【作者】 邢鲁华；

【导师】 陈青；

【作者基本信息】 山东大学 ， 电力系统及其自动化， 2014， 博士

【摘要】 直流输电线路保护和故障测距是直流输电工程保护系统的重要组成部分,担负着快速检测和清除线路故障的任务,其运行性能将直接影响直流输电系统和电网的安全运行。统计研究表明直流输电线路已成为直流输电系统中故障率最高的元件,而直流输电线路保护的正确动作率只有50%。我国直流输电工程的发展位于世界前列,但对现有直流输电线路保护与故障测距装置核心技术的掌握仍然不足,缺乏系统的理论支持,已投运直流输电工程的保护系统大多采用ABB和SIEMENS两家公司的技术路线。提高我国高压直流输电线路保护与故障测距的理论水平和加快直流保护系统的自主研发势在必行。现己投运的直流输电线路主保护易受雷电、换相失败等暂态过程的干扰,耐受过渡电阻能力有限,判据门槛值整定计算复杂。国内外学者致力于对现有直流输电线路主保护进行改进或提出新型主保护原理,其中部分保护新原理存在理论不完备、保护判据所用信号能量小、对装置采样率要求高、缺乏整定依据或整定计算依赖仿真结果等问题。高压直流输电线路故障测距所采用的原理可分为行波法和故障分析法。目前运行中的直流输电线路故障测距装置均采用行波原理,行波故障测距的可靠性在高阻接地故障和波头识别失败时受限。基于故障分析法的故障测距原理性能稳定,故障测距精度一般没有行波法高,部分原理耐受过渡电阻能力有限。全面深入的高压直流输电系统故障暂态分析可为直流输电线路保护与故障测距原理的研究工作奠定基础。本文研究了高压直流输电系统故障暂态特性分析需要考虑的影响因素,深入分析了相应影响机理,给出了仿真案例实现方案,并对直流线路电气量的暂态特征进行分析；提出了耐受过渡电阻能力强、判据门槛值整定不依赖于仿真计算的高压直流输电线路主保护原理和可靠性良好、测距精度高、耐受过渡电阻能力强的直流输电线路双端行波故障测距新算法。主要研究内容及结论如下：(1)高压直流输电系统故障暂态特性研究。现有直流输电系统故障暂态分析相关内容大多作为线路保护与故障测距研究的考虑因素出现在文献的理论分析和仿真验证中,受文献篇幅和考查内容所限。本文从直流输电线路保护与故障测距角度出发,开展了较为全面的高压直流输电系统故障暂态特性分析。对直流输电系统的基本控制原理和控制系统的分层结构进行研究,分析了控制系统对故障暂态的响应时间和电气量的故障稳态值；研究了两端双极直流输电系统多种可能运行方式的运行条件与控制策略,并对不同故障前运行方式下直流线路故障电压电流的暂态特征进行了对比分析；分析了直流滤波环节的阻抗特性及其对故障后暂态过程的影响,提出在直流输电线路故障暂态电压电流信号的低频带特征分析中,可将直流滤波器和平波电抗器视为固定阻抗；分析了故障类型、故障位置和过渡电阻值对直流线路故障电压电流暂态特征的影响；研究直流输电线路的雷电放电计算模型,给出了雷击暂态仿真中雷电流源、杆塔模型、绝缘子闪络模型和输电线路模型的仿真建模方法,对故障性雷击和雷击干扰下直流线路电压电流的暂态特征进行了分析；研究了直流输电系统换相失败的形成机理、判断标准和单双极换相失败的仿真方法,分析了换相失败情况下直流线路电压电流的暂态特征。以上工作可为后续高压直流输电系统故障暂态分析研究提供直接有效的参考,为直流输电线路保护与故障测距原理研究奠定基础。(2)考虑故障选极的高压直流输电线路保护原理研究。分析了故障后直流输电线路电压突变量的暂态幅值特征,发现故障极线路的电压突变量幅值大于健全极,且电压突变量的积分值能够更好地体现这一特征；提出了利用两极线路电压突变量积分值的比值构造的故障选极判据,给出了判据门槛值整定方法；分析了故障后直流输电线路电流突变量的暂态极性特征,发现故障极线路两端电流突变量的极性在区内故障时相反,在区外故障时相同；提出了利用故障极线路两端电流突变量极性构造的区内故障判据,并采用平稳小波变换提取电流突变量的极性。由此构成的高压直流输电线路主保护满足选择性和速动性的要求,判据门槛值整定方法简洁且不依赖于仿真计算；在10kHz及以上的采样频率范围内均可实现；只需对端电流突变量的极性信息,对通信通道的可靠性要求较低,尤其适用于需要选择故障极的情况。基于中国银东±660kV直流输电工程的实际参数,本文建立了±660kV高压直流输电系统的PSCAD仿真模型,利用仿真数据验证了考虑故障选极的高压直流输电线路保护原理在不同故障情况下的动作特性。仿真结果表明,该保护原理在两端双极直流输电系统的多种运行方式下能够快速选出故障极和判别直流输电线路保护区内故障,耐受过渡电阻能力强,可实现高压直流输电线路的全线速动保护。(3)基于电压和电流突变量方向的高压直流输电线路保护原理研究。考虑故障选极的直流输电线路保护一般在极-极故障这一罕有情况发生时不能正确工作,因此,本文提出了直接判别直流线路保护区内故障的直流输电线路保护原理。对故障后直流线路电压和电流突变量的暂态特征分析发现,直流输电线路两端电压和电流突变量的方向在直流输电线路保护区内故障和区外故障时不同；通过将电压和电流突变量在一段时间内的积分值与设定门槛值比较,提出了电压和电流突变量的方向判据；通过比较线路两端电压和电流突变量的方向,提出了基于电压和电流突变量方向的高压直流输电线路保护原理。该保护原理的判据门槛值整定不依赖于仿真计算；仅利用线路两端电压和电流突变量的方向信息便可准确识别直流输电线路保护区内故障,对通信通道的可靠性要求不高；不需要进行采样数据同步处理；电压和电流突变量方向判据仅计算5ms数据窗内的积分值,对数据计算速度和采样频率要求较低,采样频率为10kHz及以上时即可满足保护判据计算要求。利用±660kV高压直流输电系统的PSCAD仿真数据对该保护原理在不同故障情况下的动作特性进行了验证。该保护原理在直流线路保护区内故障性雷击、高阻接地故障和极-极故障时能准确动作,在雷击干扰和线路保护区外故障等情况下不误动,能实现直流输电线路的全线准确速动保护,适用于双极直流输电系统的多种运行方式,实用性强。(4)高压直流输电线路双端行波故障测距新算法研究。分析了故障行波在直流输电线路上的传播特点,发现可用行波波头传播特性曲线表征故障行波在线路上的传播过程,联立直流输电线路本端和对端的行波波头传播特性曲线可计算出故障位置。本文通过检测沿线分布电流的初次突变时刻求出线路两端的行波波头传播特性曲线,提出了直流输电线路双端行波故障测距新算法及其实现策略。该故障测距算法无需另外增加测量点,对通道的可靠性要求不高,算法数据窗口短,可不受控制系统调整的影响。基于PSCAD的仿真结果表明,本文故障测距算法在两端双极直流输电系统的多种可能运行方式下,在线路全长范围内均能实现准确测距,故障点靠近线路中点时测距准确度升高,测距精度不受过渡电阻值和直流线路出口故障的影响,最大故障测距误差约为线路全长的0.1129%。相较于现有高压直流输电工程中应用的双端行波故障测距,虽然本文故障测距算法的计算过程较为复杂,但是其可靠性、抗干扰能力和耐受过渡电阻能力有显著提高,而故障测距误差与之基本相同,保留了行波故障测距原理定位精度高的优点。因此,本文故障测距算法可作为现有直流输电线路双端行波故障测距的有效补充。本文研究内容及成果对提高直流输电线路保护与故障测距理论水平有重要学术价值,可为构建快速可靠的直流保护系统、加快直流系统故障恢复速度和保护设备的自主研发等提供理论支持,选题具有工程实用意义。更多还原

【Abstract】 As important parts of the protection system in HVDC (High Voltage Direct Current) projects, the protection and fault location for transmission lines have to detect and clear faults rapidly, and their operating performance will directly affect the safe operation of HVDC transmission systems and the grid. Statistical studies show that the HVDC transmission line had become a component with the highest failure rate in HVDC transmission systems. However, the correct action ratio of protections for HVDC transmission lines was only50%. Development of HVDC projects in China is at the forefront of the world, but we have few core technologies of existing protection and fault location devices for HVDC transmission lines, and there is lack of systematic theories. Protection systems in existing HVDC projects mostly adopted technologies