大型电力系统的信息分类过滤方法研究

在大型电力系统中,电力调度和管理是通过各类融合信息得以实现,需要对电力系统的信息进行分类处理,并对干扰数据进行有效过滤,提高电力系统的运行和调度能力。传统的信息分类过滤方法采用K-means数据聚类算法,当电力系统的数据变化幅度较大时,对干扰数据的过滤效果不好。提出一种基于小波多窗谱特征提取的大型电力系统的信息分类过滤方法。采用小波多窗谱特征提取算法对多维数据进行数据特征预处理,在二维空间中进行最近邻点模糊搜索,得到大型电力系统信息数据的最近邻聚类的模糊聚类中心,优化大型电力系统数据信息聚类目标函数,实现对信息的分类过滤。仿真结果表明,采用该算法进行大型电力系统信息分类过滤,能有效反映电力数据的信息特征,提高信息分类过滤的准确性,抗干扰能力较强。     

Hilbert-Huang变换在电力系统过电压识别中的应用

将希尔伯特-黄变换(HHT)方法引入到过电压信号分类识别研究中,该方法由经验模态分解(EMD)与Hilbert变换两部分组成,能够定量、准确地对信号幅值及频率特征进行刻画。采用HHT方法对7种电力系统中常见的过电压信号进行了分析计算,结果表明HHT方法计算得到的瞬时幅值谱、Hilbert边际谱、Hilbert时频谱,能够作为特征量对不同种类型过电压进行分类识别。基于HHT算法与RBF神经网络搭建了过电压信号分层识别系统,并以实测过电压数据对其进行验证,结果表明,该分类识别系统能够有效地对过电压信号进行分类识别,并具有较高的识别率。     

基于混合模糊聚类分析的汽轮发电机组振动故障诊断

针对模糊C-均值(FCM)算法在汽轮发电机组振动故障诊断中的不足,提出了一种加权混沌优化FCM(WCOFCM)算法。WCOFCM算法首先将混沌优化策略与传统FCM算法相结合,用混沌变量搜索对模糊聚类目标函数进行全局寻优,并结合梯度算子,使方法有效收敛到极值点。然后依样本相似度原理对样本特征进行加权,对不同的特征赋予权重,突出敏感特征对聚类结果的主导作用,提高了聚类性能。最后依据聚类有效性函数指标自动确定聚类数,实现自适应分类。用该方法对国际标准测试数据进行了聚类分析实验,并将该方法应用于某发电厂汽轮发电机组振动故障诊断,其结果表明该方法有效降低了误分类率,能对汽轮发电机组振动故障进行有效诊断。     

AI优化模糊核聚类算法的变压器DGA分析

针对模糊聚类及核聚类算法在电力变压器DGA分析中存在的初值敏感及易陷入局部极值点的问题,提出了一种人工免疫优化模糊核聚类的新算法。该算法将基于克隆选择原理和亲和力成熟的免疫克隆算法与模糊核聚类算法相结合,采用群体搜索策略,将待分类的数据对象视为抗原(Ag),把聚类中心看作抗体(Ab),通过免疫系统不断产生抗体,识别抗原来优化FKCM的目标函数,能快速地获得全局最优解。仿真结果证明了该算法在变压器故障诊断上的可行性和有效性。     

电力系统粒子群优化模糊聚类算法及其应用

电力系统数据信息处理与应用领域广泛涉及数据挖掘与特征提取问题,为了提高其中聚类算法的有效性,提出了一种粒子群优化算法(PSO)与模糊C均值算法(FCM)有机结合的粒子群优化模糊聚类算法。该算法用PSO优化过程代替FCM中的基于梯度下降的迭代过程,充分利用PSO具有全局寻优、快速收敛的特点,使算法具有很强的全局搜索能力,有效地避免了FCM易陷入局部极小的缺陷;同时也降低了FCM对初始值的敏感度。还通过核方法,将低维特征空间的样本通过核函数映射到高维特征空间,增强了特征的优化,使特征在高维空间更易聚类。电力系统负荷样本聚类的应用仿真研究结果表明:与单纯FCM法相比,该算法聚类更准确,效果更佳。     

电力系统粒子群优化模糊聚类算法及其应用

电力系统数据信息处理与应用领域广泛涉及数据挖掘与特征提取问题,为了提高其中聚类算法的有效性,提出了一种粒子群优化算法(PSO)与模糊C均值算法(FCM)有机结合的粒子群优化模糊聚类算法.该算法用PSO优化过程代替FCM中的基于梯度下降的迭代过程,充分利用PSO具有全局寻优、快速收敛的特点,使算法具有很强的全局搜索能力,有效地避免了FCM易陷入局部极小的缺陷;同时也降低了FCM对初始值的敏感度.还通过核方法,将低维特征空间的样本通过核函数映射到高维特征空间,增强了特征的优化,使特征在高维空间更易聚类.电力系统负荷样本聚类的应用仿真研究结果表明:与单纯FCM法相比,该算法聚类更准确,效果更佳.     

