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 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.     

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.     

Research on the protection coordination ofpermanent magnet synchronous generatorbased wind farms with low voltage ridethrough capability

This paper proposes a pattern recognition based differential spectral energy protection scheme for ac microgrids using a Fourier kernel based fast sparse time-frequency representation (SST or simply the sparse S-Transform). The average and differential current components are passed through a change detection filter, which senses the instant of fault inception and registers a change detection point (CDP). Subsequently, if CDP is registered for one or more phases, then half cycle data samples of the average and differential currents on either side of the CDP are passed through the proposed SST technique, which generates their respective spectral energies and a simple comparison between them detects the occurrence and type of the fault. The SST technique is also used to provide voltage and current phasors and the frequency during faults which is further utilized to estimate the fault location. The proposed technique as compared to conventional differential current protection scheme is quicker in fault detection and classification, which is least effected from bias setting, has a faster relay trip response (less than one cycle from fault incipient) and a better accuracy in fault location. The significance and accuracy of the proposed scheme have been verified extensively for faults in a standard microgrid system, subjected to a large number of operating conditions and the outputs vindicate it to be a potential candidate for real time applications     

Modeling methodology and faultsimulation of distribution networksintegrated with inverter-based D

This paper proposes a pattern recognition based differential spectral energy protection scheme for ac microgrids using a Fourier kernel based fast sparse time-frequency representation (SST or simply the sparse S-Transform). The average and differential current components are passed through a change detection filter, which senses the instant of fault inception and registers a change detection point (CDP). Subsequently, if CDP is registered for one or more phases, then half cycle data samples of the average and differential currents on either side of the CDP are passed through the proposed SST technique, which generates their respective spectral energies and a simple comparison between them detects the occurrence and type of the fault. The SST technique is also used to provide voltage and current phasors and the frequency during faults which is further utilized to estimate the fault location. The proposed technique as compared to conventional differential current protection scheme is quicker in fault detection and classification, which is least effected from bias setting, has a faster relay trip response (less than one cycle from fault incipient) and a better accuracy in fault location. The significance and accuracy of the proposed scheme have been verified extensively for faults in a standard microgrid system, subjected to a large number of operating conditions and the outputs vindicate it to be a potential candidate for real time applications     

利用站域信息的智能变电站变压器后备保护方案

采用复压过流原理的变压器后备保护方案存在灵敏度不足、整定配合复杂、故障切除延时过长等问题。提出在智能变电站中采用主后备分离模式的变压器保护配置方案。单独配置的后备保护,利用站域共享信息,以方向比较原理为基础确定故障位置,实现对变压器内部故障、中低压母线故障、死区故障和断路器失灵的后备保护功能。对于不对称故障采用负序、零序方向元件,对于三相故障采用基于正序电流幅值相位比较的方向元件。通过在PSCAD中建立典型的110 k V变电站模型,对于各种故障类型进行仿真,验证了所研究的后备保护方案的有效性。     

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.     

一种改进的纵联零序方向保护方案

相较于单回线,同塔双回和多回输电线路发生故障时零序特征更为复杂多变,导致传统的纵联零序方向保护误动或拒动频发。首先从灵敏度、弱电强磁和跨线故障三个方面分析了传统纵联零序方向保护的性能,指出其中存在的问题。然后,提出了一套新型的纵联零序方向保护方案:通过零序方向电压补偿算法提升零序方向元件在高阻故障下的灵敏度,通过零序综合方向元件消除零序互感的影响,构造了跨线故障识别逻辑。最后,通过三个现场实例分析,验证了该算法的有效性。     

A novel protection scheme for synchronous generator stator windings based on SVM

This paper proposes a novel scheme for detecting and classifying faults in stator windings of a synchronous generator (SG). The proposed scheme employs a new method for fault detection and classification based on Support Vector Machine (SVM). Two SVM classifiers are proposed. SVM1 is used to identify the fault occurrence in the system and SVM2 is used to determine whether the fault, if any, is internal or external. In this method, the detection and classification of faults are not affected by the fault type and location, pre-fault power, fault resistance or fault inception time. The proposed method increases the ability of detecting the ground faults near the neutral terminal of the stator windings for generators with high impedance grounding neutral point. The proposed scheme is compared with ANN-based method and gives faster response and better reliability for fault classification.     

