Hilbert-Huang变换在距离保护中的应用

克服电力系统故障暂态信号中非整数次谐波和衰减直流分量的影响,准确提取信号的基频分量,对于距离保护装置准确判断故障位置具有重要意义.文中通过利用Hilbert-Huang变换,得出一种新的故障信号基频分量提取方法.仿真表明,该方法既克服了传统傅里叶算法易受衰减直流分量影响的缺点,又弥补了各种基于周期信号模型的傅里叶改进算法在故障信号中存在非整数次谐波时基频分量提取准确度下降的不足,能够有效提高距离保护的测量精度.     

故障测距中的差分傅氏滤波改进算法

针对电力故障信号提出了差分傅氏滤波的改进算法,用构造补偿角的思想,解决了相角差值问题,并提高了精度.Matlab仿真实验比较了四种算法对仿真信号的滤波结果,表明了该改进算法滤波计算量较少,精度高,滤除衰减直流分量和谐波分量的能力强;追加实验表明了改进算法受非整数次谐波的影响较小.将各滤波算法应用于Matlab故障测距仿真系统,验证了改进算法适用于各种故障类型信号的滤波,计算量较少并能提高测距精度.     

故障测距中的差分傅氏滤波改进算法

针对电力故障信号提出了差分傅氏滤波的改进算法,用构造补偿角的思想,解决了相角差值问题,并提高了精度。Matlab仿真实验比较了四种算法对仿真信号的滤波结果,表明了该改进算法滤波计算量较少,精度高,滤除衰减直流分量和谐波分量的能力强;追加实验表明了改进算法受非整数次谐波的影响较小。将各滤波算法应用于Matlab故障测距仿真系统,验证了改进算法适用于各种故障类型信号的滤波,计算量较少并能提高测距精度。     

采用Prony与粒子群算法的电力暂态信号分析

为了提高对含有谐波/间谐波、衰减直流分量和噪声的电力故障暂态信号的分析精度,提出了基于改进Prony算法与粒子群优化算法相结合的电力故障暂态信号分析方法。该文先采用多小波方法对信号进行消噪处理,再利用差分算法滤除衰减直流分量并对高频信号进行放大,以提高Prony算法的分析精度;然后利用改进Prony算法估计出信号中含有的频率个数和相关参量的粗略估计值,以此为基础建立电力参数模型,以得到的相关参量的粗略估计值作为算法的初始种群值,并估计出各参量的范围,最后采用粒子群优化算法对模型进行求解。仿真结果表明,所提方法能对所研究的电力故障暂态信号进行精确分析。     

采用改进Prony算法的电力系统故障暂态信号分析

为提高对含有谐波、间谐波和衰减直流分量的电力系统故障暂态信号的分析精度,提出基于改进Prony算法的暂态信号分析方法。Prony算法的模型具有能较准确描述故障暂态信号特征、直接提取信号频率的优点。先采用差分算法滤除衰减直流分量并对高频信号进行放大以提高Prony算法的分析精度,利用Prony算法对信号中含有的频率分量进行估计,以确定神经网络的神经元个数和训练的初始值。将各频率分量的频率作为神经网络训练待定的权值,同时估计各频率分量的频率和幅值。仿真结果证明了所提方法的快速性和有效性。     

一种基于富氏算法的交流采样精确算法

分析了衰减非周期分量对富氏算法的影响,并在此基础上提出了一种新的滤波算法,算法适用于输入信号中除包含直流分量、整数次谐波分量外,还包含衰减非周期分量的情况,该算法能弥补任意衰减时间常数的衰减非周期分量对全波富氏算法的影响,从而求得精确的基波分量和谐波分量。用电磁暂态仿真程序ＥＭＴＰ进行了大量仿真实验,验证了此算法的优良性能。     

基于傅里叶算法的衰减直流分量消除的研究

针对消除衰减直流分量算法中,存在用时长和误差大的缺陷,提出一种在假定输入信号只含有基频分量、衰减直流分量和各整次谐波分量的情况下,对全波傅里叶算法进行改进.其基本原理是对衰减直流分量的正弦、余弦分量的系数进行补偿,消除衰减直流分量对全波傅里叶算法的影响.并用Matlab对算法进行仿真,从仿真结果可以看出,在不考虑非整次...     

有效滤除偶次谐波的改进半波傅立叶算法

目前的改进半波傅立叶算法,能有效滤除电力系统故障时暂态电信号中的直流分量及奇次谐波分量,从而比较准确地算出基波分量.但信号中若含有较大成分的偶次谐波,算法将出现较大误差.提出一种新的改进半波傅立叶算法,即通过适当增加采样点数,来进一步有效滤除偶次谐波,从而较好地提高算法精度.改进后的算法可应用于快速和准确的微机保护.     

