水轮发电机不同材料灭磁电阻特性研究

发电机组常采用灭磁电阻进行灭磁，不同灭磁电阻具有不同的电气特性。分析了水轮发电机灭磁过程，并利用电磁暂态分析软件ATP-EMTP建立了水轮发电机灭磁仿真模型，在考虑转子铁芯饱和对灭磁过程影响前提下，对不同类型电阻的灭磁性能进行了比较。仿真结果表明，非线性灭磁电阻的灭磁性能优于线性灭磁电阻，为发电机灭磁电阻的选型、设计、制造及故障分析提供了参考。     

百万千瓦汽轮发电机灭磁兼过电压保护研究

本文以一台典型的百万千瓦汽轮发电机为例,研究其灭磁兼转子回路过电压保护的主回路方案和主要元器件参数设计选型。其中灭磁电阻分别选用ZnO非线性电阻及线性电阻二种方案,并进行二者的分析比较,得出推荐性结论。     

200MW发电机转子回路的改进方案探讨

某发电厂200MW发电机转子回路采用线性电阻灭磁,放电间隙+过电压击穿保险作为转子过电压保护,这种传统励磁回路设计和选用的设备在实际运行中缺陷明显。目前,国内已有许多机组采用高性能氧化锌电阻(ZnO)作为转子灭磁电阻和过电压保护,实用效果显著。     

秦山核电厂310MW发电机灭磁及转子过电压保护装置的改进

分析了秦山核电厂310MW发电机改造前灭磁与转子过电压保护装置存在的问题,介绍了对发电机灭磁及转子过电压保护回路进行的相应改造。     

新安江水电厂发电机转子过电压的防治及DMX新型灭磁开关的应用

新安江水电厂发电机转子过电压的防治及ＤＭＸ新型灭磁开关的应用新安江水电厂章柏寿１早在１９６３年，我厂为模拟运行中发电机转子灭磁开关ＦＭＫ误跳产生过电压的情况，曾进行了过电压测量试验，如图一。试验表明，ＦＭＫ（ＤＭ２型）跳开后，转子回路产生过电压，其幅...     

淮北发电厂5号机励磁回路的技术改造

传统的励磁回路采用线性电阻灭磁,间隙保护作为转子过电压保护,这种励磁接线具有很多缺点。目前,系统内已有许多机组采用高性能氧化锌电阻作为转子灭磁电阻和过电压保护,具有良好的实用效果。介绍了淮北发电厂５号机励回路技术改造情况和高能ＺｎＯ电阻的原理及其在励磁回路中的应用。     

荆门热电厂4号机励磁回路技术改造

现场试验和运行经验显示荆门热电厂4号机励磁回路存在灭磁开关运行不可靠的问题。线性电阻灭磁易在转子上产生高电压,灭磁时间长,而转子过电压保护效果又较差,针对以上问题,进行了相关设备的技术改造,采用氧化锌(ZnO)非线性电阻灭磁。介绍了基于高能ZnO电阻的过电压保护器工作原理,结合ZnO电阻性能、灭磁装置和转子过电压保护的相关技术要求总结了灭磁系统技术参数的选择、计算方法。现场发电机空载和短路试验情况下灭磁试验表明,该项改造达到了预期效果。     

非线性电阻用于灭磁和转子过压保护

我公司运用氧化锌(ZnO)非线性电阻技术,解决大型汽轮发电机灭磁、转子绕组过电压保护两个关键性技术问题的过程。本文详细阐述了"DM2开关+熔丝+非线性电阻"的灭磁方案,以及非线性电阻灭磁的优点和带来的经济效益。对国外引进的碳化硅(SiC)灭磁装置经技术改造后,使转子绕组过电压时不必再停机。还进一步介绍了非线性电阻灭磁在理论研究方面取得的进展,对最近采用的"DMX 断路器+非线性电阻"优化灭磁方案进行了评述。同时,对"磁场断路器+非线性电阻"灭磁方案的前景作了乐观的预测。     

