Adaptive restarting method for LCC-HVDC based on principle of fault location by current injection

The existing LCC-HVDC transmission project adopts the fixed-time delay restarting method. This method has disadvantages such as non-selectivity, long restart process, and high probability of restart failure. These issues cause a secondary impact on equipment and system power fluctuation. To solve this problem, an adaptive restarting method based on the principle of fault location by current injection is proposed. First, an additional control strategy is proposed to inject a current detection signal. Second, the propagation law of the current signal in the line is analyzed based on the distributed parameter model of transmission line. Finally, a method for identifying fault properties based on the principle of fault location is proposed. The method fully considers the influence of the long-distance transmission line with earth capacitance and overcomes the influence of the increasing effect of the opposite terminal. Simulation results show that the proposed method can accurately identify the fault properties under various complex fault conditions and subsequently realize the adaptive restarting process.     

农村配电网单相接地故障定位方法研究

介绍了国内外农村配电网单相接地的故障定位方法,提出了一种基于小波变换对信息进行处理的反射行波分析法。利用农村配电网架空线路带有分支的特点,对各个分支点的反射波进行信号分析,根据小波变换后的模极值和矩阵特征值来确定故障位置。结果表明反射行波分析法能准确地确定故障位置。     

A Novel Scheme to Connect Wind Turbines to the Power Grid

In this paper, a new scheme is proposed to connect wind turbines to the power grid. This scheme helps in limiting the fault currents as well as in voltage unbalance compensation. Voltage is injected in series with the transmission line to limit the fault currents as well as to balance the voltages. This scheme allows wind turbines to remain synchronized to the grid during faults or during low voltages and is useful for doubly fed as well as squirrel cage induction generators.      

形态小波在输电线路故障测距中的应用

如何准确提取行波浪涌到达时刻,是输电线路行波测距领域中的一个重要研究课题。提出一种新的输电线路故障测距算法,该算法通过形态学算子构造非线性提升方案,从信号的时域上提取奇异点,能够较为快速和准确地定位奇异发生的时刻,适合应用于输电线路故障测距。仿真结果表明,基于提升方案的形态小波（MW）在进行输电线路故障测距时能够不受故障类型、故障点位置、过渡电阻和故障合闸角的影响,与传统的小波算法相比,具有算法量小和易于实现的特点。     

基于深度学习与不平衡样本集的输电线路故障分类

针对输电线路各类型故障样本间的数量不平衡会造成人工智能算法对故障中的少数类样本识别精度不足的问题,提出了一种基于Borderline-SMOTE(BSMOTE)算法与卷积神经网络(CNN)相结合的输电线路故障分类方法.该方法首先利用BSMOTE算法对位于分类边界上的少数类样本进行过采样合成处理,改善样本间的不平衡度,然...     

New Fault Location System for Power Transmission Lines Using Composite Fiber-Optic Overhead Ground Wire (OPGW)

This paper describes a new method of locating the section where an electrical fault occurs on a power transmission line using Composite Fiber-Optic Overhead Ground Wires (OPGWs). This fault location (FL) method locates the fault section by measuring the current induced in the ground wire (GW), i.e., OPGW in this system. The OPGW currents are measured at many towers which divide the power line into sections. Data is transmitted to a central monitoring station as an optical signal through the optical fibers included within OPGW. Prior to the development of this new FL system, a simulation of power line faults using Electro-Magnetic Transients Program (EMTP) was conducted. As a result, the following two points were clarified; 1) Since OPGW current changes with line condition, it is quite difficult to define a fixed threshold level to locate fault sections accurately. 2) The distribution pattern of OPGW current along the power line has clear features around the fault point, so it is possible for electric power engineers to find the fault section by relative comparison. Therefore, the FL algorithm to be developed should have the capability of finding out the fault section with a human-like method of recognition. Fuzzy Theory, an attempt to include this kind of humanlike way of thinking into computers, was investigated and a new FL method applying this theory was developed. Fig. 1 shows the OPGW current distribution pattern of a typical grounding fault calculated by EMTP as an example.     

