论文总字数：27772字

摘 要

未来电力系统发展的主要方向将继续是基于电压源变换器(VSC)的直流电网技术。直流电网不仅被认为是传输规模大、传输效率高且具有良好可靠性的远距离新能源传输通道，而且可以搭建各地区不同情况交流电网的异步连接，强化大规模输配电网运行的稳定性。直流输电电网线路的安全保护是直流电网安全稳定运行的最重要的基础保证，也是直流电网建设技术工程应用中最高优先要考虑和解决的问题。换流站是直流电网中的重要组成部分，由于换流站扩展拓扑的特殊性，直流电网中直流线路的故障特征在控制及其保护系统上相比于现有的高压直流电网线路的保护系统是非常严格的。因此，研究我国直流电网建设中直流线路故障的特点及保护原理的完善性具有十分重要的科学技术意义。本文以我国目前直流电网中直流线路的维护方案与保护措施和原理为主要研究目标，对以下几个方面进行了深入的研究：

（1）从时域和频域两个不同的角度对直流电网中直流线路短路故障进行分析。详细介绍了直流线路两极间短路的暂态过程，分别为计算单变流器与直流电网之间的短路暂态电流提供了参数。在充分考虑换流站扩展拓扑接线及不同故障类型的基础上，采用频域分析法对各线路末端电压行波头进行了详细的分析计算。

（2） 针对具有能量保护特性的高压直流输电线路，提出了一种基于不同传输通道的能量保护方法。该区域的两个断层的复杂特征，根据统计分析的结果，两个断层的过渡阻抗电压在频率上的差异在两端的高频复杂数量的大小远远大于两个断层的外部，同时一个故障端过渡电阻的复杂存在将直接导致终端电压高频电容的大幅降低。不同区域的电路故障可能会有其对应的各个过渡频率阻抗电压与末端能量的巨大差异，同时为了有效减小过渡频带末端电阻对其性能的负面影响，构建了一种可以用来检测低频电压高，根据两端电压的能量差百分比进行保护的快速方法。电压保护的工作原理是必须同时使用基于单个端子的输入电压控制信息，保护的工作时间窗短，动作快。

关键词：直流输送电网；故障原因分析；直流线路保护；过流保护

Abstract

In the future, the main direction of power system development will continue to be the DC grid technology based on voltage source converter (VSC). DC power network is not only considered as a long-distance new energy transmission channel with large transmission scale, high transmission efficiency and good reliability, but also can build the asynchronous connection of AC power grids under different conditions in different regions to strengthen the stability of large-scale transmission and distribution power grids. The safety protection of the HVDC transmission network lines is the most important basic guarantee for the safe and stable operation of the HVDC network, and it is also the highest priority to be considered and solved in the construction technology engineering application of the HVDC network. Converter station is an important part of the DC power network. Due to the particularity of the extension topology of converter station, the fault characteristics of DC lines in the DC power network are very strict in the control and protection system compared with the protection system of the existing HVDC power network lines. Therefore, it is of great scientific and technological significance to study the characteristics of DC line faults and the perfection of protection principle in the construction of DC power network in China. In this paper, the maintenance scheme, protection measures and principles of DC lines in China's current DC power network are taken as the main research objectives, and the following aspects are deeply studied:

(1) The short circuit fault of DC line in DC power grid is analyzed from two different perspectives, time domain and frequency domain. The transient process of short circuit between two poles of DC line is introduced in detail, which provides parameters for calculating the transient current of short circuit between single converter and DC grid respectively. On the basis of considering the extended topological connection of converter station and different fault types, the frequency domain analysis method is used to analyze and calculate the voltage traveling wave heads at the end of each line.

(2) For HVDC transmission lines with energy protection characteristics, an energy protection method based on different transmission channels is proposed. Two fault complex characteristics of the region, according to the results of statistical analysis, the transition of two faults in frequency impedance voltage difference on both ends of the high frequency complex number is much larger than the size of the two external fault, at the same time a transition resistance of complex fault will directly lead to the terminal voltage high frequency capacitance greatly reduced. Different parts of the circuit fault may have its corresponding each transition frequency impedance voltage and energy at the end of the huge difference, at the same time in order to effectively reduce the resistance on the performance at the end of the transition band negative impact, build a kind of can be used to detect low frequency high voltage, according to the percentage of energy difference on both ends of the voltage protection method of quickly. The working principle of voltage protection is that the input voltage control information based on a single terminal must be used at the same time, and the working time window of protection is short and the action is fast.

Key words: DC transmission network; Fault cause analysis; DC line protection; Over current protection

目 录

摘要 I

Abstract II

第一章 绪论 1

1.1课题研究背景与意义 1

1.2研究现状和存在的问题 2

1.2.1研究现状 2

1.2.2现有保护的分析 3

1.2.3课题关键问题 4

1.3本文主要工作 4

第二章 直流电网直流线路短路故障特征分析 5

2.1直流线路故障分析 5

2.2换流站拓扑结构及接线方式 6

2.2.1 MMC拓扑结构 6

2.2.2接地方式及主接线选择 7

2.3直流线路短路电流计算 9

2.3.1单换流器短路电流计算 9

2.3.2直流电网短路电流计算 12

2.4线路末端电压行波波头特征 13

2.4.1线路末端等量简化模型 13

2.4.2单极线路末端行波波头 14

2.4.3双极线路末端行波波头 16

2.5 小结 18

第三章 基于电压不同频段能量特性的直流线路保护新原理 19

3.1 区内外故障行波波头特征差异 19

3.1.1 区内故障传递函数 19

3.1.2 区内外故障特征对比 20

3.2 基于电压不同频段能量特性的线路保护原理 22

3.2.1 故障检测判据 22

3.2.2 区内外故障识别判据 22

3.2.3 故障选极判据 23

3.2.4 保护算法流程图 24

3.3 仿真验证 24

3.3.1 仿真模型 24

3.3.2 典型故障仿真 25

3.4 相关影响因素的讨论 26

3.5小结 28

第四章 结论 29

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