非线性电阻用于灭磁和转子过压保护十年的回顾与展望

回顾了运用氧化锌（ＺｎＯ）非线性电阻技术,解决大型汽轮发电机灭磁、转子绕组过电压保护两个关键问题的原因和经过。着重介绍了非线性电阻灭磁的两个方案,以及在理论研究方面所取得的进展。     

发电机转子灭磁及过压保护装置改进方案分析

分析了网内几种发电机转子灭磁及过电压保护装置的特点及存在的问题,总结了应用ＭＢ６系列发电机转子灭磁及过压保护装置的经验。     

喷淋脱硫塔内除雾器运行特性

除雾器的除雾效果对脱硫系统的稳定运行、烟道腐蚀及烟气排放有重要影响,研究不同空塔流速及组合条件下除雾器的除雾性能很有必要。为此,建立了接近实际工程的喷淋脱硫塔实验台,研究了空塔流速、喷淋层与除雾器距离、不同雾化喷嘴等对除雾器出口液滴含量、粒径分布的影响,以及管式除雾器性能。研究结果表明：空塔流速对一级除雾器出口液滴含量的影响较大,对二级除雾器出口液滴含量有一定影响;除雾器出口液滴粒径随空塔流速提高而减小;喷嘴雾化粒径变小后,一级除雾器出口液滴含量明显增加;喷淋层与除雾器间距对一级除雾器出口液滴含量有较大影响;管式除雾器对除雾器出口液滴含量影响不大。     

基于LabVIEW的磁电系数自动化测试平台搭建

磁电耦合系数的测定是进行磁电复合材料研究的前提。在系统介绍磁电耦合测试的基本原理及其实现方法的基础上,利用一个线圈同时产生交流和直流磁场,避免了多个线圈之间的互感,并借助Lab VIEW软件,搭建磁电耦合系数的全自动化测试平台。利用该自动化磁电测试系统,对环氧树脂粘接而成的Metglas/PZT/Metglas磁电复合材料进行测试,测试结果显示,磁电谐振峰与样品阻抗谐振峰测试结果一致,且反复测量结果误差小于1.4%。研究表明,基于Lab VIEW的磁电系数自动化该测试系统误差小、稳定性好。     

Magnetoelectric Effect in Composites of Magnetostrictive and Piezoelectric Materials

In the past few decades, extensive research has been conducted on the magnetoelectric (ME) effect in single phase and composite materials. Dielectric polarization of a material under a magnetic field or an induced magnetization under an electric field requires the simultaneous presence of long-range ordering of magnetic moments and electric dipoles. Single phase materials suffer from the drawback that the ME effect is considerably weak even at low temperatures, limiting their applicability in practical devices. Better alternatives are ME composites that have large magnitudes of the ME voltage coefficient. The composites exploit the product property of the materials. The ME effect can be realized using composites consisting of individual piezomagnetic and piezoelectric phases or individual magnetostrictive and piezoelectric phases. In the past few years, our group has done extensive research on ME materials for magnetic field sensing applications and current measurement probes for high-power electric transmission systems. In this review article, we mainly emphasize our investigations of ME particulate composites and laminate composites and summarize the important results. The data reported in the literature are also compared for clarity. Based on these results, we establish the fact that magnetoelectric laminate composites (MLCs) made from the giant magnetostrictive material, Terfenol-D, and relaxor-based piezocrystals are far superior to the other contenders. The large ME voltage coefficient in MLCs was obtained because of the high piezoelectric voltage coefficient of the piezocrystals and large elastic compliances. In addition, an optimized thickness ratio between the piezoelectric and magnetostrictive phases and the direction of the magnetostriction also influence the magnitude of the ME coefficient.     

A new magnetoelectric resonance mode in bilayer structure composite of PZT layer and Terfenol-D/epoxy layer

Magnetoelectric (ME) composites with a bilayer structure were prepared by easily combining Pb(Zr,Ti)O₃ layer and Terfenol-D/epoxy layer. A new second flexural ME resonance mode was investigated and confirmed by vibration modal analysis. A giant ME coefficient at the first flexural resonance mode (2.79 V/cmOe at 35 kHz) is much larger than that at the transverse resonance mode (1.31 V/cmOe at 122 kHz). A flat ME response of about 360 mV/cmOe occurs in the range from 50 to 80 kHz, which shows a large bandwidth. This bilayer structure is expected to achieve a giant ME effect at relatively low frequency.     