基于堆叠自动编码器的输电线路故障选相方法

针对人工神经网络(ANN)用于输电线路故障选相时收敛性差的问题,提出一种基于堆叠自动编码器(SAE)的故障选相方法,即先构建SAE深层架构模型,再将线路两端采集的故障电流、电压及相关序分量组成的综合电气量数据作为输入特征对SAE进行两阶段训练学习,该模型可充分提取输入量的高阶特征,能够对复杂故障数据进行较好地分类,进而得到精准的选相结果。仿真试验和现场实际故障数据的测试结果表明,该方法受故障位置、过渡电阻、系统电压及负荷水平等因素影响小,较人工神经网络(ANN)有更优的收敛性能和选相准确率。     

基于行波时域分析和VMD的多分支输电线路故障定位

考虑多分支输电线路的行波时域特性,提出一种基于行波时域分析和VMD的多分支输电线路故障定位方法,利用主干线路时域信息和支路频域信息进行故障定位。首先,分析了主干线路的行波时域特性,根据故障后到达主干线路首末端的初始行波时间差判定故障区段;然后,利用VMD分解故障电压行波信号,通过MUSIC谱估计获得其固有频率主成分;最后,利用初始行波时间差、固有频率主成分与故障距离的关系来确定主干线路和分支线路故障位置。仿真试验结果表明,该方法提高了行波时域分析的可行性,避免了固有频率的频谱混叠问题,具有较高的定位精度,为多分支输电网的故障定位提供了新思路。     

特高压直流对同塔交流线路的过电压影响分析

随着我国电力工业的发展,特高压直流输电凭借其在远距离输电上的优势而成为我国特高压发展的重要方向。局部地区电力走廊紧缺,使交直流同塔架设输电线路成为必然。当交直流导线同塔架设时,将在导线间产生很强的电磁耦合。主要研究特高压直流线路故障对同塔架设交流线路过电压的影响。根据规划中的锡盟—上海交直流同塔多回输电线路相关数据,采用电磁暂态程序建立了详细的直流换流站模型以及交直流同塔架设输电线路模型,研究了特高压直流输电线路故障对同塔架设的超高压交流线路的影响,并分析了不同故障类型、运行工况、耦合段线路长度、耦合段位置等因素对交流感应过电压的影响。结果表明,交流线路上的感应过电压幅值在交流线路绝缘水平允许范围内;直流发生接地故障时,交流线路通过耦合作用在直流故障弧道产生潜供电流。分析了交流线路不同换位方式对直流线路潜供电流的影响,并对限制措施提出了建议。     

输电线路暂态信号检测方法比较分析

输电线路发生故障产生的暂态行波是一个突变的、具有奇异性的信号,正确检测出信号的突变点即暂态行波波头是利用行波进行保护和测距的核心。对电网中断路器操作、电容投切、一次电弧、单相短路、雷击等产生的暂态信号进行了仿真．并分别利用小波变换模极大值、小波变换Lipischitz a、小波变换能量谱检测行波波头进行比较分析。EMTP仿真分析表明,三种方法均有提取行波特征,且采用小波能量谱检测输电线路暂态行波波头到达的时刻最精确,故障定位精度最高。     

Current phase comparison pilot scheme for distributed generation networks protection

The trends of the actual distribution networks are moving toward a high penetration of distributed generation and power electronics converters. These technologies modify contribution-to-fault current magnitudes and raise concern about new protection parameters settings to accurately detect faults on distribution networks. This paper proposes a differential phase jump pilot scheme to detect faulted branches in distribution networks. The aim of the proposed scheme is to provide an efficient algorithm with functions of fault detection and isolation, which are part of the self-healing functions used for smart grids. The proposed scheme is based on the current phase jump measured in each node with fault inception. Then, by comparing the phase jump obtained with the prefault conditions and rate changes, it determines the fault direction enabling a trip signal to the corresponding nodes to isolate the branch under fault. A distribution network has been modeled in PSCAD/EMTDC program to verify the proposed algorithm, taking into account distributed generation provided by both wind turbines (doubly fed induction generator and permanent magnet generator with full converter) and solar photovoltaic installations. The behavior of the current phase jump has been studied for both generation and load nodes. This algorithm is not affected by the magnitude of current and voltage and has been tested varying fault location and resistance along the modeled distribution network.     