傅氏算法在失灵保护中的改进研究

故障信号中的衰减直流分量对断路器失灵保护动作的影响很大,需要完全滤除掉此分量;针对传统全波傅氏算法消除采样信号中衰减直流分量存在的问题,进行计算误差分析;假定在输入信号只含有基频分量、衰减直流分量和各整次谐波分量时,提出一种改进的全波傅里叶算法;对传统傅氏算法和改进算法分别进行仿真,仿真结果验证改进算法能够完全滤除衰减直流分量。     

基于Morlet复小波的牵引网故障相量估算法研究

牵引网故障前后稳态相量幅值和相位的估算对测距的精度有着至关重要的影响.提出了基于Morlet复小波的相量估算算法,由于采用具有较好频率特性的Morlet复小波,因此该算法的稳定性优于传统傅里叶算法,同时不受整次、非整次谐波及非周期衰减分量的影响,相量估算精度高,鲁棒性强.进一步讨论了各参数对算法性能的影响以及参数选择方法.最后将该算法应用于牵引网典型故障电流工频相量的提取,仿真分析表明其计算精度高,可充分满足测距的要求,因此有很高的工程实用价值.     

An Innovative Decaying DC Component Estimation Algorithm for Digital Relaying

We propose a new decaying dc component estimation algorithm for digital relaying. Fault currents tend to include a dc decaying component. This component decreases the accuracy and speed of the protection relay operation. The proposed algorithm can estimate and eliminate the dc decaying component from fault current signals after one cycle from the fault instant. Also, it can be applied to a conventional discrete Fourier transform to calculate phasor quantities of fault currents in a digital protection relay. In the proposed algorithm, the dc decaying magnitude and time constant are estimated exactly by integrating fault currents during one cycle. The dc decaying component is eliminated by subtracting the dc value at each sampling instant. To verify the performance of the proposed algorithm, we performed a dc component estimation test and distance protection test using PSCAD/EMTDC. The results of the PSCAD/EMTDC simulation showed that the proposed algorithm can estimate dc components exactly from fault currents and can be applied to digital protection relays for phasor extraction.      

电力系统故障暂态信号分析中基波提取的新方法

电力系统故障暂态信号中基频分量的定量分析是电力系统微机保护的重要依据。已提出的基波提取算法主要有谐波分析法、暂态波形分析法。本文从谐小分析法的故障信号模型出发,给出了计算衰减直流分量的初始值和衰减率的公式,从而在滤除衰减直流分量的基础上再利用富氏算法就能得到的基频分量的精确值。在此基础上,本文又给出了精简的算法。它能在保证良好精度的基础上又满足保护快速及算法简单的要求。仿真结果证明了这些算法的有效     

Removal of decaying DC in current and voltage signals using amodified Fourier filter algorithm

Protecting transmission lines frequently involves applying distance relays. Protective relays must filter their inputs to reject unwanted quantities and retain signal quantities of relevant interest. Accuracy and convergent speed of filter algorithm are essential for protective relays. A widely applied filter algorithm, the discrete Fourier transform (DFT) can easily remove integer harmonics using simple calculation. However, the voltage and current signals contain serious harmonics and decaying DC during the fault interval. In addition, the decaying DC and higher order harmonics seriously decrease the precision and convergence speed of fundamental frequency signal from DFT. In this investigation, the authors derive a novel algorithm which combines the appropriate analog low pass filter and modified full cycle DFT (FCDFT) or half cycle DFT (HCDFT) algorithm to remove the decaying dc in a voltage or current signal. Using the Electromagnetic Transients Program (EMTP) simulates the transient responses of transmission lines during the fault period. Applying the proposed algorithm in distance relays effectively suppresses the decaying DC and quickly decomposes the accurate fundamental frequency components     

Fourier Transform-Based Modified Phasor Estimation Method Immune to the Effect of the DC Offsets

This paper proposes a Fourier transform-based modified phasor estimation method to eliminate the adverse influence of the exponentially decaying dc offsets when discrete Fourier transform (DFT) is used to calculate the phasor of the fundamental frequency component in a relaying signal. By subtracting the result of odd-sample-set DFT from the result of even-sample-set DFT, the information of dc offsets can be obtained. Two dc offsets in a secondary relaying signal are treated as one dc offset which is piecewise approximated in one cycle data window. The effect of the dc offsets can be eliminated by the approximated dc offset. The performance of the proposed algorithm is evaluated by using computer-simulated signals and Electromagnetic Transients Program-generated signals. The algorithm is also tested on a hardware board with TMS320C32 microprocessor. The evaluation results indicate that the proposed algorithm can estimate the accurate phasor of the fundamental frequency component regardless of not only the primary decaying dc offset but also the secondary decaying dc offset caused by CT circuit itself including its burden.      

Real-time electrical variables estimation based on recursive wavelet transform

In frequency and phasor estimation algorithms, the undesired components are required to be filtered out from the original signals. In power systems, the undesired components are the decaying dc offset and harmonics. These components could cause delay in algorithm convergence time and deviation from the desired results to a great extent. This paper proposes a new recursive algorithm for accurate and fast estimation of the instantaneous electrical variables such as frequency, amplitude and phase angle. The new algorithm provides an improvement over the existing recursive wavelet transform and, therefore, it is called IRWT. The IRWT performance is compared with the commonly used full-cycle discrete Fourier transform (DFT) and the recursive wavelet transform (RWT) methods. Since it uses a special mother wavelet function, it reduces computational complexity compared to the conventional DFT based method. Compared to the recursive wavelet transform (RWT) method, it has a faster response time. It is shown that IRWT possesses an improvement over a wide range of decaying dc component, harmonic distortions, frequency deviation and sampling frequency compared to the previously proposed methods. This characteristic of IRWT makes it a good candidate for the real-time applications in any power systems.     

