基于广域测量系统的电力系统多摆稳定性评估方法

电网规模的扩大使电网稳定性问题更加突出,电力市场运行机制也迫切要求稳定分析的定量化。广域测量系统(WAMS)的出现为电力系统多摆稳定性评估提供了新的契机。该文基于WAMS提供的系统实时同步运行轨迹,根据发电机动能-功角曲线定义了曲率矢量,并分析了其与单机稳定性的关系。通过理论推导证明了这种关系的有效性,提出将该曲率矢量作为单机稳定测度函数,进而提出一种系统稳定识别判据。最后分别在IEEE-9节点系统和电科院6机22节点系统上进行仿真,仿真结果验证了该判据的有效性。     

A Cantilever Force Sensor Combined With a Spherical Reflecting Mirror for Sensitivity Enhancement of an Optical Detection System

By fabricating a microspherical reflecting mirror (MSRM) on the tip of a cantilever, the deflection angle of the laser beam is significantly magnified. Therefore, the sensitivity of an optical sensing system is enhanced. The curvature of the spherical reflecting mirror determines the system sensitivity. Given a certain bending amount and a fixed distance between the cantilever and the position-sensing detector, the cantilever combined with an MSRM with a smaller radius of curvature produces a larger optical deflection, i.e., better system sensitivity. Also, under a given radius of curvature of the MSRM, the system sensitivity can be adjusted by changing the incident angle. A larger incident angle exhibits better system sensitivity/responsivity.     

尾水管空腔涡对抽水蓄能电站系统稳定性的影响北大核心CSCD

抽水蓄能电站在我国发展势头强劲,但发电工况中由尾水管空腔涡导致的机组功率振荡现象频发,严重危及电站和电网安全。本文为了研究空腔涡对输水发电系统稳定性的影响,从一维频域角度,分别构建了包括空腔涡在内的单管单机调节系统的传递函数和一洞两机系统的总体矩阵,并进行相应的稳定性计算分析。结果表明:与调速器影响相比,空腔涡影响对输水发电系统的稳定性起着决定性作用。当空腔涡诱发功率振荡时,系统不存在稳定域;当系统受到空腔涡影响却不足以发生功率振荡时,存在与无空腔涡时基本相同的稳定域。但空腔涡参数量级很小,随时可能因机组运行工况的变化而变化,进而诱发功率振荡。这为实际电站运行避免空腔涡引起系统失稳提供了理论依据。     

一种电力系统稳定性动态分析的统一方法

为了解决电压稳定问题,基于电力系统动态分析的微分代数模型,提出了一种有效的动态稳定分析和失稳类型判别方法。利用带预测-校正步骤的延拓算法追踪平衡解流形,并采取考虑平衡解流形曲率大小的自适应策略控制步长,在平衡解流形曲率较小处采用较大步长,而在平衡解流形曲率较大处采用较小步长;在计及元件动态特性的基础上,利用小扰动法在每个平衡点分析电力系统的动态稳定性,并用数值摄动法计算状态矩阵;利用状态变量的模式参与因子判断系统的动态失稳类型。使用本文所提方法对New England 10机39节点系统进行了仿真分析,实验结果证明了本方法的有效性和实用性。     

边界元积分法分析椭圆模式和远场特性

近年来各种兼具高品质因子和定向输出的变形微纳谐振腔得到广泛研究,主要是可以用在光电集成的极低阈值激光器中。通过边界元方法计算了从圆到椭圆变形过程即中模场,品质因子以及远场特性的随短半轴变化,模拟结果表明椭圆曲率越大,模式的品质因子逐渐下降,而模场由回音壁模式逐渐向法玻腔模式转化,但是在转变过程中出现因模式耦合效应导致模式品质因子的异常改变,远场出现被调制的现象,该机理为实现定向输出并且高Q值的激光器提供新的设计思路。     