of ABB and SIEMENS. Improvement of the theoretical level of protection and fault location for HVDC transmission lines and to speed up the independent R&D of HVDC protection system in China are imperative.The main protections for HVDC transmission lines being put into operation are vulnerable to disturbance of transient process, such as lightning and commutation failure, and have limited anti-grounding-impedance ability and complex setting calculation of criterion threshold value. Scholars are committed to improve the main protections for HVDC lines being put into operation or to propose novel main protection principles. Some of the proposed novel protection principles have shortcomings of incomplete theory, signal used in protection criterion having small energy, limited anti-grounding-impedance ability, high requirements of sampling frequency, lack of basis for setting calculation or the setting calculation depending on simulation results, etc. The currently methods for locating faults on HVDC transmission lines include traveling-wave-based methods and fault-analysis-based methods. Fault location devices for HVDC lines being put into operation adopted the traveling wave principle, and the reliability of traveling-wave-based methods will be limited for detection failure of the wavehead and high grounding impedance faults. Fault-analysis-based methods have stable performance. However, accuracy of fault-analysis-based methods is generally lower than the traveling-wave-based methods, some of which have limited anti-grounding-impedance ability.Depth fault transient analysis of HVDC transmission systems can lay the foundation for research on protection and fault location principles for HVDC transmission lines. In this paper, considering influence factors for fault transient characteristic analysis of HVDC transmission systems are studied, corresponding influence mechanisms are deeply analyzed; simulation cases and their implementation schemes are given, and transient characteristic analysis of electrical quantities on HVDC lines is carried out. Main protection principles for HVDC transmission lines are proposed, which have high anti-grounding-impedance ability, and their setting calculations of criterion threshold values do not depend on simulation results; a novel two-terminal traveling-wave-based fault location algorithm for HVDC transmission lines is presented, which has good reliability, high positioning accuracy and high anti-grounding-impedance ability. The main research contents and conclusions are as follows:(1) Research on fault transient characteristics of HVDC transmission systems.The existing related contents of fault transient analysis for HVDC transmission systems are mostly considered in theoretical analysis and simulation test of research on protection and fault location for lines, which are limited by the literature space and test contents. From the protection and fault location for HVDC transmission lines point of view, more comprehensive fault transient analysis of HVDC transmission systems is carried out in this paper. The basic control principles of HVDC systems and hierarchical structure of the control system are studied, response time of the control system to faults and steady values of electrical quantities after faults are analyzed; operating conditions and control strategies of various possible operation modes of both ends bipolar HVDC transmission systems are studied, and transient characteristics of fault voltages and currents on DC lines under different modes are compared; analysis of impedance characteristic of the DC filter link and its influence on the fault transient process are put forward, and it is pointed out that the DC filters and smoothing reactors can be taken as fixed impedances in characteristic analysis of low frequency of fault transient voltage and current signals on the DC lines; influence of fault types, fault positions and the values of grounding impedance