海上风电柔性直流送出线路的纵联保护方法

海上风电柔性直流送出系统常采用伪双极接线。当发生单极接地故障时,电流纵联保护不能可靠地区分区内、外故障。针对该问题,提出了一种适用于海上风电柔性直流送出线路的行波方向纵联保护方案。分析了伪双极直流系统的单极接地故障特征,提出了电流纵联保护在海上风电柔直送出线路的问题。基于行波原理,提出了不受暂态分布电容电流影响的保护方案。该方案利用线路两端的行波方向保护分别进行故障方向判断,然后通过方向纵联判断区内、外故障。PSCAD仿真验证了该方案能快速、可靠地识别故障,且具有较强的抗过渡电阻能力。     

Fault location method applied to transmission lines of general configuration

Power quality is an important concern once automation is present in almost all industrial process. Since fault occurrences affects the power quality considerably, in this paper is proposed a new fault location method applied to transmission lines constituted of any configuration, as example double circuit, untransposed sections, and multiple derivations.In order to locate the fault, the method uses voltage and current phasors gathered from terminals with measures, however the method does not need these measures from all terminals.The proposed method is composed of three blocks to locate the fault, which are: Algorithm’s Main Control, Grid Scanning Process, and Objective Function’s Minimization Process.A large number of simulations were conducted and the results show the accuracy and efficiency of the method, even in cases of high impedance faults.     

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.     

采用电流突变量夹角余弦的直流电网线路纵联保护方法

直流线路的保护是多端柔性直流电网发展面临的关键问题之一。文中针对现有纵联电流差动保护存在的问题,提出了一种采用电流突变量夹角余弦值的纵联保护方法,它利用线路两端电流突变量计算夹角余弦值从而进行区内、外故障判断。区内故障时,线路两端电流突变量方向相反,夹角余弦值为负值;区外故障时,线路两端电流突变量方向相同,夹角余弦值为正值。保护方法采用改进电压梯度法快速启动,并利用正、负极电压比值来识别故障极。仿真表明,所提出的保护方法不仅可以可靠识别区内、外故障,同时具有较强的耐过渡电阻能力且不易受线路分布电容电流的影响。     

Wide area measurements based faultdetection and location method fortransmission lines

Electric power grids are critical infrastructure for delivering energy from generation stations to load centers. To maximize utilization of assets, it is desirable to increase the power transferred over transmission systems. Reliable protection of transmission systems is essential for safeguarding the integrity and reliability of the power grid. Distance protection is the most widely used scheme for protecting transmission lines. Most existing protection systems use local measurements to make a decision while pilot protection is used in some circumstances. Distance protection may fail under stressed operating conditions, which could lead to cascading faults. This paper proposes a system integrity protection scheme by utilizing wide area measurements. The scheme partitions the system into subnetworks or protection zones and employs current measurements to derive a fault identification vector indicating the faulted zone. Then the fault location is pinpointed based on wide area measurements and network data. The proposed method is able to deal with multiple, simultaneous faults, and is applicable to both transposed and untransposed lines. Evaluation studies based on simulation studies are presented.     