A discrete Fourier transform-based adaptive mimic phasor estimator for distance relaying applications

In protection relaying schemes, the digital filter unit plays the essential roles to calculate the accurate phasor. However, while the fault current contains plentiful decaying dc component, the over-reach of distance protection will cause sever problem. This work develops an adaptive mimic phasor estimator to remove the decaying dc oscillation between voltage and current and obtains the accurate apparent impedance. First, a discrete Fourier transform-based mimic phasor estimator is developed. Then, an adaptive scheme is proposed to obtain the decaying time constant. Unlike the fixed decaying dc time constant used in a digital mimic filter, the proposed algorithm adopts the transmission-line parameters information hiding in the voltage and current measurements to adaptively approximate the decaying dc time constant to the accurate value. Thus, the estimation error in the mimic filter due to the time constant mismatch can be eliminated. Both full-cycle and half-cycle versions are developed in this work. Simulations results illustrate the effectiveness of this new algorithm for distance relaying applications.     

A new PMU-based fault detection/location technique for transmission lines with consideration of arcing fault discrimination-part I: theory and algorithms

A new fault detection/location technique with consideration of arcing fault discrimination based on phasor measurement units for extremely high voltage/ultra-high voltage transmission lines is presented in this two-paper set. Part I of this two-paper set is mainly aimed at theory and algorithm derivation. The proposed fault detection technique for both arcing and permanent faults is achieved by a combination of a fault detection index |M| and a fault location index |D|, which are obtained by processing synchronized fundamental phasors. One is to detect the occurrence of a fault and the other is to distinguish between in-zone and out-of-zone faults. Furthermore, for discriminating between arcing and permanent faults, the proposed technique estimates the amplitude of arc voltage by least error squares method through the measured synchronized harmonic phasors caused by the nonlinear arc behavior. Then, the discrimination will be achieved by comparing the estimated amplitude of arc voltage to a given threshold value. In addition, in order to eliminate the error caused by exponentially decaying dc offset on the computations of fundamental and harmonic phasors, an extended discrete Fourier transform algorithm is also presented.     

Removal of dc offset and subsynchronous resonance in current signals for series compensated transmission lines using a novel Fourier filter algorithm

In this paper, a novel Fourier filter algorithm for high-accuracy and high-convergence-speed fundamental frequency component calculation of series compensated transmission line is proposed. The performance of digital relaying is highly reliant on the algorithm of digital filtering, especially involving the dc offset and subsynchronous resonance. Input signals of protective relays must be filtered in advance to reject unwanted quantities and retain signal quantities of interest. Accuracy and convergence speed of filter algorithms are essential for protective relays. However, the voltage and current signals contain large harmonics and dc offset during fault intervals. A widely applied filter algorithm, the Discrete Fourier Transform (DFT), can easily eliminate harmonics via simple calculations. The dc offset heavily influences the precision and convergence speed of fundamental frequency component from DFT. Under high resistive fault conditions, the current signals will have subsynchronous resonance. The subsynchronous resonance current and voltage signals influence the performance of DFT much more than the dc offset. Although capable of erasing high order harmonics, the low pass filter cannot remove the dc offset and subsynchronous resonance. The Alternative Transient Program (ATP) of the Electromagnetic Transients Program (EMPT) is utilized to simulate the transient responses of series compensated transmission lines during the fault period. Adopting the proposed algorithm in distance relays effectively locks the dc offset and subsynchronous resonance signals and quickly estimates the accurate fundamental frequency components.     

一种提取基波分量的高精度快速滤波算法

为满足微机继电保护速动性的要求,短数据窗傅里叶算法得到了广泛应用.在系统发生故障期间,电压电流信号中包含大量的非周期分量与谐波分量,这将极大地延迟传统半波傅里叶算法的收敛速度.为此提出了基于狭窄带通滤波与半波傅里叶算法相结合的快速滤波算法,该算法充分利用了狭窄带通滤波算法对低频和高次谐波良好的抑制作用,同时结合了半波傅里叶算法计算实部受衰减直流分量影响小的特点,计算速度快,且滤波效果明显优于传统算法.     

交流1000kV特高压线路三相故障暂态过程分析

通过理论分析和仿真验证得到特高压线路三相故障后相关暂态电气量的特点:特高压线路故障电流中除有一很大的衰减直流分量外还存在高频分量:故障电压中也含有较大的高频分量但没有直流分量;故障高频分量的初始值与短路角(以电压角为基准)有关.当故障角为90°时.高频分量的初始值最大:高频谐波的频率与故障距离和系统运行方式有关.系统方...