on the transient characteristics of faults on DC lines are analyzed; calculation model of lightning discharge of DC transmission lines are studied, simulation modeling methods for lightning current source, tower, flashover model of insulators and transmission lines in lightning transient simulation are given, transient characteristics of voltages and currents on DC lines under lightning induced fault and lightning disturbance are analyzed; The formation mechanism and determination standard of commutation failure in HVDC systems and the simulation methods of monopolar and bipolar commutation failure are studied, analysis of transient characteristic of voltages and currents on DC lines for commutation failure is presented. This work can provide direct and effective reference for subsequent studies on fault transient analysis of HVDC transmission systems, and lays a foundation for the research on protection and fault location principles for HVDC transmission lines.(2) Research on the protection principle for HVDC transmission lines considering faulted pole selection.Transient amplitude characteristics of voltage fault components on DC lines are analyzed, and it is found that amplitudes of voltage fault components on faulted pole lines are larger than those on the healthy pole, as the integral values of voltage fault components can better reflect the characteristic. Criteria for faulted pole selection are proposed, using the ratio of amplitudes of voltage fault components on bipolar lines, and the setting method for threshold values of the criteria is also given. Transient polarity characteristics of current fault components on DC lines are analyzed, and it is found that polarities of current fault components at the two ends of faulted lines are opposite for internal faults, which are same for external faults. Polarities of current fault components at two terminals of the faulted line are used to propose the criteria for internal faults. The stationary wavelet transform is used to extract polarities of current fault components. The selectivity and rapidity of the proposed main protection for HVDC transmission lines are satisfied, and the setting method for threshold values is simple and does not depend on simulation results. The protection can be realized with a sampling frequency of10kHz and above, only needs the polarity information of the current fault components at the other end, and has low requirement for reliability of communication channel, which is especially applicable in need of faulted pole selection.Based on parameters of the±660kV Yindong HVDC transmission project in China, a PSCAD simulation model for the±660kV HVDC transmission system is built, and is used to test the performance of the protection principle for HVDC transmission lines considering faulted pole selection. Simulation results demonstrate that the protection can select the faulted line rapidly and distinguish internal faults under different operation modes of a two terminals bipolar HVDC transmission system. The protection has high anti-grounding-impedance ability and can realize high speed protection on the whole DC transmission line.(3) Research on the protection principle for HVDC transmission lines based on directions of voltage and current fault components.The protection for HVDC transmission lines considering faulted pole selection will not act correctly for line-to-line fault, which happens rarely. Therefore, this paper presents a protection principle that discriminates internal faults for HVDC transmission lines. Transient characteristic analysis of voltage and current fault components on DC lines shows that, the directions of voltage and current fault components measured at the two terminals of the DC lines are different for internal faults and external faults. Direction criteria for voltage and current fault components are proposed by comparing the integral values of voltage and current fault components in a period of