Low cost microcontroller based fault detector,classifier, zone identifier and locator for transmission lines using wavelet transform and artificial neural network: A hardware co-simulation approach

A low cost, fast and reliable microcontroller based protection scheme using wavelet transform and artificial neural network has been proposed and its effectiveness evaluated in real time. The proposed scheme, based on the hardware co-simulation approach performs all the functions of transmission line protection i.e. fault detection/classification, fault zone/section identification and location estimation. The fault detection/classification and zone identification algorithms use fundamental frequency current component to estimate a fault index. The fault location estimation module uses wavelet transform coefficients in hybridization with a parallel artificial neural network structure. For hardware implementation, a 8-bit ATmega microcontroller is used and interfaced with the simulated power system model using Integrated Development Environment (IDE). The scheme is tested on a power system model of 400 kV, 50 Hz three phase double circuit line with source at both the ends. Laboratory tests have been performed in real time for 20,000 fault cases including evolving faults with varying fault resistance, fault inception angle, fault distance, direction of power flow angle and its magnitude. The tests confirm the suitability and reliability of proposed scheme even with Current Transformer (CT) saturation. The implementation of the proposed approach on a low cost microcontroller with the lesser execution time, makes the prototype ideal for implementation on a digital platform (digital relay), thus leading to financial viability and sustainability of the protection scheme.     

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.     

A critical fault detection analysis & faulttime in a UPFC transmission line

This paper discusses a critical study of fault detection and fault time analysis in a Unified Power Flow Controller (UPFC) transmission line. Here the Discrete Wavelet Transform (DWT) and Discrete Fourier Transform (DFT) approach are used for processing the faulty current signal to obtain fundamental current signal. The extracted fault current signals from the current transformer are fed to DWT and DFT approach for computing spectral energy (SE). The differential spectral energy (DSE) of phase currents are evaluated by taking the difference of SE obtained at sending and receiving end. The DSE is the key factor for deciding the fault in any of the phase or not. The Daubechy mother wavelet (db4) is used here because of its high accuracy of detection with less processing time. The novelty of the scheme is that it can accurately detect the critical fault variation of the line. Number of simulations are validated at the extreme condition of the line and compared to other conventional existing scheme. Multi-phase fault in double circuit line, CT saturation, UPFC operating condition (series voltage and angle), UPFC location and wind speed variation including wind farm simulation are validated to verify the performance of the scheme. The advantages of the scheme is that it works effectively to detect the fault at any stage of critical condition of the line and fault detection time remains within 20 msec (less than one cycle period). This scheme protects both internal and external zone including parameter variation of the line.     

基于分布参数模型的混合输电线路精确测距及重合闸方案

华东镇海—舟山500kV线路工程采用复杂的电缆-架空线混合输电线路,发生故障时无法准确对故障位置进行定位,且现有的重合闸方案无法实现自动识别架空线路故障并投入重合闸。文章提出一种基于分布参数模型的混合线路故障测距方案,方案采用正序故障分量,利用混合线路各段准确参数,分别采用线路两侧电气量计算沿线各点的电压有效值。根据两侧电气量计算的故障位置电压有效值相等的特点,对故障位置进行准确计算。且针对实际工程对重合闸的需求,提出一种故障位置区段定位方法。该方法通过比较用两侧电气量计算的电缆和架空线交界处的电压有效值对故障所在区段进行定位,以实现故障点位于电缆线路时不重合,故障点在架空线时重合闸。仿真结果表明,采用华东镇海-舟山500kV线路工程各段准确参数,各故障位置、各故障类型测距误差均不大于2.5%或±1km,测距结果不受过渡电阻影响,且可实现自动识别架空线故障并投入重合闸。     

A new single ended fault location algorithm for combined transmission line considering fault clearing transients without using line parameters

In this paper a new single ended fault location method is proposed for underground cable combined with overhead lines. In this algorithm fault clearing high frequency transients are used instead of fault-generated transients and the line parameters are not needed. In the proposed algorithm, samples just from voltage transients generated by fault clearing action of circuit breaker are taken from the sending end of the cable line. Applying wavelet transform, the first three inceptions of traveling waves to the fault locator are detected. Using these, the proposed algorithm at first identifies fault section, overhead or cable, and then wave speed is calculated and at last location of fault is determined accurately. Because of using only voltage samples taken from one terminal, it is simple and economic and does not need to GPS and data communication and synchronization. Extensive simulations carried out using SimPowerSystem toolbox of MATLAB, confirm the capabilities and high accuracy of the proposed method under different system and fault conditions.     

