Real time evaluation of DWT-based high impedance fault detection in EHV transmission

It is possible to capture the required travelling wave information contained in fault transients using wavelet transform. This paper presents practical real time testing for the high impedance fault (HIF) detection algorithm based on real time accidents data. The proposed scheme is implemented for HIF detection in extra high voltage transmission lines. The classifier is based on an algorithm that uses recursive method to sum the absolute values of the high frequency signal generated over one cycle and shifting one sample. Characteristics of this scheme are analyzed by extensive real time studies that clearly reveal that this technique can accurately detect HIFs in the EHV transmission lines within only half a cycle from the instant of fault occurrence. The reliability of this scheme is not affected by different fault conditions such as fault distance and fault inception angle.     

High impedance fault detection methodology using wavelet transform and artificial neural networks

This paper presents a new technique based on the combination of wavelet transform (WT) and artificial neural networks (ANNs) for addressing the problem of high impedance faults (HIFs) detection in electrical distribution feeders. The change in phase current waveforms caused by faults and normal switching events has been used in this methodology. The discrete wavelet transform (DWT) used decomposes the time domain current signals into different harmonics in time-frequency domain and extracts special features to train ANNs. This preprocessing reduces the number of inputs to ANN and improves the training convergence. The ANN structure and learning algorithm used in this method is the multilayer perceptron network and Levenberg-Marquardt back-propagation algorithm, respectively.The signal data of several HIFs, low impedance faults (LIFs) and normal switching events have been obtained by the simulation of a real distribution network, with five feeders, under these different operations conditions, using SimPowerSystem Blockset of MATLAB. The results obtained have validated the effectiveness of the proposed methodology to detect HIFs and discriminate them from normal transient operations.     

基于故障分量综合阻抗的T接线路纵联保护新原理

提出了一种适用于T接线路的基于故障分量综合阻抗的纵联保护新原理,利用故障时线路三端电压故障分量相量之和与电流故障分量相量之和的比值来判断线路上是否发生了故障.外部故障时,该比值反映线路的容抗,其模值较大;内部故障时,该比值反映系统电源阻抗和线路阻抗,其模值相对较小,据此可以区分线路上的内部和外部故障.根据新原理构成的保护不需要对电容电流进行补偿,可用于带或不带电抗器补偿的线路,在原理上不受过渡电阻的影响,而且当T接线路内部发生故障而有汲出电流时,保护的灵敏度也不受影响.EMTP仿真验证了新原理的有效性.     

Distance protection using a wavelet-based filtering algorithm

This paper presents a novel filter design technique based on the maximal overlap discrete wavelet transform (MODWT). Time and frequency response of the designed filters are compared to the ones of traditional discrete Fourier transform (DFT) based filters. The obtained results show improvements on response speed when comparing to full cycle traditional filters and improvements on frequency response when compared to half cycle traditional filters. According to these characteristics, the designed filter may be used in secure high-speed distance protection, since it provides fast relay operating times, without compromising their frequency response.     

基于故障分量虚拟阻抗的线路差动保护原理

针对传统纵联保护的不足,提出了一种基于故障分量虚拟阻抗的线路差动保护原理。考虑分布参数的影响,利用线路两端故障分量推导线路中任意点处的电压、电流故障序分量,并将二者之比定义为虚拟阻抗。取线路中点处各序的电流故障分量和虚拟阻抗构成保护判据,识别各种类型的故障。仿真结果表明,该判据能准确识别各种类型的故障,灵敏度和可靠性较高,且不受故障位置、过渡电阻、负荷电流、分布电容及信息同步的影响。     

输电线路故障行波保护综述

输电线路行波保护利用故障产生的行波快速识别故障,具有超高速动作性能,且不受电力系统振荡、过渡电阻、分布电容电流和电流互感器饱和等因素的影响,是理想的超特高压线路继电保护方式。该文首先回顾了行波保护的发展历程,从行波信号的提取、信号处理技术的发展和工程实践这三个方面总结了国内外的研究现状;其次介绍了主要行波保护的基本原理,分析了各类行波保护原理的优缺点,总结了相关理论研究的进展情况,并针对各类行波保护原理进行了横向比较及适用场景;然后探讨了行波保护技术实用化需要解决的主要问题,并提出了相应的解决方案;最后展望了行波保护的发展趋势,为后续行波保护技术的研究提供参考。#$NL关键词：输电线路;行波保护;保护原理;故障;超高速保护#$NL中图分类号：TM77     

