Wavelet transform based digital protection for transmission lines

This paper presents a high speed, computationally efficient scheme for protection of transmission lines. The relay logic consists of three parts: directional protection, fault classification and fault location. Wavelet transform is used for extracting information from the fault transients and only the first level high frequency details of the voltages and currents are used. Proposed protection logic compares the directional signals from both terminals to discriminate between faults inside and outside the zone of interest. Fault classification is achieved using local terminal current information. An estimate of the location of the faults is obtained utilizing single faulted phase current information from both terminals. The logic is deterministic and can work reliably in the presence of fault resistance, load variation and CT saturation. The validity of the proposed logic was exhaustively tested by simulating various types of faults on a four bus meshed system modeled in EMTP/ATP.     

Wavelet based transformer protection using high frequency power directional signals

This paper proposes a novel wavelet transform based relaying scheme for power transformer protection. The relay logic consists of two parts: disturbance detection based on first level high frequency details of the voltage signals only and fault discrimination using a power based directional signal derived from the first level high frequency details of both voltage and current signals. The logic is deterministic, computationally efficient, fast, secure and highly reliable. The operating time is 6 ms, about 1/3rd of power frequency cycle (20 ms). The scheme uses only the sign of the directional signals, rather than the difference in their magnitudes, hence it can work reliably in the presence of transformer tap variation, fault resistance and CT saturation. The validity of the proposed logic was exhaustively tested by simulating various types of internal and external faults, energization conditions and load variations on a 132 kV system modeled in ATP/EMTP with a 31.5 MVA, 132/33 kV, Y–Δ transformer. The proposed logic was able to correctly discriminate between internal faults, external faults and non-fault disturbances for all the 880 test cases.     

A novel probabilistic neural network‐based algorithm for classifying internal fault in transformer windings

The major function of protective devices in a power system is to detect the occurrence of faults and to isolate the faulty sections from the rest of the system. Much progress has been made in the development algorithms for detecting faults in power transformers, which depend on transients‐based techniques. This paper presents an algorithm based on a combination of discrete wavelet transforms and probabilistic neural networks (PNNs) for classifying internal faults in a two‐winding three‐phase transformer. Fault conditions of the transformer are simulated using alternative transients program/electromagnetic transients program (ATP/EMTP) in order to obtain current signals. The mother wavelet Daubechies4 is employed to decompose the high‐frequency components from these signals. All three phases of the differential current signals are used in the fault detection decision algorithm. The variations of first‐scale high‐frequency component that detects fault are used as an input for the training pattern. The training process for the neural network and fault diagnosis decision is implemented using toolboxes on MATLAB/Simulink. Various cases and fault types based on the Thailand electricity transmission and distribution systems are studied to verify the validity of the algorithm. Backpropagation neural network is also compared with the PNN in this paper. It is found that the proposed method gives satisfactory accuracy with less training time, and will be particularly useful in the development of a modern differential relay for a transformer protection scheme. © 2013 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

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...     

方向高频保护的动作行为分析：第一部分：复杂系统的复故障计算

方向高频保护高压和超高压输出电线路的主要保护方式,其动作性能对电力系统的安全运行影响甚大。     

DYNA-TEST simulator for relay testing. I. Design characteristics

The authors describe a new digital dynamic testing (DYNA-TEST) simulator developed for protection relay applications. This simulator is capable of producing voltage and current transients that correspond to actual fault events in the power systems. Fault transients are generated either by simulating power system faults using an electromagnetic transient program or by replaying records of fault signals captured in substations by digital fault recorders. These signals are used to test protection relays. Such an approach to relay testing represents a major improvement over steady-state testing     

A novel scheme for current-only directional overcurrent relay

Overcurrent relays are widely used as main protection in sub-transmission and distribution systems. In mesh and multi-source networks, application of directional relay is unavoidable. Traditional directional overcurrent relays use the reference voltage phasor as the polarizing quantity to estimate the direction of the fault. Traditional direction distinguishing scheme is unreliable in the case of close-in faults. In this paper, a novel algorithm for directional overcurrent relay is proposed. The new algorithm uses only current signals for determining the fault direction. It uses superimposed component of the current signal and does not require phasor estimation. This new algorithm uses pre-fault current signal as the polarizing quantity. The proposed method is tested on simple power system in different situations. The results show it leads to fast and reliable directional protection.     

