Recursive functional expansion technique for computer-based impedance and differential protection

The development of a recursive functional expansion algorithm for extracting the desired frequency components from transient power system relaying signals is presented. The applications of this algorithm to impedance detection in transmission line protection and to harmonic restraint in transformer differential protection are discussed. The recursive algorithm generates fast fault detection timings for transmission lines and does not have restrictions on sample rate, data window or spacing of samples with respect to time. For power transformer differential protection, the combined second- and fifth-harmonic amplitude of the differential current is compared with the fundamental amplitude to arrive at a trip decision.     

Fast digital distance algorithm using FIR filtering

In digital transmission line distance protection schemes based on microprocessors, the post-fault data window required to cope with transient signal components forms the major part of the total relaying time. As a result, short relaying times and accurate impedance calculations are difficult to achieve when the signals have substantial transient components. This paper establishes that a simple series R-L model of the transmission line is an adequate basis for many practical cases. Based on an analysis of an impedance calculation method using an R-L model, a digital filtering technique is proposed which requires a very short time window and little computation. The algorithm is therefore suitable for microprocessor implementation. Laboratory test results are included.     

基于平方根滤波法参数辨识的变压器保护新方法

针对无功补偿用的并联电容以及超高压长输电线分布电容的存在,容易引起二次谐波判据制动的变压器差动保护误动,提出了一种基于平方根滤波法参数辨识的保护方法。参数辨识法依据变压器在内部故障时其结构及某些参数会改变,而励磁涌流及外部故障时不变的原理,利用变压器绕组的漏感值是否发生变化作为区分变压器内、外部故障与涌流的判据。和应涌流与励磁涌流的本质相同,只是变压器铁心发生了饱和,其内部结构及漏感等参数并不改变。大量仿真实验验证该方法的可行性和有效性,当励磁涌流、和应涌流与区外故障时能够可靠闭锁差动保护,而区内故障时保护能够准确动作。该方法计算量小、数值稳定性好,避免了最小二乘、卡尔曼滤波等算法可能发散的问题。     

A new distance relaying algorithm based on complex differential equation for symmetrical components

This paper presents a new digital impedance measuring technique for transmission lines that combines symmetrical components and the complex differential equation of an equivalent fault loop circuit. The phase voltages and currents at the relaying point are transformed into symmetrical components using Fourier filters of short window length. Depending on fault type, an appropriate fault loop circuit is formed, signals of which are the appropriate symmetrical components, while a parameter of which is the positive sequence impedance being a geometrical measure of the distance from the relaying point to a fault. The impedance, however, is measured very fast by on-line solving the complex differential equation originated for this fault loop circuit. Consequently, this approach combines frequency domain estimation of symmetrical components (accurate filtration) and time domain measurement of positive sequence impedance (high speed response).

The presented method suits well the protection of parallel lines against high-resistance faults occurring very close to the far end of a line. A new method is proposed for detecting high-resistance faults and deciding which line out of two parallel lines actually suffers a fault.

The included EMTP test results demonstrate the efficiency of the proposed relaying algorithm.     

Digital Filtering Algorithms for the Differential Relaying of Power Transformer: An Overview

This paper reviews the digital differential relaying algorithms proposed by different authors for the protection of power transformer and compares them as to their speed of response, computational burden, and the capability to distinguish among an inrush, over-excitation, and transformer internal fault. The mathematical basis of each algorithm is described. All the algorithms are capable of discriminating an inrush, over-excitation, and transformer internal fault.     

基于小波分析的超高压输电线路保护新方法

暂态信号分析是电力系统故障诊断和暂态保护的基础和依据,小波变换为暂态信号分析提供了强有力的数学工具.应用小波变换对超高压输电线路的暂态电压、电流分量进行分析和处理,提出了一种利用经小波滤波后综合电压量确定故障方向和相别.在电压增量中提取行波信号来快速计算故障距离的新方法.ATP-EMTP和Matlab/Wavelet Tool- box仿真结果表明,提出的保护方案具有很好的快速性和可靠性.     

Power Transformer Differential Protection Based On Optimal Probabilistic Neural Network

In this paper, the optimal probabilistic neural network (PNN) is proposed as the core classifier to discriminate between the magnetizing inrush and the internal fault of a power transformer. The particle swarm optimization is used to obtain an optimal smoothing factor of PNN which is a crucial parameter for PNN. An algorithm has been developed around the theme of the conventional differential protection of the transformer. It makes use of the ratio of voltage-to-frequency and amplitude of differential current for the determination of operating condition of the transformer. The performance of the proposed heteroscedastic-type PNN is investigated with the conventional homoscedastic-type PNN, feedforward back propagation (FFBP) neural network, and the conventional harmonic restraint method. To evaluate the developed algorithm, relaying signals for various operating condition of the transformer, including internal and external faults, are obtained by modeling the transformer in PSCAD/EMTDC. The protection algorithm is implemented by using MATLAB.     