A combined impedance and traveling wave based fault location method for multi-terminal transmission lines

A new fault location method suitable for multi-terminal transmission lines that combines the advantages of both impedance and traveling wave based methods has been developed and presented in this paper. The proposed method first determines whether the fault is grounded or ungrounded by comparing the magnitude of the ground mode wavelet coefficients at the measurement end. Next, the impedance based method is used to identify the faulted half of the line in the case of two-terminal line and the faulted line section as well as the faulted half of the line section in the case of multi-terminal lines. Finally the fault location is determined by taking the time difference between the first two consecutive aerial modes of the current traveling waves observed at one end of the multi-terminal line. The proposed method has been tested on four- and five-terminal transmission lines with different types of faults, fault resistances and fault inception angles using ATP simulation.     

A new faulty section identification and fault localization technique for three-terminal transmission line

Owing to mal-operation of the conventional scheme during high resistance ground fault near tap point, a new faulty section identification and fault localization technique for three-terminal transmission line is presented in this paper. The proposed technique utilizes time-synchronized voltage and current signals from all the three terminals. Initially, fault detection based on estimation of superimposed voltage of tap point with reference to all three terminals has been carried out. Subsequently, utilizing the above three estimated superimposed voltages; faulty section identification criterion is formed. Finally, fault localization i.e. estimation of the value of fault distance and resistance has been performed. The authenticity of the proposed technique has been verified by simulating an existing 400 kV Indian three-terminal transmission network in PSCAD/EMTDC software. The simulation results point out that the proposed technique is able to identify the faulty section correctly. Moreover, it precisely estimates the value of fault distance and fault resistance as the percentage error for fault location and resistance remains within ±1.5% and ±3.5%, respectively. Likewise, its performance remains unaffected during wide variation in fault and system parameters. At the end, comparative evaluation of the proposed technique with the existing protection scheme clearly shows its superiority.     

Fast isolation of faults in transmission systems using current transients

This paper presents a protection scheme that is capable of very fast isolation of faults in high voltage transmission systems. Proposed scheme comprises set of relays connected through a telecommunication network, located at different nodes of the system. Relays use wavelet coefficients of current signals to identify the fault directions relative to their location. Fault directions identified at different locations in the system can be combined to determine the faulted line (or busbar) and isolate it. A robust single ended traveling wave based fault distance estimation approach is proposed as a backup in case of communication failure. Investigations were carried out using time domain simulations in PSCAD/EMTDC for a high voltage transmission system.     

Improved fault location algorithm for radial distribution systems with discrete and continuous wavelet analysis

This paper presents a novel wavelet based approach for fault location using voltage transient waveforms in power distribution systems. The proposed method includes two main stages. Firstly, the approximate location of the fault or fault section is determined using a new algorithm with discrete wavelet transform. The difference between arriving times of transient components in different measurement units is used for this purpose. The accurate location of the fault is determined in the second stage. Depending on the determined fault section, the difference between arriving times of transient components in different measurement units or the frequency content of the voltage transients are used. The time difference and frequency content are calculated using discrete and continuous wavelet transform (DWT and CWT) respectively. The proposed technique is implemented on an unbalanced 34 bus distribution system with two distributed generation units which is simulated in ATP–EMTP. The comparison of the results of the proposed method with previous works verifies its better accuracy and more robustness to fault conditions including fault inception angle and fault resistance.     

