Fault diagnosis in distribution networks with distributed generation

The penetration of distributed generation (DG) in distribution power system would affect the traditional fault current level and characteristics. Consequently, the traditional protection arrangements developed in distribution utilities are difficult in coordination. Also, the reclosing scheme would be affected. With the rapid developments in distribution system automation and communication technology, the protection coordination and reclosing scheme based on information exchange for distribution power system can be realized flexibly. This paper proposes a multi-agent based scheme for fault diagnosis in power distribution networks with distributed generators. The relay agents are located such that the distribution network is divided into several sections. The relay agents measure the bus currents at which they are located such that it can detect and classify the fault, and determine the fault location. The proposed technique uses the entropy of wavelet coefficients of the measured bus currents. The performance of the proposed protection scheme is tested through simulation of two systems. The first system is a benchmark medium voltage (MV) distribution system and the second system is practical 66 kV system of the city of Alexandria.     

电压电流能量信息融合的低压交流电弧故障检测

针对串联电弧故障检测判据选择难、阈值设置难的问题,本文在传统基于电流检测方法的基础上融合使用电压信息,提出了一种电压电流能量信息融合的交流电弧故障检测方法。以分析开关电源和非开关电源类负荷下的各自故障特征为基础,提出了利用电压半波总能量的开关电源类电弧故障直接判定方法,并融合使用电压电流特征能量波形相关性实现故障线路的选择;提出了基于敏感域电压电流最大瞬时特征能量相位匹配的适用于非开关电源类负荷下的故障检测方法,以特征能量相位信息构建判据,克服了传统检测方法的阈值设定困难问题。本文检测方法判据虽利用了负荷分类思想,但由于开关电源类负荷下的故障检测可利用电压半波总能量幅值实现故障直接判定,因此实际应用中无需辨识负荷类型。相较传统利用电流特征的检测方法,本文方法具有判据简单、易于阈值设定的优势。试验结果表明,本文方法可有效用于多种类型负荷的电弧故障检测,检测时间满足相关标准规定。     

基于改进经验小波变换和改进多视角深度矩阵分解的直流配电网故障检测方案

为快速检测及可靠识别直流配电网故障，提出一种基于改进经验小波变换和改进多视角深度矩阵分解的直流配电网故障检测方案。通过最小二乘法非线性拟合故障电流局部的相频谱函数，基于此在一定的条件下修改经验小波函数的相频响应，使之尽可能与故障电流的局部相频特性相匹配；运用改进经验小波变换分解电流，计算细节分量c3的模极大值，构造故障检测判据；设计一种权重自学习网络，依据数据对分类任务的重要性分配不同的权重，嵌套于多视角深度矩阵分解模型前端，运用改进多视角深度矩阵分解模型对电流分量c1 — c3、极间电压udc这4个视角的数据进行故障特征提取，通过软分配层实现故障的分类。仿真测试结果表明，所提故障检测方案能够满足故障检测速动性、可靠性的要求，故障分类准确度高，为后续故障处理奠定了良好基础。     

Identifying Single-Phase-to-Ground Fault Feeder in Neutral Noneffectively Grounded Distribution System Using Wavelet Transform

A scheme of single-phase-to-ground fault feeder identification in distribution networks with the application of a wavelet transform technique is presented in this paper. The scheme uses zero-sequence current traveling waves to identify the faulted feeder, and the busbar residual voltage to determine an event caused by fault or switch operation. The current traveling waves measured by zero-sequence current transducers are decomposed using wavelet multiresolution analysis. The local modulus maxima of the wavelet transform are extracted to determine the time of the initial traveling wave. The wavelet transforms on all feeders at the time are compared in magnitude and polarity with each other to identify the faulted feeder. The feeder identification is independent of the network neutral-point grounding mode. The proposed scheme was implemented and verified using Electromagnetic Transients Program (EMTP)-generated signals. The scheme proved to be robust against transients generated during normal events, such as feeder energizing and de-energizing as well as capacitor bank switching.     