Digital protection of transmission lines using block pulse functions

An application of block pulse functions for digital protection of transmission lines is presented. A digital relay algorithm is developed to extract fundamental frequency components. These components are then used to calculate the impedance as seen from the relay location of a transmission line. The method is offline tested using realistic relaying signals of a 230 kV three-phase transmission line, and the results are compared with those of an algorithm based on Haar functions. The proposed algorithm is computationally simple and flexible to use with any sampling frequency.     

An ANN based approach to improve the speed of a differentialequation based distance relaying algorithm

This paper presents an artificial neural network (ANN) based approach to improve the speed of a differential equation based distance relaying algorithm. As the differential equation used for the transmission line protection is valid only at low frequencies, the distance relaying algorithm requires a lowpass filter, removing frequency components higher than those for relaying. However, the lowpass filter causes the time delay of the components for relaying. Thus, the calculated resistances and reactances do not converge directly to the fault distance even after data window occupies post fault data. Faults with the same fault inception angle have similar shapes of impedance loci. If an ANN is trained with the shape of various impedance loci for fault distances and fault inception angles, it can predict the fault distance with some values of calculated resistances and reactances before they converge to the fault distance. Therefore, the ANN can improve the speed of the distance relaying algorithm without affecting its accuracy. Moreover, the proposed approach can speed up more when a higher sampling rate is employed. The proposed approach was tested in three rates of 24, 48 and 96 samples/cycle (s/c) in a 345 (kV) transmission system and compared with the conventional distance relaying algorithm without ANNs from the speed and accuracy viewpoints. As a result, the approach can improve the speed of the relaying algorithm     

750 kV及特高压输电线路的暂态电流研究

特高压输电线路分布电容大,分布电感小,电阻小,且传输距离远,故障暂态量大且暂态过程明显。研究特高压输电线路在故障和合闸过程中的暂态电流特征,对于分析保护的动作行为很有意义。针对750kV及特高压带并联电抗器的输电线路,采用简化模型推导了故障及合闸过程中的暂态电流公式。分析了影响暂态电流中自由分量频率和幅值的各种因素。大量ATP仿真验证了理论分析的正确性,并讨论了不同暂态情况下保护算法可能受到的影响。     

Fuzzy logic-based relaying for large power transformer protection

Power transformer protective relay should block the tripping during magnetizing inrush and rapidly operate the tripping during internal faults. The frequency environment of power system has been made more complicated and the quantity of 2nd frequency component in inrush state has been decreased because of the improvement of core steel. Then, traditional approaches will likely be maloperated in the case of magnetizing inrush with low second harmonic component and internal faults with high second harmonic component. This paper proposes a new relaying algorithm to enhance the fault detection sensitivities of conventional techniques by using a fuzzy logic approach. The proposed fuzzy-based relaying algorithm consists of flux-differential current derivative curve, harmonic restraint, and percentage differential characteristic curve. The proposed relaying was tested with relaying signals obtained from Salford EMTP simulation package and showed a fast and accurate trip operation.     

自适应短数据窗抗电流互感器饱和线路差动保护算法

深入分析了超高压线路差动保护中电流互感器(TA)饱和时的2个重要特征:一是区外故障时TA的工作磁链需要一定的时间累积才能达到饱和点,故障发生初始时刻并不会马上饱和;二是TA在每个周期内由于工频交流分量的负向去磁作用,TA总是一段时间内工作在线性区,一段时间内工作在饱和区.在此基础上,提出了综合利用附加制动区判别法和短数据窗自适应差动保护算法,利用附加制动区来判别区内、区外故障,当区外故障时一旦工作点进入附加制动区,则自适应增大出口判别次数,利用短数据窗差动保护算法本身的线性区范围性能保证保护可靠不误动;当区内故障时,出口判别次数自适应减少,保证差动保护快速动作.动模数据验证结果表明所提出的方法是可行、有效的.     

Short-term wind power forecasting using adouble-stage hierarchical ANFIS approachfor energy management in microgrids

Determination of the output power of wind generators is always associated with some uncertainties due to wind speed and other weather parameters variation, and accurate short-term forecasts are essential for their efficient operation. This can efficiently support transmission and distribution system operators and schedulers to improve the power network control and management. In this paper, we propose a double stage hierarchical adaptive neuro-fuzzy inference system (double-stage hybrid ANFIS) for short-term wind power prediction of a microgrid wind farm in Beijing, China. The approach has two hierarchical stages. The first ANFIS stage employs numerical weather prediction (NWP) meteorological parameters to forecast wind speed at the wind farm exact site and turbine hub height. The second stage models the actual wind speed and power relationships. Then, the predicted next day’s wind speed by the first stage is applied to the second stage to forecast next day’s wind power. The influence of input data dependency on prediction accuracy has also been analyzed by dividing the input data into five subsets. The presented approach has resulted in considerable forecasting accuracy enhancements. The accuracy of the proposed approach is compared with other three forecasting approaches and achieved the best accuracy enhancement than all.     