基于波形参数法的电场畸变对局部放电特性影响分析

通过搭建局部放电纳秒级放电电流测试系统,研究了针-板电极的畸变电场下局部放电的特性,以及针尖曲率半径和铝箔尺寸变化对放电特性的影响。研究表明,不同电场畸变条件下放电存在较大差异。当介质表面无铝箔覆盖时,正极性放电电流幅值大于负极性放电电流,其电流脉冲上升沿和下降沿都要小于负极性放电,这可以用流注理论很好的进行解释。当介质表面有铝箔覆盖,针尖曲率较小时,放电情形类似于无铝箔覆盖的情况;而当针尖曲率较大时,负极性脉宽小于正极性脉宽,其电流幅值大于正极性脉冲。由此推测,在针尖曲率较大铝箔覆盖时放电机理发生了改变,产生了不同于流注放电的另一种放电。本文的研究为波形参数法区分不同放电类型打下了基础。     

Unidirectional, Efficiency-Controlled Coupling from Microcavity Using Reflection Feedback

We propose a microcavity-to-waveguide side coupling system with a reflector at one end of the waveguide for the feedback. Using this system, one can get a unidirectional output from a microcavity-based light emitter, where the output coupling efficiency and the cavity loss can be enhanced or suppressed through tuning optical phase of the feedback. Theoretical calculations are confirmed by finite-difference time domain (FDTD) simulation of the coupling between a photonic crystal cavity and a microfiber with a perfect mirror attached. Unidirectional coupling from the photonic crystal cavity to the fiber with efficiency of 90% is demonstrated in the simulation     

光纤F-P电压传感器

设计了一种新型的光纤电压传感器。将Fabry-Perot腔(简称F-P腔)粘在石英晶体上,根据石英晶体的逆压电效应,在高压作用下晶体会发生形变,使粘于其上的F-P腔腔长发生改变,相应在F-P腔中的干涉波长也发生变化。通过可调F-P腔对其输出光谱进行扫描,以实现光谱恢复,得到中心波长的变化,根据中心波长与干涉腔长的关系,实现对电压的实时测量。实验结果表明,该电压传感系统可靠性好,精度高。     

针-板电极下针尖曲率和铝箔尺寸对放电机理的影响

为研究电力设备中不均匀电场下的气体间隙击穿现象,通过搭建局部放电ns级放电电流测试系统,研究了针-板电极下针尖曲率半径和铝箔尺寸变化对放电特性的影响。在无铝箔覆盖时,随着针尖曲率半径的增大,电流脉冲幅值增大,其上升沿、下降沿和脉宽都减小。正极性放电电流幅值大于负极性放电电流,其电流脉冲上升沿和下降沿都要小于负极性放电,这可以用流注理论很好地进行解释。随着铝箔面积的增大,电流脉冲幅值和上升沿都减小,下降沿和脉宽增大。然而负极性脉冲上升沿在铝箔直径为5mm时出现最小值。当介质表面有铝箔覆盖,针尖曲率较小时,放电情形类似于无铝箔覆盖的情况;而当针尖曲率较大时,负极性脉宽小于正极性脉宽,其电流幅值大于正极性脉冲。由此推测,在针尖曲率较大铝箔覆盖时放电机理发生了改变,产生了不同于流注放电的另一种放电。     

Partial discharges in a cavity at variable applied frequency part 1: measurements

In this paper partial discharges (PD) in disc-shaped cavities in polycarbonate are measured at variable frequency (0.01 ? 100 Hz) of the applied voltage. The advantage of PD measurements at variable frequency is that more information about the insulation system may be extracted than from traditional PD measurements at a single frequency (usually 50/60 Hz). The PD activity in the cavity is seen to depend on the applied frequency. Moreover, the PD frequency dependence changes with the applied voltage amplitude, the cavity diameter, and the cavity location (insulated or electrode bounded). It is suggested that the PD frequency dependence is governed by the statistical time lag of PD and the surface charge decay in the cavity. This is the first of two papers addressing the frequency dependence of PD in a cavity. In the second paper a physical model of PD in a cavity at variable applied frequency is presented.     

从防电击事故理解和采用IEC标准的必要性

1.概述自80年代开始,我国鼓励在产品生产和工程建设中采用ＩＥＣ标准,我国的产品质量和工程质量因此得到了相当的提高。由于种种原因,我国不少电气标准还未做到与ＩＥＣ标准接轨,而只是向国际标准靠拢,标准与标准间也不完全协调衔接,因此电气安全水平还相对较低。随着我国...     