A fault location technique for rural distribution feeders

This work presents a digital fault location technique for rural distribution feeders, using the voltage and current data at a single location. Rural distribution feeders include single-phase, two-phase, and three-phase laterals off a main three-phase primary distribution feeder. The fault location scheme presented here attempts to account for the multiphase laterals, the unbalanced conditions, and the unsymmetrical nature of distribution feeders by continually updating voltage and current vectors at set locations within the system. The updated voltage and current vectors are the estimates of the 60-Hz phasor quantities obtained using a recursive optimal estimation algorithm. The distance to the fault is then estimated using a method based on the apparent impedance approach and the updated voltage and current vectors. Another consideration is the ability to determine the fault location on a lateral. A simulation of an actual rural distribution feeder using the Electromagnetic Transients Program (EMTP) is used to test the approach     

电力系统的集成保护

通过介绍一种新颖的配电网保护方案来阐述集成保护的优越性。这个基于暂态极性方向比较的保护方案以伴随故障出现的暂态电流信号的检测和处理为基础,在配电网的各个变电站安装有专门设计的保护继电器,继电器的暂态检测单元检测故障生成的故障分量电信号,并将暂态极性识别算法应用于叠加故障分量信号上,判断信号的极性。通过对来自连接到变电站的所有线路的信号极性进行比较,可以确定出故障的方向。通过处理来自各变电站的方向信息,判别出实际的故障线路,从而实现电网的集成保护。     

基于电流相角突变量方向的有源配电网保护

随着分布式电源(DG)的大量接入,配电网的结构由传统的辐射型改变为多端电源系统。由于DG出力的随机性,传统的基于电流幅值的保护方案很难整定。通过研究故障前后电流相角的变化,得出了电流相角突变量方向与故障位置的关系,并由此提出一种新的电流纵联方向保护方案。由于该方案只利用电流信息,避免了安装电压互感器。对于规模巨大的配电网,具有经济性。由于只需传输判定结果,降低了对通信通道的要求。最后,通过仿真分析,对保护方案进行了验证。     

Fault Location in Neutral Non-effectively Grounded Distribution Systems Using Phase Current and Line-to-line Voltage

Abstract—A scheme of single-line-to-ground fault location in neutral non-effectively grounded distribution systems is proposed in this article. The characteristics of phase current traveling waves and line-to-line voltage traveling waves are analyzed. The wavelet transform technique is used to extract the information of the arrival times, polarities, and amplitudes of the recorded traveling waves. The fault location scheme can simultaneously realize faulty feeder identification, fault section location, and fault position location even if only two-phase current transformers are installed in the Phases A and C and feeder terminal units only to provide line-to-line voltage information. The effectiveness and practicability of the proposed scheme have been verified by PSCAD/EMTDC simulation results.     

含分布式电源的三相不平衡配电网连续潮流计算

连续潮流是电力系统电压稳定分析的重要工具。针对含不同类型分布式电源的配电网及其三相线路参数和负荷不平衡的情况,提出了一种三相配电网连续潮流方法,由切线预测环节和牛顿法校正环节组成,并采用局部几何参数化策略处理三相不平衡系统PV曲线的斜锐角现象。考虑了PV和PQ节点类型分布式电源的限值约束,给出了新的节点类型双向转换逻辑和分岔点类型识别方法。通过对IEEE 33节点配电系统进行算例仿真,表明所述算法可以有效追踪三相配电系统的PV曲线,准确计算电压稳定临界点并识别分岔点类型。     

光学电流传感器用于配电网单相接地故障电流检测

针对小电流故障选线及定位困难的状况,从改善量测手段的角度考虑,提出光学电流传感器（OCT）在小电流故障选线定段中的应用方案。给出2种形式的零序光学电流传感器（ZOCT）结构,即组合型ZOCT与全光纤型ZOCT,分别适用于电缆线路和架空线路,并对方案的可行性及ZOCT的实现问题进行了论证。     

基于电压偏差向量2-范数的主动配电网故障定位新方法

随着分布式电源在配电网中渗透率的提高,现有的一些故障定位算法可能失效,对此,提出了一种基于最小电压偏差向量2-范数的故障定位算法。首先,根据配电网各节点注入的等效故障电流计算各电源处电压变化值,并比较各电源处电压变化测量值与电压变化计算值之差,搜索差值向量最小2-范数对应的故障电流注入节点从而确定故障区段的第一个节点,其次,通过该节点两侧电压差值变化确定故障区段的另一节点,实现故障区段定位。最后,利用IEEE 34节点三相不平衡系统进行了故障定位分析,结果表明算法物理意义明确、计算过程简单且具有良好的故障定位准确度。     

A new and accurate fault location algorithm for combined transmission lines using Adaptive Network-Based Fuzzy Inference System

This paper presents a new and accurate algorithm for locating faults in a combined overhead transmission line with underground power cable using Adaptive Network-Based Fuzzy Inference System (ANFIS). The proposed method uses 10 ANFIS networks and consists of 3 stages, including fault type classification, faulty section detection and exact fault location. In the first part, an ANFIS is used to determine the fault type, applying four inputs, i.e., fundamental component of three phase currents and zero sequence current. Another ANFIS network is used to detect the faulty section, whether the fault is on the overhead line or on the underground cable. Other eight ANFIS networks are utilized to pinpoint the faults (two for each fault type). Four inputs, i.e., the dc component of the current, fundamental frequency of the voltage and current and the angle between them, are used to train the neuro-fuzzy inference systems in order to accurately locate the faults on each part of the combined line. The proposed method is evaluated under different fault conditions such as different fault locations, different fault inception angles and different fault resistances. Simulation results confirm that the proposed method can be used as an efficient means for accurate fault location on the combined transmission lines.     