Fast and accurate parameter estimation algorithm for digital distance relaying

Response of digital distance relaying depends on the fast and accurate calculation of parameters such as voltage and current phasors and fault impedance. This paper describes a new apparent impedance estimation algorithm that is based on modal components theory. It is shown in the paper that the proposed algorithm has several advantageous features in terms of speed and accuracy over previously suggested symmetrical and modal components based algorithms. The paper discusses a procedure for deriving a fault impedance estimation algorithm that can be used for protecting power transmission lines. The proposed algorithm was evaluated using an alternative transient program (ATP). The program models a power system, simulates many fault conditions on a selected transmission line and generates fault data. The relay software then obtains filtered, scaled and sampled data and calculates fault impedance using the proposed algorithm. The relay characteristic makes trip decisions based on the fault impedance estimates. The paper shows the feasibility of the proposed algorithm for first zone distance protection. Some results of these studies are presented and discussed in the paper.     

基于Hausdorff距离算法的自适应线路差动保护方案

为同时提高传统电流差动保护的速动性、灵敏性与安全性,提出一种基于Hausdorff距离算法的自适应线路差动保护方案。该方案应用Hausdorff距离算法对线路两侧电流进行实时短窗计算,并据此调整保护制动系数,以提高保护的耐受过渡电阻及抗电流互感器饱和能力,具有自适应、免整定的优良特性。基于PSCAD的仿真测试验证了所提方案的可行性及优越性。     

变压器空投导致相邻元件差动保护误动分析及防范措施

现场发生多起变压器空投导致相邻正常运行的发电机、变压器以及线路差动保护误动的事故,严重影响电网的安全稳定运行。结合现场录波数据与数字仿真,考虑励磁涌流、和应涌流以及互感器饱和等影响因素,文中对差动保护误动的原因展开研究,指出励磁涌流导致的互感器饱和是差动保护误动的主要原因。在此基础上提出了投入谐波闭锁判据、改进比率制动特性等防范措施。现场录波数据和仿真试验结果验证了所研究结论的正确性及应对措施的有效性。     

Digital protective relaying algorithms and systems — An overview

This paper gives an overview of the digital algorithms and systems for protective relaying. First, digital relaying algorithms are discussed. Classification and categorization of the proposed algorithms are given. The major classes are: transmission line protection, transformer protection, bus protection, and generator protection. The categories correspond to the different schemes used for the signal processing. The discussion of algorithms is concluded by giving some basic results related to the comparison and selection of the algorithms. A particular methodology is proposed if one is to investigate and compare digital algorithms using more elaborate quantitative techniques. The second major topic discussed is related to the digital implementations of the protective relays. Major philosophies used in designing digital relaying systems are outlined. These philosophies include the following design approaches: a centralized relaying system using a minicomputer; a decentralized relaying system where each protection function is implemented using a separate microprocessor; an integrated relaying system where a number of dedicated microprocessors are connected together in a protection system; an integrated substation control and protection system. Finally, expected trends in the areas of algorithm developments and system implementations are indicated.     

小矢量算法在发电机继电保护中的应用分析

提出一种基于小矢量算法的发电机差动保护新方案。发电机发生故障后的暂态电流中包含各种谐波分量,由于小矢量算法对谐波电流具有一定的放大作用,当两侧电流谐波含量区别较大时,将有利于保护动作。裂相横差保护和不完全差动保护由不同分支组成,两侧电流受故障影响程度也不同,电流谐波含量就有区别,因此可以采用小矢量算法提高保护性能。大型发电机内部故障产生的巨大短路电流可能引起其电流互感器饱和,从而影响保护的动作性能,而基于小矢量算法的差动保护方案具有较强的抗电流互感器饱和的能力。     

基于后向预测Prony算法的超高压输电线路暂态量保护方案

提出了一种基于故障后暂态电流信号的保护方案,利用运算法详细推导了分布参数下超高压输电线路各种故障类型时电流暂态信号的成分,分析结果表明故障后的暂态信号包含谐波形式的高频分量,其频率和相位特征能够可靠区分区内、外故障和各种故障类型.使用后向预测Prony算法作为提取暂态电流特征的工具,并对方程组的求解使用QR分解以缩短算...     

基于感应电压比的大型变压器继电保护

在电力变压器保护过程中,励磁涌流可能导致大型变压器差动继电保护误动作,为了解决此问题,从变压器电磁特性出发,以电流和电压两个暂态变量为基础,提出了利用主侧和二次侧绕组的感应电压比来实现变压器继电保护的方法。整个大型变压器保护系统以DSP为内核,采样信号经DSP判断处理后经过光电隔离输出给保护设备,后台软件控制保护设备动作,从而实现对大型变压器的保护。新判据能够快速可靠地判别变压器内部故障电流和励磁涌流;出口动作具有较高的可靠性和时效性。