基于故障特征频率的单端行波测距新方法

当电网某线路发生故障时,其暂态信号分别向故障点两侧传播,测量到的频率与故障点到观测点的距离有确定的数学关系。基于特征频率的暂态信号分析方法不需要提取行波波头到达时刻,避免了行波时域分析时由于波形畸变造成的测距误差。在研究前人的成果与不足基础上,提出了应用于中压配电网单端行波故障测距新方法,大大提高了信号频率分辨能力与测距精确度。该方法首先通过以故障波形信息自建立母小波函数,提高了母小波的适应性与特征频率提取的分辨能力;由上一步确定的故障特征频率,再从小波尺度图进一步对其进行修正。大量的仿真实验证明,基于该方法的单端故障测距适应性好,定位精度高。     

对称小波构造方法及其在电机故障信号处理中的应用

对称小波或反对称小波具有线性相位或广义线性相位，因而在信号的分解和重构中非常重要，它可以避免信号失真。在工程中广泛使用的Daubechies小波和Symmlet小波都不是对称小波，作者使用的对称小波构造方法是一种通用的方法，并就Db4和Sym4小波构造了对称小波，构造出的对称小波的计算量是原先小波的一半，提高计算速度。仿真结果表明，由Db4构造的对称小波包与Db4小波包相比，在信号分解与重构过程中具有频率泄漏少、能量集中、计算量小和实时性好等优点。     

Real‐time spectral analysis

For signal analysis, the Fourier transform and the linear prediction methods are the main approaches. In recent years, the wavelet transform, which gives an expression in the time–frequency domain, has been attracting attention. In the wavelet transform, scale and shift operations are used to analyze regional waves in the signal. In this paper, we propose a new method for signal analysis. Instead of the wavelet, short sine waves and cosine waves which have slightly different frequencies and phases established beforehand are used. These frequencies and phases play the same role as wavelets in analyzing regional waves in the signal. However, our proposed method is different from the wavelet transform because it does not use multiresolution analysis. In conventional spectral analysis methods, all data are prepared beforehand and calculations are performed by using these data. In the proposed method, the spectrum is updated whenever new signal data come in. We show that the amount of calculation is markedly reduced and that real‐time spectral analysis can be achieved. Finally, we present an analysis of Japanese vocal sounds using the proposed method. © 2007 Wiley Periodicals, Inc. Electr Eng Jpn, 161(1): 43–50, 2007; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20504     

采用Gabor变换的局部放电信号时频分析

局部放电信号频率是时变的,为更好地反映它的时频特性,采用一种时频分析方法Gabor变换,将它应用于局部放电信号分析中,并利用不确定原理选择高斯窗函数作为Gabor变换的基函数,提高了分析结果的时频聚集性。通过对实际局部放电信号进行分析处理,结果表明在选择合适的窗函数参数的情况下,基于Gabor变换的时频谱能够细致的刻画信号在时频平面上所发生的变化过程,准确反映了局部放电信号的时频特性,可有效满足对局部放电信号进行时频分析的要求,有利于对信号特征的提取。     

Service calls [From the Editor's Desk]

When the phone call came asking me to consider taking the role of Editor-in-Chief for IEEE Microwave Magazine, my first thought was "save yourself--decline!" Like every other electronics engineer I know, I was already multitasking, juggling several projects at once. Most of us agree to take on (and take home) more work than we probably should.     

Decision trees and wavelet analysis for power transformerprotection

This paper proposes decision trees (DTs) and wavelet analysis for the protection of large transformers. The DTs assimilate a large number of measured and derived quantities such as wavelet decomposition and harmonic coefficients. Wavelet decomposition is performed on 32 samples from a one-cycle window. The DT input vector contains eight wavelet coefficients from one level of resolution and other variables such as RMS differential current, RMS restraining current, percent differential current, and second and fifth harmonics. The eight detail coefficients are sorted so that the DT input vector remains relatively constant for a quasiperiodic signal as the observation window moves along the time axis. DTs are trained on data extracted from a large number of simulations. Accuracies around 95% are obtained in the presence of CT saturation when using either wavelets or harmonics in addition to the differential and restraining currents     

汽轮发电机组转子动静碰摩故障检测的小波分析方法研究

利用小波分析技术对汽轮发电机组动静碰摩的振动信号进行分析,给出碰摩故障信号在不同尺度下的分析结果。通过多尺度分析,使碰摩故障特征在相应的尺度图上得以体现出来。文中比较了具有相似频谱特性的两类故障信号的小波分析结果,得出了理论分析结果,为汽轮发电机组碰摩故障识别提供了新的思路。最后运用小波碰故障的准确定位进行了讨论。     