Transmission line individual phase impedance and related pilot protection

This paper proposes a kind of new Individual Phase Impedance (IPI) and a novel pilot protection scheme for transmission line based on the IPI. The IPI is calculated by the ratio of the voltage difference of fault-superimposed component to the current difference of fault-superimposed component at both terminals of the protected line. The IPI has accurate mathematical expressions and reasonable physical definitions for various line models. The calculated result of IPI can be used to distinguish the internal faults from the external faults. When the IPI is identical to the value of line positive-sequence impedance, the external fault is detected; otherwise, the internal fault is detected if it differs from that value. The feature of the pilot protection scheme is that the inter-phase coupling relation and the distributed capacitance based on the three-phase line model are directly considered and included in the IPI expression. The novel pilot protection can be used for long distance HV transmission lines with some preeminent performances which are deficiency in the conventional directional comparison pilot protection and current differential protection. The test results obtained by EMTP simulation and from a laboratory model of a simplified real power system have demonstrated that the pilot protection is of high reliability and good adaptability.     

A novel pilot protection principle for VSC-HVDC cable lines based on fault component current

This paper presents a novel pilot protection principle for VSC-HVDC cable lines based on fault component current. In the transient process of cable line, if a fault occurs over the cable line, the current measured at both convert stations would have the same changing direction and the signs of the fault component current at both convert stations are the same to each other; otherwise, if a fault occurs beyond the cable line, the current measured at two convert stations would have the opposite changing direction and the sign of the fault component current at both convert stations are opposite to each other. According to this characteristic, the directional element can be located at both convert stations and state signal can be sent to the other station. Thus, the pilot protection principle can be implemented only using two terminal current. In addition, the setting principle is proposed based on fault component current in this paper. The proposed pilot protection principle is simple, reliable, and practical. It can be implemented with a low sampling rate and does not need the current data synchronization seriously. Compared with current differential protection, the proposed method has a low requirement on baud rate. At the same time, various faults are simulated by using the system of VSC-HVDC built in PSCAD/EMTDC, in which frequency-dependent parameter cable line model is adopted. The simulation results show that the method can identify the fault reliably and rapidly in different conditions only using the current measured at both convert stations and has sufficient sensitivity for high resistance ground fault.     

Powerformer定子单相接地保护研究

提出一种基于故障分量能量函数的Powerformer定子单相接地保护新原理。不同于传统保护方案需要测量发电机中性点和机端的基波零序电压和3次谐波电压,文中提出的方法利用Powerformer机端处的零序电流和母线处的零序电压,通过分析能量方向检测接地故障,对于发电机区内故障和区外故障具有很好的区分性。MATLAB仿真结果证明,在不同的故障情况下,该方案具有较高的灵敏性和可靠性,能够满足Powerformer的保护要求。     

基于分布参数模型的高压直流输电线路距离保护

对于距离保护而言,没有必要全线准确测距,只要边界准确,能正确区分区内、区外故障即可.文中针对直流输电线路两端连接有平波电抗器,具有明显的边界特征,提出一种高压直流输电线路距离保护时域算法.该方法建立在分布参数模型基础上,通过保护安装处的电压、电流量,计算得到线路末端的电压、电流量,再应用微分方程算法计算出故障距离,以此作为保护动作依据.针对直流线路近端故障时,测距误差大且保护可能拒动的问题,提出了两段式距离保护的解决方法.仿真表明,基于该算法的保护可以正确辨别区内、区外故障,在全线范围内动作快速、可靠.     

发电机匝间保护与负序功率方向元件

在采用纵向零序电压的方式来反映发电机的匝间短路故障时,为防止电压互感器(TV)断线误动作,采用TV断线闭锁逻辑。然而由于某些保护制造厂逻辑功能软件的不严密,在发电机TV一次断线时,匝间保护时常发生误动作。提出增加用负序功率方向元件来进行判断内外部故障,可以有效防止匝间保护误动作。     

新型变压器零序差动保护方案设计

从保护方案设计和保护逻辑两方面详细论述了一种新型的变压器零序差动保护方案。方案设计中引入了外部故障异步区分、方向判据及二次谐波闭锁判据来可靠区分区内、区外故障,并介绍了差动电流、制动电流的选取。经试验证明该方案安全可靠,能够充分发挥零序差动保护对接地故障灵敏度高的优势。目前,该方案已实际应用于某变压器的保护装置中。