STATCOM不对称控制策略下线路距离保护测量阻抗的改进算法

在电网三相电压不对称时,采用不对称控制策略能够保证静止同步补偿器（STATCOM）安全,实现良好的电压控制效果。针对较为复杂的单回并补双回线路,分析了线路短路后距离保护动作条件,证实采用不对称控制策略的STATCOM可能引起故障相保护拒动及非故障相保护误动。计及STATCOM注入电流,改进了故障测距算法。将故障距离值与线路正序阻抗配合,修正距离保护测量阻抗值。仿真结果验证了所提算法能够保证距离保护正确动作,避免接入STATCOM后重新整定距离保护。     

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.     

基于Hilbert-Huang变换的HVDC突变量方向纵联保护方法

高压直流输电线路的行波保护存在对装置采样率要求高及耐受过渡电阻能力差等问题。作为后备保护的纵联电流差动保护,为了防止线路分布电容等问题导致的误动,失去了速动性的优点,动作时间较长。利用HVDC线路发生区内外故障时,两端保护装置检测的电压和电流突变量的极性差异,提出基于Hilbert-Huang变换的突变量方向纵联保护方法。在分析不同故障时电压和电流突变量相位差别的基础上,采用Hilbert-Huang变换求取突变量相位差,识别两者的极性差异,进而判断故障发生的方向。基于PSCAD/EMTDC搭建了高压直流输电仿真模型,仿真结果表明,所提方法在各种故障情况下都能够实现保护的快速识别,可靠性高,且受过渡电阻的影响较小。     

A novel summation impedance protection adaptive to high‐resistance earth fault detection

While the high‐resistance earth fault frequently occurs on extra high voltage (EHV) transmission lines, existing protection schemes show great limitation for coping with this kind of fault scenario when the fault resistance is very high. In this paper, a novel protection methodology combining the measured impedance of the two ends is introduced, and a so‐called summation impedance protection, making use of this critical information, is thus put forward and assessed. Emphasis is placed on the principle of the summation impedance protection and its adaptive thresholds. A simulation model based on EMTDC/PSCAD, by which the performance of the summation impedance protection is evaluated, is then established. As confirmed by quantitative theoretical and experimental studies, the results indicate that the proposed protection scheme works well even when the fault resistance is extremely high under the internal fault condition, and it keeps itself from maloperation as an effect of its adaptive thresholds wherever an external fault occurs. These results highlight the necessity to work in conjunction with the existing main protections of transmission lines, by which means an enhanced ability to cope with the high‐resistance single‐phase earth fault can be achieved. © 2015 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.     

基于故障分量正序、负序和零序综合阻抗的线路纵联保护新原理

提出了故障分量正序综合阻抗、负序综合阻抗和零序综合阻抗的概念。发生区外故障时,故障分量正序综合阻抗等于线路正序容抗,负序综合阻抗等于线路负序容抗,零序综合阻抗等于线路零序容抗,数值较大;被保护线路上发生区内故障时,故障分量正序综合阻抗、负序综合阻抗和零序综合阻抗分别反映系统和线路的正序、负序和零序阻抗,数值较小。根据该特征,可以区分线路上是否发生故障,据此提出了基于故障分量正序综合阻抗、负序综合阻抗和零序综合阻抗的纵联线路保护原理,不需对电容电流进行补偿,灵敏度高,不受过渡电阻的影响,整定原则明确,定值裕度大。     

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.     

输电线路单端故障定位的阻抗-行波组合算法

为了提高输电线路单端故障定位的可靠性和精确性,提出了集测量阻抗法与行波法于一体的阻抗-行波组合算法。由测量阻抗法粗略地计算故障点位置,由该距离分别确定故障点反射波和对端母线反射波到达观测母线时刻的区域,分别在相应的区域内检测故障点反射波和对端母线反射波到达观测母线的准确时刻,并根据检测结果进行故障定位。该算法中测量阻抗法保证可靠性,行波法提高精确性,两者具有优势互补性。仿真试验验证了所提出的组合算法的正确性。     

高压直流输电线路暂态保护分析与展望

现时高压直流输电线路保护广泛采用ABB或西门子保护方案和配置。通过对ABB和西门子行波保护动作特性仿真结果分析及运行经验表明,二者保护方案无法可靠、灵敏地切除高阻接地故障,且易受噪声等外界信号干扰。同时,对国内外直流线路暂态保护的新思想进行分析总结,提出了提高高压直流输电线路暂态保护抗过渡电阻能力及区内、区外故障暂态分析所必须解决的几个关键性问题,为日后高品质直流线路保护判据的提出提供研究方向。     

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.     