光纤张力筛选机监控仪的宽频波自适应分析

对光纤张力筛选机导轮振动产生的宽频且局部密集信号进行了研究,提出并测试了一种宽频波自适应精细分析方法。对FFT分析数据进一步进行峰值搜索、谱线交叠识别、复解析带通细化和频谱校正等分析和处理,可以在不改变采样频率和采样个数的情况下获得准确的频谱信息。对叠加信号进行分析的结果表明,本文方法具有很高的分辨率和计算精度。实际频率分辨率比常规FFT算法提高了近20倍,特别适合于高精度智能光电光纤张力筛选机监测仪的宽频波精细分析。     

A wavelet approach to fast approximation of steady‐state waveforms of power electronics circuits

Waveforms arising from power electronics circuits often contain slowly changing segments with high‐frequency details concentrated near the switching instants. Such a feature is consistent with the localization property of wavelets which are known in the signal processing literature to be highly suitable for describing fast changing edges embedded in slowly varying backgrounds. This paper considers the application of wavelet approximation to the steady‐state analysis of power electronics circuits. The basic procedure of wavelet approximation is reviewed, and an improved approach by mixing wavelets of different levels is described. When applied to power electronics circuits, the method yields efficient solutions because only a relatively small number of wavelets are needed and the proposed algorithm involves only matrix operations, permitting the steady‐state waveforms to be found fast. Copyright 2003 John Wiley & Sons, Ltd.     

Welcome to IMS 2009

The International Microwave Symposium (IMS) returns to Boston this June, and on behalf of the entire steering committee, I am pleased to invite you to join us and participate. The IMS was last held in Boston in 2000 and broke records in virtually every category. Given the current economic situation around the world, we are tempering our expectations for 2009. Still, early indications point to a very successful symposium. Perhaps this is because IMS offers such broad and deep coverage of everything in the microwave and RF fields. If there is one event people participate in year after year, it is the IMS. Every year, I look forward to meeting up with friends and colleagues from near and far, and I look forward to doing so again in 2009. I hope to see you in Boston this June!     

布里渊传感中高精度测量的布里渊谱去卷积法

在泵浦探测型布里渊分布式传感器中,结合直流和短脉冲(1 ns)激光作为探测光,可用底部为高斯型和顶部为洛伦兹型的双重结构来描述布里渊光谱。由于两者的相互作用,利用从洛伦兹型部分提取厘米级分辨率的空间信息改进了一种光谱去卷积方法,考虑应变区域相关性,在洛伦兹型部分确定布里渊谱峰的数量和频率,从而获得精确应变信息。最后,对最优直流电压进行了探讨。     

子波最小相位对最小平方反褶积效果影响

常规地面地震勘探中,地震波高频损失的影响因素有许多。为此,人们研究了各类反褶积方法提高分辨率。但是这些方法很多都是带有一定假设的,比如,假设子波是最小相位而且稳定的。本文研究了子波的最小相位性在提高地震资料分辨率中的重要性。准确的提取出地层的反射系数,是地震资料处理过程中重要而关键的一步。本文研究了不同相位子波(最小相位和混合相位)和对反褶积效果的影响,并且用最小平方反褶积来验证。实验结果表明,子波的最小相位性对最小平方反褶积效果有显著影响。     

一种生成双正交紧支复小波的Lifting方法

提出了一种构造双正交紧支复小波的方法：以现有任何一种正交或双正交实小波为基础,可构造出消失矩阶数可任意选定的无穷多个相频特性（包括线性相位特性）不贩双正交紧支复小波。其特点为：由于是双正交紧支型,可采用Mallat算法等快速算法,因此使用时实时性好;因为是复小波,所以能提取电力系统重要的相信息;具有多种相频特性,便于与相频特性多变的电力系统信号匹配等,因此这类小波在电力系统有广泛的应用前景。文中还给出了构造双正交紧支最小波的实例。     

Artifact cleaning of motor imagery EEG by statistical features extraction using wavelet families

Electroencephalogram (EEG) and its sub-bands represent electrical pattern of human brain. EEG signal contains transient components, spikes, and different types of artifacts due to eye blinking, movement of the person, anxiety, and so forth, during EEG capture. Wavelet transforms are powerful mathematical tool for sampling approximation to get clean EEG. It also helps in filtering, sampling, interpolation, noise reduction, signal approximation and signal enhancement, and feature extraction. In this paper, we have analyzed artifact cleaning via PSD graphs and statistical features extracted from motor imagery EEG-like standard deviation variance. For this, we considered 19 channels EEG signal and applied orthogonal Daubechies wavelet, bi-orthogonal rbio wavelet and Coifman wavelets to check the better performance of different wavelets. Coifman wavelet uses both scaling function and vanishing moments for sampling approximation and hence give smooth sampling compared to rbio and Daubechies wavelet transforms. Coif is a compactly supported wavelet system which also helps in smooth sampling approximations than other wavelets in the state of arts. The detailed coefficients and approximate coefficients can be further used for extracting features from EEG and classification purposes. Artifacts cleaning is thus observed better in coif wavelet analysis compared to other wavelets from the power distributions as power spectral density (PSD) graphs, standard deviation and variance obtained. Matlab R2013b is used for filtering and sampling EEG. Python 2.7 is used for statistical features extraction.     