Use of Fuzzy Neural Network in Industrial Sorting of Apples

In this paper, an automated system and methodology for nondestructive sorting of apples are presented. Different from the traditional manual grading method, the automated, nondestructive sorting equipment can improve the production efficiency and the grading speed and accuracy. Most popular apple quality detection and grading methods use two-dimensional (2D) machine vision detection based on a single charge-coupled device (CCD) camera detect the external quality. Our system integrates a 3D structured laser into an existing 2D sorting system, which provides the addition third dimension to detect the defects in apples by using the curvature of the structured light strips that are acquired from the optical system of the machine. The curvature of the structured light strip will show the defects in the apple surface. Other features such as color, texture, shape, size and 3D information all play key roles in determining the grade of an apple, which can be determined using a series of feature extraction methods. After feature extraction, a method based on principal component analysis (PCA) for data dimensionality reduction is applied to the system. Furthermore, a comprehensive classification method based on fuzzy neural network (FNN), which is a combination of knowledge-based and model-based method, is used in this paper as the classifier. Preliminary experiments are conducted to verity the feasibility and accuracy of the proposed sorting system.     

Curvature quantified Douglas-Peucker-based phasor measurement unit data compression method for power system situational awareness

Facing constraints imposed by storage and bandwidth limitations, the vast volume of phasor measurement unit (PMU) data collected by the wide-area measurement system (WAMS) for power systems cannot be fully utilized. This limitation significantly hinders the effective deployment of situational awareness technologies for systematic applications. In this work, an effective curvature quantified Douglas-Peucker (CQDP)-based PMU data compression method is proposed for situational awareness of power systems. First, a curvature integrated distance (CID) for measuring the local flection and fluctuation of PMU signals is developed. The Douglas-Peucker (DP) algorithm integrated with a quantile-based parameter adaptation scheme is then proposed to extract feature points for profiling the trends within the PMU signals. This allows adaptive adjustment of the algorithm parameters, so as to maintain the desired compression ratio and reconstruction accuracy as much as possible, irrespective of the power system dynamics. Finally, case studies on the Western Electricity Coordinating Council (WECC) 179-bus system and the actual Guangdong power system are performed to verify the effectiveness of the proposed method. The simulation results show that the proposed method achieves stably higher compression ratio and reconstruction accuracy in both steady state and in transients of the power system, and alleviates the compression performance degradation problem faced by existing compression methods.     

The growth of prebreakdown cavities in silicone fluids and thefrequency of the accompanying discharge pulses

Measurements have been made of prebreakdown cavities in silicone fluids, and of the current pulses that accompany cavity growth. These experiments were carried out in silicone fluids of 0.65, 10, 100 and 1000 cS viscosity. Cavity growth, driven by the electrostatic field, is limited at low viscosities by inertia, and at high viscosities by viscous drag. The electrostatic force on the cavity wall is related to the local field and to the space charge density in the liquid adjacent to the cavity. We are concerned with the relationship between the electrostatic force and the cavity growth, and with the discharges that accompany cavity growth. Discharges occur in well-defined pulse trains: the first pulse in a train generates the cavity, and subsequent pulses are due to discharges within the cavity. Knowing the scaling laws for cavity growth we can use the time between the first and second pulses to estimate the cavity size when the first cavity discharge occurs; this gives a cavity diameter of ~5 to 7 μm. The next pulse cannot occur until the charge from the previous discharge has dispersed. We find that the time between pulses Δt is strongly viscosity dependent; at high viscosities the average time between pulses at is proportional to fluid-viscosity, but in the low viscosity limit the dependence approaches η^1/3. To explain this viscosity dependence we consider three mechanisms: (1) a decrease in charge density due to increase in cavity size; (2) ion detrapping from the cavity wall and drift in the applied field; and (3) diffusion of an impurity species to the cavity surface, charge exchange to create a mobile ion, and its subsequent drift in the field. Our experimental results are consistent with the cavity expansion model, but there is evidence of diffusion effects in low viscosity liquids, and with ion-drift at high viscosities     

