导　　师： 陈皓勇

学科专业： 080802

授予学位： 硕士

作　　者： ;

机构地区： 华南理工大学

摘　　要： 当线路发生故障时，如果不能为线路上所储存的能量提供一个通道，则故障点电流能被难消除。由于直流线路故障电流不会像交流线路一样大，所以通过比较正常和故障时的稳态电流来判定是否发生故障是较为困难的。目前国内的主流特高压直流输电工程多采用行波保护为主保护，并配有基于电压水平的突变量保护和线路纵差保护作为后备保护。行波保护是采用故障后初始行波阶段的行波变化率和变化量来作为保护的判据，当发生高阻、远距离接地故障时保护的灵敏性不足。而突变量保护同样受到过渡电阻和故障距离的影响，同时在发生换相失败、交流母线故障时有误动的风险。对于直流线路纵差保护而言，能否区分区外故障和区内故障是关键所在，同时通讯通道的可靠性也是影响纵差保护的主要原因之一。 我国直流输电工程日益增多，而且规模越来越大，但在线路保护的理论研究和核心的技术上有较大的差距，严重滞后了我国直流的自主性发展。在南方电网的事故统计报告中可以发现，仅有一半左右的线路故障能够被检测。大量的工程运行事故凸显了研究直流线路保护的必要性和紧迫性。 本文首先基于行波理论分析了故障后线路电气量的暂态特性，同时基于在建的糯扎渡电站送电广东±800KV直流输电工程研究了该工程的线路保护与策略方案，并通过PSCAD仿真工具对该工程发生故障时线路保护动作情况进行了仿真测试，为该工程以后的调试、运行提供参考。实验表明在给定的定值情况下，当发生典型故障时线路保护能够合理动作。本文还探讨了过渡电阻、故障距离和交流母线故障对线路保护的影响，实验结果显示：过渡电阻对电压的变化率和电流的变化量影响较大，且会延长电压变化量和电流变化量达到定值的时间：当电阻增大到80欧姆时电流变化量判据无法满足导致行波保护不能启动，而突变量保护在过渡电阻为130欧姆时无法启动。故障距离同样会影响到电压变化率、电压变化量以及电流变化量，使上述判据的幅度变小并能延长满足定值的时间。因此得出高阻远距离接地故障是导致行波保护和突变量保护拒动的主要原因之一。对于专为高阻接地时所设置的后备保护，该工程的线路纵差保护能够满足要求，即在高阻接地时不拒动；交流系统故障时行波保护和线路纵差保护不会误动，而突变量保护则存在误动的风险。因此引入了电流变化量作为突变量保护的判据之一，有效避免了当交流母线发生故障时该保护误动的发生。 When faults occur in the transmission line, the fault current will be hard to remove if itfails to produce a channel for the energy stored on the line. Since the DC line fault current isnot as high as AC line fault, it can be difficult to estimate whether fault occurred bycomparing the stable current in normal and fault conditions. Currently the most UHVDCtransmission project use traveling wave protection as its main protection, with the protectionbased on the amount of voltage mutation and longitudinal differential protection as backupprotection. Traveling wave protection uses the traveling wave’s change rate and gradient ofthe initial traveling wave period as the protection criterion, and it lack the sensitivity when ahigh impedance long-range ground-fault occurs. The derivative protection will be affected bytransition resistance and the fault distance. Also this protection may operate wrongly when ithas a commutation failure or AC bus fault. As for longitudinal differential protection, how toproperly distinguish internal faults and external faults is the key, and also the reliability of thecommunication channel is one of the important factors. DC power transmission project in China is increasing and scale is more and more lager,but there is a large gap in line protection theoretical research and core technology, which isseriously lagging behind the autonomy development of our DC. It can be found in the reportof the accident statistics of the China Southern Power Grid, that there is only about half of theline fault can be detected. A large number of engineering accidents highlights the necessityand urgency of the study of DC control protection. This paper first analyzed the transient characteristics of the electrical quantities bytraveling wave theory, and studied the line protection scheme of the±800kV NuozhaduHVDC transmission project, which is under construction. In addition, the paper simulated theline protection action when faults occur through the PSCAD simulation tools. The resultsshow that in the case of a given constant value, when a representative fault occurs, the lineprotection have a better operation. Moreover, this paper explored the impact of transitionresistance，fault distance and AC fault on line protect. The experimental results show that:transition resistance have a bigger influence on the voltage’s change rate and current variation,also it can delay the time of the voltage variation and current variation to the constant values: when transition resistance reaches to80ohms, the current variation criterion unit has beenunable to meet the criterion and would cause the traveling wave protection can not be started;when transition resistance is upwards of130ohms, the voltage’s change rate can not besatisfied, leading to mutations in the amount of protection can not be started. However, faultdistance have an influence on the three factors, also it can decrease the amplitudes amd delaythe time of the criterions to the constant value. Line differential protection which is designedfor high transition resistance fault as a backup protection, can meet the requirement thatneither refuse to act during high earthing resistance fault nor mal-operation during the ACfaults. When there is a AC fault, the traveling wave protection and longitudinal differentialprotection can not operate which is reasonable, but the derivative Protection have amal-operation risk. So the current variation was introduced as a criterion of derivativeprotection to prevent from mal-operation effectively.

关 键 词： 行波保护 突变量保护 线路纵差保护 过渡电阻

分 类 号： [TM773]

领　　域： [电气工程]