基于小波理论的局部放电超声波信号分析

变压器局部放电超声波信号在变压器内部中传播复杂 ,探头所接受到的超声波信号是一种时频有限的非平稳信号 ,所以运用小波分析处理超声波信号十分有效。通过实验得到处理超声波信号最合适的小波 ,同时给出合适的小波参数 ,最后对实际得到的超声波信号进行处理 ,结果表明利用小波分析处理超声波信号效果令人满意     

Wavelets: a new tool for the resonant grounded power distributionsystems relaying

This paper introduces wavelets and shows that they may be efficient and useful for power distribution relaying. The wavelet transform of a signal consists in measuring the “similarity”between the signal and a set of translated and scaled versions of a “mother wavelet”. The “mother wavelet” is a chosen fast decaying oscillation function. Wavelets are used to analyse transient earth faults in a 20 kV resonant grounded network as generated by EMTP. It is shown that wavelets may be employed for analysing records to study efficiently the faulted network. Moreover, this new technique can actually be implemented in real time for protection devices. Thus, it is suitable for application to protective relays     

Application of Wigner-Ville distribution in electromigration noise analysis

Electromigration noise analysis has shown great potential for the nondestructive evaluation of electromigration performance of metal stripe. However, contradictive conclusions have been published from the electromigration noise analysis. These contradictive conclusions mainly stem from the complex dynamics of the atomic movement during electromigration, rendering the electromigration noise as a nonstationary signal, and, hence, the standard Fourier transform is not adequate. Among the various nonstationary signal analysis tools, Wigner-Ville distribution is used for the analysis of electromigration noise data for the first time. It is found that much "hidden" and useful information in the noise data can be revealed by using this distribution. These information will enable us to "see" the dynamic of the atomic movement during electromigration, enhancing our understanding of electromigration processes.     

Double AC photoreflectance spectroscopy of semiconductors

We report a new way of making photoreflectance (PR) measurements to overcome the problem of photoluminescence (PL) that is often encountered in low temperature PR measurements. In conventional PR, the probe beam is dc while the pump beam is chopped and in phase detection is done at that chopping frequency. At low temperatures a large PL signal arises at the chopping frequency of the pump beam (a laser) and swamps the PR signal. We overcome this problem by chopping both the pump beam as well as the probe beam at two different frequencies and detecting the PR signal at the sum frequency. This way we avoid the PL signal which now comes at a frequency which is not the frequency of detection. In this paper we discuss the details of this technique and present some low temperature PR data on epitaxial GaAs and GaAs-In_x Ga_1-xAs-GaAs strained layer quantum wells along with fitted lineshapes to show the feasibility of this technique     

非线性相位带限正交小波及其在电力系统故障检测中的应用

阐述了非线性相位带限正交在小波理论与工程实用方面的重要意义,介绍了作者提出的非线性相位带限正交小波－混合正交小波基的优点与构造方法,并以检测电力系统典型故障波形为例,证实了这种小波相对于常用的时域紧志小波的优越之外。     

The selection of the frequency range for high-voltage on-sitetesting of extruded insulation cable systems

High-voltage on-site tests of extruded insulation cables are necessary to check the quality of the installation of the system. The test voltage should simulate the stress under service conditions, and generate the same failure mechanism. With respect to an optimum design of test systems, a frequency range of 20 to 300 Hz, proposed in the latest IEC Draft for on-site testing of extruded insulation cables, seems to be reasonable. The test results on model cables can be used for real cables concerning the influence of the waveform on the breakdown voltage. The withstand voltage decreases with increasing frequency. The withstand voltage and the electrical breakdown field strength are very close together for frequencies between 20 Hz to 300 Hz. Mechanical defects, as well as water trees, reduce the breakdown voltage at 0.1 Hz more than at 20 to 300 Hz, but the absolute test voltage values are higher, and the breakdown mechanism is different compared with voltages of power frequency or adjacent frequencies. For on-site tests, frequency-tuned resonant test systems (ACRF) can be recommended because they have a very good weight-to-test power ratio, and very low power demands