白莲河抽水蓄能电站机组功率振荡分析

针对白莲河抽水蓄能电站在低水头大开度下发电运行时发生的机组功率振荡现象,本文旨在探究其产生原因并分析功率振荡与系统相关参数之间的关系。首先构建了包括尾水管空腔涡的机组一维时域分析模型;其次采用特征线法对该现象进行了数值模拟及与实测结果对比分析,最后对空腔涡参数、调速器参数、导叶最快启闭速率、调节模式与机组功率振荡之间的关联进行了敏感性分析。结果表明,功率振荡是由空腔涡引起的;调速器参数和导叶最快启闭速率对空腔涡作用下的功率振荡几乎没有影响,功率振荡主要取决于空腔涡空化柔性系数和质量流量增益。这为抽水蓄能电站安全运行提供了相关的理论依据。     

Microstrip bandpass filter design using split‐path method and optimized curvature corrections

Bandpass filters with wide pass‐band are an essential requirement in various equipments of satellite and defence communication sectors. Here a method of split‐path interactions is proposed to approximately predict the resonant frequency and topology of bandpass filters which otherwise fall under the category of heuristic designs. Curved transmission lines are often required to make filter structures physically compact; however, curvature effects create errors in the theoretical (design) prediction of resonant or central frequencies for bandpass filter design. Earlier propositions on curvature corrections had been considerably precise, but recent design standards demand even higher accuracies. The prime feature of this work is the use of a meta‐heuristic optimization (i.e. Particle Swarm Optimization) technique in curvature corrections for the first time which brings accuracies of over 99% in the corrected results. The split paths used in this design are suitably curved, with the proposed optimized curvature correction technique, so as to attain a compact size of the filter. The resulting filter has a low insertion loss of around −1.00 dB and a sharp stopband cut‐off. Fabrication was done on a FR4 microstrip substrate with a good agreement between measured and simulated results. Copyright © 2015 John Wiley & Sons, Ltd.     

2.85GHz回旋波整流器高频系统的设计及优化

对2.85 GHz回旋波整流器的高频互作用区进行了研究与设计;运用CST分析了高频结构中耦合环结构的变化对高频系统S参数的影响,在此基础上对腔体结构做了优化;并用CST PIC对其进行了粒子模拟,优化解决了电子注的加入对谐振腔特性的影响。最后设计出了工作在2.85 GHz,具有较高能量转化效率的回旋波整流器高频互作用区。     

非黎曼空间测地逼近及其在电力系统非线性自适应控制中应用

电力系统是由输电线把许多发电机群联接起来的统一体，一般，其表征空间是非黎曼空间，空间的测地离差取决于空间的曲率和挠率。本文提出了测地逼近（轨线逼近）的概念并应用于电力系统非线性自适应励磁控制（ＮＡＥＣ）参数设计。设计过程包括两部分：首先在测地线（轨线）某些离散点上求得最佳励磁控制（ＯＥＣ）参数以保证测地线（轨线）稳定；其次，用非线性回归法求得沿测地线（轨线）的ＮＡＥＣ参数曲线实现测地逼近。数字仿真表明：所设计的ＮＡＥＣ可以大大提高系统的稳定性，所提出的方法是实用而有效的。     

The effect of tip curvature on the prebreakdown streamer structurein cyclohexane

In this paper the effect of tip curvature on the generation and propagation of prebreakdown density change streamer in cyclohexane was investigated. The streamer inception voltage increased with tip curvature, which was higher for a positive point than a negative one. The initial structure of the streamer was a single filament for both polarities in cyclohexane. For a negative point, the streamer structure changed from sphere to hemisphere, pagoda and bush-like form with increasing tip curvature and applied voltage. A slim channel connecting the streamer with needle tip was clearly observed for tip radii >5 μm, while it was not for those <3 μm. For positive streamers, on the other hand, it changed from slow bush-like form to fast filamentary with increasing tip curvature and applied voltage. Both magnitude and propagating speed of the streamer at its inception voltage increased with a tip curvature. After the growth stopped, they broke up into small bubbles and contracted with damped oscillation. From the spatial distribution of the field strength between the point and plane calculated by the finite element method, it was found that there exists a specific distance from the tip where the field strength is equal under any tip radii used in this study for both polarities. This distance and field strength may considered to be the minimum length and field for an electron avalanche in liquid