发电机进相试验分析与探讨

为了保持系统电压平衡和稳定,探讨发电机的进相能力对系统电压质量的影响.介绍发电机进相试验的限制因素及具体试验步骤.对岩滩电厂6号发电机进相试验结果及相关数据进行分析,得到该机组安全进相运行容量.通过发电机进相试验,可得到发电机在各种工况的运行参数,掌握发电机在进相运行下的静稳态能力.发电机进相试验所得的数据,为电网调度部门绘制发电机运行PQ曲线、下发低励限制定值和安排机组进相运行提供了科学依据.     

新疆主电网发电机进相试验与数据分析

新疆主电网近几年发电机开展了进相运行,通过进相试验总结了这些发电机进相运行的特点.以吉林台水电站2号水轮发电机和玛纳斯发电厂3号汽轮发电机进相试验数据为例,论述利用曲线拟合的方法,得到发电机进相运行的P-Q及发电机定子端部温升的拟合曲线及拟合公式,并从拟合误差数据判断拟合的效果,对发电机进相运行具有一定的指导意义.     

双馈风力发电机运行方式的研究

针对能源发展的突出问题,分析了风力发电的重要性,分析说明了双馈风力发电机结构特性和运行原理,对双馈风力发电机运行方式进行了分类汇总,指出了各种运行方式的适用范围,分析了独立运行发电机组的性能,通过对双馈风力发电机运行方式的比较分析,得出了双馈式风力发电机并网运行的重要性,详细论述了双馈风力发电机的并网运行.     

大型汽轮发电机失磁异步运行分析计算

通过对大型汽轮发电机失磁异步运行电磁过程的分析,建立了以发电机为主,包括电网、励磁系统和原动机调速器系统在内的整体数学模型,并结合发电机转子涡流场和定子端部磁场的有限元分析计算,对600 MW汽轮发电机失磁异步运行进行了仿真研究,为发电机的设计和运行提供理论依据.图14参2     

湖南电网并网发电机进相运行现状与分析

发电机进相运行是改善电网电压质量的一种有效而经济的手段.文章根据发电机进相运行试验情况,分析了影响湖南电网并网发电机进相运行的实际限制条件,为电网今后制定运行方式提供依据.     

基于Crowbar保护控制的交流励磁风电系统运行分析

随着越来越多的交流励磁风力发电机接入电网运行,新的电网运行规则要求发电机在电网电压跌落时仍能保持不间断运行.为保护转子励磁电源和发电机,常采用Crowbar保护电路来限制电压跌落时转子回路的最大电流.文中通过仿真详细研究了电网故障时交流励磁风电系统的运行行为,就电压跌落程度及旁路电阻取值对Crowbar保护控制的影响以及采用Crowbar电路的系统运行特点进行了讨论分析.仿真结果验证了Crowbar电路的有效性,该方法可实现故障时交流励磁风力发电机不间断运行.     

金鸡岭热电厂发电机两种励磁方式的比较

发电机励磁系统原理及运行要求 发电机在运行时为了使转子建立磁场,转子绕组必须通入相应的直流电流,而产生这个磁场的直流电流,称为发电机的励磁电流.供给同步发电机转子励磁电流的电源以及其有关装置统称励磁系统.同步发电机运行的可靠性与其励磁系统有十分密切的关系.在电力系统正常运行的情况下,励磁系统要维持发电机或系统的电压水平,合理分配发电机间的无功负荷,提高电力系统的静态稳定性和动态稳定性,必须满足以下要求.     

汽轮发电机失磁异步运行仿真分析

指出汽轮发电机失磁异步运行可以减小起停机成本,而且对电网的安全稳定运行有重要意义.采用Simulink软件搭建了汽轮发电机失磁异步运行的仿真模型,仿真得到了励磁回路短路和开路两种失磁情况下的电机动态特性,为汽轮发电机的失磁保护及运行控制提供了依据.     

汽轮发电机电晕预防措施的研究

研究和分析了汽轮发电机电晕产生的机理、部位及其危害,再结合一些案例介绍了在发电机设计、制造工艺、运行阶段以及检修等方面应采取的预防措施.汽轮发电机电晕预防措施的研究及应用将对发电机组安全运行具有积极意义.     