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.     

含光伏电源配电网的复合序网自适应保护

含光伏电源(PV)的配电网,因光伏电源容量、并入位置不同,导致传统的三段式电流保护不能准确动作。针对这一问题,提出根据保护点复合序网电压和电流进行自适应电流保护整定的方案。首先,提取故障电压和正序故障电流相位差来判定故障发生在光伏电源上游还是下游。然后,由序分量判定故障类型,选定故障区域。最后,利用复合序网电压求取保护安装处的电流整定值,进行自适应保护动作。通过仿真验证了该保护方案可根据光伏电源并入位置、容量、发生故障位置的不同,实现自适应在线保护整定,能够有效提高本地保护范围。     

逆变器功率管开路故障诊断方法综述

作为各种新能源发电设备和驱动系统的核心部分,逆变器的安全性和可靠性对整个系统的安全稳定运行至关重要。近年来,高电压等级、高功率密度和高集成化的逆变器已成发展趋势,但增加更多的开关器件也会增大其故障概率,因此,采取快速有效的方法对逆变器的故障进行诊断十分重要。针对逆变器功率管故障诊断,目前的分类方法主要分为基于解析模型、基于信号处理和基于数据驱动3种。为使诊断方法分类简单直观,从实际电路中检测变量的角度,在电流、电压和功率3个方面对国内外文献进行整理,阐述了各类方法的原理、适用范围和优缺点,最后概述了逆变器故障诊断的难点和未来的发展趋势。     

智能配电变压器的串变调压和基于漏磁的绝缘故障检测技术

为了解决分布式能源接入配电网后电压的频繁波动和双向潮流问题,提出一种基于串联变压器的调压技术。利用真空接触器和晶闸管来控制串联变压器的变比和星-角变换,实现电压的快速调整。分析了基于串联变压器的调压原理及基于真空接触器和晶闸管的混合开关调压技术。此外,还提出了基于漏磁通的绕组绝缘故障监测技术,说明它的原理、实现技术和实验验证原理。分析结果表明,提出的技术能够有效地解决配电网电压频繁波动的问题,提高配电变压器的寿命、降低配电变压器的损耗,同时提高配电变压器的智能化程度和可靠性。     

基于线路电流二阶导数的中压直流系统故障识别方法

直流线路故障的快速有效识别是基于电压源型换流器的中压直流配电系统发展的关键技术之一。直流线路故障电流上升十分迅速,系统中电力电子器件过载能力小。因此以串入直流线路限流电感的中压直流配电系统为基础,分析直流系统的故障特性,在此基础上提出基于线路电流二阶导数的中压直流配电系统直流线路故障快速识别方案。该方案能够实现故障侧、故障类型及故障线路极性的快速识别,进而实现对线路的保护。最后基于Matlab验证了所提故障检测方案的有效性,并与基于线路电流一阶导数的故障检测方案进行了对比。仿真结果表明所提方法在故障电阻、故障距离及负载发生变化的情况下仍可实现直流线路故障的快速准确检测,且相比基于线路电流一阶导数的直流线路故障检测方案具有更好的选择性。     

含分布式光伏及储能变流器的微网故障特征与保护

在并网时,微网中所含的分布式电源可能包括恒功率控制的光伏变流器或电流下垂控制的储能变流器,其中传统电流下垂控制的储能变流器在电网电压跌落时所输出的较低的故障电流,以及可能会出现的功角失稳现象都为其故障保护带来了困难,而基于滞环控制的改进电流下垂控制可以使其在电网故障时保持功角稳定,同时具备低压穿越能力,给故障电流带来新的特征,有利于故障检测以及保护判据的配置。本文考虑变流器的低压穿越特性,分析了含分布式光伏及储能变流器的微网内部不同位置发生故障时的电流特征,利用正序电流故障分量与母线正序电压故障分量的相位差来判断故障方向,并提出基于EtherCAT工业以太网的集中式保护方案。最后,通过仿真与实验验证了所提方案的可行性。     

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     

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