基于多方向元件的串补线路协同保护新方法

串补线路故障特征的复杂性加大了保护装置可靠动作的难度,为提高串补系统保护可靠性,提出一种多方向元件相互配合的串补线路方向保护方案。该方案利用负序电流值及故障前后的测量电流相位差判断故障类型,针对不对称短路、三相短路及负荷变动分别采用负序、工频方向及突变量电压电流相角差判断保护装置是否动作。PSCAD仿真表明,在系统发生电压反向、电流反向、经过渡电阻接地以及负荷变化等情况下该保护方案均可准确判断故障位置,从而使保护装置正确跳闸。同时,该方案不受MOV不同导通状态的影响,具有较好的保护性能。     

A practical fault location approach for double circuit transmission lines using single end data

Double circuit transmission lines are frequently subjected to a variety of technical problems from the perspective of protection engineering. These problems are mainly due to the mutual coupling effects between adjacent circuits of the line. In this paper, a new fault location approach for double circuit transmission lines is introduced. It depends only on the data extracted from one end of the line. This practically facilitates implementing and developing this approach, as it needs no information from the other end. The approach is based on modifying the apparent impedance method using modal transformation. Depending on modal transformation, the coupled equations of the transmission line are converted into decoupled ones. This greatly eliminates the mutual effects resulting in an accurate estimation for the fault distance in a straightforward manner. Also the effects of prefault currents, charging currents, and the unknown fault resistance on the estimation accuracy are compensated. The proposed approach was tested via digital simulation using ATP-EMTP in conjunction with MATLAB. Applied test results corroborate the superior performance of the proposed approach.     

配电网故障定位容错算法

非健全故障信息下故障区段的快速准确定位对于提高配电网供电可靠性具有重要作用。分析首端电压、电流量和短路回路等值电抗的关系,提出基于径向基函数(RBF)神经网络的短路回路等值电抗估计方法,仿真分析表明短路回路等值电抗估计结果受故障距离、过渡电阻的影响较小。然后,以馈线终端设备(FTU)故障信息和短路回路等值电抗为故障特征,应用改进的BP神经网络构建故障区段定位模型。对大量测试样本的分析表明,改进的BP神经网络建立的故障区段定位模型比极限学习机网络算法的定位精度高、泛化能力好,短路回路等值电抗能够辅助修正FTU故障信息的畸变,提高BP神经网络故障定位的容错性。     

Application of a distance relaying scheme to compensate fault location errors due to fault resistance

This paper proposes a distance relaying scheme based on the current phase jump behavior during fault conditions to improve the apparent impedance estimated by the distance relay. For a nonpilot protection scheme, the measured impedance is affected by error due to the combined effects of fault resistance and prefault load. An experimental relation between the current phase jump introduced with fault inception and the X/R ratio seen by the distance protection is deduced. The phase jump correction factor obtained is an exponential function of the X/R ratio of the line. This factor is applied to the apparent impedance measured by the relay and it allows mitigating the adverse effect of prefault power. The relaying scheme improves significantly the accuracy in estimation of the resistive fault location. The application of this scheme does not require communication links from the remote end of line and is applicable to all types of fault.     

基于电磁时间反转理论的非全程同杆双回线故障测距

为了解决非全程同杆双回输电线路故障测距中存在的双端数据不同步以及伪根识别的问题,首先利用故障区段识别函数组的正负相位特性确定故障发生的区段.在确定故障区段的基础上,采用了一种基于电磁时间反转的频域前行电流法进行故障测距.然后将故障区段两侧的电压、电流解耦后进行快速傅里叶分解,提取工频分量下的电流前行波并求取共轭.最后计...     