发电机出口PT断线故障分析与探讨

在机组并网运行过程中,发电机出口PT断线故障时有发生,造成发电机各参数指标异常,影响机组安全运行.结合某电厂发电机出口PT配置,对两起发电机出口PT断线故障处理进行详细分析,避免了大型发电机组因出口PT故障而停运,同时探讨了改进措施和注意事项,为同类型发电机出口PT故障处理提供了指导.     

Bringing an emphasis on technical writing to a freshman course inelectrical engineering

The authors have recently added a strong writing component to one of their freshman courses in electrical engineering. The students prepared two kinds of reports-memoranda and formal engineering project reports. The authors' instructional objectives were to execute well these two forms: to write with a professional tone, and to make good choices about which technical material to include. To meet these objectives, model memos and engineering project reports were developed, lectures about these memos and reports were presented, a Web site for the course was developed, the technical aspects of the reports were graded by a student hourly grader, the writing aspects of the reports were evaluated by a professor, and followup debriefings were conducted at the lecture class meetings. The authors report on the development process and discuss student response to the course     

基于双轴各向异性磁阻传感器电流测量系统的研究

根据各向异性磁阻传感器(AMR)测量导线产生磁场强度的原理,利用两个双轴各向异性磁阻传感器建立虚拟等腰直角三角形结构的理论模型,并提出计算虚拟等腰直角三角形中任意位置的定位算法,实现对电流的非接触式测量。建立传感器单元和测试平台,设计Kaiser窗函数和卡尔曼滤波器处理外部磁场的影响。最后通过实验验证了提出结构、定位算法和信号处理的正确性。     

Surface microstructuring of aluminum alloy 2024 using femtosecondexcimer laser irradiation

Surface microstructuring and modification of aluminum alloy 2024-T3 were investigated using a femtosecond pulse laser irradiation. The surface micrographs of the scanning electron microscopy were characterized as a function of incident laser fluence. The surface features ranging from submicrometer to micrometers were developed through the variation in laser fluence and laser pulse count. Results indicated that surface patterns were uniquely constructed in a controlled use of pulsed laser parameters for the ablation. Two ablation regimes were found in the logarithmic dependence of the ablated depth on laser fluence and two components were attributed to the optical and energy penetration. A thermal dynamic model was adopted to analyze the ablation processes, and the theoretical analysis agreed well with the experimental results     

Design investigation of a linear motor for artificial heart driving

The authors have been considering the use of a linear pulse motor (LPM) as a driving source of a totally implantable artificial heart (TAH), and have developed a series of artificial heart models that incorporate such a motor. The newly developed linear-type TAH (linear TAH) has two blood-pumps, which are inflated and deflated alternately by the LPM, causing a pusher plate to pulsate the blood. This paper deals with the performance calculation of the LPM using the loading ratio. Some motors manufactured for driving TAHs were then selected to compare their machine parameters. The selected motors were LPM, linear oscillatory actuator, brushless dc motors, and ultrasonic motor. Two parameters were selected for the comparison: the mechanical output/volume ratio and the motor constant. The results may be summarized as follows: 1. The LPM was designed based on the loading ratio, and the kinetic thrust and velocity were obtained at the range of 77 newtons and 80 mm/s, respectively. 2. The loading ratio of the LPMs were more than eight times larger in comparison with the rotary motors that were used in industrial machines. 3. The motor constants of the LPMs were recognized to be one figure larger than that of the brushless dc motors. In order to reduce the volume of the linear TAH, it is necessary to increase the drive velocity of the LPMs. Application of the linear motor to a nonpulsatile artificial heart will be one way to achieve this. © 1998 Scripta Technica, Electr Eng Jpn, 123(1): 43–50, 1998     

四相聚磁型无源转子横向磁通永磁电机交直轴电感及电磁转矩分析

以一种新型四相聚磁型无源转子横向磁通永磁电机为研究对象,基于三维有限元法,利用4/2变换公式计算出不同工况下电机的交、直轴电感大小,并深入分析其变化规律和影响因素。在此基础上,利用得到的电感数据,计算出不同电流控制角下的电磁转矩,并与仿真数据相比较,总结其变化规律。研究结果为该类电机的设计分析和控制方法提供了一定的参考依据。     