A novel algorithm for discrimination between inrush current and internal faults in power transformer differential protection based on discrete wavelet transform

This paper proposes a novel methodology for transformer differential protection, based on wave shape recognition of the discriminating criterion extracted of the instantaneous differential currents. Discrete wavelet transform has been applied to the differential currents due to internal fault and inrush currents. The diagnosis criterion is based on median absolute deviation (MAD) of wavelet coefficients over a specified frequency band. The proposed algorithm is examined using various simulated inrush and internal fault current cases on a power transformer that has been modeled using electromagnetic transients program EMTDC software. Results of evaluation study show that, proposed wavelet based differential protection scheme can discriminate internal faults from inrush currents.     

超高压线路暂态保护中雷电干扰与短路故障的识别

未导致故障的雷击可能会造成超高压线路暂态保护的误动,对这种雷电干扰的识别是暂态保护实用化必须要解决的一个棘手问题。全面分析了输电线路中雷电干扰和故障情形的模量行波大小与行波波形,发现如下特征：感应雷作用下三相线路中的线模量远小于地模量;重型直击雷的波头部分和截波处都突变剧烈;轻型直击雷的波尾时间显著小于短路行波的持续时间。基于此,提出了轻型直击雷、感应雷与重型直击雷、普通短路故障的识别原理,以及利用小波变换的雷电干扰实用识别算法,大量EMTP仿真表明该识别原理可行、算法可靠,有望解决暂态保护在雷电干扰时的误动问题。     

Series faults in six-phase electric poer systems

The planning and design of transmission systems require the analysis of systems under steady-state as well as under transient conditions.This paper addresses a group of medium-fast transients in six-phase systems created by faults which do not involve any connection between conductors or between conductors and ground. This type of imbalance is referred to as a series fault; it arises, in most instances, when poles of a circuit breaker fail to open, thus creating an unbalanced series impedance condition. The various cases of series faults or open-line faults for six-phase transmission systems are analyzed in this work using the method of symmetrical components and Thévenin's theorem for two-port networks. A numerical algorithm for each of the various series fault cases is also developed here. This will allow us to determine the unbalanced currents resulting from an unbalanced series impedance condition.     

Faults locations in automated distribution system

This paper presents new techniques for locating short circuit and open conductor faults on automated distribution system. This is a unique method where short circuit and open conductor faults are treated simultaneously. The proposed fault location scheme is capable of accurately identifying the zone in which fault occurs. Temporary faults are also detected which may not result in a blown fuse. Data is made available to the substation remote terminal unit from various automated distribution system equipments. Decision is taken based upon the magnitude of fundamental frequency component of voltage and current phasor. Testing of proposed fault location method has been demonstrated on the laboratory model for its practical use. Analogues simulation results are obtained using electromagnetic transients program (EMTP).     

Low-cost, fault-tolerance applications

This article describes an approach for designing various low-cost, fault-tolerant uniprocessor applications using a multiprocessor. The proposed software-based fault-tolerant model is an economic and effective solution towards tolerating transients and intermittent faults that may occur during the run time of a multiprocessor application system. In this article, the proposed technique adopts the strategy of defensive programming based on time redundancy. This article focuses on protecting an application from faults by running multiple copies of the application on a shared-memory multiprocessor. It saves the costs of developing various independent versions of an application program. This is a significant step towards designing a reliable system at a low cost.     

基于电弧复小波检测的单相自适应重合闸

提出一种单相自适应重合闸的新方案。该方案利用复小波分析来检测电弧产生的谐波,并以此区分输电线路的单相瞬时性故障和永久性故障。故障发生后,对于不同的故障性质,线路首端重合闸安装处的电压谐波含量是不同的。根据电压谐波含量的特征,提出利用复小波相位和幅值的新算法综合判别来快速确定线路的故障性质。该方法可以在熄弧之前进行判断,保障了最佳重合时间。线路故障仿真验证了该算法的有效性和实用性。     

基于对称分量变换的暂态电流极性方向比较保护算法

研究了一种新的基于暂态电流极性比较的方向保护技术.使用对称分量变换对三相暂态电流行波信号进行解耦,然后用其电流模量小波变换后的模极大值极性关系,辨识区内或区外故障:线路内部故障时线路两端的电流模量小波变换模极大值极性相同,而线路外部故障时则相反.该算法用单一模量对各种故障类型都可以给出正确的结果,较好地克服了以往采用Clark变换和Karrenbauer变换使用单一模量情况下对某些故障不能正确反应等缺陷.EMTDC仿真实验证明了算法的可行性.     