适用于单/双回线的双端非同步故障测距方法

单/双回线之间存在线间互感、跨线故障等特征差异,严重限制了单回线测距原理在双回线路中的应用。文中提出了一种适用于单/双回线的双端非同步故障测距方法。首先基于单回线网络结构,利用双端电压幅值比推导出双端非同步的故障测距方程。然后从双回线的网络结构和非对称参数着手,基于星角变换和六序变换原理分别建立单/双回线之间的联系桥梁,使基于单回线所提测距原理在双回线测距中能得以应用。仿真验证表明所提方法继承了双端工频测距法的优点,且无需双端数据同步,在单/双回线全线环境下均具有较高的测距精度,适用范围广。     

A transient current based double line transmission system protection using fuzzy-wavelet approach in the presence of UPFC

This paper presents a wavelet fuzzy based protection scheme for a double line transmission system with unified power flow controller. The protection scheme makes use of current signals at both the ends of transmission line which are synchronized with the help of global position system clock. A wavelet based multiresolution analysis is used to find the detailed coefficients of these signals which are utilized to calculate fault index. These fault indexes are compared with a threshold value to detect and classify faults on transmission system. The approximate decomposition of the current signals is utilized to locate the fault using Fuzzy logic from their respective terminals. The proposed algorithm has been tested successfully for various faults at different locations.     

High‐speed directional relaying using adaptive neuro‐fuzzy inference system and fundamental component of currents

This paper proposes an adaptive neuro‐fuzzy approach for fault direction estimation in sectional transmission lines. The ANFIS (adaptive neuro‐fuzzy inference system) network is designed by selecting different input and output member functions and rules for training and testing of fault cases. The fundamental component of current obtained from three‐phase current employing discrete Fourier transform (DFT) is given as input to the ANFIS module. The trained ANFIS module is then tested for detecting the fault direction. The relay is located at middle section‐2, which is considered as the primary section to be protected. It takes section‐1 as reverse section and section‐3 as forward section. This method is not affected by the variation of fault type, fault inception angle, fault location, and fault resistance. The biggest advantage of the ANFIS method is that it can detect the fault direction within 1 ms in almost all cases, which is much less than the implemented distance relaying scheme. The second advantage of the method is that it takes less number of training samples to detect the direction accurately as compared to other training algorithms like ANN, SVM, etc. The third advantage of the proposed scheme is that it offers protection to 99% of line length in all the three sections. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

不接地系统单相断线故障分析及区段定位

由于绝缘导线的应用,配电线路断线故障发生概率增大,现场缺乏有效的检测技术措施。针对不接地系统,建立了单相断线不接地故障模型。在考虑断线位置、故障线路对地电容占系统总对地电容的比例和负载阻抗的大小及其分布等因素的影响下,分析了中性点偏移电压、断口前后相电压以及线电压的变化规律。根据相电压和线电压的变化规律分别提出单相断线不接地故障区段定位的方法。所提方法可利用配电网自动化平台或者故障指示器系统实现,提高了断线故障区段定位的可靠性和适应性。最后用Matlab仿真验证了方法的正确性。     

A new wavelet based fault detection,classification and location in transmission lines

This paper deals with the application of wavelet transforms for the detection, classification and location of faults on transmission lines. A Global Positioning System clock is used to synchronize sampling of voltage and current signals at both the ends of the transmission line. The detail coefficients of current signals of both the ends are utilized to calculate fault indices. These fault indices are compared with threshold values to detect and classify the faults. Artificial Neural Networks are employed to locate the fault, which make use of approximate decompositions of the voltages and currents of local end. The proposed algorithm is tested successfully for different locations and types of faults.     

基于电压相位比较的双馈风电场输电线路单相接地距离保护

基于双dq坐标系的双馈感应发电机(DFIG)暂态模型,推导了DFIG正、负序突变量阻抗表达式并研究其相角变化特征。针对DFIG突变量阻抗角变化,提出一种单相接地时故障点序电流与保护安装处序电流之间相位差的计算方法,从而得到以保护安装处电压为参考值的故障点电压和补偿电压的相角。以区内外故障时故障点电压和补偿电压之间的相位关系为依据,提出适用于双馈风电场输电线路的电压相位比较距离保护方案。仿真结果表明,所提方法不受过渡电阻、故障位置及系统运行方式的影响,能够准确判别区内外故障。