高以及前期同类项目的失败对农户采用气化装置产生负面影响.通过综合分析使社会对秸秆气化项目形成客观公正的认识.在此基础上,探讨了秸秆气化项目持续健康发展需要注意和解决的一些问题.     

闭式冷却塔内冷却盘管传热热阻分析

通过对闭式冷却塔内冷却盘管各热阻的数量级分析,认为在实际计算中,管壁导热热阻比其它热阻小一个数量级,计算中可忽略,但其余热阻均不可忽略。影响盘管总热阻大小的因素很多,从数学上分析了各热阻对总热阻的影响,找出影响盘管总热阻的主次因素,为冷却盘管的研究、设计及运行管理提供参考。