利用改进Crowbar电路提高DFIG低电压穿越能力

在分析传统Crowbar保护电路的基础上,提出利用串联制动电阻的改进Crowbar保护电路.利用MATLAB/Simulink仿真平台建立了基于双馈感应风力发电机(DFIG)的风电场并网仿真模型,针对提出的改进保护电路,对双馈感应风力发电机在电网电压跌落的情况下的运行特性进行了仿真研究,并将两种电路的保护效果进行对比,结果表明,该改进保护电路设计合理,有效地提高了DFIG的低电压穿越能力.     

Impact of Shaft Stiffness on Inertial Response of Fixed Speed Wind Turbines

Future power＇ system faces several challenges, one of them is the high penetration level of intermittent wind power generation, providing small or even no inertial response and being not contributing to the frequency stability. The effect of shaft stiffness on inertial response of fixed speed wind turbines is presented. Four different drive-train models based on the multi-body system are developed. The small-signal analysis demonstrates no significant differences between models in terms of electro-mechanical eigen-values for increasing shaft stiffness. The natural resonance frequency of drive-train torsion modes shows slightly different values between damped and undamped models, but no significant differences are found in the number-mass models. Time-domain simulations show the changes in the active power contribution of a wind farm based on a fixed speed wind turbine during the system frequency disturbance. The changes in the kinetic energy during the dynamic process are calculated and their contribution to the inertia constant is small and effective. The largest contribution of the kinetic energy is provided at the beginning of the system frequency disturbance to reduce the rate of the frequency change, it is positive for the frequency stability.     

Impact Analyses of Wind Farm on Performances ofTransmission Line Relay Protection

A simulation system for power grid with concentrated based on the electro-magnetic transient model of wind turbine （DFIG）, which is built by real-time digital simulator （RTDS） large-scale wind farm integration is established equipped with doubly-fed induction generator Using the hardware communication interface of RTDS, a closed-loop testing experiment is accomplished to study the impacts of large-scale wind farms on the existing relay protection devices for wind farm outgoing transmission line. This paper points out problems existing in current relay protection devices as follows： fault phase selector can select unwanted phase due to the changes of fault features caused by special network connection of wind farms; blocking condition for distance protections needs to be re-examined due to the weak power-feed characteristics of wind farms; and power frequency parameter based relay protection devices cannot accurately operate due to the special transient voltage and current characteristics of wind farms during fault period. Results lay the foundation for improving the performances of the existing relay protection device and developing new principle relay protection.     

同心球所夹空间电场的电像法求解

采用电像法分析研究了二同心导体球所夹空间的静电场分布。     

“归纳、对比”教学法在结构力学课程中的应用

鉴于结构力学课程的重要性,应通过对比分析对课程内容进行归纳总结,包括几何组成分析的重要性及技巧、特殊结构体系内力求解方法、超静定结构两大求解方法、结构位移计算公式等等,以帮助学生举一反三,使其能将学到的知识更好地运用到解决实际工程问题中去。     

碱回收白泥回收窑结圈产生原因及机理探讨

造纸碱回收白泥回收窑结圈产生的原因及机理比较复杂,文章分析了白泥及结圈沉积物的化学成分,从原料、燃料及操作参数条件等方面论述了结圈产生的主要原因;探讨了结圈形成及硬化的机理,并介绍了预防及处理结圈的主要措施.     

可穿戴式工频电场测量仪的研制

为减少作业人员检修配电设备时的触电风险,研制一种方便携带的工频电场测量装置十分必要。文章介绍了一种可穿戴式工频电场测量仪的原理及实现方法,并通过试验对其性能进行了验证。靠近带电体时,可穿戴式工频电场测量仪能够通过光电和声音的形式进行报警,提醒配电检修人员勿忘验电流程,改善依靠人眼目测安全距离误差大的现状,可有效地提高携带者安全意识和水平。     

国产电镀黄铜生产线技术研发

介绍国产电镀黄铜生产线技术研发现状,给出工艺流程和生产线工艺参数。生产线长度260～280 m,年生产能力1万～1.5万t,可同时处理42～56根直径0.76～3.2 mm钢丝。采用明火加热炉,Dv值可达80 mm.m/min。采用水浴索氏体化处理,焦磷酸盐电镀铜,硫酸盐电镀锌,感应加热热扩散,得到铜质量分数67.0%左右的高铜黄铜镀层,产品完全满足帘线钢丝的拉拔要求和钢帘线与橡胶的黏结力要求。     

发芽和提取条件对玉米胚芽中超氧化物歧化酶的诱导作用

为提高玉米超氧化物歧化酶(SOD)的活力和提取率,在不同条件下对玉米进行发芽处理,从发芽玉米中剥离胚芽,并在磷酸缓冲液中浸泡,再提取SOD,并测定SOD总活力。结果表明：玉米在30℃、有光照条件下发芽4d,剥离的40g胚芽在0.05mol/L 200mL磷酸缓冲液中浸泡36h,通过胶体磨研磨浸提1h,60℃热沉淀15min,用1.5倍－20℃的丙酮沉淀SOD,经Cellulose-DE-52层析,再经SephadexG-75层析,得到的玉米SOD比活力最高,为4487.28U/mg pro,比未发芽的玉米胚芽提取的SOD的比活力(924.18U/mg pro)提高了3.86倍。     

基于PLC、HMI的火焰淬火机床系统的设计

为了提高采煤机链轮、刮板机链轮和大型齿轮等产品的淬火质量和效率,同时也为打破德国＂贝丁豪斯＂公司在国际上对火焰表面加热自动淬火技术的垄断,填补国内火焰自动淬火技术的空白,本文基于西门子可编程控制器（PLC）和人机界面触摸屏（HMI）,配套相关的组态软件,通过传感与通信技术,完成了火焰淬火机床系统自动化控制。HMI对火焰淬火全过程实现智能化可视操作及实时、历史信息监控。通过试验,达到了淬火硬度要求,加热时间较贝丁豪斯公司的产品缩短了近30%,淬火效率和质量有了很大的提高。