基于XGBoost的配电网高阻接地故障检测方法

配电网高阻接地故障具有电气量微弱、与正常运行工况相似等特点,因此难以检测。针对传统指标阈值法常由经验整定,在复杂环境下适应性较差、灵敏性不足等问题,提出一种基于极端梯度提升(extreme gradient boosting, XGBoost)的配电网高阻接地故障检测方法,以避免复杂的阈值整定。首先,通过建立10 kV中压配电系统高阻接地故障的等效模型,获取高阻接地故障和正常运行工况的零序电流数据。然后,在对数据进行归一化处理的基础上,利用XGBoost直接从原始量测信息中学习其与高阻接地故障的映射关系,构建高阻接地故障检测模型,以降低因特征提取产生的误差。最后,大量仿真结果表明,所提方法对高阻接地故障检测具有较好的灵敏性和速动性,并且在噪声和数据缺失等情况下表现出较强的泛化能力。     

一种采用纵向阻抗的变压器保护算法

针对变压器差动保护需要通过二次谐波等算法来识别励磁涌流的问题,在纵向阻抗保护原理的基础上提出一种基于故障序分量的变压器保护算法。利用故障序分量纵向阻抗在内部故障小于变压器漏阻抗,在外部故障、空载合闸大于变压器漏阻抗的特点,算法能够可靠识别故障区域。在变压器空载合闸时依据输电系统中稳定的阻抗关系,可以有效抵御励磁涌流的影响,使得保护算法在空载合闸时可靠不动作。同时考虑区外故障电流互感器可能发生的各种饱和情况,算法能够正确识别故障区域,具有较强的抗干扰能力。通过在PSCAD中进行仿真试验,结果表明算法不受电流互感器饱和、励磁涌流的影响,具备较强的可靠性和抗干扰能力,拥有良好的工程应用前景。     

特高压直流输电线路接地极线路高阻故障测距方法研究

直流接地极线路不同于直流输电线路,其在正常运行下,电压电流的值均很小,且极址点是通过阻值很小的过渡电阻接地,因此接地极线路精确定位是故障测距的难点。理论分析和仿真表明,当接地极线路发生接地故障,且接地点电阻大于或等于极址电阻时,流入故障点的电流很小,利用沿线电压分布推导得到的故障点电压不再是电压在线路上分布的最小值,而极址点电压是沿线电压分布的最小值。因此根据故障点电压相等来构造测距函数的测距原理存在不足之处。利用极址点电压相等构造测距函数,提出一种基于故障录波数据的耐受高阻接地的直流接地极线路故障测距新方法。大量仿真表明,该算法可以实现接地极线路的精确定位,对采样率要求不高,便于工程实际运用。     

基于故障分量原理的配电网高阻接地故障检测方法

配电网中发生高阻接地故障时,短路电流小于传统过流保护的阈值,无法被常规保护装置检测和清除。若不及时消除短路电路,极易演化成严重故障。针对该问题,文中首先分析发生高阻接地故障时配电网的故障分量特征和基于母线处的正序电压故障分量与其相连接的各馈线正序电流故障分量的相位差特征,给出适用于配电网高阻接地故障检测的故障判据。然后,为解决配高阻接地故障检测过程中系统不平衡引起的一系列问题,制定了相应的故障检测启动判据。基于该故障检测判据和启动判据,制定基于故障分量原理的配电网高阻接地故障检测方法。最后,在PSCAD/EMTDC仿真软件中建立含架空线路的中压配电网模型,仿真结果验证了所提高阻接地故障检测方法的正确性。     

高频保护通道故障监测方法的研究

电力系统高频保护是保证电力系统通信正常工作的一个重要保护系统,在线监测高频通道对电力系统安全运行具有重要意义。文章论述了高频通道的组成情况,在比较几种在线检测方法的基础上,选择了输入阻抗法进行数值Matlab仿真。仿真结果表明,可以将高频通道中不同元件损坏时的输入阻抗变化作为故障监测的依据,为高频保护通道在线监测系统提供一定的理论指导。