电力系统暂时过电压多级支持向量机分层识别

提出了一种电力系统暂时过电压多级支持向量机（M-SVM）分层识别的方法。根据暂时过电压分类,建立暂时过电压分层识别系统,并采用“二分树”法构建多级支持向量机分类器。在变电站实测过电压数据的基础上,提取了三相及零序电压的时域统计特征和小波时频特征,同时对特征量进行逐级选择,将这些特征量作为M-SVM的输入,实现暂时过电压类型辨识。现场数据测试表明,采用的M-SVM分层识别方法具有训练样本少、训练时间短、识别率高的优点,可较好地应用于电力系统暂时过电压类型识别。     

基于特征加权模糊聚类的电力负荷分类

电力用户的负荷分类为电力系统和电力部门的系统规划、负荷预测、分时电价等研究提供了基本的指导工作。利用基于变分模态分解（variational mode decomposition,VMD）和模糊C均值聚类算法（fuzzy C-means,FCM）实现电力负荷的分类研究,针对FCM中欧氏距离的特征权重唯一的问题,利用基于特征加权的模糊聚类方法,提出基于特征加权的VMD-FCM聚类算法。根据电网实测负荷数据,VMD算法可对数据的固有模态有效分解,结合FCM算法引入的权重系数,显著提高了算法收敛速度和聚类准确度。对聚类结果分析表明：所提VMD-FCM聚类方法能够有效区分不同负荷类型,具有实际应用价值,从而为电力系统的设计规划提供指导作用。     

基于改进模糊聚类分析的电力系统不良数据辨识

针对当前电力系统不良数据检测辨识方法的缺点,提出一种基于增强型万有引力搜索-模糊C均值算法(EGSA-FCM)的电力系统不良数据辨识新方法。通过提出的增强型万有引力搜索算法(EGSA)对SCADA系统上传的量测数据进行搜索,获得较好的初始解,再运用FCM算法获得良性数据和不良数据的分类,最后通过COS聚类有效性判定指标判断最优聚类数目,得到最佳聚类结果和不良数据。将方法应用于IEEE14节点电力系统和大庆某区域电网中,结果表明能有效避免误检和漏检的发生,检测结果更加准确。     

基于模糊聚类-量子粒子群算法的用电特性识别

为解决应用传统模糊C均值（fuzzy C-means, FCM）算法进行电力负荷模式提取时存在的对初始聚类中心敏感、聚类数目不易确定等问题,构建表征聚类效果的目标函数,并针对传统智能寻优算法易收敛、陷入局部最优等缺陷,采用一种量子编码的粒子群算法进行全局寻优以确定最佳聚类中心及分类数目,在确定最佳聚类中心及聚类数目基础上,构建能够全面反映各类型负荷的特征向量,最后通过与传统FCM算法下的计算结果进行对比,验证了该方法在用电识别方面的有效性及正确性。     

The effect of distribution system grounding on MOV selection

Since most MOV arresters do not incorporate a gap in their design, the arrester is always in conduction and considered to be much more prone to damage due to steady-state line-to-neutral overvoltage. The authors investigate design parameters that affect this overvoltage, using a calculation method that considers a detailed representation of neutral grounding electrodes and their resistances which are normally neglected when symmetrical components method are utilized. It is found that obtaining a 25 Ω ground footing resistance does not ensure low overvoltages during line-to-ground faults; the highest overvoltages during line-to-ground faults can be found on short feeders and for faults close to the substation; small neutral wire can significantly increase overvoltages; and broken neutrals can result in overvoltages exceeding 1.5 per unit during line-to-ground fault conditions (neglecting transformer saturation)     

Control of dynamic overvoltages due to load rejection by static shunt compensation

A digital computer method used to evaluate the performance of a static shunt compensator as a device for controlling dynamic overvoltages caused by load rejection is presented. A typical system of a generating station connected to a load centre through an EHV transmission line with a static compensator at the load end is considered, and the envelopes of dynamic overvoltages following load rejection are evaluated. Detailed mathematical models incorporating the dynamics of a synchronous machine, transmission network and static shunt compensator are employed in the analysis. The static shunt compensator is shown to be an effective tool for controlling dynamic overvoltages. The application of this analysis for choosing an economic voltage rating of the surge arrestor is highlighted.     

Die Berechnunǵ von Blitzüberspannunǵen an elektrischen Anlaǵen mit Keilwellen

Übersicht Blitzschläge in Freileitungen führen zu Überspannungen, die sich als Wanderwellen ausbreiten. Die Berechnung dieser Überspannungen wird durch die systematische Anwendung von Keilwellen vereinfacht. Zur raschen Berechnung der Überspannungen in einfachen Anlagen werden Formeln hergeleitet, mit denen auch die Schutzwirkung von Überspannungsableitern berechnet werden kann. Anwendungsbeispiele veranschaulichen den Rechnungsgang und geben Aufschluß über die Anwendungsmöglichkeiten.