A Haptic Feedback System for Lower-Limb Prostheses

A haptic feedback system has been developed to provide sensory information to patients with lower-limb prostheses or peripheral neuropathy. Piezoresistive force sensors were mounted against four critical contact points of the foot to collect and relay force information to a system controller, which in turn drives four corresponding pneumatically controlled balloon actuators. The silicone-based balloon actuators were mounted on a cuff worn on the middle thigh, with skin contacts on the posterior, anterior, medial, and lateral surfaces of the thigh. Actuator characterization and human perceptual testing were performed to determine the effectiveness of the system in providing tactile stimuli. The actuators were determined to have a monotonic input pressure-vertical deflection response. Six normal subjects wearing the actuator cuff were able to differentiate inflation patterns, directional stimuli and discriminate between three force levels with 99.0%, 94.8%, and 94.4% accuracy, respectively. With force sensors attached to a shoe insole worn by an operator, subjects were able to correctly indicate the movements of the operator with 95.8% accuracy. These results suggest that the pneumatic haptic feedback system design is a viable method to provide sensory feedback for the lower limbs.     

Transmission line tower models in frequency domain

This paper proposes a transmission line tower model in frequency domain for back-flashover analysis, which has a uniform characteristic impedance and a uniform propagation constant. Most conventional tower models are constructed as a constant and uniform parameter transmission line that is independent of frequency. However, the authors' models have the frequency dependency of the characteristic impedance and the propagation constant to express the frequency characteristic of the transmission line tower. Two models, a cylinder model and a four-frames model, were investigated to simulate the tower. Their surge responses were computed by numerical electromagnetic field analysis based on the moment method. From the results, the two-port circuit constants were calculated in the frequency domain, and the characteristic impedance and the propagation constant are derived from them. The complex artificial oscillations appeared in frequency dependency of the parameters because the parameters were calculated numerically. The equations with analytical form were obtained by approximating with a smooth curve to the oscillations. It is possible for the equations to represent the transmission line constants as a function of geometrical parameters such as the tower height and the radius. Close agreement was found between the surge response computed by the numerical electromagnetic field analysis and the result calculated by inverse Laplace transformation of the analytical equations. To prove the model, the experimental results were compared with the computed ones of the cylinder model that has arms, and it was shown that the new model agrees closer with the experiment than conventional transmission line models.     

Synthesis of TiO2nanospheres through microemulsion reactive precipitation

In the present work the preparation of titania nanosized spherical powders through a microemulsion precipitation method was investigated. The process is based on the precipitation of particles from a solution containing low-cost precursor, previously emulsified in an immiscible liquid. The precipitates were obtained dropping an acqueous solution of TiCl₄into a stable microemulsion containing a light mineral oil and a surfactant. Different mixing techniques were evaluated. The synthesized titania nanopowders were characterized by XRD, BET, TGA and DTA, SEM and TEM. The as-synthesized powders were mainly amorphous and were subjected to thermal treatment. Nanosized homogeneous spherical powders with average particle size of 6 nm after synthesis and 30 nm after heat treatment were obtained.     

谐波对电能计量装置影响的误差分析

讨论了无谐波和各种谐波情况下感应式和电子式电能表的计量原理及其误差分析,通过实验初步分析理论。通过对比无谐波和各种谐波条件下的电能计量情况,分析谐波情况下感应式电能表计量误差的复杂性,并对其规律进行总结。     

精炼菜籽绝缘油的介电性能

为了研究植物绝缘油在变压器等充油高压电气设备中的应用,分析了精炼处理后菜籽绝缘油的主要介电性能,并进行了试验研究和理论分析,采用介电谱测试仪测量了菜籽绝缘油试品的相对介电常数和介质损耗因数,分析了两性能参数随试验温度、频率变化的规律,并参照相关标准对菜籽绝缘油的体积电阻率进行了研究。同时,测试了#25矿物绝缘油相应的介电性能参数。通过比较分析两类绝缘油介电性能参数温度谱、频率谱的试验结果发现,相对于矿物绝缘油,植物绝缘油具有良好的介电性能。