Laboratory investigation of an amplitude comparator baseddirectional comparison digital protection scheme

A directional comparison digital protection scheme has been implemented with a 16-b single-board computer at each end of a physical model of a transmission line, with communication between the two ends. The protection algorithm makes use of the fundamental frequency components of the deviation signals of the voltage and phase-shifted current. Software routines have been developed for fault monitoring, directional determination, and the trip/block decision. Graphics features incorporated in the software are explained. Tests for various faults conducted on the physical model of a double-circuit transmission line show that the direction to a fault is determined in 3 to 7 ms. The blocking features of the relay are demonstrated     

Directional Traveling-Wave Protection Based on Slope Change Analysis

This paper presents a new approach that deduces the fault direction based on the traveling-wave directional principle. The algorithm by means of wavelet transforms decomposes the voltage signals and calculates the spectral energy at selected detail which allows detecting the fault and to choose the phase to make the slope change analysis. This analysis provides a clear indication of fault direction from the comparison of the slope change polarities of the voltage and current at selected phase during quite a short time. The algorithm, which belongs to the ultra-high-speed protecting relaying, is able to discriminate the direction for all kinds of faults and is not affected by the change of the fault angle inception.     

Time Series Modeling of Voltage Profiles Along Transmission Lines

This paper presents a new method for calculating the voltage profile along a given transmission line during a system transient. This may be used for detecting harmful levels of voltage signals that appear along the length of a long transmission line during transients caused by switching events or faults. It may also be useful in obtaining screen shots of waveforms to be used in animation of traveling wave transients. The voltage profile is recovered by developing a time-series model for the voltages at intermediate points along the length of the line. The proposed method is novel in the sense that once the time-series model is developed, the technique does not require any further simulations for the calculation of the voltages at intermediate points. A transient simulator such as the Electromagnetic Transients Program is utilized to obtain the necessary historical information of the voltages at terminal ends and at the intermediate points to be used in developing the time-series model. This paper presents several examples where voltage profiles are obtained during different types of transient events     

基于数学形态学的单端定位保护新原理

利用多分辨形态梯度结合多层形态滤波器,提出了一种基于单端暂态电气量的定位保护新原理。在多分辨形态梯度的基础上,将得到的各级形态梯度均进行形态滤波,以有效抑制各种随机噪声和脉冲噪声。并通过暂态信号的相对传输时间和极性确定故障发生的精确位置。EMTP仿真结果表明该方法对超高压输电线路不同位置的各种故障均具有较高的测距精度。同时,该算法的计算量较多尺度小波变换的计算量小,有利于工程实现。     

Directional relaying using support vector machine for double circuit transmission lines including cross-country and inter-circuit faults

The conventional distance relaying algorithms are unable to detect the inter-circuit faults, cross-country faults, high resistance faults which may occur in a double circuit line. This paper presents combined Discrete Wavelet Transform (DWT) and Support Vector Machine (SVM) based directional relaying and fault classification scheme including inter-circuit faults, cross-country faults and high resistance faults. SVM modules are designed for forward or reverse fault identification and fault classification using single terminal data. The 3rd level approximate discrete wavelet transform coefficients of three phase current signals only have been used. Proposed method is tested with variations in fault type, fault location, fault inception angle, fault resistance, inter-circuit faults, and cross-country faults. The proposed method based on SVM does not need any threshold to operate which is an exceptional attribute for a protective function. As SVMs are not based on comparing with some threshold, rather initially the SVMs are trained with the wide variety of fault patterns which is an offline process and then the trained SVMs are tested online to detect and classify the fault within short time. The test results show that all types of shunt faults can be identified within half cycle time. The proposed scheme offers both primary protection to 95% of the line section and also backup protection to 95% of the adjacent reverse and forward line section also.     

新型大型发变组主保护方案的研究与试验——微机故障分量功率方向保护的应用

本文提出新型大型发变组主保护方案，其特点是基于故障分量原理，无需发电机中性点量，能够适应于各种绕组结构的发电机。文中围绕新方案的判据和算法，装置的硬软件构成进行讨论，并对动态模拟试验及其结果作了介绍。