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Calculation of lightning overvoltages on electric systems using ramp functions

Contents Lightning strokes onto overhead lines cause overvoltages in the connected electric systems, propagating as traveling waves. For estimations of these overvoltages a simple method is developped in this paper. Applying ramp functions and using traveling wave methods simple formulae are derived, applicable with a good accuracy. The influence of lightning arresters protecting the systems against the overvoltages is taken into consideration. The method is used in some examples, showing how the method may be applied.

     

考虑铁磁元件励磁特性的电网暂态计算

介绍含铁磁元件电力网络的合闸暂态过电压的模拟计算方法,其中铁磁元件的非线性特性励磁曲线采用逐点线性化方式加以处理。首先给出了变压器的等值电路模型,再以该模型为基础,运用国际上流行的电磁暂态计算软件ATP分别对计及与不计变压器励磁支路的系统网络进行了合闸暂态模拟,对比模拟结果表明:非线性励磁曲线的考虑能在一定程度上对合闸过电压产生影响。     

全封闭组合电器变电所的过电压保护和绝缘配合问题

本文研究气体绝缘变电所的过电压。对某些典型接线的GIS变电所的雷电过电压,文章采用电磁暂态计算程序进行了计算。在计算的基础上提出限制这些过电压以及绝缘配合的一些初步建议。有一种类型的过电压可能是对GIS来说要求更为严格的,即在主回路中操作引起的某些高频操作过电压。对GIS的保护来说,氧化锌避雷器比带间隙避雷器被认为更有效。     

Scale model experimental study on the effect of lightning stroke inclination on the overvoltages across insulator strings

An experimental study on the overvoltages across insulator strings resulting strokes has been carried out on a 500 kV double-circuit vertical-suspension transmission line using a scale model. The effect of lightning stroke inclination on the insulator string overvoltages has been investigated under different conditions of stroke current rise time, tower footing resistance, and strike location on the transmission line. The results show that, for an inclined lightning stroke, the overvoltages appearing across the insulator strings of the phases located at the same height are not the same. The difference between these overvoltages increases with increase in inclination. The effect of lightning stroke inclination for practical values of tower footing resistance and stroke current rise time has been verified. It is also shown that direct strikes on the tower produce higher insulator string overvoltages than midspan strikes.     

Steep fronts at transient recovery voltages appearing with the interruption of inrush currents of transformers

High lightning overvoltages do not appear in underground substations connected to transmission cables. Consequently, it is very important to thoroughly investigate switching overvoltages and to achieve rational insulation coordination for apparatus installed in such underground substations. This paper discusses the occurrence of steep fronts at transient recovery voltages (TRV) appearing at circuit breakers when the inrush currents of transformers are interrupted. Caused by a steep front at the TRV, reignitions occur at circuit breakers, resulting in the generation of high overvoltages with high frequencies. The overvoltages are among the highest switching overvoltages appearing at the terminal of a transformer. The authors clarified the mechanism of the generation of steep fronts at TRV by means of EMTP analysis, as well as by carrying out tests in a high‐power laboratory. © 2001 Scripta Technica, Electr Eng Jpn, 135(1): 24–32, 2001     

Comparative analysis of techniques for control of switching overvoltages during transmission lines energization

The energization of long transmission lines can cause high overvoltage stresses not only along the transmission line, but also in the rest of the network. The traditional method of limiting switching overvoltages to acceptable levels is the use of circuit breakers equipped with pre-insertion resistors. The present paper describes a study comparing this traditional method with two other alternatives for the limitation of switching overvoltages during line energization in an actual 500 kV transmission system: the use of metal oxide surge arresters at both line closing of circuit breaker poles. Digital simulations were made with PSCAD/EMTDC software and the degree of shunt compensation is considered as an independent parameter.     

Insulation co-ordination for gas-insulated transmission lines (GIL)

In this paper focus is given to the insulation co-ordination of a closed system with integrated surge arresters. The calculations of transient overvoltages are made with typical applications of the integration of GIL in the 400 kV net of overhead lines. The overvoltages in the system are calculated and discussed for system lengths of 1 km and 10 km. Recommendations for such applications for the insulation levels are given. The GIL design configuration, the lightning overvoltages of overhead lines, and the overvoltages in the GIL are discussed under respect of overvoltage protection measures. Together with the use of surge arresters the insulation levels due to overvoltages are discussed. The insulation co-ordination is a very important measure for system optimization. Calculated values found for the insulation level of the GIL were proven with type tests and long duration test set-ups. Some test results are also explained in this paper     

AC filter arrester application

Arresters are being used in increasing numbers to provide surge protection inside of harmonic filters. The continuous voltage across these arresters is frequently a mixture of significant magnitudes of various harmonic voltages. Temporary overvoltages may result from system overvoltages or filter overloading. This investigation considers both the continuous arrester heating caused by a mixture of harmonic voltages and the effect of temporary overvoltages in order to provide guidelines for the appropriate selection of an arrester voltage rating for this type of application