Magnetoelectric interactions in ferromagnetic-piezoelectric layered structures: Phenomena and devices

Layered magnetostrictive-piezoelectric structures are multifunctional due to their dual-responsiveness to mechanical and electromagnetic forces. Here, we discuss studies of magnetoelectric (ME) interactions in ferrite-lead zirconate titanate (PZT) and terfenol-PZT material couples. Key findings include: (1) the observation of a giant low-frequency ME effect in the layered systems; (2) data analysis based on our model for low frequency ME effects; (3) observation and theory of enhanced ME coupling at the electromechanical resonance (EMR); and (4) theory and measurements of microwave ME effects, at the ferromagnetic resonance of ferrites. The layered structures are potential candidates for sensors, gyrators and microwave devices. Low frequency sensors are feasible with excellent sensitivity to minute magnetic field variations. One could also realize composite based ferromagnetic resonance devices, such as resonators, filters and phase shifters with electric field tunability for use at 1–70 GHz.     

Microwave magnetoelectric effects in ferrite—piezoelectric composites and dual electric and magnetic field tunable filters

Magnetoelectric (ME) effects at ferromagnetic resonance (FMR) in ferrite—piezoelectric layered structures have been investigated in lithium zinc ferrite (LZFO)-lead zirconate titanate (PZT) and yttrium iron garnet (YIG)-PZT. When an electric field E is applied to PZT, the piezoelectric deformation is transmitted to the ferrite and results in a shift in FMR. Data on the field shift caused by E are presented and compared with theory. Although the strength of ME coupling is weaker in YIG-PZT than in LZFO-PZT, the E-assisted field shift in YIG-PZT is much higher than the resonance line width and is potentially useful for filter applications. An electric field tunable YIG-PZT microwave band-pass filter based on ME effects at FMR is designed and characterized. The device can be tuned over a wide frequency band with a bias magnetic field and over a narrow band with a voltage applied across PZT. Data on tuning range, insertion loss, and device characteristics are presented.     

基于物元模型的电力系统中长期负荷预测

在综合考虑电力负荷预测及物元理论特点的基础上,将两者结合,提出了一种基于物元理论(可拓工程学)的中长期负荷预测方法,对物元理论在电力系统中的实际运用进行了探讨.方法首先运用逐步回归与层次分析技术确定各种因素对电力负荷的影响权重,然后利用物元理论对选中的各影响因素与电力负荷及其增长率建立物元模型,再根据系统聚类分析的方法对电力负荷及其相关环境因素的历史样本进行归纳分类,最后采用合适的物元关联函数及灰色关联函数结合未来环境因素状态对未来负荷变化模式进行识别,从而预测出电力负荷的未来值.并以我国某地区的中期负荷预测为例,说明了其有效性.     

Analyzing surface myoelectric signals recorded during isokineticcontractions

A time-frequency approach using wavelets to study movements at different angular velocities is considered. The authors summarized the application of the continuous wavelet transform (CWT) to the analysis of the surface myoelectric (ME) signal. The present technique of determining MNF has the advantage that it is possible to determine the frequency content of the ME signal during short and nonstationary contractions. In addition, the CWT method is very reliable for the analysis of nonstationary biological signals and does not require any smoothing function as do methods based on Wigner-Ville. However, using time-frequency methods involves two main tradeoffs: i.e., potential increases in performance for a given application versus computational complexity and storage requirements. Our results confirmed earlier studies that MNF is independent of angular velocity     

J2ME在移动通讯设备编程中的应用

着重讨论了J2ME技术体系结构,阐释了J2ME手机编程的开发过程,结合笔者的开发经验,给出了以输出“Test String”为例说明J2ME的源程序编写过程,并总结了J2ME编程的特点。