基于光纤时间同步的双端行波故障测距方法

针对传统双端行波测距技术中线路双端时钟需精确对时的问题,将双端行波测距方法与光纤通信技术相结合,提出了一种基于光纤时间同步的双端行波故障测距新方法。该方法首先利用小波模极大值理论检测故障初始行波到达线路两端的时刻和极性,并根据极性判断故障线路;然后,在故障初始行波到达线路两端后,经光纤通道分别向对端发射脉冲信号,利用相关算法自动检测脉冲信号到达对端的时刻,并根据光纤通道传输时延确定故障初始行波到达线路两端的绝对时刻;最后根据双端测距方法确定故障距离。仿真结果验证了该方法的可行性。研究成果具有较高的工程应用价值。     

基于时频谱图与图像分割的柴油机故障诊断

将图像分割理论引入柴油机故障诊断中,提出一种基于时频谱图、图像分割和模糊模式识别的柴油机故障诊断新方法.首先利用二进小波对柴油机缸盖振动信号进行预处理,然后用时频谱图对柴油机气门机构4种状态下的缸盖表面振动信号进行时频分析,并将谱图结果根据图像分割理论对其等高图进行分割,最后通过选取分割后图像的特征体质心位置、特征体面积、数目和熵作为特征参数,并利用模糊C均值聚类对图像进行分类识别.试验结果表明,新方法提取的振动信号图像几何特征与形状特征参数能充分反映柴油机气门工作状态的信息,对不同类型的气门故障均能正确诊断.     

一种适用于同杆四回线单相接地距离保护的新算法

针对传统的距离保护直接应用于同杆四回线时易受零序互感的影响,使其测量阻抗精度达不到要求,从而造成保护继电器的误动或拒动,提出了一种单相接地距离保护新算法,利用12序分量法对同杆四回线进行参数解耦,结合同杆四回线单相接地故障模型,推导出保护安装处与故障点相电压之间的关系。在此基础上,根据接地故障时故障电压与故障分支电流间相角关系,分析了故障位置的零序电流与保护安装处的零序电流之间的关系式,并代入故障位置计算,从而消除故障电压对其算法的影响。大量的PSCAD/EMTDC仿真结果表明,该保护在各种单相接地情况下均具有较高灵敏度及可靠性。     

Coordinate control strategy for stability operation of offshore wind farm integrated with Diode-rectifier HVDC

Due to low investment cost and high reliability, a new scheme called DR-HVDC (Diode Rectifier based HVDC) transmission was recently proposed for grid integration of large offshore wind farms. However, in this scheme, the application of conventional control strategies for stability operation face several challenges due to the uncontrollability of the DR. In this paper, a coordinated control strategy of offshore wind farms using the DR-HVDC transmission technology to connect with the onshore grid, is investigated. A novel coordinated control strategy for DR-HVDC is proposed based on the analysis of the DC current control ability of the full-bridge-based modular multilevel converter (FB-MMC) at the onshore station and the input and output characteristics of the diode rectifier at the offshore. Considering the characteristics of operation stability and decoupling between reactive power and active power, a simplified design based on double-loop droop control for offshore AC voltage is proposed after power flow and voltage–current (I–V) characteristics of the offshore wind farm being analyzed. Furthermore, the impact of onshore AC fault to offshore wind farm is analyzed, and a fast fault detection and protection strategy without relying on communication is proposed. Case studies carried out by PSCAD/EMTDC verify the effectiveness of the proposed control strategy for the start up, power fluctuation, and onshore and offshore fault conditions.     