time with setting threshold values; a protection principle for HVDC transmission lines based on directions of voltage and current fault components is proposed by comparing directions of voltage and current fault components measured at the two terminals of the DC lines. Setting calculations of threshold values in this protection do not depend on simulation results. Only the direction information of voltage and current fault components at both ends of the line are used to identify internal faults on the HVDC transmission lines, so this protection principle has low requirements on the communication channel. This protection principle does not need synchronization of sampling data. Criteria for directions of voltage and current fault components only calculate the integral values with a data window of5ms, and have low requirements on the data calculation speed and sampling frequency. A sampling frequency of10kHz and above can satisfy the calculation of criteria in the protection.A PSCAD simulation model of the±660kV HVDC transmission system is used to test the performance of the protection under different fault conditions. The proposed protection acts accurately for lightning induced faults, high grounding impedance faults and line-to-line faults, and does not act for lightning disturbance and external faults. It can realize accurate and fast protection for the whole DC transmission line, being applicable for a variety of operation modes of bipolar HVDC transmission systems, with high practicability.(4) Research on a novel two-terminal traveling-wave-based fault location algorithm for HVDC transmission lines.Propagation characteristics of fault traveling wave on DC transmission lines are analyzed. It is found that a propagation characteristic curve of traveling wave head can be used to express the propagation process of fault traveling wave along the transmission line, and the fault location is calculated with propagation characteristic curves of traveling wave heads at the local and remote terminals of a DC line. To obtain propagation characteristic curves of traveling wave heads, initial surge arrival times of distribution currents along the DC line are detected. A novel two-terminal traveling-wave-based fault location algorithm for HVDC transmission lines is presented, which does not need additional measurements, and has low requirements of the reliability of channel. Since the data window of this algorithm is short, the algorithm will not be influenced by adjustment of the control system. Simulation results based on PSCAD show that the algorithm can realize accurate fault location on the whole DC line under various possible operation modes of two terminals bipolar HVDC transmission systems, and the location accuracy increases when the fault point is close to the middle of line when, as the location accuracy is not affected by the transition resistance value and close faults the on HVDC lines, with a maximum fault location error of0.1129%of the whole length of the DC line. Compared to the two-terminal traveling-wave-based fault location used in existing HVDC systems, calculation in the proposed fault location algorithm is more complex, but it is of better reliability, anti-interference and anti-grounding-impedance ability. It retains the advantage of high positioning accuracy of the existing two-terminal traveling-wave-based fault location method. Therefore, the fault location algorithm in this paper can be used as an effective supplement to the existing two-terminal traveling-wave-based fault location for HVDC transmission lines.Research contents and results in this paper can provide theoretical support for improvement of theory level of protection and fault location for HVDC transmission lines, construction of rapid and reliable protection system for HVDC transmission projects and independent R&D of protection devices. The work done by this thesis has important academic value and practice meanings.更多还原