提升距离保护适应性的新能源主动故障控制研究

该文以新能源送出线路为研究对象,通过研究新能源故障控制方法,提升距离保护在新能源电力系统中的适应性。首先,分析过渡电阻和逆变器控制对于距离保护的影响机理。然后,提出新能源故障控制策略,主动调整新能源输出特性,使故障附加阻抗呈纯阻性。接着通过利用有效故障阻抗、测量阻抗及故障附加阻抗在阻抗复平面中的关系,求解有效故障阻抗,以提升距离保护在新能源系统中的耐过渡电阻能力。最后,利用Matlab/Simulink仿真验证所提方法的有效性,为新能源送出线的保护与控制协调配合提供了理论基础。     

一种基于时间轴整定的T型混合输电线路故障测距方法

为解决带T型分支的多段式架空线-电缆混合输电线路故障测距问题,提出了一种基于时间轴整定的T型混合线路故障测距方法。首先,根据三个假定的端点故障位置整定出以线路任意两端时间差为基准的三个时间轴,使得在线路任意一点发生故障时总能在其中两个时间轴中找到对应点;其次,以线路三端得到的三个时间差在对应时间轴中的位置作为故障区段判据,三个判据可保证判断故障区段的准确性;最后,根据时间轴中各点与线路长度间的线性关系得出以两个时间轴为基准的两个测距结果,并将测距结果取平均值。算例仿真结果表明,所提方法正确可行、原理简单,适用于各种带T型分支的混合输电线路结构,且不受过渡电阻的影响。     

基于多源数据融合技术的输电线路故障定位方法

鉴于现有输电线路故障定位算法的定位结果各不相同影响到电力系统基于故障的快速恢复问题的分析,根据两端距离继电器的多源故障测距结果,提出了一种提高输电线路故障测距精度的新方法,该方法将两端定位结果与故障位置相互关联,据此建立基于多传感器数据融合的输电线路故障测距模型,该模型将模糊推理系统作为故障场景识别的初始融合步骤,并计算加权协方差融合(WWCF)系数,确定最终融合结果。最后利用PSCAD/EMTDC和变电站现场记录数据进行算例分析,针对不同故障类型、故障位置、故障电阻、故障起始角、潮流、线路参数和两端不同步角进行测试,结果证明所提方法的可行性和有效性。     

Enhancement of transient stability of an industrial cogeneration system with superconducting magnetic energy storage unit

This paper has developed the coordination of load shedding scheme and superconducting magnetic energy storage (SMES) unit to enhance the transient stability of a large industry cogeneration facility. The load-shedding scheme and the tie line tripping strategy by using the frequency relays have been designed to prevent the power system from collapse when an external fault of utility power system occurs. An actual external fault case and a simulated internal fault case have been selected to verify the accuracy of the load shedding scheme by executing the transient stability analysis. To improve the frequency and voltage responses, an SMES unit with various control modes has been installed in the cogeneration system. The sensitivity analysis of the SMES unit with different parameters is applied to achieve better system responses. Besides, an SMES unit with active power deviation as feedback signal is also considered to improve the electric power fluctuation of the study plant with rolling mills. It is found that the SMES system will enhance the electric power quality and minimize the economic losses of the cogeneration facility due to unnecessary load shedding.     

架空输电线路绕击与反击仿真分析及辨识

针对架空输电线路事故中绕击、反击的辨识十分困难问题,根据架空输电线路绕、反击特点,采用电力系统电磁暂态仿真软件ATPDraw构建了输电线路、杆塔、绝缘子等仿真模型,对某220 kV单回输电线路雷击与非雷击故障及绕、反击暂态过程进行了仿真,分析了不同情况下故障暂态电流极性、幅值、陡度的特征差异,并基于不同情况下导线和避雷线上故障暂态电流波形的参数提出了相应的实时监测方案。结果表明,该方案可实现对输电线路雷击过程中绕、反击的辨识。